Performance Lacking in a 383 Build.

[HO455]

Originally Posted by garyd1961

Why would you run an open spacer on a duel plane intake.
.

I too have successfully used open spacers on dual plane manifolds. In my case it was on a .030 over 400 Pontiac with #62 heads I ported, a Ram IV cam and a set of 3 tube headers. After experimenting with several different combinations of spacers between the stock intake and the Q-jet I found that a 1/2" of stacked gaskets and metal plates that matched the intake holes topped by a 3/4" open spacer made the car quicker in the 1/8 mile. In addition and more important was that it moved the power band up slightly which made it easier to launch the car without spinning the slicks. Consistency wins races. And since it was my daily driver it definitely made the car easier to drive in the rain.
If the firing order of the engine and the physical layout of the intake manifold allowed exactly equal time between intake opening signals as they reached the carburetor then it is unlikely an open spacer would be helpful but since that isn't the case your trying to make the all the compromise work the best.
The picture shows a stock Honda manifold and if you think about it, it's basically half a dual plane manifold with a spacer on it. Just laid out differently.

[hjewell2]

Originally Posted by Myself

Well, for starters he's got Edelbrock RPM heads with 64cc chambers! With that Eagle rotating assembly, that's OVER 10.5:1 compression! So, basically we have a VERY nice street strip smallblock with grandpas low compression smogger 350 RV cam in it! It's just wrong! It's like spending 75k building your dream garage and leaving a gravel floor in it......it's just wrong!

Change the cam AND intake, you will not know what to do with all the tire smoke!

Yes this is correct right to a tee.

[i82much]

I have a 396 in a 72 k10 longbed with 3.73’s and 32 inch tires, th350. It runs well but you have to realize the weight of a 4x4 truck, the weight of the tires, and the effective gear ratio have a huge impact. You have the same effective gear ratio as a car with 26 inch tires and a 3.23 axle.

If we put your 383 in a 4500 lb wagon with 3.23’s and it ran like your truck does now, would you still think it was slow?

[tim_mc]

Just a few thoughts that might give you a few ideas. I recently "woke up" my new 350 by correcting my lifter preload (long story, more below) and finding the #3 plug wire had rubbed through the woven fiberglass protector sleeve against the header and was shorting out. After fixing those issues along with a bent pushrod on #8 cylinder, my engine now has a lot of snap, idles smoothly, revs quickly and runs great.

I echo what 3767 has stated. Your setup doesn't appear to be suspect and should have a lot of low end torque like mine, although I agree with others that the Edelbrock 2101 intake might be on the small side. I went with a 2701 EPS which Edelbrock claims is good for +5 hp and +9 ft.-lbs over the older Performer intakes, but is only tapped for square-bore carbs. While I don't suggest throwing money at problems blindly, a (GM?) HEI and plug wires might be worth it if they aren't new.

Notes from GM: HEI 93440806 distributor has a preset timing curve. The timing should be set at 32 degrees total at 3,000 RPM with the vacuum advance disconnected. 10 degrees initial timing at idle should provide this total. At 1,600 RPM the mechanical advance is 12 degrees. The vacuum advance is set to 20 degrees at 7.5 in. of vacuum.
(I'm running 12 degrees of initial timing, and per GM instructions I am using ported advance. I've played with this as well and settled on using the ported vacuum with the canister that came with it.)

I would also suggest pulling the plugs and valve covers and turn the engine over by hand to see if there is anything binding or rubbing on the top end.

A couple of my recent lessons: My Brodix heads came with non-adjustable COMP pushrod guideplates, which didn't line up the rockers properly on the #3 & #4 cylinders. I switched those two plates out with COMP #4835 adjustable guideplates and got the roller tips centered back onto the valve stems. I also suspected that I had set the initial lifter preload too tight. Since I had to readjust #3 & #4 anyway, I backed off all of the rockers and went with 1/4 turn after zero lash, meaning no vertical play in the pushrod, and NOT using the "spin" method which I got wrong during engine stand assembly. You may not have anything amiss in the valvetrain, but it doesn't cost anything to check.

My setup for comparison, although not a 383:
GM crate 350 12681429 with dished pistons
Comp Cams Xtreme Energy Cam and Lifter Kit SK12-408-8, XR258HR, Dur @ 050: 206/212, Lift: .480/.487, 110 LSA (mild, but should get good mileage)
Comp roller tip rockers, 1.52 ratio, 7.266" pushrods
Brodix IK 180 heads, 70cc chamber, 180cc intake runners (could have gone with smaller chambers, but oh well)
Edelbrock 2701 Performer EPS dual plane intake, and 1905 AVS2 650CFM carb
New GM HEI 93440806 & Accel 4048 8mm HEI plug wires.
ACDelco 41-629 spark plugs, gapped 0.045".

