the cross ram intake


Staff member
the basic concept behind the design of the crossram intake is to maximize the individual intake runner length , while maintaining as close to a direct strait shot at each cylinder heads intake valve, as possible so ram tuning, or use of the fuel/air masses inertia can be used along with exhaust scavenging to maximize the cylinder fill efficiency and yet not having to deal with the height penalty that the more common tunnel-ram or individual stack injection, and frequently while utilizing two 4 barrel carbs
BTW the cam we used to get the best results with in the past on retro Z28 builds was a crane 110921 flat tappet solid lifter ,but the current roller cams would do even better, keep in mind that the cross-ram intake works best on a 350-406 with a cam and gearing that keeps the engine in the 3500rpm-7000rpm band, so both the cam and the intake design match that OPERATIONAL RPM BAND
and REQUIRES a decent set of high flow rate heads, (generally look for heads that reach or exceed 250cfm at .600 lift) with a matching 10.5:1-12.5:1 cpr and generally a 4.11:1-4.56:1 rear gear and manual transmission, when road racing, to operate correctly in its intended rpm band and flow rate. you could drop back to a 3.73:1-3.90:1 on a street car










ed33.jpg ... ossram.htm
when they were easy to get at the local speed shops buying a smokey ram, installing a crane solid lifter flat tappet cam #110921in a 11:1 compression ratio, 377,383,406 SBC with a 750-780 cfm vacuum secondary arbitrator with decent long tube 1 3/4" headers and a low restriction exhaust, in a camaro, nova or vega engine swap car with a muncie 4 speed and a 3.90:1-4.33:1 rear gear was almost a mandatory combo back in the mid 70s if you wanted to kick butt and take names




when the first few SMOKEY RAM INTAKES WERE SOLD they found several distributors would not fully seat until the intake was notched to provide the required clearance, look closely at the intake above (an early version with no clearance notch) then the two below that had the notch machined
and you,ll never be the first guy to install a wet nitrous plate and a healthy ,longer duration solid lifter cam like a crane 110921 on a 383











Ive had good results with a smokey ram with a 750 cfm holley and
Ive used the offanhauser cross-ram with several carb combinations
and gotten good results, Id generally prefer two 450-500 cfm carbs on the cross-ram but two 600 cfm would work just fine!
the important thing is carefully matching the throttles /linkage and maintaining a constant 5.5 psi of fuel pressure and Id sure prefer a fuel pump that would be rated to supply about 120-140 gph at 5 psi.
a crane 110921 flat tappet solid lifter cam,
decent heads that flow at least 250 cfm at .500 lift
(brodix IK 200 are popular) (as are 195 cc AFR)
good 1.6:1 roller rockers,
long tube headers, a low restriction 3" dual exhaust, (obviously use premium gas)
on a 377-406 10.5:1 or higher compression SBC with the drive train differential gearing
(usually with a manual transmission) in the 4.11-4.33:1 range seems to work rather well
especially in a 3000 lb or lighter car, if you drive the car like the devil himself was after your soul and was only 100 yards behind you and gaining on every lap!(so it rarely drops below 3500-rpm and spends a good percentage of the time bouncing between 4500 rpm and 6500 rpm

USEFUL LINKS|rKmBts5HrkD7LgWJ4o2CXBYhxN0k*|5qQiC0m3AGdg/



max stock spring lift clearance is about .470 lift,either of these cams works, both like 1.6:1 ratio rockers
the milder one is the better choice for a daily driver, the longer duration version gives slightly more peak hp but its also slightly less street traffic friendly

specs>> 270/280 204/214 .420/.443 112 $111.72
buy now
specs>> 275/278 209/216 .435/.455 112 $111.72


most of the SBC cross ram intakes share a common plenum, but there are several designs with a dual plenum , where each carburetor feeds the opposite bank of cylinders exclusively ... ossram.htm

viewtopic.php?f=87&t=2045 ... 1:STORES:5 ... 205077441a
the cross ram can be a challenge to tune correctly but they work great once correctly tweaked ... vl=2&prt=5

best with the manual trans and 4.11-4.56 rear gears in a light car.

