Performance Lacking in a 383 Build.

[Ptjsk]

Hey Guys,

I had my motor built from a friend who's (was), a reputable engine builder.

Unfortunately, he recently passed away.

The motor is the original 350 (to my Jimmy), and I did go with an Eagle 383 (B13005E-030), rotating assembly.

The motor has Edelbrock RPM heads, and an Edelbrock aluminum manifold. Has the Pertronix ignition module in it, and a small RV cam in it as well. The cam is a "Howards" number CL113215-10 hydraulic roller.

The original Quadrajet carburetor was rebuilt (76 jets), and placed onto the motor.

The motor runs very well, but it just seems to lack power, and doesn't provide the "punch" I was expecting.

I'm running 33" tires with 410 gears, behind a Turbo 350 transmission.

Thinking of trying to go with a Holley carburetor and see if that makes any difference.

Does anyone have a suggestion of which Holley I should use for this set up?

Thanks, Pat

[Ziegelsteinfaust]

The intake, and holley won't add the punch your looking for.

My guess is you have 882 or equivalent shooter heads. Your cam is quite a decent going for a nice DD or torque motor.

So he may of gone back to the low 8-1 compression your originally had, and the softens the whole hit of the bigger motor. You will have to take to top end off to see if adding 64cc heads will bump the compression up.

Have you tried setting initial timing to 15*, and total to 36*. Stock D chamber heads need a lot of lead in due to the slow flame propagation.

If that wakes your engine up enough for you. Then I would consider adding a dual plane high rise, and new carb. Or atleast add a 1 inch open spacer for a little more plenum volume.

[truckster]

It's not the carburetor, unless it was put back together wrong. A Quadrajet should be plenty of carburetor for that engine. Do you know what pistons were put in it? Which RPM heads? What's the compression ratio? The cam looks good, and the extra 33 cubic inches should be noticeable, but it's also possible it's a question of tuning.

[Ptjsk]

Originally Posted by Ziegelsteinfaust

The intake, and holley won't add the punch your looking for.

My guess is you have 882 or equivalent shooter heads. Your cam is quite a decent going for a nice DD or torque motor.

So he may of gone back to the low 8-1 compression your originally had, and the softens the whole hit of the bigger motor. You will have to take to top end off to see if adding 64cc heads will bump the compression up.

Have you tried setting initial timing to 15*, and total to 36*. Stock D chamber heads need a lot of lead in due to the slow flame propagation.

If that wakes your engine up enough for you. Then I would consider adding a dual plane high rise, and new carb. Or atleast add a 1 inch open spacer for a little more plenum volume.

The heads are Edelbrock 60995 heads. They have 64cc Chambers with 185cc intake runners. Valves are 2.020 intake and 1.6 exhaust.

The intake Manifold is the Edelbrock Performer 2101 dual plane intake.

My timing is right in line with what you recommend.

Pat

[Ptjsk]

Originally Posted by truckster

It's not the carburetor, unless it was put back together wrong. A Quadrajet should be plenty of carburetor for that engine. Do you know what pistons were put in it? Which RPM heads? What's the compression ratio? The cam looks good, and the extra 33 cubic inches should be noticeable, but it's also possible it's a question of tuning.

The pistons are Hypereutectic aluminum flat top with two valve reliefs. Provided with the Eagle Rotating Assembly kit.

Plus, the mechanic rebuilt the Quadrajet an has literally gone though hundreds, if not thousands of them. Not to say a mistake couldn't have been made, but probably unlikely.

Damn....just come through your area on my Elk Hunting trip! LOL!

Pat

[Ziegelsteinfaust]

Do you by chance a mechanical advance only distributor?

Maybe a bad vacuum canister?

[SkidmoreGarage]

It's not the traditional way, but consider taking the truck to a chassis dyno for tuning. It's the only way to really diagnose the issue in a deliberate way. You need data to know what to change. Could be a long list of possible causes. Could be fuel (need a wideband), could be timing, could be spark, could be the cam timing is off. Could be push rod length, could be airflow, etc.

Good luck!

[truckster]

Everything you describe should give you plenty of power. Something's not right, but it's hard to tell what.

