Need some bump stick 101

Strictly Attitude

Strictly Attitude

solid fixture here in the forum
71 chevelle 2400 lbs
355 gen1 2 bolt block
Not sure what rods or crank so assume cast on
Speed pro l2256 forged slugs
Estimating 9.5:1 compression
AFR 195cc street heads 2.05 / 1.60
Comp steel 1.5 full fulcrum roller rockers
Edelbrock rpm air gap intake
serpentine w/electric fan
Mystery cam that gots to go
700r4 just finished rebuilding
manual valve body all the goodies
2600 stall w/lockup
10 bolt 8.5 2.73 gears to yanked out this spring for 3.73 or 3.90
and 26 inch tire

I like to drive the car in the summer to work and want more an auto-x road race build then for the strip (track days) I can not fit a roller cam into my budget right now so was thinking solid flat to get the most ponies for pennies. I have been playing with the desktop dyno and allot of different solid cams lunati has been looking best in simulation but I do realize that exact ramp rates are not accurately being computed. I want to maximize power but also need a cam that operate mid throttle as well as full throttle. The tracks I plan to do track days at are Watkins Glenn and Red Rock I am about 2 years off till my build is ready for a track day as I have a son and family that come first. But auto-x and an occasional trip down the 1/4 happen every year. I narrowed down 4 cams and graphed out my results that desktop dyno gave me. I have been since then told that they will not work with my compression ratio and am back to square one. So any suggestions are welcome. I am open to brands of camshafts. If these cams are no good for my application what should I be looking for.


Here are the specs for those 4 cams
30121101 Lunati Oval TL2 solid flat
268/276 239/247 .521/.540 108 / 102
rpm 2000-6500

30121102 Lunati Oval TL2 solid flat
272/280 243/251 .530/.551 106/102
rpm 2500-6500

30121103 Lunati Drag Race TL2 believe it has a new part number
276/284 247/255 .540/.560 108/102
rpm 2500-7000

30120740 Lunati voodoo
266/276 233/241 .505/.520 110/106
rpm 2400-6600
 

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http://www.lunatipower.com/ProductGroup ... 342&cid=58

YOU WILL FIND READING THESE LINKS RATHER USEFUL

viewtopic.php?f=52&t=82

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=181

viewtopic.php?f=52&t=5154

0607phr_11_z+camshaft_basics+lobe_centerline_angle_determination_chart.jpg

Duration_v_RPM-Range_wIntakeManifold01.jpg

craneq2.gif

camcomp.jpg

lclcomp.png

BTW LOVE the GRAPHS and detailed info , that makes looking at your question and answering it with some facts much easier! :mrgreen:
first few questions
have you weighted that 71 chevelle? 2400 lbs seems unbelievably light weight?

you do realize that the 10 bolt rears life expectancy with the power increase is going to be rather limited if you start beating on it with hard launches?

who told you those cams won,t work and why did they say they won,t work?

how do you know your converter stalls at 2600rpm, and are you aware its going to change with the new engine combo?

what specs did you use to calculate compression?

what valve lift are the heads valve springs rated at and did you verify the clearances and valve spring load rates?

it should be obvious that you can,t use a 2.73:1 rear gear ratio, so swapping to the 3.73:1- 3.90:1 rear gears with those cams, is mandatory before any of them could be considered as a viable choice, and you must know your true clearances and compression ratio, and a 2600 stall converter is not ideal with ANY OF those cams.
 
Last edited by a moderator:
Compression was taken from piston specs given from jegs. Specs from the pistons have not measured with the heads off running .041 felpro head gasket and pretty sure the block wasn't decked I picked it up cheap from a friend that had it sitting in a field in a truck he said used to run 13's. I know I should have got the measurement when I had the heads off to add the AFR's.

