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Discussion Starter #1 (Edited)
What is the best intake manifold and throttle body setup (not trying to spend that much on it) to get a little more air flow (around 90mm opening) for my 408 paired with the APS twin turbo kit. Must fit under the regular hood and the Fast intakes are not an option as they are 2 piece. Should I just port my ls1 manifold and throttle body?
 

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kind of wondering why you want a 90mm opening when you are using an ls1 style throttle body. you might just want to get an afternarket 90mm+ 4-bolt style cable driven throttle body. i think edelbroke makes one that will work with bolt bolt patterns, but it will not fit under your hood.

if you just want a manifold that performs better than stock and works with the stock throttle body, weiand looks like it makes a decent manifold.
 

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90MM VS 85MM VS 78MM will make ZERO difference with a turbo. Ported stock intake would be good. The fast intake ive heard doesnt hold higher boost pressures from WHAT I'VE READ. I have 2.5" charge pipes on mine so my 92mm throttle body is pointless.

just port your stock intake and leave the throttle body alone. Theres no power in porting it because its going to be forced in and thats not the restriction.
 

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What boost are you trying to do? Don't see an issue with a fast.
Volume becomes the factor going with larger stuff. Especially going with a big motor.
I assume you are cathedral head even considering using an ls1 intake, I also assume you mean ls6.
Id you want to go cheap, stick with what you have as the whole top end will be a restriction.
 

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Put a LS2 intake on it and call it a day
 

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Put a LS2 intake on it and call it a day
well thats a step backwards from the ls1/ls6 intake. The ls2 is probably the worst factory intake.


Over 1000hp has been made on a stock 78mm throttle body.
 

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90MM VS 85MM VS 78MM will make ZERO difference with a turbo. Ported stock intake would be good. The fast intake ive heard doesnt hold higher boost pressures from WHAT I'VE READ. I have 2.5" charge pipes on mine so my 92mm throttle body is pointless.

just port your stock intake and leave the throttle body alone. Theres no power in porting it because its going to be forced in and thats not the restriction.
I think it has more to do with the cfm requirement of the engine, not the fact that it's being forced. Really, naturally aspirated airflow is forced, since it's the differential of atmospheric pressure to vacuum which is causing the air to move into the engine--it is just less dense.

All the same, i would agree with you if he had a stock 346.

I would wonder with a 408, with undoubtedly a larger camshaft, if he would benefit from a larger throttle body.
 

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What boost are you trying to do? Don't see an issue with a fast.
Volume becomes the factor going with larger stuff. Especially going with a big motor.
I assume you are cathedral head even considering using an ls1 intake, I also assume you mean ls6.
Id you want to go cheap, stick with what you have as the whole top end will be a restriction.
Ported cathedral heads can do quite well on a stroked LS. Depends on how much high rpm airflow he needs, really.
 

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There are a lot of things to consider here already...first the cubic inches being a 408 and secondly the turbo kit. I'm not familiar with the turbo kit so maybe some turbo guys can comment on if that kit is even well matched to a 408. A good top end is high $$$. If money isn't an issue then always buy the best top end you can. If on a budget then yes big power can be made with 243's, ls6 intake, and stock throttle body...especially on small cubic inch motors. On a 408 I'd be wanting better stuff it at all possible. I feel like that is too much restriction on a 408 and it will most likely result it struggles at higher rpm's. Not saying it can't work, but definitely not ideal and inefficient. Making the same or more power with less boost is ideal, but not mandatory.
 

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I think it has more to do with the cfm requirement of the engine, not the fact that it's being forced. Really, naturally aspirated airflow is forced, since it's the differential of atmospheric pressure to vacuum which is causing the air to move into the engine--it is just less dense.

All the same, i would agree with you if he had a stock 346.

I would wonder with a 408, with undoubtedly a larger camshaft, if he would benefit from a larger throttle body.
Considering a 3.5” charge pipe is 88.9mm, a 3” is 76.2mm and a 2.5” is 63.5mm.....I highly doubt a bigger Tb will help under 1000hp. That sounds like a good Dyno test idea!
 

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i hadn't really thought about the charge piping. I guess if you consider the throttle body as simply the end of the pipe, i can understand how it ends up being only a small factor in terms of airflow up until the plenum.

so, what if you increase the diameter of everything, like he mentioned?
 

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a big problem with larger dia pipe is packaging, though. also have to think of how much of an effect the intercooler will have on airflow.

all the same, he should benefit from a better intake manifold design, regardless of what throttle body he uses. i would say most of the better intake designs will have a 4-bolt style tb attachment, so he will be better off switching to at least a 90mm throttle body, anyhow, for the sake of simplicity, unless he just wants to run an adapter to run the stock throttle body.
 

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A 6.0 is obviously not the same as a 408 so not apples to apples. With the additional cubic inches a better top end is going to be more beneficial than it would on a 6.0. I don't think the throttle body itself is going to be the difference maker, but the heads and intake certainly could be. Again lots of factors and I'm still not sure what turbos he has and how well matched that kit is to the 408 to begin with which is going to be a bigger factor than the top end of the motor I would guess.

Since we are all street car guys and not race car guys...A 408 making 1000 rwhp on 15 psi is going to be more ideal than a 5.3 with 1000 rwhp with 30 psi for example. The 408 will be more responsive out of boost, most likely run cooler and have lower iat's, and probably have less issues not being worked as hard. Just a guess, but some things are harder to verify in controlled environments like engine dynos vs daily driving.
 

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More cfm, less boost, same power.
Really comes down to the way the air is being forced. Something like a ysi may run out of steam, but a pair of appropriately sized turbos, it won’t really matter.

Simply seems like it’s coming down to budget. Nothing else.
 

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Interesting comparison here. After going to a 427 and both motors with an F1X procharger they show the difference in not only peak power, but huge gains under the curve as well. Cubic inches and a better top end do matter greatly. It may not be needed with boost on a budget, but it does matter. After a short introduction on the comparison they show the dyno comparisons at about the 17:26 mark if you want to skip ahead.

 

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I don't think comparing results between turbo's and belt driven S/C's beneficial. They make boost differently. Turbo boost is all in way earlier in the curve. Blowers, especially centri's continue to make boost up top because their boost is RPM dependent. Intake choices matter more with belt driven S/C's than turbo's. What is really important to turbo intake flow is how changes affect the turbo you are using and it's boost map. If don't understand that...then you will waste money.
 
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