I had a guy bring a car to me once for lack of power. It turned out that the throttle cable was hooked up wrong and only opening the throttle 1/3 of the way. Sometimes it's simple things.

[conoco]

I have a 1972 gmc Sierra Grande k2500 which is my daily driver with a 383/ 35" tires and 4.10s/ Eaton rear end and a 4"lift. I had a holley carb in there and for the same reason I felt like I was lacking the punch I should expect in my motor. I recently switched to the Edelbrock AVS2 650 with in the last 2 months and it is like a whole new driving experience. Off the line, on the highway, pulling my trailers, driving up the mountain roads here in Alaska. Just completely different all the way around. I do have a few other upgrades but the new carb has really brought everything to life. I have no favorite between any of the carb manufacturers. They are all fit for purpose. I just happen to find one that worked for me.

*Side Note
I did play with all the different calibration set ups in my carb that edelbrock offers with the tuning kit ( took a significant amount of time but was alot of fun). It took me changing to almost all the different settings. I kept detailed notes of each setting along with changing my timing for all of them to see what worked the best. I had my timing set at 0°, 4,6,8,12 on each different set up, and ran Them all. I finally found the best set up for my truck and all the time spent doing that was well worth it. I was able to have my 16 year old son help with most of it too, so it was a win win. I do have HEI, spark plugs gapped to .045, headers, dual exhaust, performer intake, Changed my thermostat to 190° ( which made a difference believe it or not). If you would like to know everything I did I would be more than happy to share. But for me the carb was what did it.
Good Luck

[Ptjsk]

Originally Posted by Ziegelsteinfaust

Do you by chance a mechanical advance only distributor?

Maybe a bad vacuum canister?

It seems to hold vacuum and moves the timing advances when I place a timing light on it.

Originally Posted by SkidmoreGarage

It's not the traditional way, but consider taking the truck to a chassis dyno for tuning. It's the only way to really diagnose the issue in a deliberate way. You need data to know what to change. Could be a long list of possible causes. Could be fuel (need a wideband), could be timing, could be spark, could be the cam timing is off. Could be push rod length, could be airflow, etc.

Good luck!

I would be willing to do that! I'll have to see about giving that a try. Thanks!

Originally Posted by truckster

Everything you describe should give you plenty of power. Something's not right, but it's hard to tell what.

I had a guy bring a car to me once for lack of power. It turned out that the throttle cable was hooked up wrong and only opening the throttle 1/3 of the way. Sometimes it's simple things.

Yea, I've checked that out already too.

Originally Posted by conoco

I have a 1972 gmc Sierra Grande k2500 which is my daily driver with a 383/ 35" tires and 4.10s/ Eaton rear end and a 4"lift. I had a holley carb in there and for the same reason I felt like I was lacking the punch I should expect in my motor. I recently switched to the Edelbrock AVS2 650 with in the last 2 months and it is like a whole new driving experience. Off the line, on the highway, pulling my trailers, driving up the mountain roads here in Alaska. Just completely different all the way around. I do have a few other upgrades but the new carb has really brought everything to life. I have no favorite between any of the carb manufacturers. They are all fit for purpose. I just happen to find one that worked for me.

*Side Note
I did play with all the different calibration set ups in my carb that edelbrock offers with the tuning kit ( took a significant amount of time but was alot of fun). It took me changing to almost all the different settings. I kept detailed notes of each setting along with changing my timing for all of them to see what worked the best. I had my timing set at 0°, 4,6,8,12 on each different set up, and ran Them all. I finally found the best set up for my truck and all the time spent doing that was well worth it. I was able to have my 16 year old son help with most of it too, so it was a win win. I do have HEI, spark plugs gapped to .045, headers, dual exhaust, performer intake, Changed my thermostat to 190° ( which made a difference believe it or not). If you would like to know everything I did I would be more than happy to share. But for me the carb was what did it.
Good Luck

That's why I was thinking of going to another carburetor. I'm kind of at a loss here. It sure seems like it should have more power to me.

Pat

[Myself]

I see the intake as part of the problem. That's the short dual plane.....which works great on a stock 350 or my mildly warmed up 305. The Performer RPM or even the Air gap is what you want for a 383 or warmed up 350. Your combo is capable of breathing pretty heavy but that intake is not.