you might find this interesting

viewtopic.php?f=87&t=8379&p=29224#p29224 ... ossram.htm

the offy intakes still available and twin 600 cfm carbs tend to work great...but theres been lots of improvements in things like roller rockers and intakes since then, and a very similar built 383 is almost certainly going to be faster ... ossram.htm

crossr5.gif ... toview=sku ... t=OFY-5903 ... t=OFY-5902

viewtopic.php?f=86&t=1397 ... index.html


for a huge improvement in runner flow rates, yeah! it requires fabrication and a custom intake lid , if you want to convert it to efi but all the parts for carb use are easily available, but the results are far better flow than the stock CROSSFIRE crossram intake can ever provide:thumbsup:

FIRST, This will not be anything more that a brief glimpse into a subject that takes years to understand fully and Im sure there are a few people on the site that can give more exact info! This is meant to apply to the 350-383 sbc engines most of us are useing
My purpose is merely to give an idea as to the relationship between the factors and yes IM ignoring several minor factors to make things easier to understand like dynamic compression and valve timing overlap
But lets look a a few concepts

(1) There are 720 degrees in a 4 cycle engines repetitive cycle of which between about 200degrees to about 250 degrees actually allow air to pass into the cylinder, (the valves open far enough to flow meaningful air flow) and the piston has a maximum ability to draw air into that cylinder based mostly on the engines displacement and the inertia of column of air in both the intake port and the suction (or negative pressure the PROPERLY designed headers provide) this produced a max air flow thru the ports, the greater the volume of fuel/air mix effectively burn per power stroke the greater the engines potential torque production, the faster you spin an engine the greater the NUMBER OF POWER STROKES PER MINUTE, and up to the point where the cylinder filling effectiveness starts falling off due to not enough time available to fill that cylinder the torque increases, above that rpm or peak torque itss a race between more power stokes and lower power per stroke
(2) look at this diagram

As air enters an engine it normally travels thru both an intake system and the cylinder heads intake port to eventually pass into the cylinder thru the valve. The valves in a normal small block corvette engine are between 1.94 and 2.08 in diameter, thats between 2.9sq inches and 3.4 sq inches of area, but because the valves require a seat that at a minimum are about 85%-90% of that flow area we find that the intake port even with out any valve has a max flow of not more than about 90% of the flow thru a port of valve size. Or in this case 2.46 sq inches-2.9 sq inches of port area, Since you gain little if any flow having a port thats substantially larger than the valves AT NORMAL ATMOSPHERIC pressures and since you cant substantially increase the valve sizes for several mechanical reasons you must improve efficiency, this is done in two major ways, you can match the intake port length and cross sectional area to the engines most efficient rpm range on the intake side, to build a positive pressure behind the intake valve as it opens and match the exhaust length and diameter on the exhaust side to provide a negative pressure to help draw in more volume this will require the cam timing match that same rpm range of course. By experimentation its been found that air flow port speeds in the 200-320 cubic feet per minute range are about the best for a chevy V-8 now lets say you have a 383. 383/8=47.875 cubic inches per cylinder, the rpm range most used is 1500rpm-6000rpm so thats where are cam and port size must match, you can do the math , (47.875 x ½ engine rpms = cubic inches, divided by your cams effective flow duration, (use 210-235) as a default for a stock cam) x 720 degrees/1728 (the number of cubic inches in a cubic foot) to get the theoretical max port flow required (I will save you the trouble its 250cfm-275cfm at max rpms and about 2.4-2.9 sq inches of port cross section, depending on where you want the torque peak, or use this handy calculator,

Intake Runner Area = Cylinder Volume X Peak Torque RPM 88200
Or this helpful site

Either way youll find that youll want a port size in the 2.4sq “2.9 sq inch area
Now use this calculator to figure ideal port length, REMEMBER youll need to add the 6 in the cylinder head to the intake runner length to get the total length and you can,t exceed the engines REDLINE RPM which with hydrolic lifters seldom is higher than 6400rpm

