Run a fast 90 or an ls6? Help me choose!
Run a fast 90 or an ls6? Help me choose! Hello all,
I'm nearing the end of an LS swap into an 87 iroc.
Im Facing a minor intake manifold dilemma. I have a like new Fast 90, also an Ls6. One will be installed, the other sold.
I've read tons of posts on the subject. This is a street car built with midrange power in mind. Help me choose!
Here are the build specs,
Stock 2000 z28 short block
Home port 243's with a fresh valve job, shaved .025
.040 cometics
TSP 224/224 .600/.600 112 lsa
double springs
morel 5290's
Stock rockers with trunnion upgrade
manton 11/32 7.300 pushrods
truck coils
#36 injectors
Summit 85mm Throttle body
GTO Cold air intake
longtubes
Yank ss3600
strange 12 bolt 410 gears
Full weight car.
That's really the basics of it. Nothing extravagant. I paid fair market for the ls6, got a pretty good deal on the fast 90.
Which would you keep?
I'm nearing the end of an LS swap into an 87 iroc.
Im Facing a minor intake manifold dilemma. I have a like new Fast 90, also an Ls6. One will be installed, the other sold.
I've read tons of posts on the subject. This is a street car built with midrange power in mind. Help me choose!
Here are the build specs,
Stock 2000 z28 short block
Home port 243's with a fresh valve job, shaved .025
.040 cometics
TSP 224/224 .600/.600 112 lsa
double springs
morel 5290's
Stock rockers with trunnion upgrade
manton 11/32 7.300 pushrods
truck coils
#36 injectors
Summit 85mm Throttle body
GTO Cold air intake
longtubes
Yank ss3600
strange 12 bolt 410 gears
Full weight car.
That's really the basics of it. Nothing extravagant. I paid fair market for the ls6, got a pretty good deal on the fast 90.
Which would you keep?
Run the LS6 and sell me the FAST 90 
I think the 90 would yield 5-10 more hp. It's up to you if the $$ difference is worth the hp gain.
Dibs on the 90 if you decide to keep the LS6.
I think the 90 would yield 5-10 more hp. It's up to you if the $$ difference is worth the hp gain.
Dibs on the 90 if you decide to keep the LS6.
Lol, I'll certainly keep you in mind. Many of the threads i looked through stated that the Fast will lose low/mid torque. Just as many threads have folks saying the opposite......a Fast will gain power bottom to top.
I don't know what to believe at this point. I'm running a small cam because I like mid range power. But I also don't want the thing falling on its face at 5500 rpms.
I almost have my harness finished. Will need to make a choice real soon.
I don't know what to believe at this point. I'm running a small cam because I like mid range power. But I also don't want the thing falling on its face at 5500 rpms.
I almost have my harness finished. Will need to make a choice real soon.
IMHO it is more cam than intake on where the powerband is.
Just for comparison my LS6 (02 in sig) has no problem "keeping up" in the high rpm's. HP was still climbing at 6700 (on the dyno) when we let off. 540rwhp on the juice. That being said, I'm sure I would have picked up another 10-15 on my setup with a FAST.
I'm wanting a FAST on my "all out back-up" 6.0 I'm putting together (98 in sig).
Just for comparison my LS6 (02 in sig) has no problem "keeping up" in the high rpm's. HP was still climbing at 6700 (on the dyno) when we let off. 540rwhp on the juice. That being said, I'm sure I would have picked up another 10-15 on my setup with a FAST.
I'm wanting a FAST on my "all out back-up" 6.0 I'm putting together (98 in sig).
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no reason not to run the fast if you already have it. shouldn't lose any or very little down low and prolly pick up 10 or morw rw. with those 4.10's you will have plenty mid range feel. i ported that ridge out of my fast 90,would have to help flow some.
Thanks for your input guys.
My main concern is losing torque with the fast. I have no experience with either the fast or ls6, just reading old threads over the past week or so and came across a few dudes that had posted about a loss in torque.
My main concern is losing torque with the fast. I have no experience with either the fast or ls6, just reading old threads over the past week or so and came across a few dudes that had posted about a loss in torque.
What ridge is that? Haven't taken mine apart yet to look at it. Any problem areas on these?
No question about it. Fast might lose 5hp below 3000rpm but will pull away from the ls6 from there with peak gains around 15-20rwhp given your cam and ported heads.
LS6 intakes sell for a decent bit so you can likely get around $400 for it if you can wait until closer to spring when people are in the mad dash to get ready for racing and have recovered from the holidays
LS6 intakes sell for a decent bit so you can likely get around $400 for it if you can wait until closer to spring when people are in the mad dash to get ready for racing and have recovered from the holidays
Thanks for chiming in. That would be an acceptable trade off. So far everyone is on board with the Fast.
I put mine on back when the car had bolt on and TR230 cammed LS1 with stock heads. Granted I swapped from an LS1 intake to the Fast 90mm but there was no seat of the pants loss anywhere. Around 3500 rpm is where you really felt it come on much harder than stock.
LS6 to Fast will behave similar just not as drastic since the LS6 intake is better than the LS1 right off the bat.
LS6 to Fast will behave similar just not as drastic since the LS6 intake is better than the LS1 right off the bat.
Last edited by thunderstruck507; Dec 15, 2016 at 02:16 PM.