the c4-bbc engine swap

I am balancing my rotating assembly, it consists of the gm zz502 crank, gm zz502 forged rods, I havent ordered pistons yet, but I believe its JE that makes a custom slightly domed forged piston specifically for the gm/edelbrock roval ports. I was waiting on the machine shop to order the pistons, but there was a setback with the zz454 block I dropped off with them, so I am pulling this Gen vi bbc out of my 84 monte carlo, and I will have them use this block as the basis.

I am having them perform the machine work and balance everything but I am going to assemble it myself.

I was under the impression that the reason 454’s are externally balanced was because there wasn’t enough room in the crank case to put the balancing weights? I dropped off the rotating assembly and the stock gen vi bbc harmonic balancer. Are you saying that there is now a way to balance these engines internally?


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they can be internally balanced,
in fact with heavy metal slug inserts your crank can more than likely be internally balanced
(but its rather expensive to do, so going the current routes faster and cheaper)
SO YOU COULD EASILY BUILD A 489-496 bbc SINCE YOU HAVE YET TO BUY THE PISTONS & rings and get the assembly balanced (that and parts can be expensive)
and partly finance the swap selling the current crank/rods
MOST GUYS USE 6.385 RODS on a 496 BBC stroker,25337.html

increasing the displacement by swapping to a 4.25" vs a 4" stroke and upgrading to 200% stronger 6.385" rods ,
effectively boosts effective compression and easily gains you 50-70 extra free hp
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I know, but I just had a kid, and I am on a tight tight budget (as far as BBC swaps into C4 corvettes go). I already had the rotating assembly, so I gotta stick with a 468. Don't worry though, I have ARP Head studs, and ARP main studs, and I am building the engine at around a 9.5 compression ratio to be boost friendly. I plan on installing a BW S480 on the passenger side where the battery is once I get the main portion of the swap squared away.

I found another guy who has made a 4L80E to C-beam adapter, I sent him an e-mail. Unfortunately I currently do not have the skill, or the ability to fabricate it myself, so some of these parts will have to be purchased.

Also, thought you might find this interesting.

ZF6 and 4L80E are within .3-.5 of an inch of eachother in over all length from bellhousing lip to output shaft tip, and use the same 32 spline output shaft.

This means that once I figure out the C-beam adapter, I believe the stock ZF6 driveshaft will go right in. (I currently still have the Dana 36, I know theres a little bit of a length difference there too, but its a good starting place).
"I found another guy who has made a 4L80E to C-beam adapter, I sent him an e-mail. Unfortunately I currently do not have the skill, or the ability to fabricate it myself, so some of these parts will have to be purchased."

once you get that please post a detail dimensional correct machinist type drawing
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So no luck on the C-beam. Pete ZR1 sold out of his, and isn’t doing anymore. The guy making the adapters never got back to me. It doesn’t look like rocket science.

in other news, I believe the (Non zr1) c4 corvette has 9.75” of clearance from The China wall of the block to the bottom of the hood. Depending on engine mount health and hood fitment, etc. i believe through some creative fabricating and messing around with mounting holes and slots, you could maybe get that to 10”

The Bbc is at an automatic 1” (exactly) disadvantage, because the China Wall is an inch taller. That means we have about 9” to work with for intake height on a standard deck big block.

In the pictures below, I have a Holley 300-561 efi oval port intake with an Edelbrock 4bbl throttlebody 4150 (it is coincidentally both the carb base pattern, and also the edelbrock part number.

the China Wall to the top of the Throttlebody is 8.75” not including any air cleaner accessories.

the Tb itself is 2.75”

my machine shop can get an additional 1/8th of an inch off of the Throttlebody base by milling it (doable, although a little scarry). They can get me 3/8th of an inch off the manifold.

Accufab makes a 2” tall tb but $$$$$

plus, this tb has an onboard gm map sensor that accepts the stock plug. It also uses Gm tps and Iac, but slightly newer plug styles, but adapters are available.

i think the easiest solution here is a 2” drop base air cleaner with a 2” round filter, foam sealed to the hood, but it should allow the use of the stock hood easy peasy!

the picture with the air cleaner is a 1.5” drop base, with a 3” filter and a standard lid. It is 10.75” from China wall to top of air cleaner stud.

