Performance Lacking in a 383 Build.

[gmc684x4]

Do you have stock style stamped rocker arms?

"I have three questions
(1) I have read that I might need longer push rods for these heads? Im putting them on a 350 with stock stamped rocker ar ...read more
Asked by ROBERT on January 23, 2018

A:
(1) YES, if you choose to use OE stock stamped steel rocker arms, you need +.100" longer than stock push rods # 9629
(2) YES, however you need at minimum Hardened Washers under the OE stock head bolts, and you should confirm length before bolting on your engine.
(3) YES, your early model Performer intake manifold will bolt directly on without issues.
NOW, why would you consider Angle Spark Plug Cylinder Heads? The Angle Spark Plugs may not clear your exhaust. Why will you use stock stamped steel rocker arms, and hope the slot in your rocker arms accommodate the lift of the camshaft you're using. Thank you for your inquiry...."

https://www.summitracing.com/parts/edl-60995

[Ptjsk]

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!

Thanks for taking the time to write this out. I definitely need another set of eyes on it!

Pat

Originally Posted by SCOTI

I'd like to hear the theory as well.

Specs:
270/278
217/225 @ .050
.495/.500 w/1.5's
110LSA

That combo should offer plenty of cylinder pressure for low end grunt. I didn't do the math on the combo but can. I would also recommend a dyno session if possible. A 2nd set of eyes going over everything might not hurt as well. Sometimes someone else will see something differently.

*EDIT*
Quick calcs w/some guestimating:

4.030 bore; 3.75 stroke; 5.7" rod; flat-top/6cc valve reliefs; .039/4.10 bore head gasket; .025" deck clearance; 64cc heads

With a mild cam like that (34.5 IVC) & the combo mentioned; compression numbers 'suggest' around 10.4:1 static/9.18 Dynamic compression.
The heads should still work just fine. The intake while 'small' for a 3.75 stroke SBC would still work but it won't offer full top end potential. Below 3500rpm? It should be very close to the RPM series of intakes. Calcs suggest ~400hp/5krpm based on 250cfm intake flow @ .500 lift. So if that's achievable, there's something possibly not set-up correct.

Thanks a bunch for your information. I too, feel there's power somewhere that I'm not able to achieve.

Pat

Originally Posted by SkidmoreGarage

Why would spending more money on parts be the solution to the problem, that's just guessing. Engines aren't that complicated. If it feels slow (but without an actual measurement and assuming 300hp) it's probably down 100tq/100hp. Unless something is broken, you won't see that kind of power loss with just
non-ideal aftermarket parts. With an "RV cam", you should see more peak torque than HP. This should feel snappy and fast when you step on it, even if it has falls on its face once you get moving.

A dyno is probably $500, and will tell you a lot more than musical chairs with nice parts. It could also save you an engine rebuild, as a lot of power issues come with incorrect air fuel ratio. An old school guy may be able to tell you something similar with a drag strip, but that kind of expertise doesn't come cheap. With a good dyno tuner, you can also make some changes and run again.

It definitely doesn't feel snappy. In fact it feels sluggish. Even though I have 410 gears, there's no way it would break the tires loose.

I think a dyno tuner is a good way to start. Thanks for the information!

Pat

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.

Thanks Bud! I definitely don't need to worry about 2nd gear, as I can't even get the wheels to spin in 1st gear.

Pat

Originally Posted by gmc684x4

Do you have stock style stamped rocker arms?

"I have three questions
(1) I have read that I might need longer push rods for these heads? Im putting them on a 350 with stock stamped rocker ar ...read more
Asked by ROBERT on January 23, 2018

A:
(1) YES, if you choose to use OE stock stamped steel rocker arms, you need +.100" longer than stock push rods # 9629
(2) YES, however you need at minimum Hardened Washers under the OE stock head bolts, and you should confirm length before bolting on your engine.
(3) YES, your early model Performer intake manifold will bolt directly on without issues.
NOW, why would you consider Angle Spark Plug Cylinder Heads? The Angle Spark Plugs may not clear your exhaust. Why will you use stock stamped steel rocker arms, and hope the slot in your rocker arms accommodate the lift of the camshaft you're using. Thank you for your inquiry...."

https://www.summitracing.com/parts/edl-60995

No, I have roller tipped rocker arms on the motor. The engine builder based the length of the push rods off of these rocker arms.

