Why can't a 305 TPI work well above 5500RPM's. Even if you port the intake and heads, and hi-flow runners, baseplate. With a cam that has a range up to 6000RPM's, are you guys saying that it cannot be done? Just wondering, cause I want mine to redline between 5500-6000. All responses are appreciated.

 

86 the reason for the lack of performance of the TPI above 5500 (heck above 4800) has to do with the runners. Do a search and you will come up with more than enough posts about this and how to fix it.

Eric

 

TPI will restrict at higher RPM stock or even ported stock it will. You need to do the whole top end before you can see real power at the 5-6K range.

1) new heads (S/R torquer 305 or AFR's 305)
2) new base (edlebrock or TPIS ported, maybe extrude honed)
3) new runners (SLP or AS&M ported and extrude honed)
4) plenum (SR or port the living **** out of what you have)
5) new cam (something in the 5.5 to 6.0K range)
6) new exhaust (headers & cat back, don't want to choke the damn thing)
7) 52mm TB (optional)

As far as I know, with this you will see more power at the top end, and it will shift it higher but Im not sure how high it will take it, maybe 5.5K.

But as erummel said ------------------
1989 Trans Am GTA

[This message has been edited by Drakar (edited November 08, 2001).]

 

I have a 1986 Iroc also. What is holding you back more than your intake or 305 is your cam. You have the peanut cam(only around 350'' lift I think) and upgrade that with some headers and you will notice a nice difference. With that I shifted at 5500 and my peak horspower was around 4500(I know shifting to high, but the 1st to 2nd drop is huge)

Chris

------------------
1986 Iroc 355 TPI coming soon

1985 Z28/5-speed Daily Driver

 

I'm going to stir things up a bit. A while ago a guy named 85MikeTPI posted a link to his site where a I found some dyno numbers on a miniram v. tpi with the LT4 Hot Cam. Using this data:

RPM TPI TQ Miniram TQ TPI HP MiniRam HP
3600 340 295 230 201
3800 335 296 242 213
4000 333 299 253 228
4200 328 302 260 240
4400 319 302 268 253
4600 310 302 271 263
4800 299 300 272 273
5000 284 298 271 282
5200 270 290 270 286
5400 259 284 268 295
5600 247 278 264 297
5800 234 272 259 300
6000 227 263 259 300
6200 216 256 256 303
6300 211 250 254 302

I plugged all this info into a program called Graphical Analysis. As many of you well know, it isn't all about peak HP, but rather, area under the curve. The integrated results from the above graph are as follows

Integral from 3600 to 5600 RPM redline:
TPI: 524510
Miniram: 517450

Integral from 3600 to 5800 RPM redline:
TPI: 576690
Miniram: 577130

So, if you had a high flow tpi and a HOT cam and were to race a guy with a miniram and a HOT cam with an identical car and identical traction, while both of you ran your cars from 3600 rpm to 5600 rpm, you'd beat him. From 3600 rpm to 5800 rpm, you'd lose by a hair. Although, since TPI makes more torque from below 3600, if you were to race off idle with all things being equal, you'd probably beat him too.
Just a thought...

 

I'd have to question the validity of the dyno results you found, all the dyno curves I've seen with TPI intakes, show a dramatic drop off in HP after 4800-5000rpms.

Another thing to point out is you wouldn't build the bottom end (cam and CR) on an engine the same when using a MR setup, vs. the TPI.

Optimally you would want more cam and CR to operate the engine in the higher RPM range that the MR has the potential to do.

Based off the results posted above, I agree the TPI setup would probably stay with the MR'ed setup, but the where the MR would shine (properly setup) would be keeping in the 4o00+ RPM range through the gears

 

Only one problem, you arent going to shift either one of them at the same point... so your analysis is flawed before you even started. Only time they will see the same RPM range is in first gear (at least until the guy in the TPI car shifts) and then its a new ballgame. You'd have to calculate the areas under the curve considering each shift point and where the car should be shifted at to get numbers that matter.

 

Right, I agree with you, which is why I said
"while both of you ran your cars from 3600 rpm to 5600 rpm" ... Indicating that you both shifted at 5600 rpm and dropped back into 3600 rpm. Furthermore I stated "All things being equal" so no, it's not flawed.

