Suggestions for "pullover"

[Troy Patterson]

If the air cleaner is too close to the top of the carburetor, it can cause a low pressure area to be generated just above the float bowl vent tube. If bad enough, it will cause fuel to be drawn out of it. This has two effects; it reduces pressure on the fuel in the float bowl upsetting fuel metering - causing it to go lean; and the other effect is to flow unmetered fuel.

Overall, it's a mess if this is happening.

I am assuming it is a 500 two barrel. Is that correct?

Standoff is a possibility - I don't know anything about the application though. It work to minimize the effects at the carb if it were the case by making a anti reversion plate to sit under the carb such as some people run on tunnel rams.

Troy Patterson TMPCarbs.net TMP Carbs

[cspeier]

Troy, it's a dominator. Here is a pic of the scoop and how the carb sits. The Comp Cams vibration spacer has a anti-reversion plate already laid in rubber..

[bill jones]

-The communication here is beyond me.

[cspeier]

-The communication here is beyond me.

Sorry Bill, I value your knowledge..

Is it possible that the pullover is severe enough to look like standoff?

[Troy Patterson]

Alright. I've seen a circle tracker that made in the 450's in hp running a 500 cfm carb. It was allowed a roller cam and aluminum heads.

So, what size Dominator is it????

Troy Patterson TMPCarbs.net TMP Carbs

[bill jones]

-Seems to me like a 450 hp oval track engine is likely to be some sort of an 8 cylinder engine, probably twice the size of this 4 cylinder engine.

-can that 8 cylinder engine performance actually relate to what this 4 cylinder engine does?

-Seems to me that just the pulsing frequencies of the 4 cylinder is in itself enough of a difference to require an entire different way of thinking.
---------------------------------------------
-Then I wonder---why is this 4 cylinder engine built to run 10,000rpm and have such a low rpm (5200) stall rpm?----why isn't the stall up around 8000rpm?

-AND---how was the engine run on the dyno---what starting rpm and what rpm per second rate---600rpm per second?

-Was the engine ever stalled on the dyno at 5200 and then launched like you would race it?

[cspeier]

To be honest, this thing is really touchy. It seems it never does the same thing twice. I have it back to exactly like I made runs. It honestly won't shoot fuel anymore, but it basically sounds like it's on the chip at 5000 rpm. I tried the anti-pullover nozzles and they actually made it really smooth until it hits 5000. I think I'm fighting two issues, standoff and pullover??

It's sure funny how when I made the runs, the stall just stoped. (It's been down the track) I could hold it to the wood and it would only stall 52-5300 rpm. It never missed, popped, nothing. It just wouldn't stall. I also had at the time had a line pressure and internal problem. The trans had plugs in the cooler lines. I thought it had been internally by-passed and I didn’t need to run a loop. Come to find out, the internal by-pass had a pipe plug in it and wouldn’t allow the converter to exit fluid. This was hurting the stall. The converter should stall 7500+. I get the trans fixed, and it would stall again to 52-5300, but would never pop. I noticed when I would get to the stall, back off the throttle, the thing would go past the 5300 and go to 7000+. I really noticed the standoff when I leaned the carb out and added plenum/spacer combos. But like I said, I put everything back to like I made the runs and now it has a nasty pop. This is when I witnessed the pullover, while on the trans brake looking down the carb. Maybe the trans issue was simply just holding it back, now that it's fixed it wants to stall but has a carb issue.

Sounds so complicated, doesn’t it.

The engine was dyno’d from 7200-9500. The converter HAS TO STALL 7500+ or it’s going to be a PIG!!! The issue I have is I know the converter will stall the rpm I need, I just can’t get it past 5000. It has while on jack stands gone past the 5000, but only once..

