Patrick G

iTrader: (14)

I have a few choices right now. Currently, I'm running an LS6 intake with stock TB for my upcoming turbo kit. I plan on making around 800 rwhp on a low compression forged 346. On NA motors, I've picked up a solid 28-30 rwhp by going from an LS6 intake to a FAST 90 with porting by Tony Mamo. My plans were to run another Mamofied FAST in my turbo setup, but some sharp people on this board have stated that under boost the LS6 intake is better (at the same boost level).

I'm not understanding how that could be so maybe someone could explain it to me. If a ported FAST 90/90 gives me 30 rwhp on a naturally aspirated 346, why wouldn't it give me at least that if not more under boost? When I go from the LS6 intake to the ported FAST, my pressure drop is less at WOT when running NA. I pull 94 kPa at WOT with an LS6 intake and stock TB, but only 98 kPa with the ported FAST. Less restriction.

Wouldn't there be less pressure drop with a ported FAST than an LS6 intake? What about an LS2 intake. On a naturally aspirated motor, it's even worse than the LS6 intake, but some people in the know claim it's even better than the LS6 intake under boost. Totally contradicts what happens NA. Please show me the light.

ChevyChad

iTrader: (50)

As far as better flow, the advantage would be minimum because of the "forced" part of forced induction. Your turbo(s) (or SC, whatever) will flow a certain amount of air into the engine regardless of how 'easily' the intake manifold allows it to go in. The mass flow rate of air ultimately going into all the cylinders will be equal to the mass flow rate your turbo pushes out. Now what will happen though is that the boost will go up with an unported manifold (or down with a ported version- however you want to look at it), but the same amount of air will get into the cylinder either way. Think of it kind of like a garden hose flowing into a bucket. Unrestricted, it flows out easily and if you leave the hose there in the bucket for say 2 minutes, it fills the bucket up at a relatively low pressure in the hose. Now pretend you put your thumb half way over the hose- the pressure definitely goes up, but that same bucket will still be full in the same 2 minutes, it just was under more pressure to flow the same amount. I hope this is making sense here. The same applies running ported heads. Except ported heads have an advantage in that the exhaust can be ported which will allow the air to escape better. The turbo forces the same amount of air in (in theory anyways) regardless of the 'ease' in which it happens, but you need all the help you can get to get the spent exhaust gases out.

Now having explained that, I believe the FAST intake manifold is also physically weaker than the LS6 manifold, and can blow apart under boost.

Gordon0652

iTrader: (4)

Just a basic LS6 intake, i am looking to do a 750rwhp setup, and that intake will be perfect.

cracker

iTrader: (1)

A sheetmetal from beck or the GM Carb style would be best for distribution. For the power level you're shooting for, the LS6 will serve its purpose very well.

MonkeyBoneSS

iTrader: (7)

ChevyChad, nice write up. I know several FI guys running a FAST intake, they seem to be doing fine. The only bad thing I've heard about the FAST is the fact that they are a two piece design and come apart under high boost. (Where this exactly is I have no clue) Then again I've always gone by the rule of using a LS6 for security and also the ability to bump up the boost and not worry about it going to chit.

I'm sure a few others in here will chime in and give there thougths as well.

NemeSS

iTrader: (127)

would you agree that a single plane intake such as Vic. Jr. with a cast elbow plenum such as the ones used by racers used on FI motors would be the better selection, for a moderate to high psi, street/track application?

in theory this type of manifold would be the one with the least amount of restriction compared to the oem and FAST crossover runner type plenums.
assuming a proper cam profile, and turbocharger(s) selection would be used.
this type of manifold would yield the greatest overall results for even a street type car.
imo, this is the type of manifold selection i would choose for my vehicle.
what is your opinion of this manifold, Pat?
Los

c0ncEpT

iTrader: (4)

I was thinking the same way, With a better flowing intake set up you might see lets say 14psi and with the more restricting set up you might see 16psi but they will both make about the same power.

JMBLOWNWS6

iTrader: (17)

14 psi and 900 rwhp thru a fast all day long.