Like Conoco, I am a big fan of the AVS2 carb. I wound up leaning it out a bit from stock. So far I have good plug readings, easy starting, plenty of fuel for acceleration and no lean surges while cruising. I may continue to tweak the carb after getting more miles on the new engine.

Good luck!

[jimijam00]

Total timing is at 35ish, right?

[chevy71super]

I experienced the same phenomenon as i82much pointed out. When my sb350 was first built it could spin the 28ish tires over with relative ease with a turbo 350 and 3:07 gears. Fast forward to today with 35 in tires (Goodyear MT/R) and a 4:10 rear end it can barely get them to spin (Detroit locker) with less than adequate acceleration. Braking distance was also drastically increased. The price you pay for off road capability. . .

With that said a 383 the truck should behave more like it would if it had a big block so something is amiss. With big tires I would focus on how much torque the motor makes and when. As Carrol Shelby famously said “horsepower sells cars, torque wins races.” Or something like that. I also like this one:

https://images.cdn.circlesix.co/imag...6473fb4b93.jpg

[Myself]

For that engine, I would have chosen a cam more like this...
https://www.summitracing.com/parts/c...make/chevrolet
You spent the money on great street heads that can handle .600 lift.......let's take advantage of that. I would have also went with this intake...if I could find a nice one.
https://www.ebay.com/itm/Weiand-Stea...cAAOSwOmZe9m6I
That's the OLD style #8016 intake. It has much larger plenum volume than the new versions, and with a notch cut into the divider will NOT have a 2200rpm +/- flat spot, and will pull hard to 6500rpm. It's my favorite manifold for an old school sbc build.
And I would top it with a 770 Street Avenger or 750 Road Demon for great kick in the pants feel as well as good driveability. I have a 570 Street Avenger on my mild 305 that I drove daily for 16 YEARS! Also had a 670 on a mild 305 headed 350. Friend of mine went with the Road Demon and overall "feel" is the same as the Street Avenger line.
I would also like to see a bit of extra stall in the torque converter. Something like this....https://www.speedwaymotors.com/B-M-2...ns,337050.html works GREAT in a street car. Don't forget a nice trans cooler. Throw these parts on that engine and you will have NO problems roasting 33" tires with a 4.10 gear......I promise!

[garyd1961]

Originally Posted by Ziegelsteinfaust

Because it allows the individual cylinder to draw from both sides of the carb.

It evens out afr, and smooths out the carburetor signal.

Plus can reduce the needed size of a carb in many engines.

Provides extra plenum volume some combos really need with out a manifold change. A 1" spacer on a Super Victor manifold is not the same thing on a Performer dual plane manifold. Where the concept really shines by comparison.

Does it work on a dead stock low compression smogger 350. I have tried it, and got no where. This was a last tuning trick on a already well tuned engine.

This is a worse case scenario, but I have done it on a built 350 that I had for a sleeper build I was fascinated in. It had Dart iron eagle heads with about 190cc runners, and 64cc chambers. Followed up with 9.5-1 compression, and pretty wicked circle track mechanical flat tappet cam. I ported a cast iron intake to get as much advantage out of as possible. When I got it running I had the Q-jet on the manifold as normal, and it was pretty wicked. After hours of needle, and other changes.

Well a few weeks later I made a 1.5" spacer out of resin coated wood because of a article I read, and the truck was on the road fully as a back up vehicle. Plus I recovered financially, and emotionally from the project. So I had time to play again. Drivibility went up considerably, and felt power was across the board.

Its hard to say in words, but the cam/carb combo was not ideal. Just when driving the truck when the engine was up to temp it had a bunch of flat spots in part throttle. The spacer smoothed out idle, and removed all but one of the flat spots. That flat spot was at just under 2750rpm under full throttle. Plus I had to lean the carb out again due to more even air flow. So mpg would go up. It got crap mpg anyways so it would be hard to confirm, but memory says it went from 11mpg to 12 mpg. Under the more idealistic conditions, but not really noticeable bombing around town. That engine drank gas.

As for power before it could easily bark the tires hard in second. After it could continue the burn out into 2nd gear.

HotRod, and Carcraft have a bunch of articles on how they work. Plus they hopefully can explain it better then I could.

The duel plane with a modest came will give you a lot of low end torque. That seems to be what this motor was built for. If you want to convert it to a high revving high hp motor than an open spacer and big cam in the .550 lift range would make it run like a scalded dog. I had a 383 with that setup and it would run but wasn't really good for the street.
I would leave it as is and find what the problem is. Get it running right and it still should have a lot of power.

ETA, Some of you guys are suggesting a bigger cam someone even suggested one in the .600 range. That's fine if you are building something for the dragstrip but for a drivable truck on the street it's way too much. The motor should have way more power than needed with the current setup. Find what's wrong with the motor and fix it before changing the cam and intake. I'll bet once it's running right you won't want to change anything.

[Myself]

Originally Posted by garyd1961

but for a drivable truck on the street it's way too much.

