I've got a 383 stroker with an edelbrock performer plus cam #2102 (lift @ valve Int .420 exh.442)

I have a 650cfm Edelbrock thunder series carb on it right now but it is to lean and causes it to ping at rpms past 2000. The engine shop that built the motor told me that i should have a 750cfm on it. Just wondering if i would be adding to much carb it i put a 800cfm on it? the reason i ask is because edelbrock doesn;t make a 750cfm carb for the thunder series and i have already purchased the dual feed lines and filter to match the thunder series carb.

P.S When i had the motor built i had already purchased the 650cfm and the engine shop knew that was the carb i was going to use and didn;t say a word about needing more. after i broke the motor in and gave it some gas all it did was ping.so when i took it back i found out that a larger carb was needed. Really pissed me off because if they would have told me before i ran that carb i could have returned it for a full refund, not i have a used carb thats worth like have of what i paid for it.



thanks

 

650 CFM is fine for your combo.

That teeny tiny cam will protect the engine from ever running at high enough RPMs to need any more flow than that.

Carbs don't make a motor ping; too much compression, or too much timing advance, or too low octane rating of the fuel, is what causes that. You can change carbs till you're blue in the face, it'll still do it.

If you had a cam that allowed the motor to make power past 4800 RPM, you would need more carb; but for what you've got, it's probably just about perfect. I'd leave it alone, and proceed directly to the things that actually cause the problem.

 

I agree 100%... I'm running a 650 mighty demon on a 383 that is alot hotter than that combo and I don't think its choking it at all. Apparently the Demon carbs flow alot more than they are rated at.... but 650 should be more than enough to feed that mild 383 and the ping is most definitely from something else.

 

helllo

here is a link that has the math to figure out the CFM of the carb you need. http://www.geocities.com/MotorCity/Pit/5755/math.html

as for the pinging the carb mabe not dumping enough fuel

 

Edelbrock carbs are very adjustable.
Put in the metering rods or jets or piston-springs you need.
You might try going to heavier springs, if you think
you need more fuel.
...
650cfm is fine.

 

You should check you canking comp. If its over 200.psi you may have to much static comp. You can over come it with a larger cam as long as your not to high. Or even retarde the came timing will brig it down. As far as the carb goes im a holley fan but your carb will do the job you will have to adj it a bit. Im not sure but I think you have to change metteing rods? Call edelbrock tech thay may be able to help you. I forgot the simple stuff check total timing you will want 34-40 deg of total If the car is pinging start with 34 deg and use 93 oct fuel.

 

I've put 94 octane in my car snice i had the motor swapped. when the pinging started and i took it back to the shop they gave me a number to a different shop that would rebuilt my carb and make it a 750. then i called around to a few different engine shops for pricing. asked what carb is needed on my 383 SBC with cam specs ### and they all said at least a 750( i asked that before i told them that i had a 650 looking to be rebuilt).... the engine shop retarded my timing until it stopped pinging. they told me with that timing the engine would only be running 60% of its power....

 

Mississauga? I'm in London.... what shop are you dealing with? It seems like they don't really know what they're doing.

 

I can only talk from what I have tested on my cars and others that I have built motors for. I have done back to back tests on my car 650 vs 750 at the track no et gain and none lost. I had the car on dyno jet dyno motor made 415 hp at the tire na. on the 650 and the same with the 750 a 925 carb shop carb picked up 10 rwhp but at the track same et as the 650 car ran 11.30 at 119 mph. I would check cranking comp buy a comp gauge at your local parts store pull all the spark plugs unhook the ign. and make sure you spin the motor about 6-7 time on comp stroke or until the neddle stop climbing the gauge. To me it souds like you have a lot of static comp and on a 383 with a flat top piston that is about .020 in the hole and a cast iron head around 64 cc cumbustion chamber and a small cam. that combonation would ping. ask the engine shop if thay used flat top pistons in youre motor and how far in the hole were thay. a flat top piston in my opinion will not work for you even with a 76cc head.

 

hey',
Try this.
Hookup a vaccum gauge, readable from the inside.
Then tell us how much vacuum you pull at WOT.
I'd be surprised if it was more than one PSI.

 

The shop that i deal with is active racing engines in mississauga located at 939 Winston Churchill Blvd. The also are the offical engine builder of dream car garage(as im told by them). My car is in storage right now till about mar, apr (end of winter) so i can't test any of the things u guys have recommended but i will when spring hits. thanks alot for all of ur input!