[KQQL IT]

The performer intake is fine. Ran one on a good running 400 forever.

[Myself]

I just looked up that cam.........waayyy wrong for an aluminum headed 383!! I have a slightly bigger cam in my 9.5:1 iron headed mild 305!

Change to a tall dual plane and a much larger cam and you won't be wondering where your power is.

I have a feeling if we lined up with my little 305 at a stoplight you'd be VERY disappointed in your power.

The motor as a whole is built well, take advantage of it.

[geezer#99]

Originally Posted by Myself

I just looked up that cam.........waayyy wrong for an aluminum headed 383!! I have a slightly bigger cam in my 9.5:1 iron headed mild 305!

Change to a tall dual plane and a much larger cam and you won't be wondering where your power is.

I have a feeling if we lined up with my little 305 at a stoplight you'd be VERY disappointed in your power.

The motor as a whole is built well, take advantage of it.

Could you share your theory on why that cam is way wrong?

[garyd1961]

Originally Posted by Ziegelsteinfaust

The intake, and holley won't add the punch your looking for.

My guess is you have 882 or equivalent shooter heads. Your cam is quite a decent going for a nice DD or torque motor.

So he may of gone back to the low 8-1 compression your originally had, and the softens the whole hit of the bigger motor. You will have to take to top end off to see if adding 64cc heads will bump the compression up.

Have you tried setting initial timing to 15*, and total to 36*. Stock D chamber heads need a lot of lead in due to the slow flame propagation.

If that wakes your engine up enough for you. Then I would consider adding a dual plane high rise, and new carb. Or atleast add a 1 inch open spacer for a little more plenum volume.

Why would you run an open spacer on a duel plane intake.
Make sure you have fresh 93 octane gas in it. You should have tons of low end torque with your setup. Probably something simple like a vacuum leak.

[Myself]

Originally Posted by geezer#99

Could you share your theory on why that cam is way wrong?

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!

[geezer#99]

Sure he might have 10 to 1.
But why is the cam wrong?
Is it duration, lift, lsa?
What numbers would you suggest are better?

[SCOTI]

Originally Posted by Myself

I just looked up that cam.........waayyy wrong for an aluminum headed 383!! I have a slightly bigger cam in my 9.5:1 iron headed mild 305!

Change to a tall dual plane and a much larger cam and you won't be wondering where your power is.

I have a feeling if we lined up with my little 305 at a stoplight you'd be VERY disappointed in your power.

The motor as a whole is built well, take advantage of it.

Originally Posted by geezer#99

Could you share your theory on why that cam is way wrong?

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.

[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.

[Ziegelsteinfaust]

Originally Posted by garyd1961

Why would you run an open spacer on a duel plane intake.
Make sure you have fresh 93 octane gas in it. You should have tons of low end torque with your setup. Probably something simple like a vacuum leak.

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.

[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.

[HO455]

I'm sorry your friend passed away.
As to your engine delema I recommend talking to local racers about someone in your area who is good at tuning carbureted engines. As Skidmore suggested dyno time is a good way to go however it is expensive. And nowdays many dyno shops are not experienced with analog engines like yours. If someone immediately starts saying you need to change part XXX then go somewhere else. They are likely looking to up your bill because they are underhanded or they don't really know what they are doing and are hoping for the best. Ask them how changing this part will change the engine for the better. If they truly know what they are doing they wil be able to explain it so you can understand.
Once all the avenues of tuning are explored then you can decide what parts might be changed to meet your goals.
Try and remember the conversations you and your friend had about what you wanted from the engine. Maybe write them down. Your friend made choices about components based on those conversations and it may help whomever you find to help get the performance you desire.
There are many ways to build an engine and 10 times as many opinions about those. There doesn't seem to be anything particularly wrong with your current combination so hopefully you can find something as easy as recurving the distributor will wake the engine up.
As this goes forward you may have to pull the water pump off to verify the cam timing. Also be prepared to have to pull a cylinder head as any speculation on compression ratio is a waste of time until you know what the deck height is.
These are the bad case scenarios. Worst case would be something like a cam lobe gone flat or rings that never broke in properly.
Good luck and please post your findings.

[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.