Ever wonder why your engines torque curve gets higher with the engines rpm level until about 4000rpm-5500rpm(DEPENDING ON YOUR COMBO) but fades above that rpm level?
well it depends on several factors, first as long as the cylinders can fill completely you get a good fuel/air burn so you get a good cylinder pressure curve against the piston each time the cylinder fires, THE ENGINES TORQUE CURVE INCREASES WITH THE NUMBER OF EFFECTIVE POWER STROKES PER SECOND, at very low speeds theres not enough air velocity to mix the fuel correctly or produce a effective ram tuning effect but as the rpms increase the cylinders fill very efficiently until the rpms reach a point where the cylinders just dont have the time necessary to flow
enough air through the valves to fill the cylinders , remember a 5000rpm the intake valve out of 720 degs. in each cycle opens for about 250degs of effective flow even with a hot roller cam, now thats only about 35% of the time and theres 41.6 intake strokes per second , thats only 1/60th of a second for air to flow into the cylinder
Its your engines ability to fill the cylinders that increases your power and the more efficiently you do that the higher the rpm level you can accomplish that at the more power your engine makes, remember the formula for hp is (torque x rpm/ 5252=hp) so moving the torque curve higher in the rpm range increases hp but at some point the time available to fill the cylinders becomes so short that efficiency begins to drop off rapidly, the peak of efficiency is reached normally in the 4500rpm-5500rpm range, and as rpms increase its a race between more power strokes per minute trying to raise the power and the increasingly less effective percentage of cylinder filling dropping the power.
Volumetric Efficiency
The volumetric efficiency of a 4-stroke engine is the relationship between the quantity of intake air and the piston displacement. In other words, volumetric efficiency is the ratio between the charge that actually enters the cylinder and the amount that could enter under ideal conditions. Piston displacement is used since it is difficult to measure the amount of charge that would enter the cylinder under ideal conditions. An engine would have 100% volumetric efficiency if, at atmospheric pressure and normal temperature, an amount of air exactly equal to piston displacement could be drawn into the cylinder. This is not possible, except by supercharging, because the passages through which the air must flow offer a resistance, the force pushing the air into the cylinder is only atmospheric, and the air absorbs heat during the process. so, volumetric efficiency is determined by measuring (with an orifice or venturi type meter) the amount of air taken in by the engine, converting the amount to volume, and comparing this volume to the piston displacement.
this increases until the torque peak then falls as the rpms increase. Here is a rough guide to match duration to port flow at different rpm level

if youve been following along youll find that youll need intake ports about 2.3-2.9 sq inches in cross section, and between 12 and 21 long (DEPENDS ON WHERE THE ENGINE IS DESIGNED TO MAKE MAX HP) and cam timing in the 215@.050 to -240@.050 lift range, as the rpms or displacement increase either the port flow or the cams duration must increase or the engines cylinder fill efficiency rpm will drop!
Now this is important, as the port flow efficiency goes up though the use of longer and larger intake ports the cam duration could remain the same or even be lower and you get more efficient cylinder filling as the rpms increase, that’s why high efficiency port designs like on the LS1 can use lower duration cams to flow similar total air flow thru the ports than the lower efficiency ports like the old fuelie heads could but at some point all ports reach max flow and an increase in the time the valves remain open at higher rpms increases the cylinder fill efficiency and that increases the engines ability to make torque at that rpm range
if you pick a smaller runner or longer runner you should pick a cam with a shorter duration to match the resulting lower torque peak that will likely result

Id like to point out something here!
heres the combo
SBC 407
· Block, 509, +30, Zero deck, Blanked water passages, Clearanced oil ways, Lifter valley vents, ARP main & head studs, Durabond cam & Clevite 77 main bearings.
· Crank, Scat 4340 forged steel, 3.75”, internal balance, Pioneer SFI balancer + ARP bolt.
· Rods, Comp. Products 6.00” H beam bronze bushed + ARP bolts Clevite 77 bearings.
· Pistons, SRP #4032 flat top, 5cc relief, Speed Pro plasma moly file fit rings.
· Complete rotating assembly balanced. Including - Flywheel, Clutch, Balancer & Crank pulley.
· Heads, AFR 210 Race Ready, 76cc, 2.080/1.600 valves, drilled for steam. FelPro #1014 gasket.
· Cam, Comp. Cams Magnum #12-450-8 (286HR) Hydraulic roller.
230/230 @ .050, .377 lift 110 LSA 106 ICL.
· Pushrods, Howards Cams heavy wall 5/16 7.4 long.
· Rockers, Pro Magnum roller, 1.6, 7/16 stud.
· Lifters, Pro Magnum hydraulic roller. AFR Hydr-Rev kit.
· Comp Cams Springs #950 + #740 retainers installed at 1.875
· AFR rev kit, AFR stud girdle.
· Lube, Melling M99HVS pump, Canton 7qt 5 trap pan with inbuilt windage and scraper, Cooler, Accumulator, oil stat, remote filter.
· Holley 800cfm #4780C, 1spacer, Victor Jr single plane.
· Static CR 10.32, Dynamic CR 7.9.
· Quench 0.0415 (Gasket .039+ .0025 down hole).
· MSD Pro Billet Street Dizzy, MSD 6AL, MSD Blaster 2 coil, MSD 8,5mm leads.

