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Discussion Starter · #1 ·
Regarding fall of rpm's on the 1-2 shift. Should a converter always fall back the relatively same amount of rpm's no matter where the shift point in low gear? Or should it fall back to the same rpm area to make it's climb back up in high gear regardless of where it is shifted at rpm wise in low gear? Or is there no real answer?

Reason I ask, had another converter built for my car. If I shift the car at 7000 it falls back to 6200. If I shift the car at 7200 it falls back to 6200. If I shift the car at 7400 it falls back to 6200. If I shift the car at 7600 it falls back to 6200. This is the reason I had another converter built.

My question here is how do you get a converter to fall back a certain amount of rpm's on the 1-2 shift if it is that far out of control when you change your shift point?

Every converter I have used does this, is this the way it's supposed to work?


Also, whenever the progressive nitrous controller gets to 100% in low gear (usually on an .082 jet it's around 7-9 tenths into the run) no matter which converter is in it the 7531 shows an immediate flatline in low gear for like 1.2 seconds, before it begins to accelerate. I had the flatline problem in high gear last year, now it has moved to low gear and the high gear flatline is completely gone.

So far with an .082 jet in the nitrous plate it has run within a couple hundredths of 5.80 with the following changes.

1. Four different Converters
2. Three different engines ( 580 h.p., 672 h.p., and 767h.p.)
3. Same transmission, but gone through 4 to 5 times with three different planetaries. (1.80, 1.65, 1.69) Nobody ever found anything really serious wrong with it though. There was a line pressure issue but that has been resolved.
4. 5 sets of rear end gears 3.70, 4.10,4.30,4.56 and now 3.89.
5. Also found a couple weeks ago that the back brakes were engaged so much you could put the car in gear and the tires wouldn't turn. Fixed that expecting it to make some sort of difference and that didn't make any difference either.
6 Five different nitrous kits.

Also doesn't matter if you shift the car at 6800 or 7800 or anywhere in between. It will always run somewhere between 5.75 and 5.83 if it has an .082 pill in it. Which makes absolutely no sense at all to me.

On one other interesting note, if the other small block cars in my class add another 100 h.p. to their nitrous system to run in the other class where there are no jet restrictions. They will all typically pick up a few hundredths or a tenth at the maximum. My car picks up 3 tenths. WTF? This is also with 2 different converters I know of.

Any of this make any sense to you guys?


Could there be something in the car itself that is causing this issue? Or possibly something in the 7531?

So after four years and endless dollars thrown at it to find the problem. Nobody has been able to find it yet, me included.

I'm wondering if I should just get another car to put this setup in?
 

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Discussion Starter · #3 ·
i think it will always fall back to 6200 because the converter locks up at 6200 does it leave at 6200 also?

No I leave at 3200 - 3400, it flashes to 5200 on one, 5600 on one, and 5400 on another. It will hard stall flat against the brake to 4000 on one 4200 on one and 4800 on another one.
 

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Discussion Starter · #5 ·
maybe converter is built for more spray. reason why you gain 3 tenths on 100hp more nitrous and other guys dont

While that could be, one of the converters was built specifically for the small pill and still gained 3 tenths. Converter guy is still scratching his head on that one too. It was also supposed to drop a max of 1000 or so on the little pill. Well, it drops way more than that on an .082. And drops right at that on a .110. So did the other ones.

Plus one of the converters I tried came out of a car identical weight, engine, gearing , and suspension to mine and worked great in that car. But it did the same thing as all of the other converters in my car.
 

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we had a chance built for a small 150 shot and the converter leaves so soft that it leaves me to believe it will take a 300+ shot. stalls 5500 on motor and 6500 on gas but still leaves soft as hell. maybe your tune is off or that engine really loves nitrous. i have seen that before
 

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Discussion Starter · #7 ·
we had a chance built for a small 150 shot and the converter leaves so soft that it leaves me to believe it will take a 300+ shot. stalls 5500 on motor and 6500 on gas but still leaves soft as hell. maybe your tune is off or that engine really loves nitrous. i have seen that before

I don't have any problem leaving. The problem is after the nitrous gets to 100% the converter or something in the trans pulls the motor back down. It would do it last year in high gear immediately after the shift and everyone thought it was because the converter charge circuit wasn't getting enough pressure. Sent it out and had that problem addressed. Now it does almost the exact same thing in low gear.

Oh and thinking the tune was off last season is the reason I got a couple pistons and both head gaskets. I kept narrowing the window until I went past it.
 

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RED ROCKET
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I don't have any problem leaving. The problem is after the nitrous gets to 100% the converter or something in the trans pulls the motor back down. It would do it last year in high gear immediately after the shift and everyone thought it was because the converter charge circuit wasn't getting enough pressure. Sent it out and had that problem addressed. Now it does almost the exact same thing in low gear.

Oh and thinking the tune was off last season is the reason I got a couple pistons and both head gaskets. I kept narrowing the window until I went past it.

are you using a stock case?just curious.
 

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Discussion Starter · #9 ·
are you using a stock case?just curious.

Reid Case. Eight Clutch Drum, all the good stuff. Have tried different pumps, valve bodies, ringed and ringless input shafts, bushings and no bushings in converter and pump. On a side note I guess I could just go 5.80 index racing, it will run almost that exact number every pass with an .082 jet in it. No matter what the tuneup, or progressive setting. I even changed progressive controllers, no difference.
 

