Low max rpms

[rgtrough]

Hey guys, I have had my '74 383 powered coupe for just about 30 days now and am just getting to know it. It doesn't build any rpms higher than 5300. It has a edelbrock performer intake, a 270 comp cam, stock heads ported, 4010 Holley carb, stock exhaust manifolds, 2.5" exhaust pipes. I am in the process of installing dynomax 1 5/8 headers, 3" exhaust pipes, with 3" 40 series flowmaster mufflers. I am looking for 6000+ rpms. Will this combo help achive my goal? I am running a 3.55 rear gear. Thanks for any imput, lord knows I need all the help I can get.:cool

 

[Tom Bryant]

Hi Bud,

Your combination should be stronger than that. Sounds like the problem is in the tune. Do you know what your distributor curve is and where's your timing set at? Have you checked to see if the carb is open all the way when the pedal is floored? Is the secondary diphram working? How's fuel flow? Is the pump keeping up and the filter clean? The headers and exhaust are a good thing but I can't believe that the stock exhaust would hold it back that much.

Tom

 

[Jack]

Hi Bud,

Your combination should be stronger than that. Sounds like the problem is in the tune. Do you know what your distributor curve is and where's your timing set at? Have you checked to see if the carb is open all the way when the pedal is floored? Is the secondary diphram working? How's fuel flow? Is the pump keeping up and the filter clean? The headers and exhaust are a good thing but I can't believe that the stock exhaust would hold it back that much.

Tom

;stupid ditto on all points.
Does it BEGIN to drop off @ 5300 but rpm rise beyond with little power ... OR suddenly limit @ 5300 ... OR begin to drop off before it reaches stone wall @ 5300 ... OR what?

Is your 4010 a 600 or 750? “Theoretically” a 600 should get you there & then some ... but again, “theoretically.” Like Tom asked ... how’s fuel flow ... floats’ heights?
JACK:gap

 

[hotrodd]

Could be the tach, mine is off 900 rpm when it register's 4500?

 

[rgtrough]

Thanks for the imput guys, it climbs strong to 5300 then stops. I first thought I ran out of gear till I found out it was a 3.55. I meant to check wot before posting but forgot. I'll do that tonight when I get home. I got the info today from holley to find out if the carb is a 600 or 750. If it is the tuning would it run real strong and then just stop? Thanks again.

 

[JohnZ]

What does it do when it "stops" at 5300? Does it just hang there, does it miss, spit, backfire, or what? I'm sure you'll find the problem in your tune (probably ignition-related or a carb secondary problem).

Once you get it squared away, there's no reason to twist a 383 over 6000 rpm; 383's are all about low- to mid-range torque, which is what makes them killer motors on the street. I've built four of them (streetable, not "magazine motors"), and they all made around 420hp@5600 and 440 lb-ft. @ 4200 with 650 vacuum-secondary Holley 4150's.

 

[Tom Bryant]

Is that the Grand Sport?

Tom

 

[rgtrough]

Low rpms

Great looking engine JohnZ! It does not miss or sputter just quits climbing. I only wish to twist it as far as needed to run out the gears in the 1/4 mile. Right now it feels like I'm peddling uphill, shifting before I need to. If you are building peak hp at 5600, I am not reaching peak. If it is tuning I am going to need some help. I will do that in another post. Thanks for the help.:cool

 

[JohnZ]

Yup, that's the Grand Sport - you wouldn't believe what a stout 383 does for a 2300# car!

If you're not experiencing valve float and it just "runs out of breath", I'm sure you'll find the problem in your tune or fuel delivery; good luck!

 

[rgtrough]

Faulty cable bracket

Hey guys, the throttle cable bracket had slipped not allowing wot.
This adjustment now allows me to run all the way through the power range when needed. What a difference. Thanks for being here for guys like me.:cool

 

[Tom Bryant]

That's great news. Don't you just love it when the fix is so simple?