86TpiTransAm

What's the difference between the TPI and LT1 throttle bodies and if there is a difference, can I make an LT1 TB work on my TPI and how? Thanks in advance.

John Millican

iTrader: (1)

The only differance is the connectors for the IAC, TPS sensors and the throttle cable.

tpi_roc

I believe the LT1 TB throttle cable has a pully type setup and pulls over the top

86TpiTransAm

Any more info?? What's different about the IAC and TPS connections and the throttle cable? How can I modify it to work with my TPI?

John Millican

iTrader: (1)

Tell us what's going on what and why and we'll help.

I say this because there is no differance in either from a performance point of view.

86TpiTransAm

The reason I'm thinking of doing it has nothing to do with performance. It's going on my TPI 350 motor. My current TB is having issues with the spring on the throttle return. The throttle lever won't snap back fully to the throttle stop. I have two universal throttle return springs hooked up right now just so the throttle will snap all the way back and I won't idle at 1500rpms.

Anyhow, I know a guy with 3 LT1 throttle bodies and he said I could have one for free so my feeling is, why pay for a TPI TB when I can get an LT1 TB for free. IF there's any way to make it work. Thanks.

BOTTLEDZ28

iTrader: (9)

if you are getting it for free then take it. try it out and let all of us know what the differences are and include pics if possible.

John Millican

iTrader: (1)

OK '86TPI, I totally understand now. Here's what you will need.

1. IAC connector from a LT1 wire harness
2. TPS connector from a LT1 wire harness
3. LT1 throttle cable

The connectors you may be able to find at PepBoys, they have a whole isle of electrical, cost about $10 EACH! You will have to splice the new connectors into your TPI wire harness after cutting off your old connector unless you have the tool to de-pin the connectors. I am not sure but the wire colors might be the same, if not you will need a book for each car and verfiy wires.
If you need to buy both books then the cost is climbing....

Now you will have to mod the throttle cable bracket somehow because the LT1 bracket is much closer and has a large square hole for the throttle cable to go through, the LT1 throttle cable has a small square hole....more cost and time.

Your up to about $60 now you still need to buy gaskets and make it work. My suggestion is to watch the "for sale" board and get someone's stock TB when they upgrade to a 52 or 58mm TB. You should be able to get a used TPI TB for $25-50.
Also could try www.ebay.com

Kevin G

One other thing to mention is that the LT1 TB will not have a vacuum source for the EGR. You wil have to rtap in somewhere else for this.

I installed a LT1 style 58 mm TB on an L-98 many years ago. I can't remember all the details, but with a little modifications it can work.

John Millican

iTrader: (1)

Vaccum source for the EGR? I'm sure you mean the valve cover vent...

89ProchargedROC

no he DOES MEAN the EGR

there is a SMALL vacuum port on the bottom of the TB that goes to the EGR in the middle of the TPI intake

John Millican

iTrader: (1)

I see now, I never noticed that before, mine is capped. I have been without an EGR so long it slipped my mind.

86TpiTransAm

Thanks John for the advice. I think what I'll do since it seems like such work is get the LT1 TB for free and then sell it somewhere like ebay motors and then use that money to get a good used TPI TB Works for me! Thanks again.

rockind78

We'll see how this turns out. My digital camera is a piece of crap , but here goes. This is the LT-1 TB. Most of you already know what the TPI TB looks like.

rockind78

Here is the other end:

86TpiTransAm

What year LT1 TB is that? If I'm not mistaken, the first model which would have been '93 looked more like the TPI TB on the throttle side because they used the 4L60 tranny which still used the TV Cable. After GM, switched to the 4L60E in either '94 or '95, the TV Cable was gone and they switched to the throttle bracket like the one you show in your picture. I could be wrong.

rockind78

lol.........you just answered my question. I was wondering what year it was!!! I thought the guy I bought it from said '95, so what you said would make sense. I hope this it at least kind of answers your question.

86TpiTransAm

Thanks! I know the later LT1s and the LS1s had the throttle cable bracket like the one on your TB.