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Pick a head, any head.

General engine tech -- Drag Racing to Circle Track

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c1500sbc
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Pick a head, any head.

Post by c1500sbc »

I’m looking to change the heads on my 383. Currently running some Promaxx maxx series 200 heads. I really think they are holding the motor back.

Mostly a street driven truck. 95 Silverado short box, 2wd with a 5 speed. 10.68 static compression. Running 93 pump gas. Street avenger carb. Crower 238/240 at .050 mid .500 lift roller cam.

Any suggestions?
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Re: Pick a head, any head.

Post by travis »

Holding it back, how?

My opinion fwiw…I think your combo has too much emphasis on upper midrange and top end power for the weight, gearing, aerodynamics, etc. That combo would be an absolute rocket in a nova or something…in a heavy truck the weight just sucks the life out of it and the reduced low end torque is MUCH more noticeable. BTDT, and working to correct it :wink:
KnightEngines
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Re: Pick a head, any head.

Post by KnightEngines »

Keep the heads, get a porter to give them a tidy up.
Heads are not your bottleneck.
Get the comp up to 11:1, ditch the street avenger & put a proper pumper carb on there (the brawler 750's work good on this type of engine).
Pop a holley strip dominator 300-25 on it, add 10 deg of cam duration & switch to 1.6 ratio rockers on the intake.

It'll be a whole different animal.

I dyno'd a basic 383 a couple of weeks ago, cnc DRP heads, off the shelf flat tappet 252/260 on 106 cam, 1.6 rockers, super Vic intake (couldn't get a 300-25), 11:1 comp & brawler 750.
Made 525hp at 6200rpm, 487lb at 4600rpm.
Idles like a kitten, pulls 12" vac at light load.
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Re: Pick a head, any head.

Post by Fatman »

Holding it back in what way? Not enough top end? What rpm does it see and what would you like? what intake manifold and exhaust on it? Carb size?
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Re: Pick a head, any head.

Post by mag2555 »

There holding you back because there 200 cc port volume is producing less average port velocity which is in turn doing the same to the motors torque band.

I would be looking for a head in the 185 to 190 port volume range, or maybe even the trick flow 175 and then do a bowl blend on them.

The Trick flow heads pass enough cfm at .500" lift to make darn close to 500 hp
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Re: Pick a head, any head.

Post by dannobee »

Define "holding the motor back." That thing should be fast enough to scare you on the street, given that those trucks didn't hook at all.

Back to basics before changing anything major; check ignition timing and do a fuel volume test, and make sure the throttle opens all the way.
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Re: Pick a head, any head.

Post by Walter R. Malik »

Advance the cam a bunch ... like 100 degree intake lobe center-line.
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c1500sbc
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Re: Pick a head, any head.

Post by c1500sbc »

Sorry, I guess I should have expanded on what I meant. I appreciate the interest/help and the questions.

The motor only put down 320ish to the wheels and 340 ish torque. Sorry can't recall the exact numbers. This is through a manual 5 speed as well. 2wd truck.

As I have read, and y'all have reiterated, I think the motor should be making north of 450 hp and torque. Maybe even close to 500. I cant imagine i'm loosing that much power through the drivetrain?

I should have gone with the brawler when I bought this street avenger. I got impatient and just went with what the local vendor had. I didn't realize it would make any significant difference. Can someone explain why that is?

I believe the cam was installed straight up. I'm newer to engine building. Can someone explain why I should degree it differently?

I can order some 1.6 rockers for the intake side. I see that is something a lot of people do.

So to clarify, I ran it on the dyno prior to realizing that the brand new harmonic balancer TDC mark didn’t align with the timing tab. It was actually 8 degrees off. I ran it on the dyno at 26 degrees rather than the 34 I though it was running! Not sure how much of a difference that would make in power numbers but it certainly felt stronger after realizing.

I’m running 24 degrees initial and 10 degrees mechanical. All in about 3,000 rpm. AFR at WOT is mid 12’s. Which again, a tuning error on the dyno, it was in the 11’s back then and had an edelbrock at the time.

I need to research how to do a fuel volume test. Stock electric pump with a regulator running 6 psi.
Last edited by c1500sbc on Thu Jun 10, 2021 10:34 am, edited 1 time in total.
c1500sbc
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Re: Pick a head, any head.

