Technical Car Bucking At Low Speeds - What's The Deal?

Hey all, long time lurker, first time posting. My dad just bought a faux-gasser 57 Chevy. 383 stroker, M22 4 speed, 9 inch rear. When taking off from at low speeds it gets pretty bouncy. If you ride the clutch or speed up it obviously goes away, but it seems pretty excessive.

Has a crossram intake, dual Holley 450s, and 4.11 gears. Cam specs are 243/257 duration @ .050, .533/.519 lift, and a 107 LSA.

Any ideas where to start here?

 

more gas.

 

That set-up is not conducive to "slow speed" starts.

 

Are there pics of said gasser? Post them up!

 

I would start by checking the jetting in the carbs, may need bigger jets. Also check initial timing as well as mechanical advance. I would start with 12 to 14 initial with 36 -38 total, and then start playing with the springs in the dist. Also check power valve size. Holley site has instructions on how to determine proper power valve size.

 

Probably not hamb approved, but

 

Have your dad leave the stop sign at...... oh 3500 RPM and see if the car "bounces". As another said, not built for a "casual" start.

 

I have no way of telling whether you are describing an engine surge kind of thing, or a mechanical "grab" sort of thing.

often times it could also be a clutch disc with weak center springs.
I've had standard or hd discs do that. I have always had great success when I put in some heavy duty performance disc, and thoroughly washed the flywheel and pressure plate to remove any oil or grease film.
You don't have to use a heavy pressure plate if you don't want a stiff pedal, just a high quality disc such as Mcleod or zoom or something...
...that is... if this is a mechanical grab-and-chatter problem, not an engine surge problem....

why be ordinary?

 

Sounds like a lean surge, follow above tuning suggestions.

 

which also brings up another thing....
If a home made clutch linkage does not have a correctly designed floating shaft belkcrank, sometimes engine movement can make a clutch feel grabby when you are trying to feather the clutch on certain take-offs.
these are just ideas, since I have no idea how yours acts in person...

why be ordinary?

 

"lean surge" is worth investigating if it is not a mechanical type problem.

why be ordinary?

 

I don't see anything anti-HAMB at first blush, nice car.

 

The posted description isn't sufficient for anybody to give you an accurate analysis. Choose some better words.

 

I only got to drive it maybe an 1/8 mile, feels like you're learning how to drive a manual transmission all over again. A quick takeoff and it's fine. A slow crawl like you're in traffic makes for a rough ride. Speed up to maybe 15 mph and it's great. Basically I guess under 10 mph it's ready to stall.

Guess it's not the easiest thing to explain.

 

Like others said, it is lean. But, it is the idle circuit that is too lean. The idle circuit can't supply enough fuel for the greater HP of the engine, drill the restrictors to about .035 or change the idle air bleeds if they are repaceable, maybe to .o65ish.

 

Are you trying to say that it's a clutch issue or an engine performance issue? Is the engine missing is your engine backfiring? Are you having trouble at low RPMs in every gear? Is it in first gear only that you jerk around? By the way I'm surprised your post is still up as I thought gassers/pseudo gassers were frowned upon around here.

 

That is a nice looking car. That said, in driving it, I think you will find it to be a noisy extrovert that will scare old women and children.

 

Great car. It's telling you to drive it on track, balls the the walls.

 

I don't know what the issue is. No backfiring. Only low RPM first gear.

 

Drive it and enjoy it. The car is telling you that it doesn't LIKE to go slow! Anybody who would do that to a beautiful '57 should suffer just a little bit.

 

Pretty healthy cam and at 107° it will be lumpy down low and dual carbs with large volume manifold all adds up..If you are not knowledgeable at tuning it is a looong learning curve, both in research and hands on [if read the right info making better or worse]..I'd say you need local hands on help but you do not state where you are located...

 

Any idea what the reading gear is? 4:56 and higher (number) will baulk even more at low speed.

 

no one has mentioned motor mounts? if the engine is moving at all during clutch engagement you will get erratic clutch engagement.common problem with 55-57 chevys that are still using the original front of the block motor mounts and then have a trans mount at the far rear

 

That Alpine White Superbird may not be appropriate for this site, but I like it.

 

Not a bad triad of cars right there.


Sent from my iPhone using The H.A.M.B. mobile app

 

No dis meant, but sounds like operator error. Let the clutch out & get that sumbitch rollin'. No way in hell that car was assembled/intended for low gear idling.
And I agree, damn nice batch of cars ya got there.

 

Ay

Aye, I agree.

 

My fellow Buckeyes and I agree, get on it and drive it. An 1/8 mile aint even around the block.

 

had a mild big block/4 speed / 9" OT '66 car that had tall rear gears that was never happy from a dead stop at low speeds. had to gently ride the (hydraulic) clutch.

 

Don't go slow. Problem solved.