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Old 03-08-2018, 12:43 PM   #1
ThunderTruck
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Need Some Engine Advice - 383 Stroker

I have a '72 2WD C-10 with a very high-strung motor I need to mellow out for better low RPM torque.

I built the 383 years ago (I was 15 and thought I was tough but really just dumb...), and it has always just been way too revvy and boggy in the lower RPMs, and also ridiculously loud to drive.

Here are the basics of the build:
800cfm Edelbrock Thunder series Carb
Weiand Team G Single Plane Intake manifold
World Industries heads with 220cc intake runners, 64 cc combustion chamber - I think it is running 10.5 to 11:1 compression...
Crane Cams Flat tappet hydraulic cam - Advertised Duration 292/302 (Cam Timing 234/244), Valve Lift .488/.510 (with 1.5 rocker ratio)
1.6:1 Roller Rockers
MSD Ignition
Headers with 3" true dual exhaust and LOUD mangaflow? mufflers

I'm running the stock SM465 Muncie with 3.73 posi rear end, and it is just really boggy and hesitant below 3,000 RPM. I have it rev limited at 6,000 but seems like it would rev to 8k if I let it.

Here are my initial thoughts....
1. Run some break-in rockers with a 1.35:1 ratio? Maybe more expensive and difficult than just swapping the cam and keeping the 1.6 rockers, but just throwing it out there.
2. Install a dual plane manifold? Edelbrock makes some affordable options. Maybe keep the single plane and run a restrictor plate?
3. More restrictive/quieter mufflers

I'm trying to avoid swapping the heads and cam but it seems like a cam swap may be my best option. I live at 5,500' altitude so maybe I can get away with the high compression on pump gas. I've re-jetted the carb per Edelbrocks recommendations and it helped a little bit. I can't run the initial timing any less than ~18 degrees without backfiring/flames coming out carb and/or starting issues.

I'm interested to hear any and all thoughts on the easiest and most economic ways to calm this beast down!

Last edited by ThunderTruck; 03-08-2018 at 12:47 PM. Reason: Need to add tags
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Old 03-08-2018, 12:48 PM   #2
A1971Blazer
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Re: Need Some Engine Advice - 383 Stroker

Cam swap.....your cam is for high RPM (as you already know)....
the GM crate HT383 makes huge torque at low RPM...... advertised at 444ft/lbs@3000RPM....
look at that cam size if you want low end torque.... .431/.451 lift with 1.5 rockers
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Old 03-08-2018, 12:51 PM   #3
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Re: Need Some Engine Advice - 383 Stroker

Part of the "boggy" comes from the big carb and single plane intake....

I would change the cam, carb and intake.....keep the heads and exhaust....don't have as much impact.
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Old 03-08-2018, 01:13 PM   #4
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Re: Need Some Engine Advice - 383 Stroker

OK, here's my recipe. If you could change to a higher velocity (smaller port) head it'd be even better, but, assuming you keep that:

- Replace single plane Team G intake with Edelbrock Performer
- A cam with way less duration like 208 degrees at 0.050 max (factory 300hp cam is 190-something, after all)
- Large Dynomax mufflers (no drone, quiet at idle, loud under load) with pipes out to behind rear wheels at least, ideally past bumper
- Ideally, have carb dyno tuned by reputable old guy (not millennial tuner dude)

Everything else should just work. Basically you've got a motor there tuned for 6000rpm and by changing the cam and intake you "reprogram" it to run at lower RPM.

That combination would yield a torquey, quick responding truck that was made for in-town driving and the occasional blast from a stoplight. It'd be quiet unless you were trying to be loud. I think you'd enjoy it a lot more!
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Old 03-08-2018, 01:14 PM   #5
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Re: Need Some Engine Advice - 383 Stroker

Swapping from 1.6 to 1.5 rockers isn’t going to move the powerband. The valves will still open at the same time (relative to piston position) they just won’t open as much. When the valves open has more effect on where power is made than total lift.

If it was me I’d swap for a dual plane and see how you like it. If that doesn’t do enough then cam swap. You’ll eat up a set of gaskets if you end up doing a cam swap but that’s a small price to pay for experimentation.
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Old 03-08-2018, 01:29 PM   #6
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Re: Need Some Engine Advice - 383 Stroker

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Swapping from 1.6 to 1.5 rockers isn’t going to move the powerband.
Increasing rocker ratio increases duration, and the 1.6:1 rockers will have slightly longer duration as a result, moving the power band UP the rpm scale somewhat. I mean from a technical standpoint... I doubt that amount of duration would make any difference in the actual driveability.
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Old 03-08-2018, 01:34 PM   #7
ThunderTruck
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Re: Need Some Engine Advice - 383 Stroker

Awesome! Thanks for all the advice guys. I'm thinking I just need to bite the bullet and go with a cam and intake swap.

One more question on the build.

I have a 7qt oil pan with a high volume pump and the oil psi is very high even at idle, and it will spew oil out the valve covers onto the headers at higher revs. I was planning to switch to a standard volume pump, but curious if you guys had any other tricks or ideas to address this issue.
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Old 03-08-2018, 01:41 PM   #8
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Re: Need Some Engine Advice - 383 Stroker

The cam and intake will be a good start. I would definitely reconsider your carburetor as well.

A standard-volume pump is all your engine needs, and you've seen what a high-volume pump does for you.
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Old 03-08-2018, 01:47 PM   #9
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Re: Need Some Engine Advice - 383 Stroker

A high volume pump shouldn't cause problems, though a high-psi pump can. A high volume pump just has larger rotors that have the ABILITY to push more oil but since the relief valve and spring are the same, it will NOT flood the upper engine as a result.

If you have a high PSI pump though it can, at least that's been my experience.

Some people restrict oil flow to the upper gallery, though that's almost always on roller cams and I wouldn't monkey with it on a flat tappet motor.

My bet is you've actually got a higher PSI spring in that oil pump and the high volume part is unrelated.
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Old 03-08-2018, 02:29 PM   #10
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Re: Need Some Engine Advice - 383 Stroker

Quote:
Originally Posted by ThunderTruck View Post
I have a 7qt oil pan with a high volume pump and the oil psi is very high even at idle, and it will spew oil out the valve covers onto the headers at higher revs. I was planning to switch to a standard volume pump, but curious if you guys had any other tricks or ideas to address this issue.
Some thoughts:

1) Where are you leaking from? If from valve cover gasket, try some Felpro steel reinforced blue silicon gaskets. If you are running stamped steel valve covers, swap in a set of cast aluminum covers. If you are leaking out of the oil filler and PCV ports on the covers, check to make sure you have baffles installed in the covers.

2) Another way to possibly reduce the amount of oil that collects under the valve covers is to open up the drain ports in the heads to allow oil to return to the pan more efficiently.

3) Generating crankcase pressures under the valve covers from a disabled/improper PCV system?
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Old 03-09-2018, 12:08 AM   #11
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Re: Need Some Engine Advice - 383 Stroker

I agree with switching the cam and intake. I would also consider a smaller carb. You want to be careful to not go too small on the cam. Maybe something like the Comp XE262 or XE268. It partly depends on just what pistons are in the engine and what size the combustion chambers are. A smaller cam is going to increase your cylinder pressure and be more prone to detonation. A dual plane intake such as the Performer or Performer RPM would be a good choice.
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Old 03-09-2018, 10:32 AM   #12
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Re: Need Some Engine Advice - 383 Stroker

Keep the motor as is and swap out the tranny for a better geared 4 speed or a turbo 400 and high stall converter.
Whatever changes to the motor you start with will snowball into a couple grand in a heartbeat. Same or less money to swap the tranny.
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Old 03-09-2018, 11:13 AM   #13
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Re: Need Some Engine Advice - 383 Stroker

One of my favorite YouTube series is called "Engine Masters" produced by the guys from Hot Rod. They talk a lot about the philosophy and do real dyno tests with real hardware. Single-plane, dual-plane, big heads, small heads, big cams, small cams, and so on. Lots of types of engines, but a good slug of Chevy small block testing in the mix. It's worth your while to watch a few episodes. I've watched them all -- and the Chevy ones multiple times. Lots of great content.

It sounds like a really fun motor, BTW, but I totally understand your desire to tame it. I've gone extreme myself in the past and am now focusing more on a "stock" Corvette version of the 1970 small block for my C10.
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Old 03-09-2018, 12:38 PM   #14
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Re: Need Some Engine Advice - 383 Stroker

I was going to suggest you get a 3000-3500 stall but, since your "Stall" is your left leg, your best bet here is cam swap.

If it were me, I'd call up crane cams, tell them exactly which cam is in there and exactly what I want and just let them suggest a grind that would bring the HP/Torque range down to where I wanted it. They could also suggest changes to your rockers, intake and carb if necessary.

Cam + lifters ( flat tappet ) will run you under 500 so this should be an affordable fix!

Hth,

-klb
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Old 03-09-2018, 01:38 PM   #15
ThunderTruck
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Re: Need Some Engine Advice - 383 Stroker

Quote:
Originally Posted by Captainfab View Post
I agree with switching the cam and intake. I would also consider a smaller carb. You want to be careful to not go too small on the cam. Maybe something like the Comp XE262 or XE268. It partly depends on just what pistons are in the engine and what size the combustion chambers are. A smaller cam is going to increase your cylinder pressure and be more prone to detonation. A dual plane intake such as the Performer or Performer RPM would be a good choice.
Good point on the cam selection here. I just pulled the trigger on a Comp XE262 which I will plan to run with the 1.6 rockers. I also went with a Performer dual plane intake and a standard volume oil pump. I'll see how this setup works and decide if i need a smaller carb at that point.

A tranny swap might be in the cards at some point. I want to keep it manual, so thinking a 4 spd without granny low would be a nice and easy swap at some point. What do you guys think about running a splitter on the stock 4 spd?

Thanks for all the advice and pointers and I'll let you all know how it turns out - hopefully in the next few weeks.
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