Post by c1500sbc »

KnightEngines wrote: Thu Jun 10, 2021 2:08 am Keep the heads, get a porter to give them a tidy up.
Heads are not your bottleneck.
Get the comp up to 11:1, ditch the street avenger & put a proper pumper carb on there (the brawler 750's work good on this type of engine).
Pop a holley strip dominator 300-25 on it, add 10 deg of cam duration & switch to 1.6 ratio rockers on the intake.

It'll be a whole different animal.

I dyno'd a basic 383 a couple of weeks ago, cnc DRP heads, off the shelf flat tappet 252/260 on 106 cam, 1.6 rockers, super Vic intake (couldn't get a 300-25), 11:1 comp & brawler 750.
Made 525hp at 6200rpm, 487lb at 4600rpm.
Idles like a kitten, pulls 12" vac at light load.
See, that’s about what I thought this motor would make. Obviously a little less with the smaller cam and less compression but similar power. Are you saying to swap the cam out or just advance it? Also, I’m only getting about 9” of vacuum and it certainly doesn’t idle like a kitten!
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Re: Pick a head, any head.

Post by dfarr67 »

Throw a blower on it.
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Re: Pick a head, any head.

Post by BillK »

I am curious exactly what it is you dont like about the performance ? If you had never seen the dyno numbers what would you say was wrong with the way it runs now ?
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c1500sbc
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Re: Pick a head, any head.

Post by c1500sbc »

BillK wrote: Thu Jun 10, 2021 12:25 pm I am curious exactly what it is you dont like about the performance ? If you had never seen the dyno numbers what would you say was wrong with the way it runs now ?
It runs great, but it just doesn't have the power I thought it would. I was expecting something with the ability to run with a newer SS camaro or similar. It certainly isn't scary on the street. I figured with a motor/set up that I have, it would roast the tires if I punched it in second gear from a roll. It definitely doesn't do that, even with the crappy traction these trucks have.

I guess to be fair, I raced a buddies 2015 SS (not a camaro the SS sedan). All he has is long tube, cat delete and a tune. Roll raced from about 10 - 100 mph. He had me by about two cars. I realize he has an automatic 6 speed trans and a much better chassis design but I feel I should have been able to at least be nose to nose with him. Again, to be fair, this was back when it was running the untuned edelbrock and only 26 degrees of timing!

Maybe i'm wrong, maybe this is all i'll get out of it.
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Re: Pick a head, any head.

Post by 77cruiser »

Just looked up the 2015 SS looks like the test showed 12.9@110, that's why it pulled away from your truck. I had a 383 in my 4200 lb. Monte it only ran 103 1/4 mile & had just about exactly the same chassis dyno numbers as you. What's your truck weigh? I had a 95 GMC, it was about 4700, 2wd ext. cab.
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c1500sbc
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Re: Pick a head, any head.

Post by c1500sbc »

77cruiser wrote: Thu Jun 10, 2021 1:16 pm Just looked up the 2015 SS looks like the test showed 12.9@110, that's why it pulled away from your truck. I had a 383 in my 4200 lb. Monte it only ran 103 1/4 mile & had just about exactly the same chassis dyno numbers as you. What's your truck weigh? I had a 95 GMC, it was about 4700, 2wd ext. cab.
Yea, plus I know his is a little quicker than a stock model. For whatever reason I figured I could get in that mid 12 range with this set up. Truck weighs in right at 4100lbs with me in it. I weigh about 165. Unfortunately there's not much option for weight reduction!
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Re: Pick a head, any head.

Post by Adger Smith »

That much RWHP and you want more.
You have an engine that is making over one HP per Cu in for the street.
You have the similar output of some nasty factory HP engines.
350 HP 327
450 HP 454
425 HP 427
375 HP 396
Get my drift.
BTW a dyno is a tool.
Take it to another Dyno you may have 400 RWHP.
IMHO every 383 needs big head to make big power.
Every 383 I have had on our dyno wanted a lot of air flow.
They have extremely high piston speed (FPS) and to make power over 6200-6500
they have to have some real good induction.
My .02 for free
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