RPM BHP Torque
3800 367.3 507.7
3900 384.0 517.1
4000 395.1 518.8
4100 407.9 522.5
4200 418.9 523.8
4300 429.4 524.5
4400 439.6 524.7
4500 449.6 524.7
4600 462.1 527.6
4700 467.4 522.3
4800 476.6 521.5
4900 485.4 520.3
5000 489.2 513.9
5100 498.5 513.4
5200 496.0 501.0
5300 506.1 501.5
5400 508.4 494.5
5500 508.7 485.8
5600 505.6 474.2
5700 505.8 466.0
5800 505.8 458.0
5900 494.6 440.3
6000 491.9 430.6

Id like to point out something here to those of you who keep insisting that your required to run small ports sizes and dual plane intakes to make decent mid range torque
look closely at what the combo uses

Heads, AFR 210 Race Ready, 76cc, 2.080/1.600 valves, drilled for steam. FelPro #1014 gasket.
· Cam, Comp. Cams Magnum #12-450-8 (286HR) Hydraulic roller.
230/230 @ .050, .377 lift 110 LSA 106 ICL.
Holley 800cfm #4780C, 1 spacer, Victor Jr single plane

like IVE CONSTANTLY SAID, ITS THE CAM AND PROPERLY MATCHED COMPRESSION RATIO THAT HAS THE LARGEST EFFECT ON THE ENGINES TORQUE POTENTIAL, while its true that smaller ports can increase the volumetric efficiency at low rpms, they are not always required, and the tend to hurt the high rpm performance, you also don,t need a great deal of duration in the cam you pick,if the heads your useing flow decently, notice hes only running 230 @.050 lift
LARGE ports matched to the correct compression ratio and cam can make very good torque.
as always its the total combo OF PARTS and how the parts match the displacement and intended rpm range, NOT the result of a SINGLE PART choice!

if you want to build something responsive for street/strip use, these smaller 4 barrel carbs below ,make tuning easier on a car used mostly on the street


those intakes respond well to about 11:1 -12:1 compression and a crane 110921, or crower 00355 solid lifter cam ,and require a great set of cylinder heads and a low restriction exhaust, I generally ran 1.6:1 roller rockers and a manual transmission with 3.73:1-to-4.11:1 rear gears in a fairly light weight car
the basic power band in a 383 will be about 3700rpm-6300rpm. the combo won,t run well until about 3500rpm, but then hold on
If I was building one today ID
probable throw some 210cc profiler or AFR heads ... -23-degree



Last edited by a moderator:


Staff member
the cross ram intake design is designed to run in the 4000rpm and up on the 302 sbc, but the effective and useful rpm band drops as the displacement is increased, Ive had the best results with the 377 and 383,and 406 SBC, as thier increased displacement speeds the air flow rates far faster than the 302sbc z28
heres (BELOW)the three CHEVY cams that most guys used back in the day with those x-ram intakes, but all basically REQUIRE a 11.5-12.5:1 cpr and a MINIMUM of a MANUAL TRANSMISSION and 4.11:1 rear gears with 4.33:1-4.56:1 prefered
this crane 110921 cam in my opinion (and almost everyone else who tried several of them) works far better for the street/strip, especially in a 377,-406 sbc ... vl=2&prt=5


you can still get clones of the chevy cams , at survival motorsports ... cams4.html ... cams5.html

"Standard 302 (30-30) cam, P/N 3849346
Casting #3849347
254 duration @ .050" (intake & exhaust)
.485" lift (with 1.5 rockers)
114 deg. lobe separation
Exhaust Max lift @ 116 deg. BTDC
Intake Max lift @ 112 deg. ATDC

First Design Off-Road cam, P/N 3927140
Casting #3927141
Intake 257 duration @ .050" (333 advertised)
Exh. 269 duration @ .050" (346 advertised)
Lift: .493" intake, .512" exhaust
Intake Max lift @ 108 deg. ATDC
Exhaust Max lift @ 116 deg. BTDC

2nd Design Off-Road cam, P/N 3965754
Casting #3965751
Intake 248 duration (324 advertised)
Exh. 267 duration (334 advertised)
Lift: .512" intake, .535" exhaust