[MadBill]

It almost sounds like problems I've heard of on BIG turbo race boats: E.g. a tuned-to-the-max-on-the-dyno 2,000 + HP BBC that wouldn't come off idle even at WOT due to prop drag and no power.
The fix was to dump the exhaust upstream of the top prop blade, which allowed it to cavitate, thus bringing up the revs, more exhaust, more boost, "and Away We Go!" Once up to speed, only the bottom blade was in the water, so no more cavitation.
Translation: There could be a huge natural dip in the power curve at ~5,000 that gives a second, lower, 'stall' point. You wouldn't know it because you haven't dynoed that low. Then what? More dyno time at the trouble spot? A clutch in series with the converter to get the revs up? A whiff of nitrous to get over the hump? ??

[bill jones]

-I'd try something totally off the wall.

-I'd pull the carburetor off and look at installing a pair of plugs to seal off or nearly seal off the secondary barrels below the blades---and try it as a large two barrel.

-Two inch throttle bores means you might machine up a pair of plugs to drop into the secondary barrels of the 4 holes of the built in reversion plate.

-You'd have to chamfer the top of the bores and machine a corresponding lip on the plugs so the plugs couldn't fall thru.

-Then try it as a two barrel and see what happens---might be pleasantly surprised.

-Or if rules allow---do mechanical fuel injection and just use the dominator as a throttle body.

[MaxFlow]

Sounds to me as though you have alot of carb on little engine with BIG duration numbers. No power below 5000 and duration is causing big dip in the power curve coming "on the cam"

I've ran 300 .050 duration cams in 4 cylinder engines and I guarantee there is a tremendous popping, snapping sound, before she comes on the cam under load, If it even will.

You don't have to spell out the combo, but what are the .050 cam specs.

To make 450 N/A hp at 9500 you have crazy duration for sure and a "nice" set of heads.

[cspeier]

Thought of the cam MaxFlow..

It's a 281/297@.050

It does have a sweet head on it, from my friend Darin Morgan..

[Hendrens Racing Engines]

If its popping at 5000 rpm and wont go any higher until you back off the throttle a little i would guess that its very lean at that point,engines usually wont pop if there rich,thats a lot of carb to be wide open at that rpm with such a small motor,you may not have enough velocity across the boosters until the rpm gets higher.try some much smaller high speed air bleeds to see if you can make the boosters tip in sooner. you could also try covering part of the carb with your hand and see if it increases the rpm or decreases,that will also tell you if its lean at that point.Bill

[cspeier]

Something to think about. When I had the trans issue, the car would fall to 52-5300 on the shift (stall speed). It never went nasty while trying to recover from the low shift. The more I think, the more I get confused.

A good friend made this comment to me, boy how true is this??

Your not stupid. Your in unknown (undocumented) territory! Your bound to have brain busters and boat load of time to figure this thing out.

[Mark R]

I noticed where you said if you started to close the throttle the enigne would pick up rpm, that's showing it's lean, as Mr. Hendrens pointed out. Can you post a photo of your fuel cell showing the position of the pick-up? I had to work thru a similar problem with an injected hemi bonneville car, I was not the driver so I had to rely on his ability to tell me what was happening. I finally pryed out of him that it would pick up rpm if he eased out of the throttle, so I said it's going lean, to which he repiled that I was crazy and we needed to lean it out more to make it go faster. I said, go ahead if ya want to scatter parts on the salt. Anyway to make a long boring story short, I told him based on his fuel pick up location that he was creating a vortex and sucking in air with the fuel causing it to go lean. I finally convinced these guys to put this thing on a chassis dyno so I could hear what was happening and actually look into the fuel tank while the problem was happening, and sure enough it was creating a vortex like you would not believe, so with a fw baffels added in the tank and the pickup moved to the rear of the sump the thing came alive. Just one more possibilty to look at, BTW, they had the pick up dead center of a flat bottom tank, about the worst place you could have it. I hope you get it figured out soon and share with everyone what you find. good luck!

[cspeier]

The cell is round.. as you can tell. What about the return????