tg580

Is it worth it to go from an LS6 intake to a fast 78mm intake?

HioSSilver

iTrader: (8)

x2??? or a 90mm fast

Orange Juice

iTrader: (3)

This doesn't come up very much anymore but if I remember there really wasn't too much of a difference between the two. What tb are you planning on using?

Orange Juice

iTrader: (3)

Read your mod list, I think I would just stick with the ls6 intake unless someone is giving you the fast intake.

SweetS10V8

iTrader: (4)

The FAST would make more power in either the 78 or 90mm version over the LS6. I tested this years ago when the 78mm was still out. Ill see if I can dig it up.

Nitroused383

iTrader: (10)

Here is my LS6 vs Ported Fast 85 (originally fast 78) + underdrive results. I'd have to say the fast was worth 20-25 rwhp over the LS6 through. About 20 ftlbs more through the entire curve. I sold my LS6 for $300 and paid $300 for a Fast 78. No brainer... All the info is in my signature link.

LS6 vs Fast85 + underdrive, low results are bolt on results to compare

Bizzles

iTrader: (3)

wonder if this has anything to do with the 78mm for sale in the classifieds

garygnu

nitroused383 show the pics of your ported fast 78,you did some great work opening it up.

thunderstruck507

iTrader: (18)

yes, a fast 78 or fast 90 will give gains, if it's worth it depends on the price

plus later you could always look for a 90mm upper shell to put on the 78 as that is the only difference

SOMbitch

iTrader: (8)

I would just look for a used 90/90 or 92/92. They are getting cheap now.....

thunderstruck507

iTrader: (18)

depends on how much the 78 is...and you have to include the price of the throttle body into this calculation, especially for a car without cam and/or heads that isn't going to pick up as much

say you can get the 78mm for $300-400 or less and do a little easy port work and gain 10-15hp over the ls6...amazing deal

say the 90mm is $500-650 you do some of the same light porting and you still need a 90mm tb for $200+ to gain 15-20hp over the ls6...not as amazing

smok'nZ

iTrader: (160)

i have seen the fast 78 go for 400-500 never 300 someone would be stupid to sell one for the same price as an LS6.

and nobody has the upper shell anymore so if you buy a 78mm fast the most it will probally be is a ported 85mm

Nitroused383

iTrader: (10)

The restriction on 440 rwhp car is not caused from 85mm throttle body I will tell you that right now. With the LS6 intake I would drop 4-5 kpa on the map reading above 3000 rpm. Now with my ported fast 85 the most drop I see is 0-1 kpa. So my barometric pressure is around 95 kpa and I had a 5 kpa drop with LS6 intake 95/90=1.055. This means I had the potential to gain 5.5% more power just from getting my kpa restriction out. My old setup made 411 rwhp so 411x5.5%=22.6hp, as you can see the math is very close. I do not think my car would gain anything with a 90mm setup, a fast 78 just sold a few weeks ago for $350 in the classifieds. The fast 78 and fast 90 use the same runners. I spent about 15 hours on my intake, radiusing all the entrances real nice, removing all the high spots, blending the runners and port matching the bottom shell to the heads. It takes time to do a nice job and you need to take it all the way apart.

smok'nZ

iTrader: (160)

damm you put in some work there

thunderstruck507

iTrader: (18)

I agree about 85mm not being much restriction, it's not really 100% apples to apples but my uncles 850hp big block race car still only uses a 95mm or so throttle body

garygnu

you should see how good his head porting is.

03Sssnake

iTrader: (20)

I bought my FAST 78 for 250.00, incredible deal. The seller is member here and had hurt his motor, so he decided to sell off parts to fund his new motor. The FAST should be back from the porters next week and to sweeten things, I found a guy selling a 90 upper locally. I may buy that this weekend if it checks out.

86zcamaro

iTrader: (8)

So if the 90 mm is basically the same thing just the upper shell is different can it use a stock throttle body or is that the point you have to go aftermarket?

MonmouthCtyLS7

iTrader: (6)

You should see an additional 20 w/ ported fast

JustAGoat

iTrader: (6)

I agree i looked into alot dyno results (old topics on here) and found a ported LS6 and a Fast 90mm are close to the same, but the unported 90 mm fast has about 5 hp on the ported LS6.