FAST 92 vs FAST 78
Thread Starter
Burning Brakes
Joined: Nov 2021
Posts: 774
Likes: 380
From: Old Dominion - VA
FAST 92 vs FAST 78
So I have a FAST 78mm intake on the car now with a stock LS1 throttle body. I have a slight vacuum leak that I "think" is in the intake someplace. I am going to attempt to find the actual leak to be sure, but I was thinking of maybe going with a FAST 90 or 92mm and an LS2 throttle body rather than resealing the FAST 78 IF that is vacuum leak culprit. Also, the car will be going to get tuned in the next month, so if I do this I want to do it prior to tuning off course.
Any compelling reason to go to a 90 or 92 over the 78 I have? Will it be worth it?
Oh, and I know the MAP sensors are always a bit loose feeling, mine does move a bit when I push on it. Could that be the vacuum leak? I hear a whistle sound between about 1500-2200 RPM.
Any compelling reason to go to a 90 or 92 over the 78 I have? Will it be worth it?
Oh, and I know the MAP sensors are always a bit loose feeling, mine does move a bit when I push on it. Could that be the vacuum leak? I hear a whistle sound between about 1500-2200 RPM.
Drifting
Joined: Sep 2017
Posts: 1,961
Likes: 693
From: Avon Lake OH
There is an excellent intake manifold flow bench testing tread over on the LS1tech site. Big data chart here;
https://ls1tech.com/forums/generatio...l#post19997187
Wade posted his testing and tuning summary here;
https://ls1tech.com/forums/generatio...l#post20080957
Just encase you are interested in going to say a FAST 90mm, I have a used one sitting on the shelf that I bought for my car four years ago, but I decided to go in another direction. I can sell it to your for $600 plus shipping.
https://ls1tech.com/forums/generatio...l#post19997187
Wade posted his testing and tuning summary here;
https://ls1tech.com/forums/generatio...l#post20080957
Just encase you are interested in going to say a FAST 90mm, I have a used one sitting on the shelf that I bought for my car four years ago, but I decided to go in another direction. I can sell it to your for $600 plus shipping.
Le Mans Master
Joined: Feb 2021
Posts: 6,488
Likes: 4,335
From: Florida
2025 Corvette of the Year Finalist - Unmodified
2024 C5 of the Year Winner- Unmodified
2022 C5 of the Year Finalist - Unmodified
So I have a FAST 78mm intake on the car now with a stock LS1 throttle body. I have a slight vacuum leak that I "think" is in the intake someplace. I am going to attempt to find the actual leak to be sure, but I was thinking of maybe going with a FAST 90 or 92mm and an LS2 throttle body rather than resealing the FAST 78 IF that is vacuum leak culprit. Also, the car will be going to get tuned in the next month, so if I do this I want to do it prior to tuning off course.
Any compelling reason to go to a 90 or 92 over the 78 I have? Will it be worth it?
Oh, and I know the MAP sensors are always a bit loose feeling, mine does move a bit when I push on it. Could that be the vacuum leak? I hear a whistle sound between about 1500-2200 RPM.
Any compelling reason to go to a 90 or 92 over the 78 I have? Will it be worth it?
Oh, and I know the MAP sensors are always a bit loose feeling, mine does move a bit when I push on it. Could that be the vacuum leak? I hear a whistle sound between about 1500-2200 RPM.
https://ls1tech.com/forums/generatio...ml#post7248658
Team Owner
Joined: Oct 1999
Posts: 31,976
Likes: 487
From: Guinness Its whats for B'fast JAWGA
CI 3-4-5-9 Veteran
A smoke machine may help you find the leak and you might be able to rent one from your autoparts store. FAST intakes have been known to crack on the bottom. I also had one that warped at the throttle body opening to the point it didn't seal. We fixed the warped fast 90 with a top from a fast 92 which had cracked the lower.
Supporting Vendor
Joined: Sep 2004
Posts: 1,272
Likes: 1,219
Send the 78mm FAST to an LS museum and buy the larger 92 mm version
The throttle response alone is worth the upgrade and your severely limited on CFM with the small 78 mm opening of the current intake
Have me port the 92 for even more gains (adds 8 - 10 RWHP) if your looking to maximize the swap when your doing this (and port the 90mm LS2 style TB which is a natural fit in this application)
Time to step up.....I wouldn't invest more time in that older intake.....its close to 20 years old at this point
If you take the plunge you will thank me.....the response is a bunch better and it's a great SOTP feel good mod besides adding legitimate power to your bottom line
Hope this helps
-Tony
The throttle response alone is worth the upgrade and your severely limited on CFM with the small 78 mm opening of the current intake
Have me port the 92 for even more gains (adds 8 - 10 RWHP) if your looking to maximize the swap when your doing this (and port the 90mm LS2 style TB which is a natural fit in this application)
Time to step up.....I wouldn't invest more time in that older intake.....its close to 20 years old at this point
If you take the plunge you will thank me.....the response is a bunch better and it's a great SOTP feel good mod besides adding legitimate power to your bottom line
Hope this helps
-Tony
Thread Starter
Burning Brakes
Joined: Nov 2021
Posts: 774
Likes: 380
From: Old Dominion - VA
Whats important here is how your heads match up. If you have an LS6 intake with 241 heads, a bigger TB/Fast won’t help. If you have ported 243 heads or aftermarket heads, the fast 90 will help you stay up. Even then, if you’re running aftermarket heads and a high lift cam, 625+, a Tony Mamo porting on the Fast is the best match.
https://ls1tech.com/forums/generatio...ml#post7248658
https://ls1tech.com/forums/generatio...ml#post7248658
