Hello everyone, I know this has been answered in previous threads, but I couldn't find them. What will a stock TPI setup on a 1988 L98 flow? I found lots of runner flow.. but not a total CFM rating. Also, would plenum porting and minor intake and runner porting change the CFM rating? If so, by how much? (Iknow an accurate answer is next to impossible)

The reason I would like to know, is I would like to input the stock numbers in my Desktop Dyno program. I want to plan a cam swap for next year, and heads, and maybe more...


Thanx for your help in advance

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1988 Pontiac Trans Am GTA L98 5.7L, Black on Black with 114,000kms.

Best ET 14.559 @ 95.25MPH
Custom 3" Stainless Exhaust Y-Pipe back (High flow Cat and Flowmaster Mufler)

 

hmm, runner flow x 8 = total? or x 2 depending on if they give individual tube CFM or the whole runner. and the system can't flow more then the smallest part.

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- David
88' GTA 5.7L TPI MODS---> air foil, K&N, Shift Kit, 180* therm, TB bypass, Gutted CAT, Flowmaster 80 Series Muffler added to Unkown CatBack, Ported Intake

http://www.geocities.com/david_angel_16

[This message has been edited by breathment (edited November 19, 2001).]

 

Hey I've got Desktop dyno also. I used the throttle body cfm for the flow and it seemed to turn out pretty well. The number I had on the TB was 670 cfm @ 28" water which is equal to 570 cfm@ 1.5" Hg. Find/create a flow file for the stock iron L98 heads and that'll make a big difference. I couldn't find the seat to seat measurements for the stock cam so I used the economy cam from the program. I also used a single plane manifold cause I don't think the TPI in the program is correct. Set all the other stuff and it turned out 249 HP and 364 TQ. It's high, but I'm still working on it and it's close with(what I feel is) accuarate info. DD also claculates it's curves without the power loss from the accessories which could account for it being high. FYI this is for my 91 L98 so I hope it'll give ya good starting point. Good luck with it. Let me know if I can be of help.



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Stock 1991 L98...for now.

 

There are differing opinions on the subject, but I think the runners flow something like 203 cfm and the base is something like 196 cfm. I think either 88Irocs, badss, or yelofvr have some posts relating to the flow of the entire system which will be a bit more pertinent if you do a search.

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355 c.i.
Dart 180 Heads
Lunati 224/224 cam
Harland Sharp 1.5 rockers
Performer RPM Manifold
Holley 600 cfm double pumper
Hooker Super Competition Headers
Flowmaster Exhaust
Competition Engineering Sub-frame connectors
Tremec TKO
Pro 5.0 Shifter
GM posi 3.42 rear
Hurst Roll Control
13.9@102
http://www.geocities.com/thetpiguy/index.html
chemjoker@aol.com

 

Im not sure but I dont see how a single plane manifold would make it close to being acurate either. I would think that a double would be closer than that. The single plane manifolds give higher end power(right?), the tuned ports give more low end and torque, The dual planes produce more torque than horsepower but not to the extent of the tpi. I am not sure how correct this is but I dont see the single plane as giving an accurate power curve for the tpi.

 

thanx guys... I find the TPI setup in desktop dyno is pretty good... I will use 550cfm as my number. Hey.. where did you get the specs for the flow on a L98 head? I wish theyhad stock engine files already done!!

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1988 Pontiac Trans Am GTA L98 5.7L, Black on Black with 114,000kms.

Best ET 14.559 @ 95.25MPH
Custom 3" Stainless Exhaust Y-Pipe back (High flow Cat and Flowmaster Mufler)

 

I agree that a dual plane would seem like more of a logical choice for this case. And I also agree that if you took the stock TPI off and put a carb on that it would make closer to the same power with a dual plane rather than a single plane.
But TPI has more incommon with a well designed single plane or tunnel ram than a dual plane from a design and wave dynamics view. If you think of a single plane you see the opening where the carb goes and then the runners come into this open area beneath the carb. Likewise a TPI has the throttle body with a large space behind it (the plenum) that each runner draws from. In contrast a dual plane has the devider in the area beneath the carb.
In the manual for DD it says "The TPI is a single-plane design that functions like a long-runner tunnel ram." Since our TPI was desinged for the 305s they're technically not tuned for the 350s. DD says to use the single plane for many "TPI-like" intakes which is what we have.


Now that my speel is over...if you select the TPI in the program the max TQ (around 400) appears at 2000 RPM (the lowest it goes) and falls from there. Since I know that's not true I use the single plane because it gives a better result and the program suggested it. I'm also pretty sure that when parts of the intake are changed it "detunes" the intake.

I hope this clarifies things and if I'm wrong in my thoughts you're free to correct me. But it does work better this way in Desktop Dyno.


These are the numbers I have for the L99 iron head.
Pressure drop of 28 inH20. Inake of 1.94 and exhaust of 1.5
Intake
Lift Flow
.1 44
.2 101
.3 155
.4 182
.5 196

Exhust
.1 41
.2 82
.3 125
.4 137
.5 140


I found these on the one of the posts here.




[This message has been edited by Black 91 Z28 (edited November 21, 2001).]

 

http://www.vbe.com/~shadow/dyno2000.htm

 

now thats what i was looking for!!! thanx alot!!!!!!! and thanx to all the other guys.. lots of usefull info.



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1988 Pontiac Trans Am GTA L98 5.7L, Black on Black with 114,000kms.

Best ET 14.559 @ 95.25MPH
Custom 3" Stainless Exhaust Y-Pipe back (High flow Cat and Flowmaster Mufler)

 

tpis has a compete research section in there insiders hints book...... tells u flows with runners ans maf and all that stuff