Don Terrill’s Speed-Talk

B Original wrote: ↑Thu May 17, 2018 5:35 am A moderately docile GM crate 383 is rated at 435 horsepower and 445 lb-ft of torque

With Vortec heads, still 75ftlbs from 520. I had a "good" relatively developed 383, with 10.7:1, bowtie vortec heads ported by a "professional" 230°.600 108° degree cam, with close to 100 dyno pulls on it playing with everything, make 518ftlbs on its best pull(there is a thread on it here) big torque don't fall off tree's..despite what you read. And i'm not saying that my 383 couldn't be improved on either still.

But its all hyperbole, we will likely never know the results of the op's engine, It should run decent for what it is.

An LS3 from GM 376" with headers, tuned up well on an engine dyno wont make 500lbs from what I've seen. Once again, that's not the be all end all, but its all in perspective.

I'm having trouble with the compression ratio you posted. I have measured several 383 combos with flat top KB pistons and a 64 cc chamber, and they always come out to 10.4: or 10.3:1. How did you achieve these results with an inverted dome?

https://www.speed-talk.com/https://www.speed-talk.com/forum/viewtop ... &start=105

This may not be the exact manifold for l-48 but I think it is close. Even with heavy porting it knocked 50 cfm off a modified head! 041's if done right can hit 260 cfm, to me the cam is a bit weak and intake is a disaster. The thread contains the workup on this manifold. Thanks, Charlie

Carnut1 wrote: ↑Thu May 17, 2018 10:19 am https://www.speed-talk.com/l48.jpghttps: ... &start=105

This may not be the exact manifold for l-48 but I think it is close. Even with heavy porting it knocked 50 cfm off a modified head! 041's if done right can hit 260 cfm, to me the cam is a bit weak and intake is a disaster. The thread contains the workup on this manifold. Thanks, Charlie

If you can Charlie elaborate on the heads? What experience do you have with them? When do they hit the wall,
you mentioned 260 CFM. Did you have to supersize the port to hit this #? Like over 185cc?

rfoll wrote: ↑Thu May 17, 2018 9:53 am I'm having trouble with the compression ratio you posted. I have measured several 383 combos with flat top KB pistons and a 64 cc chamber, and they always come out to 10.4: or 10.3:1. How did you achieve these results with an inverted dome?

With a 12cc dish I come to 10.3-1 with flat tops it was 10.89-1 (.041 Quench)

lol.. happy dyno's, engine sim's, and optimistic illusions of grandeur.. gotta love em'. It's what makes for great magazine sales too!

With the parts mentioned, ie: shooting your ponies in their hooves with a seriously outdated iron L48 manifold?.. and a "professional port job"(and that term is used VERRYYY loosely cause anyone that get's paid is a "pro" right?).. I bet you barely if ever make 410/430. Go ahead and run it 200 times on the dyno to suss out the tune and that parts combo will also still likely fall over the proverbial cliff much past 5,500 rpm.

And there is no magic cam for that combo to run a 3.36 gear.. so don't blame the cam choice when the entire induction setup is maiming its abilities to move air and fuel. In fact.. put that same cam in control of a better set of heads with airgap manifold and holley 750 and watch it gain another 40 horses or more while extending the peak of said cliff.

Physics is fun.. at least till it doesn't agree with your wallets ability to create an actual reality.

OP, If the engine is not to be dynoed, and your Saginaw doesn't break, youll know your very low on power. Just kidding

CGT wrote: ↑Thu May 17, 2018 11:18 am OP, If the engine is not to be dynoed, and your Saginaw doesn't break, youll know your very low on power. Just kidding

Lol, can't count how many Saginaw clusters I broke. Changed at least 3 in my high school parking lot! Hahaha

B Original wrote: ↑Thu May 17, 2018 10:51 am

Carnut1 wrote: ↑Thu May 17, 2018 10:19 am https://www.speed-talk.com/l48.jpghttps: ... &start=105

This may not be the exact manifold for l-48 but I think it is close. Even with heavy porting it knocked 50 cfm off a modified head! 041's if done right can hit 260 cfm, to me the cam is a bit weak and intake is a disaster. The thread contains the workup on this manifold. Thanks, Charlie

If you can Charlie elaborate on the heads? What experience do you have with them? When do they hit the wall,
you mentioned 260 CFM. Did you have to supersize the port to hit this #? Like over 185cc?