(Thanks to Mark C.)"
Last edited by a moderator:
was looking through a new magazine the other day and saw a 302 engine build with this intake carb combo and it put down around 580hp. very nice numbers and a cool set up i wish i seen more of them around


Staff member
the offy intakes still available, just be aware it takes a high compression ration and a fairly long duration cam with matched gearing to match the x rams flow and rpm band, youll want a 355-406 displacement and a cam with about a 245- 250 dur at .050 lift and 11:1-12.5:1 cpr with a 3.90:1-4.11 rear gear to get into the ballpark
CRG Research Report

Camaro Cross-Ram Intake Manifolds

Multiple-carburetion intake manifolds were a popular performance item amongst the major auto manufacturers right on up to the Camaro's introduction for the 1967 model year. Due, in part, to some negative publicity that General Motors received in the mid-60s regarding the crash safety results of its cars, GM restrained the image of "all-out" performance by no longer allowing its car divisions to produce cars with more than one carburetor (Corvette and Corvair were the only exceptions from '67 on). Thus, the Camaro started its life without the dazzle of a flashy multi-carb system.

Informed Camaro enthusiasts are aware, however, that a cross-ram intake manifold was made available by General Motors for the Camaro. This manifold owes its existence to the Camaro racing program. The Camaros in the '67 Trans-Am series had been running the standard single four-barrel on the 302-cubic-inch engine. Their main competitors were the Mustangs and Cougars that featured 289-cubic-inch engines and two four-barrel carburetors. One might assume that since the Ford products had more carburetors, that the Camaro was out-classed that first year, horsepower-wise. Not so. According to the April '67 issue of Sports Car Graphic, the horsepower ratings for the main competitors were as follows:

Dodge Dart 365 HP (273 cubic-inches)
Mercury Cougar 390 HP (289 cubic-inches)
Ford Mustang 375 HP+ (289 cubic-inches)
Chevy Camaro 403 HP (302 cubic-inches)

The Camaro more than held its own, in large part because it had a cubic-inch edge on its competition, not to mention being equipped with a huge, 800-cfm, four-barrel carb. However, Product Promotion Manager Vince Piggins, Chevrolet Engineering, and Winters Foundry wisely didn't rest on their laurels, and proceeded to work on the development of a double-four-barrel (2x4) intake manifold, which would help to keep Camaro at the front of the pack in subsequent racing seasons. With the appearance of a new, larger powerplant from Ford (the infamous "tunnel-port" 302) in 1968, and the new AMC Javelins with their twin-four-barrel-equipped 290s, this was a wise decision.

Since GM had banned multiple carburetion from most of its production cars, a 2x4 manifold would have to be developed with the intent that it was to be sold as a service replacement part. This was a valid procedure as far as the SCCA racing sanctioning body was concerned, as long as the parts were technically available to everyone that was racing, and not just the factory racing teams. The intent was to keep the racing as close and interesting as possible and to allow the independent entries to be competitive with the factory teams.

It should be understood then that no Z-28 was ever factory-built with a cross-ram intake manifold. Not only was there no need (the racing teams were officially able to use the part without having it on the production car), but GM edict said "this shall not be done" - period. The proof that this was not a production item is in the assigned engine stampings for the 302. Flint Engine and the vehicle assembly plants would need a separate code to identify a motor assembly with any unique components. There are no obscure engine codes in the Chevrolet records to indicate that anything but a single-4-barrel-equipped 302 was ever assembled by the factory. It is possible that a dealer may have converted a car prior to delivery, but most of these manifolds were owner-installed.

GM Cross-Ram Manifold
(Click on any image to expand it)

Right Front Left Front Left Side (off car)

The cross-ram intake manifold was developed for the 302 engine using knowledge obtained during experimentation on the MK IV big-block. During the October-November 1967 time frame, the first prototype 302 cross-ram manifolds (with experimental part numbers) were cast. The identification of these early manifold parts can become confusing but, basically, the earliest bottom pieces to the manifolds had no readily visible part number and had a large Winters Foundry "snowflake" (foundry mark) on top of the #1 intake runner. The later bases typically had a part number on top of the #1 runner and a smaller version of the foundry mark. Also, the hole for the vacuum fitting was moved from the base in early units to the lid. A list of the cross-ram components, taken from an internal GM specification sheet, follows:

