I recently came across a set of 70mm TB's from SVS through their great sale (Thanks Ron!). The price was right and I figured it would be another excuse to get under the hood of my Viper and possibly do a write up of the install. I knew that by installing these TB's on my stock engine that I wouldn't see much gain in HP or TQ. I'm finding out through past threads here and abroad that installing 70mm TB's on a stock GenII engine will actually hurt performance and cause a loss of torque.
What I haven't been able to find out is why would 70mm TB's cause a loss of power on a relatively stock engine. I have installed Belanger headers and catback, hi-flow cats, K&N's, Smooth tubes, T&D rockers, Trend pushrods as well as a Vec3. My most recent dyno run (without the T&D's) produced 480rwhp and 525rwtq on a Mustang Dyno. There was power left on the table and I need to update my Vec3 to take advantage of it. I don't know what the T&D's have done to the numbers yet but I certainly feel it in the SOTP.
My assumption is that the TB's would compliment these mods. After all, if the engine has the mods to move more air and breathe better then adding TB's would be a good thing. Right? After all, the engine is a great big air pump. My second reason for experimenting with the TB's is that my Vec3 logs have shown that my engine wants to breathe better and that, besides the valve train, perhaps the intake has become a restriction at this point.
If 70mm TB's are a bad thing on my setup, why? Is it because the intake plenum needs to be matched in size to the TB's 70mm openings? Are the stock heads a restriction and perhaps a call to Greg Good for some ported heads is in order? But if the stock engine is getting all of the air it needs (supposedly) through the stock TB's, why would larger TB's cause performance to suffer? It's not as if the TB's themselves are pushing more air into the engine, they're simply acting as a gatekeeper of air, so to speak. Sure, the gates are bigger but only as much air as the engine can handle will get through.
Sorry for the rant...but I would like to know, from those in the know, the rationale behind 70mm TB's hurting performance on a stock GenII engine.
Thanks,
- Tony
What I haven't been able to find out is why would 70mm TB's cause a loss of power on a relatively stock engine. I have installed Belanger headers and catback, hi-flow cats, K&N's, Smooth tubes, T&D rockers, Trend pushrods as well as a Vec3. My most recent dyno run (without the T&D's) produced 480rwhp and 525rwtq on a Mustang Dyno. There was power left on the table and I need to update my Vec3 to take advantage of it. I don't know what the T&D's have done to the numbers yet but I certainly feel it in the SOTP.
My assumption is that the TB's would compliment these mods. After all, if the engine has the mods to move more air and breathe better then adding TB's would be a good thing. Right? After all, the engine is a great big air pump. My second reason for experimenting with the TB's is that my Vec3 logs have shown that my engine wants to breathe better and that, besides the valve train, perhaps the intake has become a restriction at this point.
If 70mm TB's are a bad thing on my setup, why? Is it because the intake plenum needs to be matched in size to the TB's 70mm openings? Are the stock heads a restriction and perhaps a call to Greg Good for some ported heads is in order? But if the stock engine is getting all of the air it needs (supposedly) through the stock TB's, why would larger TB's cause performance to suffer? It's not as if the TB's themselves are pushing more air into the engine, they're simply acting as a gatekeeper of air, so to speak. Sure, the gates are bigger but only as much air as the engine can handle will get through.
Sorry for the rant...but I would like to know, from those in the know, the rationale behind 70mm TB's hurting performance on a stock GenII engine.
Thanks,
- Tony
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