3-Bolt to 4-Bolt TB
Thread Starter
Teching In
Joined: Oct 2008
Posts: 2
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From: Lone Star
3-Bolt to 4-Bolt TB Hello everyone. I got a deal on a 90mm TB and want to replace the 2001 Z06 78mm TB. I bought an adapter and a wire harness already. Can anyone help me with how to properly route that hose from the valve cover?
Thanks for any suggestions.
Thanks for any suggestions.
Thread Starter
Teching In
Joined: Oct 2008
Posts: 2
Likes: 0
From: Lone Star
No stock LS6 78mm-80mm opening,but I am getting a new FAST intake later on. Good $$ so bought it. I think the adapter that is coming will allow the blade to open fully? That is what they said.
92mm or 90mm TB on a 78mm snout LS6 intake manifold is worthless.
The 78mm snout is the biggest LS6 intake restriction.
The 90/92mm TB will work great on matching Fast intake or LPE/TPIS mod'd 90mm snout LS6
The 78mm snout is the biggest LS6 intake restriction.
The 90/92mm TB will work great on matching Fast intake or LPE/TPIS mod'd 90mm snout LS6
TECH Regular
Joined: Oct 2011
Posts: 453
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From: Alaska
I’d like to piggyback off this thread a little bit. Has any actual dyno testing been performed to support the claim that a 90mm TB on a 78mm manifold provides no gains?
The reason I’m asking is that I have another engine platform (Gen 6 BBC) that uses the same 3 bolt throttle body as the LS engines, except that there are no alternative sized intake manifolds available to utilize a larger throttle body. I want to go to DBW and already have a stock truck 4 bolt DBW 90mm TB and a 3 to 4 bolt adapter, so it makes sense to use this rather than spend more money to source a 3 bolt DBW TB.
It seems to me that the CFM rating on the stock 78mm TB was likely already undersized for my particular application, so I see no harm in upgrading to a 90mm. In fact, I’d almost be willing to bet that there is a measurable improvement even if the intake is the bottleneck in the system.
The reason I’m asking is that I have another engine platform (Gen 6 BBC) that uses the same 3 bolt throttle body as the LS engines, except that there are no alternative sized intake manifolds available to utilize a larger throttle body. I want to go to DBW and already have a stock truck 4 bolt DBW 90mm TB and a 3 to 4 bolt adapter, so it makes sense to use this rather than spend more money to source a 3 bolt DBW TB.
It seems to me that the CFM rating on the stock 78mm TB was likely already undersized for my particular application, so I see no harm in upgrading to a 90mm. In fact, I’d almost be willing to bet that there is a measurable improvement even if the intake is the bottleneck in the system.
TECH Senior Member
Joined: Jun 2016
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From: Central Cal.
No harm, but no gain in power either. A 78mm hole passes only so much air. A 90mm TB in front of it will be fine until it hits the point where the 78mm hole will pass no more air. After that, any more pedal will have no response.
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sounds like a job for math... 
wish I had mad math skills. Here's a few possibilities where a fat TB on a skinny snout intake might show some benefits.
1) Cracking a 92mm TB open 15% at part throttle should move more air that 15% at part throttle on a 78mm TB, so the bigger TB might "feel" more responsive on a 78mm snout intake.
2) With an air ram set up like a Fast Toys ram air or Chris1313 or Douggie Box with a big intake route to move air and pressurize the intake track at higher speeds the momentum of air might jab some more air past the 78mm snout "restrictor plate" and show a gain at the drag strip. However if going to all of that prep and expense getting a 90/92 mm snout intake would make sense. $350 for adding snout to LS6 intake by TPIS or LPE or buying a Fast 90/92.
Ultimately only way to know "for sure" is careful dyno testing.
3) Tricks and techniques that help improve air flow & hp when a restrictor plate or defacto restrict or plate is used on an engine. Once could even go crazy and use a reverse pattern cam like 230/224 like the old days when we were stuck with just the LS1 intake manifold etc
Id be curious as well on this subject as it does allow more airflow when the blade is at a light tps 15%. I could use one on my 99 corvette drive by wire. The ls3 throttle body and adapter harness with 3-4 bolt tb adapter. Curious how this works out. I think for my application the ls2 90mm tb would be the way to go someone told me the ls3 90mm plate opened the other way or backwards and could operate differently.