whitedevilWS6

iTrader: (10)

so i was talkin to my old man about my plans for my motor and he said the 90/90 i bought will probably kill off my power below 4500 rpm and kill off my vacuum, vs my LS6 intake. here's my setup:

Forged LS6 (346)
AFR 205s
Comp XR281HR (228/230 ~.570 lift, 112 lsa)
LT's, ORY

is my old man just stuck in the 70's, or does his theory hold true for gen III small blocks? i personally think he's dead wrong, and the FAST 90/90 will perform greatly, but I wanted to ask around and see what more educated individuals have to say. thanks.

thunderstruck507

iTrader: (18)

I would use the fast

I felt better response everywhere then above 4000rpm there is a very noticeable difference versus the ls1 intake

never ran a ls6 so I can't comment

SShawn

iTrader: (6)

Both are good intakes, You should be fine with a 90/90, nothing some tuning shouldn't be able to fix. The FAST will make more peak hp.

02sleeperz28

iTrader: (26)

I vote ls6 intake people have made great power with it.

whitedevilWS6

iTrader: (10)

well LS6 is a no brainer, of course it will make power. i don't mind a small sacrifice in low end if the mid and high range power is way better. as long as i have some good ol' american torque, and i can roll around town at 1500 rpm, i'm happy.

TXZ28LS1

iTrader: (5)

man, ive been debating the same thing. should i use the money to buy a used fast intake or use the money for a bigger stall? will be adding heads as well.

ULTIMATEORANGESS

iTrader: (4)

with your setup id go with a FAST.

whitedevilWS6

iTrader: (10)

well it's good that i have both intakes, and i'd love to do a back to back dyno comparing the two, but i'm not about to pay full price for two dyno tunes. i thought about tuning it for the 90/90, then just throwing on the LS6 and getting a reading, but that wouldn't be too accurate since it wouldn't be tuned appropriately for it as well.

Irish350

iTrader: (14)

i had almost the exact same setup, 205s, slightly larger cam (230/236 .611/.611) and a 90/90. Definitely wouldnt go back to stock, but i never tried an ls6 on it

garygnu

if you have the fast intake use it ,you won't loose any power down low with that combo.its not the TB size ,but the runner shape and size that matters.AFR heads flow.

hitmanws6

iTrader: (20)

you could use a FAST 102 if you wanted to, the 90 will be fine for you. So will a 92

whitedevilWS6

iTrader: (10)

so only 1 vote for the LS6 then huh?

Damian

iTrader: (89)

Yes.

Virtually all "old school" advice is null and void on LS engines. The FAST would work great with your combo, but you're gonna have a hard time finding a 90. Do the 92mm setup, get a set of 36lb injectors, and make sure you have a competent tuner.

whitedevilWS6

iTrader: (10)

got a 90/90 and some SVO green tops (46# on LS1 right?) already. and have a reputable tuner lined up. too bad i have to drive 6 hours to get to the rollers...

ctd

iTrader: (1)

You really should have the Fast 90/90 ported or you will be leaving a lot on the table. Many claim to have the know how to port that properly, I would do a little research if you choose that direction. You will make more power everywhere, accelerate faster & better throttle response.

I have a very similar combination to yours & my injectors are the SVO Red Top 30lbs.

Your tuner will need proper data for which ever injectors as well as the ability to make that Fast 90/90 combo drive nicely.

I'm very old school as well & may have disagreed with your old man even back then. The same tuning problems existed back then & very few tuners had ability to make the more aggressive combo's work. I always enjoyed making the serious combinations drive like the stockers, it could be done back then as it can be done today.

The advantage with todays technology is that we can even go more aggressive with even better manners.

Nitroused383

iTrader: (10)

This is a topic that has been beat to death, try to help yourself by doing a little digging. I went from the LS6 intake to my own ported fast 85 and gained a ton of power through the entire curve, see for yourself. I didn't just slap the fast on though, I spent around 15 hours porting it and making sure everything lined up properly, which the alignment was very crappy. I also added an underdrive pulley at the same time and I'd guess it was worth 8 hp. Click my signature link for all the details, but it's just a custom 224 cam with unported 243 heads.

Bolts on vs head cam LS6 vs Fast 85 + underdrive

SweetS10V8

iTrader: (4)

your correct, your dad has knowledge from the 70s which doesn't hold true today, hes not stuck, its just what he knows!!. The FAST is definitely the way to go with your setup.

Here is why; In the 70s carburetors fueled the engines, carbs require a vacuum signal to pull fuel out of it. So if your carb was way too big it wold kill the low end because the velocity of the air going through the carb at low rpm is low. This is why they had losses in low end when you had a carb that's too big.

Now skip ahead to today, we have EFI with an injector in each cylinder. We don't carry fuel through the intake, which is called a dry intake because it only carries air. We inject fuel directly at the valve near the cylinder. So now what influences too big or too small is only the runner design of the intake manifold. Since the FAST has proven it makes power on everything from stock to wild, the runners are a best design for the street/strip cars. The throttle body is now simply an air bleed to feed the runners. The runners are what create air velocity.

So you could have a 200mm throttle body on the front of a FAST and it wouldn't matter as far as low end power or ability to make power anywhere. It simply feeds air to the 8 runners.

camz28arro

iTrader: (12)

A FAST 90 or 92, stock or ported should give the same low/midrage power as the ls6 intake but depending on the setup, make a little more power up top. A 102mm would be too big though for 346ci.

Those injectors seem to be overkill though since they are good till 550+rwhp unless you plan on spraying a dry kit.

whitedevilWS6

iTrader: (10)

^^^ how did you know?

SweetS10V8

iTrader: (4)

Incorrect, if you read what I just typed "THE RUNNERS" inside the intake determine too big, too small, or just right. The throttle body just has to be able to feed the runners.

Now a 102mm may not be needed to feed a 346ci, but its not too big, my bother runs a 102mm on his 346ci without an issue.Think about this, individual runner intakes have an infinate throttle body and run very well. They also depend on the runner size and shape for RPM range and velocity.