Fast Intake…
Thread Starter
3rd Gear
Joined: Nov 2025
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Fast Intake…
I want to install a Fast 103mm intake and throttle body on my 04 base convertible. The car puts down 410 to the rear wheels, mods are a stage 1 cam, reworked heads, full length headers, 3 inch exhaust from headers back, high performance cats 3inch X pipe to billy boat PRT exhaust, and tuned on a dyno. So my question is, can I install a 103mm throttle body and Fast intake on my car without issues. I’ve been told, I should install a 92mm because I would loose low end torque using a 103mm? All your thoughts are greatly appreciated!
Safety Car
Joined: Mar 2017
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From: Orlando Florida
I’d do a search on cowl clearance. I recall reading of the Fast being a bit taller than the LS6 manifold, and of people switching to shorter motor mounts to gain necessary clearance.
https://www.corvetteforum.com/forums/c5-tech/3329550-new-fast-102-intake-and-hood-clearance.html
https://www.corvetteforum.com/forums/c5-tech/3329550-new-fast-102-intake-and-hood-clearance.html
Thread Starter
3rd Gear
Joined: Nov 2025
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I’d do a search on cowl clearance. I recall reading of the Fast being a bit taller than the LS6 manifold, and of people switching to shorter motor mounts to gain necessary clearance.
https://www.corvetteforum.com/forums...clearance.html
https://www.corvetteforum.com/forums...clearance.html
Safety Car
Joined: Mar 2017
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From: Orlando Florida
Power loss, no. Throttle response and all around drivability yes -- but just from stories and watching Holdener on the youtube, and I'm not sure his comparisons are adequately matched to your situation.
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Safety Car
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From: Orlando Florida
According to FAST: "The FAST LSXHR 103mm Intake Manifold is ideal for generating maximum power in boosted and naturally aspirated GM LS cathedral port engines.. The manifold has been optimized to make power from 5,000 to 7,500 RPM". That would seem to support the concern for possible low end power reduction.
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According to FAST: "The FAST LSXHR 103mm Intake Manifold is ideal for generating maximum power in boosted and naturally aspirated GM LS cathedral port engines.. The manifold has been optimized to make power from 5,000 to 7,500 RPM". That would seem to support the concern for possible low end power reduction.
Le Mans Master
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I swapped to a FAST 102 intake and did an LS9 cam at the same time, so might not be a fair comparison. However, I gained 21hp and LOST 16ft/lbs of torque. Not just at peak, but across the board. This was with the same 90mm LS7 TB I had before. I think a lot of it was the cam, but the giant intake didnt help. The 102 was a pain to fit. I had to lower the engine, grind the water pump, put short button head bolts in the valley cover, and messed with 3 different rear steam vent crossovers to find one that worked. For 400whp its not worth it at all. I got mine for next to nothing, but if you havent bought one yet look for a FAST 92 or have the LS6 intake converted to the 90mm snout by TPiS.
Race Director
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I run a LS2 90mm TB on the built LS7 in my C5. Stock LS7 intake. I had been thinking about going to a 102 NW TB. That thinking stopped after talking to both NW and Tony Mamo. For an all out race car, sure. But I was told I might pick up 10whp. That's it. But seriously, the manifold and TB the OP is considering will gain a lot more problems and disappointments than HP increases on a 400hp application. NW AND Tony both said it wasn't worth it on my 600hp 427. Mainly because the NW doesn't play nice with the C5 PCM. That came right from Nick Willuams. Not to be condescending, but if its nothing but trouble, for little power gain on a 600hp 427, why would you expect anything else on a 400hp 5.7?? Probably more problems than my combo, which they said would be little gain for a lot of headaches....
Last edited by grinder11; Nov 19, 2025 at 08:39 AM.
Le Mans Master
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They really only make power at the higher rpm band, like track use, etc. You can find a variety of YouTube videos on this, plus some of the comments above. Plus there’s probably $1500 is parts plus update tuning.
Sounds like you already have a potent combo for the street. How about some lower gears for those street rips (in Mexico)?
Sounds like you already have a potent combo for the street. How about some lower gears for those street rips (in Mexico)?