tuning help

i have a blown SBC it is 441ci with a 14-71 littlefield (60o rooters) running at 31% over and with a glide. the problem that i am having is with RPM's, i leave at 5400 and it will flash to about 7000 and gain 200 rpm then i will shift around 330' and the rpm's drop to around 7000 and will climb back up to about 7400 at the lights.

am i turning the blower too fast or is my fuel off. i want to shift around 8400-8600.


we are running a Pro-Stock S-10 at 2625lb and 1.04 - 1.06 60', best of 4.65 @156


what do you think?
thanks for any help
neal

 

years ago I ran a sbc same set up and same problem, I ended up using a heavery crank also ran 4.56 gears..and you need to look into your cam specs. the best I could ever run was 6.40's in the 1/4 and always had problems keeping heads on the darn thing brodix block and heads.
as I was saying we ran a winberg crank and it was to light need more rotating weight to get RPM's..hope this might help.. remember this deal was like 10 to 15 yrs ago..now I can't remember were I put my shoes at last night..Dave

 

When did you last check your valve springs? What seat pressure have you got?

Dave, you don't wear shoes, remember?

Paul

 

Is this a recently occuring problem or has it been like this?

 

the springs are new with 330lb seat. installed 7 passes ago.

 

it has been going on all year

 

It could be a number of things. Is your throttle response good or does it labor to hit a high rev while "unloaded"? That size roots blower will take a considerable amount of power to run. Have you had your fuel system flowed? Pump checked? Is it blowing raw fuel or are you getting good and frosty plugs?

If the motor checks out fine, then you are just lugging too much gear for the power and the tire is stuck. If you are only seeing a 200 RPM gain by the 330' and you're at 7,000 until then, your convertor is plenty loose. Try some different rear ratios.

 

very good throttle responce. it will rev up to 8800 very quick in the pits.

the fuel system was bought 3 years ago and we have not checked it. it has never had fuel coming out of the pipes. we are running an Enderle 1100 that flowed 16.2 @ 4000, but it has a pump loop with 110 jet and our last run we had a 125 main. the plugs were not frosty.

we tried a 4.86 rear gear and then changed to a 5.14 at end of the year and a ati converter 9.5" with both gears. when we changed to the 5.14 we gained about 100 rpm on the top end. for the last race we changed the converter to a coan bolt-together (10") and had quicker 60' times but same top end numbers.

it comes out of the hole great for the 100' and then flat.

i do know how to post a graft but if anyone wants to look, i can email. do not have the last race on my computer at work.

 

Are you running a high speed bypass?

 

nope, just the pump loop

 

What is your first-gear ratio?

You might have change the trans ratio and then adjust the rear ratio.

 

If this has been happening only this year, what has changed between the last (good) run last year and this year when it went sour? There are so many variables it could be anything. You need to go back and look at what you changed before this happened.

 

Mybe the pump took a crap.and now your on the wrong side of the fuel curve

 

camshaft<<<<..Dave

 

convertor..

 

This is just my 2 cents but here goes,

If it was the converter it would either leave weak with a bad stator or if it was just blowing through it to 7K the rpm would still climb by the 330 so due to that and the fact that you changed converters.. I don't think its the converter.

It could also be the vavle spings but it seems like you would have seen a change when you changed them last week.

The easiest thing to fix that could be wrong would be a restricted or too small vent, filter, or fuel line. Or of course it could be the pump or the tune. That said I have a feeling if its hitting 7K at launch and only gaining 400 rpm with whatever problem it does have now when you get that problem fixed you will probably find that the converter is too loose.


Richard G

 

I have been down this road for two years on mine. A few things a convertor can do is drive through it, FATTEN the motor up where it wont pull. Since we own a track and I have a couple cars we do some convertor testing for the guy who builds mine, and I can tell you without a doubt the convertor will do what he is seeing.
You have to remember since the fuel is being dumped in, and the convertor is NOT 100% slippage it wont freewheel like a burnout or reving the motor, it still has X amount of load. Then when it catches up to itself with LESS power from the tune up it appears as though it wont rpm.

Of course many other things will do the same.
If he had a driveshaft reading It would help a bunch here.

But ignition, tune up, and other things can also do this as you well know.

 

Thats a BIG ASS PUMP TOO for that, and not alot of bypass.

 

1.80 gear glide

 

no computer last year, but running the same times