5808A5FE-91CB-445C-9F53-FB37D39CCB40.jpeg FD015051-DC2A-46A5-94A5-D18BBD8C86FF.jpeg
Also! The Edelbrock TB is set up for a 700R4 TV cable. I picked up a Spectre adjustable throttle and TV cable bracket, so I am planning on installing the constant pressure valve body, which should take some of the difficulty out of perfectly adjusting the tv cable.

i still don’t have the car back because inexplicably it is still the subject of litigation between myself and the shop that did everything but set it on fire.
you might consider fabricating something custom like this,
or custom air ducting, with a hood mod

limited hood clearance dictates use of an aftermarket intake on most C3-C4 hoods,


you can get creative and run duct work or use a custom hood design

if you think the 265cc BBC heads perk up an engine you have to try the 300cc versions,
I'e read more than a few dyno tests showing the results are very noticeably favoring the marginally larger port size especially if matched to a roller cam with at least 245 degrees of intake duration at .050 lift and at least 10.5:1 compression,
this seems to be especially true on 468 cid and larger displacement engines

300cc Competition Flow Chart



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Those are nice, I especially like the ss style scoop, but one of my original main goals was to try to keep the stock hood. A) the stock c4 is one of the best looking cars ever designed, and nobody has yet to improve upon the looks, and B) its sleeper as hell to get a big block under the stock hood.
Grumpy, have you performed the rack relocation? I have the small block out of it, empty engine bay. I am going to install my zr1 evap cover, and relocate the rack.

what did you cut the mounts with?
I used a HF die grinder/ cut off wheel on a couple, its slow but it works
Ive worked on several of these swaps, most of them other people started,
or completed, some I helped on the whole process
ITS always a good idea to try and test-fit the engine your about to install,
and accurately measure and mark on the cross member what clearance you need and where you need it!
and look into any oil pan, and other engine clearance mods that might be required

a plazma cutter might be better but I did not own one,
and a MIG welder to re-weld then 3/4" forward on the k-member/ cross frame.
be aware that the damper needs clearance in the frame, look at the pictures
this is not a project for a first time engine swapper but its certainly one,
thats manageable if you have fabrication skills an a few tools like a decent welder,
of course, accurate measuring and fabrication skills are key to getting good results
and looking at the links and pictures
it certainly helps
small notch (starting at rear and going 3" forward from rear edge X 3/4"deep X 5" wide works well in rear top surface of (K) frame cross member to clear damper and pulley)(if you use an internally balanced big block with the 6.75" diam. damper you can most likely skip the notch but with the 8" diam. damper its necessary, and some oil pans will also require the back 1 1/2 of the (K) frame to be notched at an angle sloping to the rear to clear them so you'll probably need the notch of some kind anyway)(and yes before you ask you could shim/modify the motor mounts up to get the clearance, but that would slightly raise the weight center and slightly effect the handling, and that also makes the windshield motor and distributor clearance a bigger problem)






re-read this thread and the links below
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Car is at my buddy’s shop getting the rack moved 3/4” forward. Giggity. Rebuilding the gen vi now. Its getting all new crank and rod bearings, a hone, hastings moly piston rings, mls head gaskets, comp xm284hr with titanium retainers and +.050 locks and that victor junior intake manifold I showed off earlier.


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Grumpy, i found this pulley, and its actually perfect with a short waterpump and the stock Vette accessories mounted with the kwik brackets.

do you know if the rack was relocated in this car to clear the pulley?

you can ans SHOULD always test fit your cars potential engine swap engine,
to accurately verify your car clearance issues
Its coming. I’m just trying to make sure that when I test fit it, I can say great!!! It fits!!! And go to work on getting it to run lol.

Made alot of progress today thanks to the excellent assistance of the invincible Jimmie Jacobs. Finished teardown, cleaned the block. Honed the cylinders, got almost a factory looking crosshatch pattern, although the number one cylinder looked like it was having an issue with heat that was causing some side loading. If This engine wasn’t nicknamed “Stopgap,” I would have sent this out for a .030 bore, and we unfortunately got sidelined by new part out of the box failures.

King bearings are garbage. I typically use Clevite in all of my builds, but I tried King on the advice of a buddy, and you can see in the pictures, one of the brand new bearings was total trash.

Also I ordered 2 sets of 8 count valvespring rotator eliminators, and got 1 8 count and 1 7 count.

We gapped our rings, installed our piston rings, and finished the valvespring upgrade on one of the heads.


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wow thats rather depressing.. congrats on making progress