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In the last 4 years, is there a constant that has stayed the same in the car that you have not changed??

carb
camshaft
intake manifold
ignition box
ignition coil
fuel pump
fuel pump relief pressure
.....

Does it seem like the engine just sits at a certain rpm and then, like someone flicks a switch, it accelerates again? or gradually accelerates after the flatline??
 

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Discussion Starter · #11 ·
In the last 4 years, is there a constant that has stayed the same in the car that you have not changed??

carb
camshaft
intake manifold
ignition box
ignition coil
fuel pump
fuel pump relief pressure
.....


Does it seem like the engine just sits at a certain rpm and then, like someone flicks a switch, it accelerates again? or gradually accelerates after the flatline??

The only two parts in the car that haven't changed are the rear end housing and the transmission case itself. In the car it just seems like it stays in low for an eternity. But, looking at the graph from the 7531 it gets all of the nitrous in and then just stops accelerating for like a second and a couple of tenths then starts climbing just like normal. If someone can post the data files I can send them tonight....but I've never been able to get them to post.
 

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Could the 8 clutch drum be to much for your H.P. and draging the engine down until the RPM and H.P. come up to drive them. I see a lot of 1,000 H.P. guy's running 6 clutches behind BBCs.
 

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Discussion Starter · #13 ·
Could the 8 clutch drum be to much for your H.P. and draging the engine down until the RPM and H.P. come up to drive them. I see a lot of 1,000 H.P. guy's running 6 clutches behind BBCs.

It's had a 6 clutch in it, plus the transmission in my buddies car that I borrowed the converter out of with the identical combination has a 10 clutch drum in it. Little small block makes over 1000 at the flywheel with an .082 jet. Probably close to 1200 or so on a .110 jet.
 

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Discussion Starter · #14 ·
Just some FYI, putting a different trans in the car tonight. We shall see if the trans is causing the issue. Even though it's been gone through many times. Figured what the hell, the trans case is one of the few components on the entire car that hasn't been changed.
 

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RED ROCKET
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good luck,i know you have been chasing this for a while..thats why i asked about your case,thought maybe it had an internal crack that you cant see.
 

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Discussion Starter · #16 ·
Update: Took the car out last night and ran exactly the same again. Only two things left, the rear end housing and the entire rolling chassis.
 

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The converter will always fall back to the same rpm at a given power level. If you shift at 7000 and it falls the 6200, it will also fall to 6200 from 7800 rpm.

The flat line is normal. You should see it around 6200 rpm. To shorten the distance of flat line you need more power. You say it flatlined once it hit's 100%. Well, that could be from the power driving the converter to it's flash stall and then the motor needs time to overpower it and drive it further up. Or it could be the timing or a/f ratio is not right and the car isn't making the power it should at 100%. Without the power, the car can't overcome the coupling of the converter.

Have you looked into the timing the motor is puliing out on the kit? How is the tune-up. Too fat or too lean? To get a converter off it's flatline is simple.....you need more power.
 

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Discussion Starter · #18 ·
The converter will always fall back to the same rpm at a given power level. If you shift at 7000 and it falls the 6200, it will also fall to 6200 from 7800 rpm.

The flat line is normal. You should see it around 6200 rpm. To shorten the distance of flat line you need more power. You say it flatlined once it hit's 100%. Well, that could be from the power driving the converter to it's flash stall and then the motor needs time to overpower it and drive it further up. Or it could be the timing or a/f ratio is not right and the car isn't making the power it should at 100%. Without the power, the car can't overcome the coupling of the converter.

Have you looked into the timing the motor is puliing out on the kit? How is the tune-up. Too fat or too lean? To get a converter off it's flatline is simple.....you need more power.

When you are jet limited and the tune up is spot on, it isn't so simple. And when you look at my graph on the 7531 versus the cars that are running low 5.50's. Mine "looks" better than theirs. Theirs are all over the map, and except for the one flat line in the middle of low gear mine is a complete steady perfect climb everywhere else. Plus, if I throw another hundred or more at it, the car runs faster (still a couple tenths off the pace) but the flatline is still there. Oh and the flatline is always at 5600, sometimes the car actually drops RPM also.

If I pull any less timing it will start to nip plugs. Now that being said as far as the fuel goes I feel I could get it leaner if I could get the converters not to pull the motor down so much. Unfortunately, by learning the hard way, if I pull any more fuel out of it.....it will start getting pistons and/or head gaskets because it's being lugged down, and can't accelerate.
 

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Have you had the engine(s) on a dyno?? Valve train issue at 6000ish rpm maybe that is compounding itself the more cylinder pressure it sees?? Just shooting things out there...
 

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Discussion Starter · #20 ·
Have you had the engine(s) on a dyno?? Valve train issue at 6000ish rpm maybe that is compounding itself the more cylinder pressure it sees?? Just shooting things out there...

Dyno'd at the very end of last season, right before we freshened it up. Made peak of 767 h.p. @ 7600 rpm (just motor). Right now it only has about 10-12 runs since the refresh. Figure it was probably in the 780-790 ish range after the freshen up.
 
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