Qty P/N Description
--- ------- ---------------------------
1 3941124 Manifold assembly, Inlet
1 3947032 Inlet manifold gasket unit
2 3941140 Carburetor assembly
8 120368 Nut, Carburetor
2 3881847 Gasket, Carburetor
1 3942593 Pipe assembly, Fuel pump
1 3942595 Pipe assembly, Carburetor fuel
1 3942594 Manifold, Carburetor fuel
1 3942596 Pipe assy, Carb. fuel to L.H. side carb.
1 3942597 Pipe assy, Carb. fuel to R.H. side carb.
1 3941160 Rod assy, Front to rear carb.
1 3928326 Rod assy, accelerator rea[r] pedal
1 9413182 Retainer, Accelerator pedal rod
1 3941168 Cable assy, Accelerator control
1 393292 Retainer, Cable to accelerator pedal lvr.
1 3942592 Bracket assy. Accelerator control cable
1 3921617 Clamp, Accelerator control cable
1 120706 Bolt, Accelerator control cable clamp
1 9419727 Screw, Accelerator control cable to dash
2 3942584 Screw, special 10-32 x .92 socket head
2 3942587 Spacer, special
2 9416980 Nut, Carb rod to lever screw
1 3946801 Bracket, Accelerator pull back spring
1 3939748 Spring, accelerator pull back
1 3701777 Gasket, water outlet
1 3932344 Gasket, ignition distributor
1 3941132 Gasket, Manifold top plate to base

This list of parts appears to be for the earliest cross-ram configuration, due to the use of the very early carburetor part number. These early Holley carburetors (585 cfm) may have only been used during initial development work. They were quickly replaced by two 600-cfm Holleys (LIST 4210, #3942595) which were dual-inlet units with a single accelerator pump, cam-actuated secondaries and no choke. By the summer of '68, these carbs were replaced again with a different pair of 600-cfm Holleys. These were LIST 4295, #3957859, and again featured dual inlets, cam-actuated secondaries with a secondary accelerator pump, and no choke provision.

The development of the cross-ram intake manifold had the desired results. Horsepower increased to as much as 465, with improvements in peak torque as well, up from 340 lb-ft to 365 lb-ft at 5600 rpm. Cowl-plenum-fed, cold-air induction systems, similar to that used for the 1x4 manifold, were developed and subsequently revised until the change in '69 to the familiar ZL2 hood scoop (a.k.a. the "cowl hood"). The increase in horsepower combined with help in many other areas, not to mention a certain degree of luck, helped Camaro gather the '68 and '69 Trans-Am championship.

Today, it is still possible to find an original example of one of these exotic manifolds. All it takes is a mere $3000 - $5000 and you're set! While they're a beautiful piece to behold, they generally are not street-worthy and typically wind up being more of a nuisance than a pleasure, especially if you're not going to drive the car hard. (See Author's Notes below.)

It's also noteworthy to mention that several aftermarket companies made similar cross-ram intake manifolds (Offenhauser and Edelbrock to name a couple), and while not exact duplicates, they are worthy of consideration due to their somewhat cheaper prices. The Offenhauser manifold is a fairly close copy, with the lower-half being almost identical to the GM part. The upper-half of the "Offy" manifold is similar to the GM part, but with distinct differences, including: 1) the ridge that follows the edges on the top piece is inset further than on the GM manifold, 2) the "Offy" manifold has provisions for a manual throttle linkage (the GM version doesn't), and 3) the Offenhauser name is name cast in two places. The Offenhauser base casting is quite similar in appearance to the GM part; the four photos below show the casting number and date code for each.

GM and Offenhauser Casting Details
Casting Number
Date Code


The Edelbrock cross-ram manifold is a less-faithful copy than the Offy. The bottom-half has the thermostat outlet done in the more traditional, 4-barrel-manifold style, rather than being tilted forward 90-degrees, like the other two. The Edelbrock lid also has no ridge at all around the edge (unlike either GM or Offy), has provisions for a manual throttle linkage (like the Offy), and is cast with the Edelbrock name on it. Also unlike either the GM or Offy units, the Edelbrock has neither a casting number nor a date code.


Comparison of Cross-Ram Castings
Tops, Apart Bottoms, Apart



Also note that some non-GM "side-by-side" cross-ram intake manifolds were produced (such as Edelbrock's XC8), but these do not have a removable top half and are more easily distinguishable from the GM offering. There were also alternate tops for several of the manifolds, as typified by the single-four version of the Offy cross-ram, shown below. A 3x2 top (not shown) for the Offy was also produced.