Right around 185cc

B Original wrote: ↑Thu May 17, 2018 10:51 am

Carnut1 wrote: ↑Thu May 17, 2018 10:19 am https://www.speed-talk.com/l48.jpghttps: ... &start=105

This may not be the exact manifold for l-48 but I think it is close. Even with heavy porting it knocked 50 cfm off a modified head! 041's if done right can hit 260 cfm, to me the cam is a bit weak and intake is a disaster. The thread contains the workup on this manifold. Thanks, Charlie

If you can Charlie elaborate on the heads? What experience do you have with them? When do they hit the wall,
you mentioned 260 CFM. Did you have to supersize the port to hit this #? Like over 185cc?

Jpeg states 186 but it has an angled plug so this is a pic of my Crane fireball 492's but they are very similar to the 041's. These are cut for 2.055/1.6 valve combo and have a good amount of porting. I would do the Vizard sweep a bit different on the chamber now but a set of 186's very similar to these made excellent torque on a 383 up to 6500 rpm with a healthy hyd roller cam. Thanks, Charlie

B Original wrote: ↑Thu May 17, 2018 10:57 am

rfoll wrote: ↑Thu May 17, 2018 9:53 am I'm having trouble with the compression ratio you posted. I have measured several 383 combos with flat top KB pistons and a 64 cc chamber, and they always come out to 10.4: or 10.3:1. How did you achieve these results with an inverted dome?

With a 12cc dish I come to 10.3-1 with flat tops it was 10.89-1 (.041 Quench)

You didn't mention a 0 deck. Typical 0.02"-0.25" deck will reduce those numbers by 1/2 compression point.

rfoll wrote: ↑Thu May 17, 2018 6:52 pm

B Original wrote: ↑Thu May 17, 2018 10:57 am

rfoll wrote: ↑Thu May 17, 2018 9:53 am I'm having trouble with the compression ratio you posted. I have measured several 383 combos with flat top KB pistons and a 64 cc chamber, and they always come out to 10.4: or 10.3:1. How did you achieve these results with an inverted dome?

With a 12cc dish I come to 10.3-1 with flat tops it was 10.89-1 (.041 Quench)

You didn't mention a 0 deck. Typical 0.02"-0.25" deck will reduce those numbers by 1/2 compression point.

With exception this can let your compression vary .5 compression point from one cylinder to the another. You make a very good point. I know there are a lot of guys that clean ther block use what they have and Assemble and nothing wrong with that when it suits there purposes with financial and time constraints. And I have no disrespect for anyone else that does it this way I growed up in my Granddaddy's garage and his motto was he that can do the most with the least wins and I still do let this motto play in many parts of my life.

But when I have a paying customer I let my attention to details takeover considering my average clientele doesn't want me to deliver average mechanic shop repair work.

I do this in a custom shop and sometimes i assume that everybody typically preps an American V8 block to a .035 to .041 quench clearance with block Square deck to zero piston height then bored and torque plate honed. With all referenced to main bearings bore checked and honed if necessary

Maybe I live a sheltered existence of only prepping a block this way lol

I put in a piston with a top ring, seal it with a thin swipe of grease, bring it to tdc, and cc the deck. I never believe published data. Piston volume and chamber volume are rarely what was advertised by the manufacturer. I have yet to cc an intake port and find the advertised size. The factory advertised compression ratios are theoretical, I have found them low by a full point. It's time consuming work, but it matters when you run pump gas.