Stumble On Launch

[Grumpy]

Hi

I try forums to get an advice.
The car is a drag race car.
Got a new engine 393 with double 1150 carburettors.
built for "up to 9500 rpm"
So this requires some high stall speed converter, along with the rest.
Well, my stall speed seem to be 4500 rpm.
My engine seems to have a small problem with this and needs more turns to get good power.
this is what happens:
When I get "on stage" and engage "trans brake", the engine stumbles when I pull wont rpm's up up. come up to 4500, cant get more. When I launch. then stumble the first 10-15 meters (loosing the race) before it finally give power and catch up..
This also happends at burn out--stumbeling at low rpm-- fresh when come to 5500 rpm.
Do this come from to little fuel??? 4 acc pumps, they are new and working...!
have hard time to believe this... should I adjust the pumps to engage later in throttle movement?
Advice ...?
I have thoughts that this is to much fuel...
I this only the converter..?

posting clear pictures of the car, the engine and the car as it launches would be helpful?

do you have a fuel pressure gauge with a sensor mounted at the carb inlet ports?

are you using the 50cc accelerator pumps?

what accelerator pump cams?

can you post pictures of the spark plugs?

do you have a data recorder and sensors?

whats the ignition advance curve?

is the engine still pulling hard at 9500 rpm?

whats the plenum vacuum at the point in the rpms where your engine stumbles?

whats the plenum vacuum at the point in the peak power rpms ?

what size is the fuel lines?

what is the fuel pump rated at?

what size is the return line and what fuel pressure regulator are you using?

yes a 4500 rpm stall converter ,sounds a bit too low!

what is the engine rpms going through the lights?

I assume you have a fuel cell??,

where is the fuel pump pick-up located?

whats the car weight?

what rear gear ratio?

what size tires?

whats the MPH through the lights?

1/8 or 1/4 mile?

can you post a dyno sheet with a detailed,
plotted power curve, fuel/air ratio, ignition advance, and plenum vacuum plotted ?

its not unheard of for the cars launch inertia ,
too momentarily and significantly restrict fuel flow ,
to the carbs for several seconds.
now obviously that may not be the only potential area to investigate,
and yes you may have too much air flow and to little port velocity, below about 7000 rpm,
but think logically, never assume, isolate and test and ,never guess.
.
.

guessing is a waste of time and effort,
and eventually money,
a few well thought out tests ,
can provide you,
with a great deal of useful data.
once you deal in verified FACTS you can rapidly find a way too improve performance.

http://garage.grumpysperformance.com/index.php?threads/holley-accelerator-pumps-cams.1790/

http://garage.grumpysperformance.com/index.php?threads/tuning-a-tunnel-ram-intake.5175/

http://garage.grumpysperformance.com/index.php?threads/holley-annular-vs-down-leg-boosters.5229/

http://garage.grumpysperformance.com/index.php?threads/how-big-a-fuel-pump-do-you-need.1939/

http://garage.grumpysperformance.co...l-line-sizing-return-vs-feed.3067/#post-44732

http://garage.grumpysperformance.com/index.php?threads/dual-quads.444/

http://garage.grumpysperformance.com/index.php?threads/tuning-carb-with-just-vac-gauge.14932/

http://garage.grumpysperformance.com/index.php?threads/too-much-or-too-little-fuel-pressure.13881/

http://garage.grumpysperformance.com/index.php?threads/installing-a-fuel-cell.733/#post-6470

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

 

[Maniacmechanic1]

393 is a real High winder Dirt Track Engine of past Grumpy....11k rpm is fact legends here!

I think it's a Stroker 393 Ford Winsdor....past 5.0 Renegade series race engine.
Ran simulations DD2000 on Dirt Track 393 Chevy. 150% 'VE and does not lay down. Can blow up anytime too so high rpms ! True Ti Rods needed !

Fuel delivery...
MSD Can't count on really.
Vertex magneto territory.

Stall 4500 rpm seems small.
5500-6000 better match.

 

[Maniacmechanic1]

I don't agree with Super Hot Full Drag cams either.
7k pull strong plenty for full drag.
Need some engine longevity !

 

[Grumpy]

yeah! too many people are MESMERIZED, and seem INTOXICATED ,
by PEAK HORSE POWER NUMBERS, ALONE,
not realizing a wide, instantly accessible,
and impressive TORQUE CURVE,
and proper gearing , in the drive train,
and suspension, brakes and tires, on the lightest car weight possible,
is far more important to getting the car to perform well.

 

[Maniacmechanic1]

yeah! too many people are MESMERIZED, and seem INTOXICATED ,
by PEAK HORSE POWER NUMBERS, ALONE,
not realizing a wide, instantly accessible,
and impressive TORQUE CURVE,
and proper gearing , in the drive train,
and suspension, brakes and tires, on the lightest car weight possible,
is far more important to getting the car to perform well.

Drag Racing is back Grumpy.
No Prep time clocks off.
Ultimate gamblers racing.
Chassis most important getting power down clean.
Lots of different ways to do it.
Can run to extremes best to have 3 engines. One blows swap out.
Repair the failed.

Needs to last 500-1000 full power runs my thinking.
They have to rev pretty high for top end speeds to gain pass if needed.
Not 9k unless no choice.