Hey guys,

I'm currently in the process of doing a body-off-frame restoration on my '76 to pass the time with the COVID madness still ongoing.

This is the 2nd 350 engine I own, with the first being on a K5 blazer, which I rebuilt with a few upgraded parts to up the sound and power delivery a bit. I got Comp Cams Thumpr 227/241 cams with the required hardware needed to install; springs, rods...(I know not the best for power but I wasn't really interested in making big power but rather liked the noise it made), Edelbrock 2021 induction kit, MSD Street Fire distributor and some Hedman headers. I liked the outcome and it served as my learning course into modifying American engines as I'm much more knowledgeable with turbocharged modern engines; BMW in particular.

I ordered the same cam kit, distributor, Performer 1406 600cfm carb, and headers (which I might not install) as a starting point for my C3. Again, I'm not after making crazy power so please don't roast my camshaft selection as I just wanted that lopy American V8 rumble; I have my tuned BMW M2/M4 for making big power. Anyways, I'm now looking to take it a step further after lurking and reading a lot of posts on here.

After lurking and reading through many forum posts, I'm planning on getting 64cc heads from the local junkyards (whatever I can find locally as I live in the Middle East and shipping heads that heavy from the States right now just isn't worth it for me), and flat top pistons. From my understanding this would bump up the compression enough to make the engine livelier.

Do I need to upgrade the connecting rods with the mentioned parts? I just don't want the hassle of tearing the engine apart once again down the line.

These are the parts I'm looking to get from Summit.
1) Summit Racing SUM-17351C-30
2) Summit Racing SME-3-48-05-101 (if needed)

Please let me know what you guys think overall and if you have any suggestions for me. This is a very fun learning experience and I appreciate your wisdom/experience.

Thanks in advance.

 

Gotta know what you have first. While I have no first hand knowledge of that the threshold is of say the crank/rods that is info I’d want to know before I’d make a decision.

 

No....don't mess with the rods or you will have to re-balance. They are fine at your power level.

Jebby

 

trying to spin engine over 7000? then you need bottom end work. driving like a normal human? stock bottom end is just fine.

 

No....... He’s also replacing the pistons. He should rebalance the whole deal while it’s down.

 

Ah....didn't catch that, but if he gets a piston that is the same weight, he will not have to do anything......I would research it, shouldn't be that hard.

Jebby

 

600 holley isn't a great choice

 

Delete...got my threads corn-fused

Jebby

 

Interesting that you say that. Never really thought about it. Also I just realized the pistons I was looking at from Summit have a piston head volume of +6cc which is the opposite of what I need if I'm not mistaken. If anyone can share what flat-top piston setup they went with that would be great.

Worst case if I don't touch the pistons, I can hypothetically speaking accomplish the same result with the cylinder heads no?

Edit: I just saw that the stock pistons are somewhere near 13cc's of piston head volume, so by going to +6cc is going to give me what I need correct?

 

But as he said multiple times, hes not building for power... So a 600cfm holley will actually be more responsive and run better around town than an oversized carb picked for peak hp at peak rpm... Many advertised larger holleys like the 670 avengers are really just 625cfm carbs anyway from what I recently read... Maybe the 600cfm holley will help offset some of the fuel the thumper cams are known to burn through less efficiently to make the sound..

 

600cfm Holley is all you need at the moment, however if you decide to upgrade the engine power you will have to buy a new carb. I have always liked the 750cfm "classic". It is a great carb that will work for 300hp up and past 500Hp, generally a carb only uses what the engine needs.

 

Not quite that simple. With a stock L48 piston (I'm assuming L48 at this point) your compression with a 64 cc head is in the 8.5:1 ballpark. I realize you're after the muscle car lope but you want to achieve it with the right parts or it will be un-tunable and will never run right. You need to get your cylinder quench in the right place (.040 - .045 or so) so you don't have detonation/fuel burn issues. You want your compression to be 9.0 - 9.5:1 with that camshaft. Gears and a stall converter (if auto) would be your friends too. To get your compression in the ballpark you want it in without changing anything else you want a set of heads with chamber in the 55-60 cc range assuming stock thickness head gaskets with a 16 cc dished piston.

A flattop piston with 4 cc deep valve reliefs on 64 cc heads on a .040 head gasket will get you around 9.8:1 or so. 72 cc heads would have you around 9ish. Personally I would go about this differently if I was after idle chop but this info should get you in the ballpark.

 

Forgot to add something else. You must know how far down in the hole the piston will be before you can consider head gaskets etc. I did all my figuring with the piston .025 down in the hole which is typical with OEM builds of that era. The deeper in the hole the slug is the thinner the head gasket is to get your quench right and the smaller your combustion chamber.

Basically you have to have your short block 99% figured out before you can get 100% serious on what heads to run.