Beaflag VonRathburg

iTrader: (176)

The advantage comes when you turn the fast intake up to 16psi and see the gain over the LS6 at the same boost level. The only reason people don't like the fast on forced induction setups is that some people have had them fail.

ChevyChad

iTrader: (50)

Thats awesome! I don't know what pressure specifically is the breaking point for a FAST, but its obviously good up to at least 14psi And 14psi on a FAST would most definitely be more on an LS6 (15#? 16#?) I don't know...

But there is another thing to factor in also. Say a FAST is good up to 20psi for example. Now the same amount of air a FAST will flow at 20# would be equivalent to maybe 22# thru an LS6 lets just say for arguments sake. If the breaking point of the FAST is 20, and the breaking point of an LS6 is 22 (we know its not, but just for demonstration here), there is no advantage strength-wise anyways to use the LS6 over the FAST... Interesting to think about.

But as stated a few posts ago, if you are at the power level of flowing enough air to break a FAST or LS6, you'd probably want to take advantage of a single plane intake's better distribution.

DuronClocker

iTrader: (25)

I've heard it both ways. I'm aiming for around 650-700rwhp with a D1SC next season (maybe more...depends what I decide to do for a cam...maybe you could spec one out for me, I really liked the 224/228 cam you came up with ), and I'll be selling my FAST intake to go back to an LS6. Main reason is the $550-600 I make going back to an LS6 will pay for my 8-rib belt setup. If I had the money, I'd keep the FAST, but I'm trying to keep costs down by getting rid of whatever parts from the H/C setup that won't benefit me the most.

Kinda looking at it like....okay...I've got $600 to spend, am I better off going with an 8-rib belt setup, or a FAST90? Considering I'll make far more power with the 8-rib/LS6 than the 6-rib/FAST (not to mention the fact that I need to buy a pulley setup anyways since I don't have a full kit), I'm going the 8-rib/LS6 combo.

rx_treme

iTrader: (9)

I went with ls6 just for price/performance.

Inspector12

iTrader: (29)

Patrick some had issues with the fast leaking under boost I have herd of people having failers, but have never witnessed that, and some have reported gains and some haven't, and the Victor JR with the 90 is not neccesary and has it's downfalls its not the end all for FI for sure I made great power with the LS6 and won't be changing on the TT car I will probably be changing the procharger car to an LS6 probably, but since you have an LS6 you could test it and if you don't meet your goal you could try one of the others like a Ported Fast etc... Good luck!
Jeff

speedracer5532

iTrader: (8)

I have ran 18 lbs through my Mamo ported FAST with no problems.

tomulrich

iTrader: (2)

According to FAST the material is stronger than oem. It is also rated at 80psi. You can install burst panels at 35psi...

Tom

MIGHTYMOUSE

iTrader: (59)

it doesnt matter, an ls6 intake will easily get you what you want. so why spend the money?

i have a box stock 02 ls6 intake on the car.

TNTramair

iTrader: (15)

I agree with MM. not worth the extra coin when doin FI IMO.

NicD

iTrader: (7)

Went with an LS6, a FAST is a lot of extra money for not a whole lot of gain on an FI setup. Best off putting the money into something else for the car or even just in your bank account.

Patrick G

iTrader: (14)

All this still doesn't really explain why a 30 rwhp gain with a ported FAST wouldn't be worth that or more with forced induction. The power gain is from reduced pressure drop and reduced induction restriction. Why wouldn't the power gains over an LS6 translate when running under Boost?

Stated another way:
Would everybody agree that the ported FAST would make the same power as the LS6 intake but with less boost? If so, then wouldn't the ported FAST 90 make more power with the SAME boost?

Inspector12

iTrader: (29)

I really wouldn't agree with that until I had tested it myself. But if you want to spend the money for a ported fast don't let us talk you out of it. I am just telling you what I have learned doing the FI stuff for a long time. They maybe WAY better in your opinion??? Just like some say about the Vic Jr etc... But that one I have run and I don't thing it made any significant difference in power. That is why I was telling you to start out with the LS6 and then switch and then you would KNOW if it made a difference on your setup etc...