Thanks,

Pat

[Daves70]

Torque converter too tight? A snappy motor like that may need a looser converter.

[3767]

First off pat, u have a nice set up. I’ve had those heads and they are nice. Whomever built your engine got some good parts for it. The cam is fine. For a 350, it a very good all around cam. For a 383 it’s mild. The performer rpm works best overall for these heads on the street but your intake imho is fine for what u need it for. Your not going to have the speed of a new sports car. U are just to tall and heavy for that. But, I didn’t read anyone suggesting this so....check your spark plugs and wires. Doesn’t cost a thing but time. In the wires...check to make sure they are all on tight. U should b able to pull against them and they shouldn’t just pop off. If u have an ohmmeter, check the resistance of each 1. I don’t know the brand so I will use msd as an example. They have 50 or less ohm reading. A stock style wire will have far more resistance and not give an engine like this enough fire. Plugs....just look at each 1 to c if u have any cracks n the porcelain part. Look at the gap. U need at least .045. Look at the tip. Is it all black, or is it a white grey color. This will tell u that u are getting enough fuel and u are burning it off. Lastly....if u have access to another distributor, change them out. If that is the problem, then at the very least, u have it narrowed down to where the problem maybe. Good luck and keep us posted.

[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*

[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!

[Myself]

Keep us posted with results.

[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.

[88Stanger]

Well damn, sorry for the issues you have had.
I have a 383 stroker i am going to run, with Edelbrook aluminum heads (same or close to the same as you), full roller Howards Cam, Lifters and Rockers but the cam is not an RV grind i called and got a cam grind built for the 383, Muncie 4-Speed and 3:42 posi rear.
I am interested to hear what the engine builder has to say. I built my engine, but had the machine work done a respectable outfit in town and then me and my anal build mind took a week of measuring, testing, and such to build it. I fortunately have alot of the tools to test the fitments, not saying i know what i am doing, only saying that if it is bad or not right, i can only blame myself.
I wish you all the luck possible and look forward to your excitement of how "Snapping" the torque monster has!!!

[Ptjsk]

Originally Posted by 88Stanger

Well damn, sorry for the issues you have had.
I have a 383 stroker i am going to run, with Edelbrook aluminum heads (same or close to the same as you), full roller Howards Cam, Lifters and Rockers but the cam is not an RV grind i called and got a cam grind built for the 383, Muncie 4-Speed and 3:42 posi rear.
I am interested to hear what the engine builder has to say. I built my engine, but had the machine work done a respectable outfit in town and then me and my anal build mind took a week of measuring, testing, and such to build it. I fortunately have alot of the tools to test the fitments, not saying i know what i am doing, only saying that if it is bad or not right, i can only blame myself.
I wish you all the luck possible and look forward to your excitement of how "Snapping" the torque monster has!!!

I'm hoping for information tomorrow! I'm curious to see if additional machining is going to be necessary.

Pat

[Ptjsk]

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.

No, it's actually a Jimmy. It's GMC's version of the Chevy Blazer.

I placed the 410 gears in it when I restored the vehicle last year.

I'm running 33's on them, and I did install a gear vendor overdrive unit.

Pat

['68OrangeSunshine]

Originally Posted by Ptjsk

No, it's actually a Jimmy. It's GMC's version of the Chevy Blazer.

I placed the 410 gears in it when I restored the vehicle last year.

I'm running 33's on them, and I did install a gear vendor overdrive unit.

Pat

OK, I get it. I thought the gearing sounded low, but with a GV/OD it makes more sense. With 4.10s your focus is off road, and a personal choice.
With three broken piston rods we know why you had no power. You were actually running a pumped-up 5 cylinder.
Better luck on your rebuild.
My '71 Jimmy is a 350/SM465/NP205/12Bolt-3.73Posi/ 33x12.50x15.
Yours is pretty.

[72c20customcamper]

Seems that more than one company is or had problems with their pistons TRW paid for the rebuild for my 66. Mine was catastrophic though 3 others had cracks around the wrist pins.

Absolutely no noise prior to damage