Offenhauser Single-Four

Author's Notes:

  • The information in this article is intended as a primer on the subject. For a much more detailed analysis, Wayne Guinn's book, Camaro Untold Secrets, is highly recommended reading.
  • The cross-ram intake manifold was not intended for street use, but rather for Trans-Am racing, to create power at engine speeds above 3000 rpm. That being said, many people have tried to run them on the street. Some claim to have found a combination of components (gearing, headers, carb re-jetting, etc.) that will allow satisfactory street operation of the cross-ram manifold. Whether effective or not, such tuning tips are beyond the intended scope of this article. A future article may deal with cross-ram tuning if enough definitive information can be gathered. ... toview=sku ... t=OFY-5903 ... t=OFY-5902

yes they are still available new, yes they work rather well once the engines above about 3500rpm if properly set up and tuned
and Ive used them in several engine combos






BTW heres the cam I usually use with a CROSS RAM APPLICATION ... il&p=23968
the cross ram intake REQUIRES an engine with about 11:1-12:1 compression,good headers with a low restriction exhaust, a manual transmission and 3.90:1-4.56:1 rear gears to work correctly, Ive used them mostly on 377 and 406 and 383 displacements with two identical 600cfm carbs, but I know other success full cases using two 450 cfm carbs , just be aware this intakes designed to run in the 3500rpm-7000rpm power band all the time, on a engine with open or low restriction exhaust and a solid lifter or roller cam and heads that flow a minimum of about 250cfm at .500 lift
The Engineering Truth..

The Cross Ram was never intended, nor was it developed (tuned) to be used with the Smog Equipment. The only reason it appeared in the Car Life article (and others) was to satisfy the Corporate mandate to pre-empt any negative connotations derived from the article that might imply Chevrolet was not in sync, or worse yet, ran counter to the Government mandated SMOG laws. It was a risk that Chevrolet could not afford to take for political reasons.

The true intent by Chevrolet was to have the tuner build the Cross Ram equipped 302 in the "recommended" tuned state it was developed for using Chevrolets Tubular Headers with specific timing and tuning considerations - never with the Smog Pump since it was counter indicated for performance which was implied and understood by all race tuners and street racers back in the day.


The SMOG Pump is actually a centrifugal AIR pump that forces compressed air into the exhaust manifolds to decrease the hydrocarbons by DILUTION. A totally ineffective smog reducer and supreme power waster that adds extra weight. In fact, you could make the argument that it actually increases pollution due to its inefficiency. No one was fooled by it back in the day.

The Smog Pump will cost you 15 important hp in the lower rpm ranges that you will not want to lose
Use of the equipment prohibits optimum jetting and timing and therefore;
The optimum power/torque distribution curve is not achievable and at best you will end up with a de-tuned 302

Bottom Line - The only reason the 302 appeared in some publications with the Smog Equipment was to appease Corporate Management and placate the Government. Understanding that, if you go with-out the pump as intended, you will benefit from maximum power which is consistent with Chevrolets true intent for the Cross Ram and from a pure nostalgic point of view be in sync with what everyone actually did back in the day. That is the true spirit of the Cross Ram equipped 302.






related info

YES READ THE LINKED INFO ITS WORTH THE EFFORT ... sram1.html Ram FAQ's.htm ... index.html ... index.html
Last edited by a moderator:
grumpy i had mentioned something to you about a 400 block with a 302 crank to use in my 73 240z. this intake carb combo sounds perfect for the performance and rpm range i was looking for. agree? now the only problem is building a valvetrain to handle 10,000 rpm haha
yeah thats what i was thinking tunnel ram on a 400 with a 302 crank (think its 321 ci?) with 11to1 comp with ram air livin on methanol would be ahelluva steet engine in my z with a 4 speed and 411 gears.

how many rpms can you build a valvetrain to handle? and would i be able to find a cam to work in the 4000 to 9000rpm range?


