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Username Post: stumble at race track        (Topic#356713)
artic-trans-am 
Poster
Posts: 11

Reg: 02-05-08
06-07-19 05:21 AM - Post#2767872    

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 wnt 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 finaly 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 belive 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..?



 


Shepherd 
Frequent Contributor
Posts: 1785

Loc: Lake George, NY
Reg: 11-11-15
06-07-19 08:46 AM - Post#2767885    
    In response to artic-trans-am

Tough to diagnose from here, but I would think a single 1150 carb would be plenty for any built 383 sbc.



 
55 Shaker 
Member
Posts: 1494

Age: 69
Loc: north central IL.
Reg: 03-13-06
06-07-19 09:35 AM - Post#2767889    
    In response to artic-trans-am

If you got a cam big enough to wing it 9500 RPM (which I doubt) you need a higher stall convertor. JMO.

The older I get, the more dangerous, I am !!!!


 
rumrumm 
"18th Year" Silver Supporting Member
Posts: 2086
rumrumm
Loc: Macomb, IL
Reg: 10-18-01
06-07-19 11:41 AM - Post#2767897    
    In response to 55 Shaker

It sounds like you are over-carbureted to me. How do your spark plugs look? What are the specs on your cam? How much compression? What heads? And what point are you shifting?

Lynn

"There's no 12-step program for stupid."


383 sbc, Eagle, AFR, SRP, CompCams, Edelbrock, FiTECH. Dyno #'s: 450 hp @ 5700, 468 lb. ft. of torque @ 4300.



Edited by rumrumm on 06-07-19 11:43 AM. Reason for edit: No reason given.

 
Shepherd 
Frequent Contributor
Posts: 1785

Loc: Lake George, NY
Reg: 11-11-15
06-07-19 03:46 PM - Post#2767913    
    In response to rumrumm

No, way too much carburetion, crazy!!



Edited by Shepherd on 06-10-19 04:29 AM. Reason for edit: No reason given.

 
grumpyvette 
Senior Chevytalk Moderator -- Performance Subject Matter Expert --
Posts: 17348
grumpyvette
Age: 71
Loc: FLORIDA USA
Reg: 03-16-01
06-08-19 11:46 AM - Post#2767954    
    In response to Shepherd

  • Quote:

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?

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?

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?

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.

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

http://garage.grumpysperformance.com/index.php?thr...

IF YOU CAN,T SMOKE THE TIRES AT WILL,FROM A 60 MPH ROLLING START YOUR ENGINE NEEDS MORE WORK!!"!
IF YOU CAN , YOU NEED BETTER TIRES AND YOUR SUSPENSION NEEDS MORE WORK!!


Edited by grumpyvette on 06-08-19 12:04 PM. Reason for edit: No reason given.

 
artic-trans-am 
Poster
Posts: 11

Reg: 02-05-08
06-10-19 03:30 AM - Post#2768085    
    In response to grumpyvette

Hi
Sorry my late reply. Didn't get any notice in my mail box.
Ok..
This engine was not built by me. I swapped it for a BBC i didn't like. To heavy for my car.
Engine is built with alu rods, kompression 14:1, brodix heads, modifyed for bigger springs. Cam is spessial. Dry sump. This have run in dyno and in other cars. Run well.

Ok, my first thought is that this is too much carburators too. But this again was run in a dyno test. With NOS also.(this is not connected now)
I could try to find new carbs, maybe 2x750 cfm is ok.
I can try to make a new top plate to my intake also and run one 1150 carb.

Have trouble to post pictures here....
Go to my facebook page to see pictures:
https://m.facebook.com/firehillracing/



Edited by artic-trans-am on 06-10-19 04:46 AM. Reason for edit: No reason given.

 
Shepherd 
Frequent Contributor
Posts: 1785

Loc: Lake George, NY
Reg: 11-11-15
06-10-19 04:28 AM - Post#2768087    
    In response to artic-trans-am

Good plan.



 
artic-trans-am 
Poster
Posts: 11

Reg: 02-05-08
06-10-19 05:17 AM - Post#2768094    
    In response to grumpyvette

Thanks for your interest in my problem. I try to answer you here




posting clear pictures of the car, the engine and the car as it launches would be helpful?
go to my facebook to see pictures. Not the best. But you get the idea.

do you have a fuel pressure gauge with a sensor mounted at the carb inlet ports?
have fuel gage at the regulator and a secondary electric to view from driver

are you using the 50cc accelerator pumps?
yea 4x50 cc
what accelerator pump cams?
yellow

can you post pictures of the spark plugs?
I will do when I get one
do you have a data recorder and sensors?
no, WBO2 is on the way inn
whats the ignition advance curve?
max at 34

whats the plenum vacuum at the point in the rpms where your engine stumbles?
have no vacuum instrument, but think I have one in my garrage. I see if I have time to mount.
whats the plenum vacuum at the point in the peak power rpms ?
sorry, dont have this now
what size is the fuel lines?
AN8 up to fuel regulator, then AN6.

what is the fuel pump rated at?
dont think that is the problem at the first sec of burn out/race

what size is the return line and what fuel pressure regulator are you using?
dont remember right no, I check
I assume you have a fuel cell??,
yea, with foam

where is the fuel pump pick-up located?
bottom rear in fuel cell

whats the car weight?
1200 kg
what rear gear ratio?
4.56

what size tires?
33

whats the MPH through the lights?
let fix the start problem, first

1/8 or 1/4 mile?problem is at burn out

this is the quick reply I will get you the other info.



 
65_Impala 
Very Senior Member
Posts: 4227

Reg: 12-29-02
06-10-19 08:12 AM - Post#2768105    
    In response to artic-trans-am

Yes you've got a lot of carburetor, but I would put money on 4500 rpm being too low a stall speed for an engine built to make power up to 9500 rpm.

I would also bet that the converter is wrong if you didn't get one custom built to match your engine and drivetrain.

You should have the dyno curves to help you pick the stall. Give that along with the car details to a custom manufacturer and they'd get you something that would work.



 
artic-trans-am 
Poster
Posts: 11

Reg: 02-05-08
06-19-19 03:07 AM - Post#2768802    
    In response to 65_Impala

Change to 1 carb, helped allot.
Had to go 6 step up on jet's now i dont get next to nothing lag/hesitation.

but I have a Proform race-series 950 carb with 4150/4500 spacer. Maybe I should try this one too.
I have even parts for this one to change to E85 fuel....



Edited by artic-trans-am on 06-19-19 03:17 AM. Reason for edit: No reason given.

 


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