But then again........so is a 10.5:1, aluminum headed, 383..

[Ptjsk]

I can't thank you guys enough for providing your input.

The first thing I'm going to do on Monday is see if I can't find a dyno for it.

Hopefully, that will be able to provide some guidance as to what the motor needs.

Thanks again for all the information.

Pat

[Myself]

Keep us posted with results.

[JMD]

How sure are you that the 15* of initial timing is actually 15*? When the pointer is at the TDC mark on the balancer, are you sure that the #1 piston is truly at TDC?
Aftermarket balancers and timing pointers can be inaccurate. If you’re setting your timing based on an incorrect TDC position, your 15* of initial could be more like 10*

[HO455]

Originally Posted by Myself

But then again........so is a 10.5:1, aluminum headed, 383..

Nobody runs a LS3 in their DD truck?

[KQQL IT]

What do the plugs look like?

[garyd1961]

Originally Posted by Myself

But then again........so is a 10.5:1, aluminum headed, 383..

No it's not, a 383 can be a real torque monster and still run smooth. The only thing about the 10.5:1 compression would be the need for premium gas. The aluminum heads just make it easier to run the high compression on pump gas.

[Ptjsk]

Well.....after several months the motor is back out of the Jimmy.

I have 5 broken pistons (at the skirts), and 4 of them have chunks broken off of the top of them.

I really don't know how the hell it even ran.

Keith Black Hypereutectic Pistons. Top oil ring gapped to .026 thousandths.

I think the original engine builder just totally screwed the pooch! Pistons were noisy as hell from day one! Unfortunately, he's since passed.

Pretty much have to start over after throwing thousands down the drain.

I'll find out next week if I have to bore it more or not, and what the plan of attack will be.

Pat

[Bad4wd]

Since the motor out getting rebuilt. Replace the transmission with a 700r4. First gear alone will smoke 35” tires with a built 383 and 4.56 gears and go down the freeway at 75. With a 350 trans good luck.

[sick472]

I've had a similar problem with the hyperutectic pistons and poor machine work. Those pistons, iirc, require a tight tolerance for the bore sizes and if they are not just right...its "so long pistons". My block was overbored in two of the cylinders and could not be bored any further to jump to the next size pistons. I had to find another block.

Hypers don't swell and contract as much a forged pistons do and like a tighter bore. If all is right, they don't knock on a cold start up like forged, but if the bore is too large...they don't swell up enough to fill the bore and slap themselves to death.

Scrutinize your bores before the rebuild.

[CUSTOM/10]

Hey Pat,
Sorry to hear about your engine. If you build another 383 build check the length of the cylinder bores, some blocks have shorter bores and are not good for the longer stroke of a 383. ( 880 block being one ) The piston skirts stick out to much at the bottom of the stroke and cause piston rattle and the skirts brake. It sounds like this is possibly what happened to your engine.

Gary

[SCOTI]

Based on your (this) experience, I'm thinking if you still want a 383/stroked sbc, maybe just get a short block assembly from an established business. Put your parts on it & enjoy...

[Mike C]

I've been following along on the thread you have on the Corvette forum. Will be interesting to see what you find out and how you work to prevent it in the future.

[SkidmoreGarage]

Originally Posted by SCOTI

Based on your (this) experience, I'm thinking if you still want a 383/stroked sbc, maybe just get a short block assembly from an established business. Put your parts on it & enjoy...

This sounds like a great suggestion. Building an engine is best done by a company which specializes in building a lot of engines, in a clean room, and gives a warranty.

[Ptjsk]

Yea, you guys have given me good suggestions.

I do now have it at a very reputable engine builder. He is going to assess the motor and provide me with information that will decide which way I go.

Thanks,

Pat

['68OrangeSunshine]

Is this in a Blazer [K/5] type truck? Even though GMC called them K/1500, not ''K/750''.
Or are you using Jimmy as a nickname for a GMC pickup?
4.56:1 is unusually low for a rearend on a light 1st gen suv. Most are 3.73:1 or even 3.07:1 in a half ton.
If you're talking about a 3/4 ton GMC, never mind. But 4.56:1 on a half ton Blazer is real low. And you'd do better with higher gears, like 3.73.

[SCOTI]

Originally Posted by '68OrangeSunshine

Is this in a Blazer [K/5] type truck? Even though GMC called them K/1500, not ''K/750''.
Or are you using Jimmy as a nickname for a GMC pickup?
4.56:1 is unusually low for a rearend on a light 1st gen suv. Most are 3.73:1 or even 3.07:1 in a half ton.
If you're talking about a 3/4 ton GMC, never mind. But 4.56:1 on a half ton Blazer is real low. And you'd do better with higher gears, like 3.73.

It all depends on the final tire size & how the vehicle is used. 4.56's might be too low for you, but just right for another enthusiasts combo.