How restricting is the stock throttle body on a 305 TPI?

Hi guys, just as the question says, is it worth changing out? Thanks

Nope. Leave it alone.

According to TPIS you are better served by the factory 48mm TB and a ported plenum than a 52mm or 58mm TB and an unported plenum. First you need to remove the plenum and port it if you haven't already done so. And if you have no other mods you need to do more to justify the need for more air in (more cubic inches, heads, cam, headers and so forth).

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92BLKL98
'92 Black Z28 Hardtop w/Harwood 2" cowl ind. hood Modded 700R4, MSD
Ignition, March Underdrives, TPIS Fastpak, Ram air w/gutted filter box, SLP Prom, Flowmaster, & free mods, removed cats, Amsoil synthetic lubes, CE SFC's, Edelbrock STB,Spohn TA,Roadtech LCA's and Panhard Rod, Energy Susp., PST polygraphite bushings, KYB Shocks.

Do you guys know of a site that has pics of exactly what needs to ported in the plenum?

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Mario,
White 94 Z28 (http://www.z28roc.cz28.com/index.html)
Yeah I got a few mods
Video (http://www.z28roc.cz28.com/purge.mpg)
Black 87 IROC-Z (http://www.z28roc.cz28.com/iroc5.jpg)

What about Underdrive pulleys, are they worth anything?

It's not as restrictive as the base and runners...

Underdrive pullies are a waste of time i think. Removing pulleys, thats another story!

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Denny Villemure
1989 Camaro IROC-Z Convertible, 305 TPI, 2.73 Gear, Flowmaster 2 chamber. 15.60 on motor, 14.20 on a 75 shot from NX. Woo hoo!
www.denny.cz28.com (http://www.denny.cz28.com)

<font face="Verdana, Arial" size="2">Originally posted by AutoRoc:
It's not as restrictive as the base and runners...

Underdrive pullies are a waste of time i think. Removing pulleys, thats another story!

</font>

Very true, as for pullies my March kit is pretty, but I had to remove the crank pulley, it slowed the alternator too much. They don't gain you enough hp to be worth the effort.


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92BLKL98
'92 Black Z28 Hardtop w/Harwood 2" cowl ind. hood Modded 700R4, MSD
Ignition, March Underdrives, TPIS Fastpak, Ram air w/gutted filter box, SLP Prom, Flowmaster, & free mods, removed cats, Amsoil synthetic lubes, CE SFC's, Edelbrock STB,Spohn TA,Roadtech LCA's and Panhard Rod, Energy Susp., PST polygraphite bushings, KYB Shocks.

[This message has been edited by 92BLKL98 (edited July 23, 2002).]

The best thing to do in any motor is to get more air in and get more air out. They are simply an air pump. First you have to start with THE most restrictive pieces. Thats the biggie no one seems to understand. I have seen lots of flow charts that indicate the plenum, runners, and base to be very restrictive when all assembled but not so bad when measured separateyl. Why? Because the transitions from one piece to another were poorely designed. For example, the runners to the Base manifold meet at roughly a 30* angle, no good for smooth air-flow. It creates turbulence. Start with the other parts of the TPI first man. Once you are up over 350 hp then worry about the 48mm TB.

Stealth Ram that air hog! http://web.camaross.com/bb/wink.gif

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'91 RS Camaro - red/black, '95 LT1-based 355 w/ the infamous red intake

'00 C5 Coupe - black/black coupe, 6-spd, factory polished rims.

Chewbacca is NOT dead!

bs.cz28.com
350.streetracing.org/lt1d.html

I agree with you guys, on a 305 or mild 350 the stock throttle body is very sufficient, I noticed my biggest gains on the 86 305 TPI I have when I added the SLP cold air kit and ported the plenum! Now the exhaust is a completely different story...lol
Perry

[This message has been edited by Perry93TransAm (edited July 24, 2002).]

<font face="Verdana, Arial" size="2">Originally posted by Kodiak2727:
What about Underdrive pulleys, are they worth anything? </font>

http://www.fl-thirdgen.org/underdrive.html

here's what happened on my '95 3.4 v6 when i installed underdrive pulleys.

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fl-thirdgen.org#0004
moderator @ www.fl-thirdgen.org (http://www.fl-thirdgen.org) '86 t/a, 3.27, auto, homemade CAI, hypertech AFPR, comp cams 1.52 roller tip rockers, holley prostrip annililator ignition system, shift kit,
OEM corvette 2100 rpm convertor, lakewood adjustable panhard rod and trailing arms, edelbrock 6872 headers, catco 6007 3" cat, flowmaster 17151 3" single outlet catback. 14.91 @ 90.57 177.7rwhp 356.4rwtq

pull <font face="Verdana, Arial" size="2">Originally posted by Z28ROC:
Do you guys know of a site that has pics of exactly what needs to ported in the plenum?

</font>

here's what i did:

http://www.fl-thirdgen.org/mrr23-5.html



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fl-thirdgen.org#0004
moderator @ www.fl-thirdgen.org (http://www.fl-thirdgen.org) '86 t/a, 3.27, auto, homemade CAI, hypertech AFPR, comp cams 1.52 roller tip rockers, holley prostrip annililator ignition system, shift kit,
OEM corvette 2100 rpm convertor, lakewood adjustable panhard rod and trailing arms, edelbrock 6872 headers, catco 6007 3" cat, flowmaster 17151 3" single outlet catback. 14.91 @ 90.57 177.7rwhp 356.4rwtq

Thanks mrr23.

Here is a link I have stumbled onto in regards to porting.. http://sethirdgen.org/TPIbase.htm . I also had some pics bookmarked that i cant seem to locate at the moment that showed the restrictive area behind the throttle body that is knocked out.. guess it shrouds the egr p-way but needs to go.. will post it when i find it.. going to do mine this weekend hopefully..

Leave the Throttle body alone. There is much more you can do first. As for pics. Go here this is the best site I have seen about that hands down.

http://www.gmtips.com/3rd-degree/dox/tips/tips.htm

He goes through free mods, porting, wiring, all kinds of stuff. Do some of the things he has done and you will see an improvement..

Kevin

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86 Chevrolet Camaro Iroc Z-28 Fully Loaded With T-Tops
Mods;
Spohn SubFrame Connectors, S&W Race Car Chassis 8 point Roll Cage, 1997 SS Aniversary 3.42 POSI Rear End with 12" Rotors and 4 Piston PBR Calipers, Balanced Drive shaft... Others soon to come...

Best times before any mods done, Complety Stock;15.6 @ 87mph
Waiting for the tracks to open again to see what I got going on Now!

ntimad8.cz28.com

I ran a 13.5 @ 103.7 w/ a stock Throttle body and Stock Runners.

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Webmaster:SETHIRDGEN (http://sethirdgen.org)
GM Tech
ASE Master Auto Technician + L1
1987 Trans Am: 357ci
Ported TFS heads, ZZ4 cam, headers & exhuast and other go fast goodies
13.53 @ 103.77

Well aren't you just special http://web.camaross.com/bb/tongue.gif

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1991 Camaro RS
www.sethirden.org