Low end not there but 326 hp and 438 tq at the rear wheels

[nicanor]

We put the 670 carb in and capped off the vacuum advance and that moved the curve up about 1000 rpms. Hp is 329 was 293 and tq is now 438 was 401. Runs great on the freeway and after initial acceleration.

It is a Whiplash cam and 452 heads.

Problem is, it has no low end acceleration, even bogs, then off like a jack rabbit.

I brought the rpms up to 3000 with the clutch depressed and in first gear (3:23) then let the clutch go at 3000 rpms and tire spun a second then stopped and the car bogged. When accelerating normally from a stop in first gear the car stumbles and is difficult to accelerate. Then when we get up a little speed and rpms, it drives well. Just no power in the initial acceleration.

Thanks for all the help so far,
Barrty

 

[moparchris]

Re: Low end not there but 326 hp and 438 tq at the rear whee

We put the 670 carb in and capped off the vacuum advance and that moved the curve up about 1000 rpms. Hp is 329 was 293 and tq is now 438 was 401. Runs great on the freeway and after initial acceleration.

It is a Whiplash cam and 452 heads.

Problem is, it has no low end acceleration, even bogs, then off like a jack rabbit.

I brought the rpms up to 3000 with the clutch depressed and in first gear (3:23) then let the clutch go at 3000 rpms and tire spun a second then stopped and the car bogged. When accelerating normally from a stop in first gear the car stumbles and is difficult to accelerate. Then when we get up a little speed and rpms, it drives well. Just no power in the initial acceleration.

Thanks for all the help so far,
Barrty

Its all in the carb. I recommend getting the book on how to tune Holleys. The dyno tuner should have addressed all these issues. That is what you pay him for. Now its time to play with it and get the carb to work right.

 

[ACME A12]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Hit it with a hammer. If the problem persists, then it is electrical... :basketcase:

:jester:

 

[droptop]

Re: Low end not there but 326 hp and 438 tq at the rear whee

What are the specs on the camshaft? Did you degree it in?

 

[nicanor]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Cam specs listed in post below with regards to dyno run. The cam was degreed in by an engine machine shop. I hope they degreed the cam correctly.

Thanks,
Barry

 

[george68hemirr]

Re: Low end not there but 326 hp and 438 tq at the rear whee

HOW IS THE FLOAT LEVEL??

 

[zupanj]

Re: Low end not there but 326 hp and 438 tq at the rear whee

I can't tell from your first post what the cam overlap is but I would suspect that is part of the problem. My 383 behaved in exactly the same way and I believe it was a combination of too big a cam and very low compression. My sense from a number of Moparts posts that if you replaced the pistons with KBs the actual compression ratio could be under 8:1. I am pretty sure my engine had that situation. While I couldn't spin the tires from a standing start, once I got above 3000 rpm it would run pretty good. I had it dyno tuned but there was only so much they could do. They got it to the point that it didn't stumble when I let out the clutch. One comment the guys who dynoed the car made was that lower gears would really wake it up. I never found out because I went another route.

 

[mcmopar]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Those 3.23 gears aren't helping either. You've moved the hp and torque curves into a higher rpm range so in order to get there quicker you need a bit more gear. 3.55's or better yet 3.91's will wake your combo right up. If your car is equipped with an automatic you should put a shift kit in the trans along with a higher stall converter. It is all a matter of getting the right combination together. Having a killer engine isn't the be all, end all of the equation. Everything else has to be factored in as well. No doubt, some carb work will help - and maybe some curve work will need to be done to the distributor. Then you'll need to spend some time on finding the the right initial and centrifugal timing settings for the street. One thing is for sure - you'll gain lots more knowledge about your car and when it all comes together it will be a great ride!

 

[nicanor]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Thank you for the posts.

The trans in the RR is a stock 4 speed. I talked to Hughes Engine and the cam they recommended was the Whiplash cam. Many told me the 770 Holley was too big. So I put on a 670 Holley. The car stumbles on initial acceleration but it didn't
before the start of the dyno tune. I don't believe it had a lot of acceleration, but it didn't stumble.

I hope they while I'm away for a week that they'll be able to find the problem.

Thanks again,
Barry

 

[droptop]

Re: Low end not there but 326 hp and 438 tq at the rear whee

"Lobe Separation Angle 107º"

I think this is your problem. Both valves are open at the same time. The stumble is a lean condition.:cents:

 

[zupanj]

Re: Low end not there but 326 hp and 438 tq at the rear whee

"Lobe Separation Angle 107º"

I think this is your problem. Both valves are open at the same time. The stumble is a lean condition.:cents:

I agree.

 

[mcmopar]

Re: Low end not there but 326 hp and 438 tq at the rear whee

"Lobe Separation Angle 107º"

I think this is your problem. Both valves are open at the same time. The stumble is a lean condition.:cents:

I don't agree because of this quote:
The car stumbles on initial acceleration but it didn't before the start of the dyno tune.
Obviously the dyno tuner did something to cause the stumble which was not there prior to the dyno tuner fiddling with it. I agree with Chris - sounds like the tuner messed up the carb settings.

 

[moparchris]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Hit it with a hammer. If the problem persists, then it is electrical... :basketcase:

:jester:

I hear ya brother.

 

[69hemibeep]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Hit it with a hammer. If the problem persists, then it is electrical... :basketcase:

:jester:

I hear ya brother.

In my tool box is what I call a ford hammer, its the biggest in the garage

 

[classracer]

Re: Low end not there but 326 hp and 438 tq at the rear whee

You need to find out what kind of compression ratio you really have. Run a compression test, as this will give us an idea. The lower the compression, the engine will want a little more squirter and more initial timing. If the piston is down in the hole, you are using a thick head gasket, and the heads have not been cut very much; you actually compression ratio could be below 8:00 to 1. I had a 70 RR 4 spd with with Trw L2266f -60 pistons ( the 10:00 to 1 comp. piston), ported heads, old torker intake, 780 holley, Trw .480" lift w/230 dur @.050 cam. Long story short, it was a turd. The compression ratio ended up being just under 7.5 to 1. The fix after a lot of trial & error was to increase the squirter size from .031 to .037 and run 30 degrees initial timing with a total of 38 degrees. The performance difference was night and day, as it was worth over a 1 second at the drag strip.

 

[classracer]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Another thought is to check how far the throttle blade are open. If they are open to far at idle, they can uncover the idle transfer slot. This can also cause a stumble.

 

[mcmopar]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Hey Jim - good to see you back on the board.

 

[V269]

Re: Low end not there but 326 hp and 438 tq at the rear whee

Sure sounds like it needs more fuel if you say it bogs. Bigger jets, squirters , pumps or a combination of these. :cents: