3800 TB findings

[imported_Ron Vogel]

OK, this is a liitle towards the ragged edge. I've reached a point that is not making any sense. With my personal TB I have been able to step down all the way to a 3.0" pulley and see 2 degrees of KR. It's a stock bore, but the frontend is ported into somewhat of a velocity stack, with the exception of a little hump to shroud the IAC port and a flat area at the roof to steer flow more easily past the the short turn radius of the SC inlet. The shaft has been thinned alot, and I run a '98 LS1 MAF. So I came up with some prototypes of a 72mm bore, modeled after my current set-up, but using the L67 MAF. One was a '97 style with a '99 MAF, the other is a '99. With both I am seeing more KR, unless I fuel them up. I was able to get LT trims at idle to 0 on both with no mini-afc, but when I do, part-throttle KR starts showing up. So I adapted a L67 MAF onto my modified stock bore TB, and the problems go away. Watching the fueling, I know all three had very linear performance. It may just be my set-up, my boost is 1/2 to 1psi higher with the bored TB's. I do have my egr blocked off, with the inlet to it going directly into the manifold with fresh air. Next I'll try blocking off the EGR at the intake manifold and hooking the EGR directly to my air intake before the maf to see if that helps. If anyone has ideas on this it would be great.
BTW; I'm running stock cam/no rockers/no IC/full 3" exhaust/ high flow cat/DP

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[J.E.T.]

What was the question :huh: ?

 

[imported_Ron Vogel]

Maybe, I was talking/typing out loud...

Not really sure why more airflow before the heads is causing KR?

I think meself just answered that...I cringe at doing it, but may have to put on a smaller pulley until flow is improved in the heads. OR---keep it on with a smaller bore TB until I do the heads!

Whatever I do, looks like my car is going to take the leap from test mule, to quick car. I'm getting sick of swapping different combinations on and off the thing constantly, crap..I've had 5 different TB's on it this year alone!

If anyone is wondering why I've been messing only with the Mickey mouse intake and exhaust stuff; it's because I was trying to see the max out for stock valvetrain components (ie: heads/cam/rockers stock) without going to an intercooler or N20. I see alot of promise for water/alky injection, or propane for this set-up, but I don't want to mess with either at this time. My prediction was a 13.4@103, but at this point I'm 3tenths short and 2mph shy. So headwork here I come!

 

[98 TGP TOY]

My theory on why the stock "velocity stack" tb is helping you out more comes from my thermo class. What you are basically doing is making a "nozzle" out of your stock tb when you taper it down. The nozzle has three effects:

1: Velocity increases
2: Pressure decreases
3: Temperature decreases

So the pressure decrease would be the reason for the boost drop. The temperature decrease would help with cooling off the air and knocking down KR.

So that is my theory on why the stock "velocity stack" TB is working better. Again, just a theory.

 

[rob]

ALMEN.......Yes, increase velocity.
Ron, if you reaching your limitations. Re-introduce the TB relocater. It certianly will stack he air going it. Remember when you discovered the low-end tourque improvement. Should provide a longer cooler intake charge. Tunnel ram effect if you will. Instead of going out (diameter) go longer IF you can keep the velocitiy up you got something.

Should produce some more torque as you already found.

 

[98 TGP TOY]

One more lil tidbit. I had a talk with my thermo proffesor and it made a lot of sense to me. I was asking him about velocity stacking an intake system before the TB, and he said "why would you want to do that". Because when you increase that velocity you have a pressure drop. And if you think about it, pressure is the most important aspect of an engine. And eventually all the air is going to stop anyways, so whats the point in getting it there quicker, when you could have gotten it there with a higher pressure. Also any velocity increase you get at the TB will instantly disappear when you get to the manifold because there is a bigger volume in the manifold so it acts like a diffuser.

The benefit I see from velocity stacking would be the drop in temperature. Now the other thing is that this guy doesnt specialize in engine thermodynamics. So alot of this may be theory, but it sounded like he has been in that discussion before. Just some information Im passing along, take it for what its worth

 

[imported_Ron Vogel]

Well, I see where this is going. I had thought no real benefit could come of the larger bore until more aggresive mods were done to the valve train. Since I'm futzing with a different TB on my car now, I'm tweaking mine again. I can always reduce the bore of the outlet, but I want to do more of it at the roof to take advantage of the sort turn radius in the SC a little better than I am now. The only issue with that is the IAC, so that'll have to be dealt with. I still have room to open up the front air horn a little more too.

 

[beyerch]

Originally posted by 98 gtp toy@May 5 2004, 11:30 AM
One more lil tidbit. I had a talk with my thermo proffesor and it made a lot of sense to me. I was asking him about velocity stacking an intake system before the TB, and he said "why would you want to do that". Because when you increase that velocity you have a pressure drop. And if you think about it, pressure is the most important aspect of an engine. And eventually all the air is going to stop anyways, so whats the point in getting it there quicker, when you could have gotten it there with a higher pressure. Also any velocity increase you get at the TB will instantly disappear when you get to the manifold because there is a bigger volume in the manifold so it acts like a diffuser.

The benefit I see from velocity stacking would be the drop in temperature. Now the other thing is that this guy doesnt specialize in engine thermodynamics. So alot of this may be theory, but it sounded like he has been in that discussion before. Just some information Im passing along, take it for what its worth

I disagree.

I don't think a drop in temperature is that great of a deal. Ask yourself a simple question, *WHY* is the temperature dropping.

All of the air that you are pulling in is at X degrees. Unless you are externally pulling the heat out of the air somehow (say intercooler), you are not removing any heat.

Basically here is what is happening.

Y = Pressure (air molecules)
X = temperature

X = some function of Y

If you lower Pressure, temperature lowers.
If you increase Pressure, temperature increases.


Now more specifically if you increase pressure, you are packing in more air into the same amount of space. This increases the temperature (X) because each air molecule has a heat value. If you add 2x air, you are going to increase the temperature in that space.

If you lower the pressure, you are "unpacking" the air so that there are less molecules packed together. This means there is less heat in a given spot.

Dropping pressure gives you the lower temperature but only because you are removing air and that is what makes the power ! The trick is to get in the most air (pressure) at the lowest knock possible.

As far as the TB testing in general, if you are not logging fuel readings, all of that time is wasted. modifying the TB alters the MAF reading to some extent and you need to keep that into mind at all times. One reason for a particular maf getting part throttle knock could be that the sensor is not getting a very accurate reading of the air and its not telling the PCM an accurate flow #, this would cause the PCM to not add enough fuel and that would cause for your KR. A good hint of this is if the fuel trims are way out of whack. If you have a huge + trim value, expect part throttle knock.

Charles

 

[BumpinGTP]

me confused :wacko:

 

[98 TGP TOY]

Charles, I agree completely on the temperature drop. The only reason it drops is because of the pressure. What I meant to say, is "the only benefit that I could see would be".

The trick is to get in the most air (pressure) at the lowest knock possible.

This is sort of what I was going for with the first paragraph of my second post.

It seems to me that using a tapered TB is going to be better than stock, because you will get more air in due to the larger bore at the front of the tb. But i believe that just using a larger bore and not tapering it will be better, in the long run, than a tapered TB. Simply because you are maintaining a higher pressure, and still have the same mass flow. The velocity doesnt increase, but that isnt important in engines, pressure is.

IE....Stock TB < Tapered TB from 73mm (inlet) to 69mm (outlet) < Bored TB 73mm

OK, i made up the numbers, but thats because I forget what you guys bore it out to, but the idea is what im going for.

Did i lose anyone.....besides bumpin

 

[Fish]

I was gone as soon as this thread started.

 

[imported_Ron Vogel]

As far as the trims, that's where I'm confused at. I get the trims to work very well on this model, and the fueling is very linear as the stock TB. I use a flat plane and the distance relation to that plane to get the readings I want from the maf. Other than that, the proportion of the new bore/old bore to the inlet is the same. I expect the readings to have +LT's, and they should; more air is getting in. However, I'm limiting it to a certain extent to keep the computer happy and give room for more mods. Where I see a problem crop up is around 4K RPM, it's at that point fueling comes in. I adjust my mini-afc in 1% steps and see KR start 500rpm higher. I'm scanning LT's, RPM, 02's, KR.

 

[98 TGP TOY]

Oh yea, and applying this all the what I think to original question was.

I think the reason he saw less boost and a kr reduction is because the air cooled off and dropped in pressure. Thats all i was really getting at.

Now im off to my thermo final

 

[imported_Ron Vogel]

Originally posted by 98 gtp toy@May 5 2004, 01:36 PM
Oh yea, and applying this all the what I think to original question was.

I think the reason he saw less boost and a kr reduction is because the air cooled off and dropped in pressure. Thats all i was really getting at.

Now im off to my thermo final

Well, good luck and thanks for the info...

And, thanks Charles too...


One more thing though, I noticed during WOT that the IAC opens up. Could this be steering the airstream? If it is, it gives me some ideas on tweaking.

 

[imported_Ron Vogel]

OK, figured it out. Obviously my pulley is really small for my combo, but it's staying on...! I had the MAF spaced to high, and brining it down 1/8" got me fueling right. I upped the mini-afc 2%, and it goes like hell now with 2 degrees KR. I'm seeing the part throttle kr because the smaller pulley still gives me some boost, even as the timing hasn't changed to PE mode, so the 22-25 degrees of advance are still there during boost. The points above about the longer runner are valid though, and I'm making a one-off TB, with a stainless insert velocity stack to check it out. It tapers from 4" to 3" right before the blade, the taper length is about 4 1/2". I'm milling off the front of the TB to make a flat surface to mount the insert. Hoping to get it done before the mod day, 'cause it's going to look pretty cool. It has to be used with a LS1 maf though, but I like that set-up better anyway. My personal TB is off, and I've gotten very aggressive with the "stack" porting on it. If it goes to swiss cheese, I've got a few cores to replace it with now so I'm going for broke with it.

 

[98 TGP TOY]

Great to hear Ron, glad you got it all figured out. You know, I may have to play with those numbers one of these nights to see what the real pressure change and temperature change are. Just to see if it should really make a difference. Im just curious now, and since its not hw, its more fun