I was using the search function and doing some research, and what the guy I quoted makes sense... that the LS2 intake is optimized for a larger displacement engine, whereas the LS6 is designed for a stock displacement engine. I am doing a 383 swap, and I am thinking that the LS6 manifold I have on my car now is going to be a restriction, and I would like to step things up. I don't want to spend a grand on a FAST 90/90 combo right now, would an LS2 intake be a better choice? Thanks!

 

Everything I've read says the LS2 manifold actually flows less than the LS6 one. Not worth the expense. Save up for a FAST, or don't bother.

 

tho I picked up a cheap LS6 intake for now...

 

 

That is on a STOCK CID motor. The LS2 intake does out flow a LS6 on larger CID motors. Also, the LS2 intake does out flow the LS6 on stock CID in a S/C application.

Keith

 

That's my point.

 

I haven't bothered putting a lot of thought into it, but I'm curious exactly why cubes matter. A na 500 hp 346 will be sucking more air than a na 400 hp stock LS2 any rpm where its hp is greater. I guess there are some dynamics to consider.....

I've seen a couple of articles like this......

LS6,LS2,etc. comparo on LS2 crate motor

edit... I haven't really seen any side-by-side dyno numbers on a 400+ ci motor, tho. Anyone have any data of that form?

 

Exactly. How would cubes alone make a difference? Obviously, the higher power motor is pumping more air through.

 

One of my ported FAST 90's was worth 32 HP over a stock (un-ported) LS2 intake when tested on an SF902 engine dyno with the same TB within 30 minutes of one another, NO other changes....basically the time it took us to swap the intakes on the dyno.

That's an insane gain for a manifold swap....most people are lucky to get that much with a headswap.

BTW, this was a stock 6.0 liter LS2 shortblock and in theory it takes the same airflow to make "X" amount of power. A larger motor is simply capable of moving the same quantity of air at lower RPM's simply due to its displacement advantage. Basically what Im saying is a weak manifold on a small motor will be just as weak on a larger motor (or potentially worse) because the larger engine has a bigger appetite for airflow.

As others have mentioned....save your money for a FAST or dont bother and consider having it properly ported for even stronger gains from the swap.

BTW....had I compared my ported intake versus an LS6/78 mm set-up my guess would have been closer to a 25 HP delta....the LS2 has been proven to make 5-7 HP less than an LS6 out of the box. They do come around a little when ported but will never get close to the gains of a ported FAST (might knock the difference in half).

Hope this helps....

Tony

Edit: To clarify what I said regarding "bone stock short", it did have a street friendly 230/232 hyd. roller and AFR 205 cylinder heads. It wasnt bonestock as in stock cam and stock heads (just the short was untouched) but in fact IMO is more representative of the type of a build you guys would consider (aftermarket heads and cam) when pondering the value of the FAST versus LS2 intake.

 

Can we get a fluid flow/mass transfer engineer type involved here to tell us how the intake knows the displacement of the vacuum source beneath it?

Charlie

 

So what you're saying is stick with the LS6 until I get my tax refund then get the FAST 90 combo?

 

That pretty much sums it up.....LOL

Tony

 

How will a fast 90 do on a 346 with ported heads and a small 224/228 cam?? Is it worth switching from an LS6 intake to the Fast then...

 

With a premium set of heads (AFR, ETP, TFS, etc.) or a very good ported factory piece (much rarer than the advertising of most lead you to believe) you will see a 20-25 HP gain with a properly ported FAST 90/90 set-up.....gains in peak TQ usually 15-20 ft/lbs. Serious gains but of course the swap isn't exactly inexpensive. In the big picture though the porting actually adds value and reduces your cost per HP by almost 25%.

Here is something I copied and pasted which was part of a different thread related to swapping to the FAST and the typical costs and gains realized (note all of the gains are from an LS6 baseline....add at least 5 more HP if you currently run an LS1 or LS2 intake). The ported gains I quote have been taken from my own R&D as well as independent dyno data of customers I have helped with the porting.
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For grins I just whipped up this spreadsheet....prices and performance may vary slightly but I think the general point I am making would still be intact.

Manifold....................Avg Retail $$...........Typical Gain.........Cost/HP

Stk FAST 78....................700............... .........8....... ............. $87
Stk FAST 90 (w/ TB).........1200......................13 ................. ...$92
FAST 78 opened to 85mm...900.......................11..... .......... .....$82
Ported FAST 78................1200.................. ....18........... .........$67
Ported FAST 90/90............1700...................... 23............... .....$74

The key is to understand that the snout doesn't represent the largest restriction in the FAST hence the smaller gains when messing with it. Reshaping and reconfiguring the ports are where the larger gains in airflow and power can be unlocked....
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The FAST is a no brainer if your looking to try and get some big numbers out of any displacement combination and was one of the key mods that allowed my mild mannered 224 cammed 346 to approach 480 RWHP (with the ported 90/90 set-up). From something as docile as that to a fire breathing 427 stroker, its the key to unlocking some additional power by not strangling the cylinder heads with a more restrictive intake ultimately reducing the "net" flow the engine sees.

There are tons of other posts about this topic....use the search feature and start doing your homework if your not up on it as much as you might want to be.

Tony M.

 

Thanks, I'm not sure on how well the heads flow. The are ported 241's from TPIS. The car is a 2003 and currently has a 216/220 cam, TPIS headers, Corsa exhaust making 385rwhp. I want to add a ported Fast 90 and a 224/228 or a 228/232 .580 lift on a 114LSA. We would like to see 420rwhp or so...

 

Thats a reasonable expectation.....even if the heads are so-so the ported 90 will add 18-20.....the more aggressive ramp profile of the 224/228 cam coupled with a little bit of additional valve duration should cover the rest.

Assuming the same dyno, I think 420 would be about what I would have guesstimated anyway. If it hit 415 or 425 I wouldn't be surprised either....you get the picture. It will still be perfectly streetable as well....just make more power everywhere....especially upstairs.

BTW, the bigger cam makes it a no brainer but will knock a little of the bottom out of it, especially if you have close to stock compression. Can't go wrong either way really but if you want to try and get the best all around gains, go with the smaller cam....if your getting sucked into the chassis dyno numbers and occasionally race the car to take better advantage of the top end charge hang your hat on the 228/232 piece.

Let me know if I can help you with the 90/90 set-up....

Regards,
Tony