Hi Everyone,

I need some sound advice from the experts on this site with regards to carburetion for my zz502. I purchased this engine from Chevy a few years ago. It was a little different than most over the counter 502's because it came with:

8.75:1 compression (standard is 9.6:1)

Edelbrock Performer RPM aluminum rectangle port marine heads 118cc - 2.25/1.88. (standard is oval port)

Edelbrock Performer RPM intake manifold

Crower stainless rockers

Speed Demon 850 carb

It still retains the original cam ( The duration at .050” tappet lift (intake/exhaust) is 224/234; (intake/exhaust) is 527/544)

It was originally dynoed by GM with 508 hp at 5600 rpm and 531 ft lbs torque at 3900 rpm. I've been running a Holley Commander 950 with wideband that's just worn me down over the past few years. I just don't have what it takes to adjust this system properly. I'd like to throw a carb and intake back on for simplicity. This car is street driven almost everyday during the summer and fall.

What would you recommend for my 502 with regards to:

Intake : Performer RPM dual-plane or single-plane like a Victor JR?

Carb: 770 cfm, 850 cfm, 950 cfm? Vacuum or mechanical secondaries? I'd like to run an electric choke. Demon or Holley?

Cam: Would you recommend an upgrade for my current cam while retaining my cylinder heads or just keep the original?

The engine is in my 69 RSSS. The car has a manual 5-speed TKO 600 (2.87, 1.89, 1.28, 1.0, 0.64). As far as the weight of the car, I'd imagine the car is quite heavy due to options: Rally sport option, power windows, extra sound deadening, sub woofer, stainless fuel tank, scatter shield, etc, etc.. It's definitely not a lightweight. I'm running a three inch exhaust from the headers back.

Traction has always been a problem in the past. 1st and 2nd gear are pretty useless with the 502.

I just want a great running engine with a power-band at the right place for my car. What would you recommend?

Thank you for any suggestions, Paul

I sure wish I had your problem(lol). I wouldnt know what carb size but if I was guessing I would say 850 holley vac secondarys, dual plane intake, and keep the cam you have. Im sure you will get more educated answers than what I could tell you though.

Carb Solutions formula for a Street Car:
C.I.X RPM, divided by 3456= cfm
In your situation - 502X 5600, divided by 3456= 813 cfm [800 or 850 cfm]

HP1000
Victor Jr. since its a 5spd.
Bump the comp. and cam from 230s to 250s duration depending on how much and where you wanna make the power. Dont forget the exhaust and fuel system as theres a bunch of 12sec 500 cube bbc's because theyre all choked up - this aint no 350sbc.

A Victor Jr on a 502 is like a dual plane on a 427, I would put the victor on it.
950 HP works very well on these engines
Depending on the rpm you want to turn a cam change can be done to put the power where you want it.

Why not put the original Performer and 850 Speed Demon back on there??? If it's street only car there's very few times you can even ever get to the higher rpm levels to make the Victor worth it.

Thanks for the replies. I'd like to keep the compression where it is although I know it would be much better with more. I just don't want to open this engine up yet. The engine has plenty of uummmfff on the low end, actually too much with standard street tires. That's why I was thinking about sticking with a single plane, but my concern lies also with throttle response. Will I lose it with a single plane and a carb?
As far as carbs, Holley seems to be recommending 770 cfm vacuum secondaries for most 502's now (according to Jeg's tech). Is it due to economy (gas prices) or do the vacuum secondaries perform better? I was always told to stick with mechanical secondaries with a manual trans - is this the right thing to do?

Hi paul, I started with a 502 450 hp motor years ago started with a 750 holley ran great. I changed the cam and had heads completely ported with port matched intake (factory 375 intake) it dynoed at 583 at crank. I had Nickeson carburators in Bristol Pa. do a carb for the car it was a 750 hogged out to a 980 cfm, ran great! Also my motor had 8:75 compression also when I started. With head work it has slightly more compression due to decking. Good luck!

Paul that Nickerson Carburators is off of exit 6 on njtpk. He specializes in 502, He is very big in the race boats which have alot of dual 502's in them.

paul, green that thing up for spring man, cut your carbon footprint back a little, order a nice alcohol carb and run her on corn man, some power there. get a bigger e/85 friendly fuel sys and be the trend setter, cops may reduce some speeding penalties if you explain how green your car is. challenge others to go green.

Thanks for the replies. I'd like to keep the compression where it is although I know it would be much better with more. I just don't want to open this engine up yet. The engine has plenty of uummmfff on the low end, actually too much with standard street tires. That's why I was thinking about sticking with a single plane, but my concern lies also with throttle response. Will I lose it with a single plane and a carb?
As far as carbs, Holley seems to be recommending 770 cfm vacuum secondaries for most 502's now (according to Jeg's tech). Is it due to economy (gas prices) or do the vacuum secondaries perform better? I was always told to stick with mechanical secondaries with a manual trans - is this the right thing to do?

Single plane on a 502 CID will tame down the low end grunt a tad but will effectively allow the engine to run better overall. The Vic Jr is a small single plane. On 502 CID it will effectively be smaller then it would say on a 427.. . .a full rack on ribs to an 8 year old is alot of food. . .. a full rack to 20 year old college student is a snack. You'll like the victor...

the holley efi should be much better than any of the carbs as far as overall driveability, why are you wanting to change it, instead of getting help to set it up properly?

So the majority says to stick with a single plane with the larger cfm carb. I can deal with that. As far as why I don't try to tune it - actually, I've taken it to two high profile racing shops here in NJ a total of three times now and spent a large sum of money with no real improvement. I've spent countless hours trying to tune it myself over three years now. I've come pretty close to breaking down and weeping a few times too. I'm very grateful to the people who have tried to tune it properly, but the results have been less than I had hoped for. I can't hang on forever. For what I spent on the tuning jobs, I could have bought a couple of carbs and a couple of intakes. To be quite honest, I'm scared to have it tuned again because I've become too accustomed to upsets. Most tuners that I've spoken with deal with the accels, but know nothing or very little about the Commander systems. I would love to have my system working properly, but I'm being burnt financially as well as mentally. I don't know which way to turn anymore.
I am extremely thankful to all of you for the advice. I need positive guidance more than anything else right now.