The heads have the AFR factory springs that are supposed to b ePAC Racing Spring 1.290" OD Hydraulic Roller Dual Valve Spring, 135 lbs on seat, .600" maximum lift, Max RPM 6300-6800

The gentleman said not enough compression was weary on there opinion because they did not back it up. So I figured I would see what other people think. Just said in there experiance I do not know there experiance but I do know they recommended 10 less degrees in the duration at .50. They also suggested a Isky Mega cam 180. I don't need to throw a Lunati in they just did better in dyno simulation.
 
are they flat top pistons?
what size combustion chambers on the AFR heads?

and the rear gear ratio needs to be changed and car weight is highly suspect<are you going to change the rear gears before the cam swap? its going to run like crap with a decent cam yet matched to a 2.73 gear, and of the cams listed none will function well with a 2600 rpm stall speed converter! and none will work with the 2.73 gears

some basic related reference material

viewtopic.php?f=52&t=5154

viewtopic.php?f=52&t=324

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=727

viewtopic.php?f=52&t=82
 
yes they are flat top with 6.10cc calve reliefs

The heads are 65cc combustion chamber

yes the gearing will be changed to a 3.73 or a 3.90 gearing the same time the cam is changed.
 
https://www.uempistons.com/index.php?ma ... aaaf4455f4

viewtopic.php?f=52&t=727

viewtopic.php?f=52&t=1070

yes your compression ratio is near 9.5:1 if those are correct specs,you generally want to have a 8:1 dynamic compression ratio with pump gas, a few quick calculations indicate the intake valve should close at near 60 degrees
Intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees so your looking for a cam with .050 intake valve closing at about 45 degrees after bottom dead center as a listed close point. on a 110-108 LSA too maximize low and mid range torque


READ THIS
viewtopic.php?f=52&t=1477


READ THIS
viewtopic.php?f=52&t=4299

this puts us in the 236-to-240 degrees duration at .050 range, which indicates that if properly installed the cam you selected below should work once the rear gears are correctly matched, but from experience I can tell you a 3000 rpm stall converter would help, and the 3.90:1 ratio will be a better match with that current stall and the 2600 stall even with the 3.73:1 rear gear is going to be a P.I.T.A. to live with , and damn near useless with the 2.73:1 rear gear and that cam

this is the closest match of the 4 listed choices, but only with a 3200 stall and the 3.73:1 rear gears

30121101 Lunati Oval TL2 solid flat
268/276 239/247 .521/.540 108 / 102
rpm 2000-6500


THIS IS a VALID SECOND CHOICE
30120740 Lunati voodoo
266/276 233/241 .505/.520 110/106
rpm 2400-6600
 
Also plan to beef up the rear with a true trac and some stronger gears richmond or motive not sure yet but will not be running slicks on the car. How do you feel about lunati as cam choice?
I have allot of reading to do to get the cam math down a little better
How do you feel the lunati 30121101 is going to act on the street?
idle and vacuum are my concerns
If vacuum is an issue can it be corrected with a reserve canister for brakes?
I appreciate the answers and the guidence I have found my way here through google more than once looking for information which is why I joined.
 
Strictly Attitude said:
Also plan to beef up the rear with a true trac and some stronger gears richmond or motive not sure yet but will not be running slicks on the car. How do you feel about lunati as cam choice?
I have allot of reading to do to get the cam math down a little better
How do you feel the lunati 30121101 is going to act on the street?
I THINK, YOULL HAVE A VERY NOTICEABLE LOPE IN IDLE, and the BRAKE VACUME MAY NEED A AUX BOOSTER
idle and vacuum are my concerns
If vacuum is an issue can it be corrected with a reserve canister for brakes? ( YES it can,)
I appreciate the answers and the guidence I have found my way here through google more than once looking for information which is why I joined.

I think the cam , if matched to that 3.73:1 or better yet the 3.90:1 rear gear in that combo should work out reasonably well.
Id be looking for a FORD 9" differential with disc brakes , before spending money and time on a flimsy 10 bolt rear, but thats just me!
Click to expand...