Staff member
150plusoutfitters said:
yeah thats what i was thinking tunnel ram on a 400 with a 302 crank (think its 321 ci?) with 11to1 comp with ram air livin on methanol would be ahelluva steet engine in my z with a 4 speed and 411 gears.

how many rpms can you build a valvetrain to handle? and would i be able to find a cam to work in the 4000 to 9000rpm range?

that is very true shaft rockers i could probably afford to go with but exotic heads springs? i know beehive springs allow you to rev higher but ive also heard contradicting stories that you can hit a valve if you mis shift. i just dont fully understand behind beehive springs. also exotic heads would you be referring to overhead cam heads?


Staff member ... toview=sku ... toview=sku

stuff like this gets expensive fast

heres a 600hp build with far cheaper heads but its still a darn expensive combo


if youll forget spinning the darn combo past 7000 rpm youll find its far cheaper to control the valve train, and if you increase the displacement to 355-406 its going to be much easier to build a killer power curve with reasonably priced parts.....theres a reason 99% of the people don,t build 302-331 sbc engines...its that you can make significantly more hp and have far less breakage with a 383-427 displacement at lower stress levels
i agree with you completely building a 383 or a stroked 400 would produce more power and torque and building an 18' brodix motor would be sweet. with a stroked 400 would be looking at 600hp+ easy. but im the kindof guy that would build something different and try to beat the guys building those motors more of a challenge more of a sense of accomplishment, just my opinion although i really dont know half of what you do about engines
maybe you can appreciate where im coming from


Staff member
maybe IM just getting older, but Id build a 355,377,383, or 396 sbc and put 302 or 327 valve cover and air-cleaner Id stickers on it,
Im not knocking the idea, of building something a bit differant, but build something usefull for the application, that will have instant power when you floor it, that won,t drain your bank account and be less than useful on the street, or at under 4500rpm on the track,where youll spend at least some time.
now Ive built lots of those smaller engines, but I don,t see ANY advantages to building anything under 350 cubic inches, you can spin a 350sbc to 7500 rpm if its built correctly, and 6800rpm is certasinly do-able with a 383,sbc, but whats the point if all your doing is abusing the valve train,... the power curve starts to fall off after you reach a certain point in the power curve in any combo thats even vaugely street drivable on pump gas well before you get to 6500 rpm with either combo.
what IM suggesting is stickers are cheaper than exotic valve trains and haveing a 450hp-475 hp even 500hp, in a much cheaper to build and more dependable sbc will provide plenty of tire smoking fun.
yes you can build a powerful 302,sbc, but having a sbc that sounds cool but watching tail lights is going to get old fast, your very unlikely to find ANY experianced engine builder that will tell you he can build a 302 sbc that will keep up with a 355,377,383,396,or 406 sbc in the identical weight car if the gearing, suispension and tires are matched to the engines power curve. spinning an engines valve train and rotating assembly over about 7000-7500rpm gets real expensive fast, and staying under 6500rpm can be done far cheaper and still make decent hp.
you don,t need valve train control issues


if everytime you walked into a room you hit your head on a low solid oak door frame, youll eventually learn to duck your head if youve got any sence, well 90% of the guys building sbc engines learned the lesson, they build the best combo, one that both wins races and doesn,t cost an arm and a leg,... same deal, learn from the guys before you ,so you don,t bump your head beating it on a solid door frame (REALITY)

want that differant sound?
build a 383 with stack injectors,
have 180 degree headers fabricated for your engine, and run a roller cam with a 105-106 lsa and 11:1 cpr
haha lol you are awesome grumpy. i completely agree that a big cubic inch small block would be faster and who knows what i will decide on when i do the build. i guess im a dreamer. i just think building a v8 with a rediculous powerband like a crotch rocket would be something that alot of people would respect and envy i know its probably not possible with todays technology but hey just cause it hasnt been done yet doesnt mean it wont ever be done right? maybe im an idiot maybe not. anyways i dont want to waste your time but i was wondering just for shits and grins what was the most youve heard of a v8 revving and or any engine for that matter and i dont think bikes like the suzuki gsxr have the air?valve spring combination that are in f1 cars do you have any idea how they do it? stock i4 bikes like the suzuki rev to 16k+.
f1 engines amaze me and being able to play a freakin song with the engine is bordering on rediculous. how a motor can go from one rpm to another so quick like notes in a song is beyond anything i will ever comprehend


Staff member
got a couple hundred thou$and dollar$ you can buy a couple to play with :lol: in your band!! :roll:
haha an f1 motor in a z holy crap i think i just fell in love haha i want to see somebody with resources far more than what ive got do that build.

maybe a rock band with some killer guitar haha