 

Mine does.
BD3



------------------
86 IROC mods:retro-fitted to a Comp Cams 210-215 499/499 112 roller cam,T.E.S.,Hooker Aerochamber catback
T.P.I.S. airfoil,Dan Burk ported intake system,,March
pulleys,Accel 8.8wires,ign.mod,Crane PS-91 coil,Crane HI-6S ign.box
RAM AIR induction,gutted MAF,
B&M shift kit,3.73 rear gears,Accel afpr,Hypertech stage 2 chip,Random Tech.cat.,Lakewood lower control arms,Lakewood adj.panhard rod,mac subframe connectors,PST polygraphite bushings 14.281 @ 95.45 2.004 60' on street tires
"The more I learn about women,the more
time & money I spend on my IROC"

 

Sure it does. I bet with your superior knowledge of airflow dynamics you chose the ideal cam profile. Or you just wait too long to shift...........

------------------
1991 Firebird
350 L98 (was a 305 TBI),T-5,Edelbrock TES and cat back,Accel manifold
NOS,subframes,jegster torque arm,MSD Digital 6
AFPR,Lakewood lcas
Hurst linelock,SLP cam (206 212 .480 .486),relocated battery,cold air,Hypertech chip,centerforce df,clutch
poly bushings and mounts
AFR 190s
Harland sharp 1.5 rockers
autopower rollbar

12.33 @ 114.83 juiced uncorrected

13.510 @ 102 non juiced uncorrected

 

I guess you haven't seen my dyno graph. Engine's a 355 with TF 23* heads, LT4 HOT cam, Hooker shorty headers, Edelbrock manifold, and stock runners. See the dyno graph here:

http://users.erols.com/gcwestph/Dyno2.jpg

I agree on both counts here, especially on a bigger cam for the MR vs. long-tube runners.

------------------
Greg Westphal
'87 IROC 355TPI/A4

 

Actually yea after re-reading your post about 500 times youre right its not a flawed analysis for exactly what you stated. However, its kinda pointless since neither one of them is going to be running the same RPM range at the same time in a race.

 

Unless, when you build your engine, you first decide that you will not rev the engine past 5600 rpm, then it's a pretty important piece of information. Not to mention the fact that the test was done with the HOT cam which is designed to make power at a higher RPM range, which means there might be a little bit more left in the tpi.

 

Wow, very flat HP curve, nothing I've seen posted before for the stock TPI's, I wonder if what I'd been noticing was with the stock base? Or you just found a real good combo. How much do you think an aftermarket set of runners would help you? Do you think the HP would still be flat? I'd think so.

 

If my word isn't good enough for you how about the word of one of the moderators like Ed M?He's driven it in Virgina & at Maple Grove raceway.
BD3

------------------
86 IROC mods:retro-fitted to a Comp Cams 210-215 499/499 112 roller cam,T.E.S.,Hooker Aerochamber catback
T.P.I.S. airfoil,Dan Burk ported intake system,,March
pulleys,Accel 8.8wires,ign.mod,Crane PS-91 coil,Crane HI-6S ign.box
RAM AIR induction,gutted MAF,
B&M shift kit,3.73 rear gears,Accel afpr,Hypertech stage 2 chip,Random Tech.cat.,Lakewood lower control arms,Lakewood adj.panhard rod,mac subframe connectors,PST polygraphite bushings 14.163 @98.16 2.004 60' on street tires
"The more I learn about women,the more
time & money I spend on my IROC"

[This message has been edited by IROCZ4BD3 (edited November 10, 2001).]

 

BTW if I was waiting to long to shift it how do you explain my new best since I waited even longer to shift it outta first and second?Outta first at 6500,outta 2nd at 5500.
BD3

 

Well, I attribte that to the fact that your first to second gear ratios are wide. Shifting higher allows your 305 to get back into the more powerful part of the power band. Ideally, if you had more gears shifting at 6500 would probably not be beneficial.

------------------
1991 Firebird
350 L98 (was a 305 TBI),T-5,Edelbrock TES and cat back,Accel manifold
NOS,subframes,jegster torque arm,MSD Digital 6
AFPR,Lakewood lcas
Hurst linelock,SLP cam (206 212 .480 .486),relocated battery,cold air,Hypertech chip,centerforce df,clutch
poly bushings and mounts
AFR 190s
Harland sharp 1.5 rockers
autopower rollbar

12.33 @ 114.83 juiced uncorrected

13.510 @ 102 non juiced uncorrected

 

I have a pretty good combination of parts, with the exception of the stock runners. I'll be installing a set of heavily-ported SLP runners sometime this month, then going to the dyno in the next month or 2. I expect that the HP curve will rise from 4000 rpm on up, peaking around 5600-5800 rpm if things go right. I'm shooting for 300 rwhp, but would be happy with 290 by the end of the year.

------------------
Greg Westphal
'87 IROC 355TPI/A4