DID YOU LOOK THRU THE PREVIOUS, posted LINKS ON CAM DURATION AND COMPRESSION AND LSA, EARLIER IN THE THREAD< AND UNDERSTAND OR HAVE QUESTIONS?

https://www.uempistons.com/index.php?ma ... aaaf4455f4

viewtopic.php?f=52&t=727

viewtopic.php?f=52&t=1070

READ THIS
viewtopic.php?f=52&t=1477


READ THIS
viewtopic.php?f=52&t=4299

youll be well ahead of 80% of the guys building engines if you understand the basics, a couple hours spent reading can save weeks of wasted time and dollars

some basic related reference material

viewtopic.php?f=52&t=5154

viewtopic.php?f=52&t=324

viewtopic.php?f=52&t=1070

viewtopic.php?f=52&t=5078&p=14433#p14433

viewtopic.php?f=52&t=727


LINKS RELATED TO DIFFERENTIAL

viewtopic.php?f=71&t=1198&p=2858&hilit=+ford+inch+width#p2858

http://dazecars.com/dazed/narrowinga9.html
 
Truetrac diff is not the best choice with slicks.
Detroit locker in a 9" or Dana 60.
Full Race Spool Best.
If Dana & have spare $ get a Titanium Race Full spool.
 
87vette81big said:
Truetrac diff is not the best choice with slicks.
Detroit locker in a 9" or Dana 60.
Full Race Spool Best.
If Dana & have spare $ get a Titanium Race Full spool.
Click to expand...
don't plan on running slicks
 
I am still reading and absorbing and I am sure I will be for a few days I plan on the cam in the spring along with the rear gearing or complete rear change we will see where the number one factor money leads me on that road.
 
Strictly Attitude said:
87vette81big said:
Truetrac diff is not the best choice with slicks.
Detroit locker in a 9" or Dana 60.
Full Race Spool Best.
If Dana & have spare $ get a Titanium Race Full spool.
Click to expand...
don't plan on running slicks
Click to expand...
Does your Chevelle have the factory Posi ?
10-Bolt Chevelle 8.2 Rear had a skinny Pinion gear shaft diameter.
1.438".
The GTO Rear 8.2 is much stronger. 3.90 -4.33 Had a special Borg Warner 4 pinion spider gear unit.
Bigger bearings.
Buick 1970 GS Stage 1 455. cars had the strongest 10-bolts.
Larger bearing on carrier Ring gear side.
12- bolt Chevy Stonger.
Dana 60 & 9.300 57-64 Pontiac Olds strongest ever in production cars.
 
Research Grumpy's links.
Educate yourself.
The Transmission & Rear Diffetential & Chassis just as important as The Engine build.
It may not be wise to put $900 of new parts into a Chevy 8.2 Rear.
Its just going to blow up at 400-425 hp mark.
350-400 Ft lbs torque. Flywheel power.
Stock 28 spline axle shafts suck too in Chevy 8.2.
They break your Chevelle is damaged fast in seconds.
Kiss rear quarter panels bye bye.
Its a boat anchor rear diff the Chevy 8.2".
 
8.5 not an 8.2 it has both ears I will see about getting a pic for you I would not bother with an 8.2 one of the weakest gm reared ever made
 
Its hard to see clear from my phone.
Be on the computer later to take another look.
The ears are present.
Does it have the smooth differential cover with no creases at 11 & 2 O'clock ??
If not its a GM CORPORATE 8.5.
Chevy 8.2 had same style rear diff cover as 12-bolt.
 
GM Corporate 8.5 good for up to 500-550 Flywheel Ft/lbs torque.
Momentarily .
Not no higher . My experience building & using them.

With the rear diff cover off, in the center of posi unit there will be an S shaped clutch pack preliad spring also.
Diff case cross shaft pin runs through spring cutout.
Some Pontiac Grand Prix 8.5 had no clips. Bearing end axle shafts lke a 9", Dana 60, 9.300 Pontiac.
Be ball bearing or tapered roller bearing axle shaft bearings.
 
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