Well I finally finished the Fast 90 / LS2 TB install. The issue I had with it setting codes when switched on turned out to be a bad TB that I bought as "new" from the "other" forum.
My first impression is not good. Although it is definitly stronger at WOT, it now has a "soggy" bottom end and mid range. It has no hesitation from idle, but it feels just like I installed a hugh non-lockup stall converter. Going along at 40mph in third and easing into the throttle, it is very unresponsive.
The thing I liked most about my car after my Dart head install was the crisp, off-idle reponse. You could hardly tell it had a stall converter until you nailed it, but now. I will try and contact some tuners and get their thoughts to see if this can be "tuned out" If any of you have done an install, let me know what you thought of the change.
If I can't "tune it" it for better low end, I will have to go back to LS6/Ported TB

 

Watch out for FAST leaks. I had the FAST/LS2 setup. It leaked like hell when torqued to spec and reset and overtorqed. Never settled in but did not have the throttle response issue you describe.

 

One other thought, sell the FAST 90 setup and go with the FAST 78 and ported TB. That is what I have been researching.

 

Tony Mamo of AFR says the FAST/LS2 90 combo is the best, but you need to port the TB, as there's lots of material restrictions before the butterfly plate, and on it as well. Supposedly easier to tune than a NW or FAST TB, too. (I've heard stay away from FAST)

 

I did some porting on the TB. I removed the "ridges" directly in front of the TB and blended it in. I thought it turned out very good.
The "off idle" (0-10mph) is not bad. It is a little less crisp than before, but not real bad. The iritating part is the part throttle acceleration. It seems like you just have to just keep giving it more and more throttle to get it to accelerate.

 

This's not the first time I've heard this complaint. Too bad, since I've got this exact setup to soon install. Maybe the tuner can improve throttle response?

 

I've e-mailed a few including mike Norris who did the tune on it after the head install. I'll see what they say
I guess the reason it's confusing me is that if the 90mm setup was too big for a stock cube motor (larger runners etc) it seems like it would sort of "fall on it's face" off idle, but it doesn't really do that
If the larger runners made it lose a few ftlbs of torque a low rpm, it shouldn't matter too much, but this install has made it a different car to drive!

 

Mine idles fine, but from 1800-3000 rpms is drives like crap. I thought it was a vacuum leak, but why would it idle fine?

 

it's pretty hard for an intake manifold design to provide low end grunt power and high RPM total HP.

As in all things, a package approach is better than the sum of individual parts. Just as when you added headers you could have sworn the stock exhaust manifolds gave you more low end power (or felt like it anyway) the same concept applies. You may need more gear, you may need to change your cam to take advantage of the benefits of the LSX/Fast intake. No one is advertising that intake as a "torker" model (to borrow an Edelbrock descriptor).

When you have a lower gear you can more ably take on a bigger cam and/or take on a more aggressive intake (those that remember street tunnel rams).

The Fast intake is a quality piece. You just have to know how to take advantage of it's power potential.

 

That's exactly what I'm experiencing.

2ndVette
I aree that you have to match parts. My entire modding program was "planned out" to give the most power while maintaining low end torque and drivability AND being low maintance (a med duration cam verses long for low end torque, an "average" lift cam to ensure long spring life even if it did sacrafice a couple of hp, 205 heads for good port velocity etc, etc)
My problem is that this swap didn't just cost me a few ftlbs down low, it completly changed the way the car drives !!
I'm just trying to find out if this is the norm,or can it be "tuned out" so it regains its drivability. If not, then this is not a true street intake for a stock cube car

 

I have seen curves that pick up power with this setup throughout the RPM range, and the common denominator is Tony Mamo. With his flow bench and knowledge he can get this setup to perform. It really comes down to $$$ in the end.

 

You're proably right; He definitly seems to know this stuff. I am discussing some possible solutions with him now by PM. If he can get this combo going, I'll let you know what the issue was and the results
The alternate solution will be returning to the LS6 / ported TB with less hp but a LOT more torque.

 

My LSX/LS2 TB works well. Both TB and manifold were ported and I run an SD tune.

 

I had the Fast 90 (port matched) / LS2 (hand ported) installed with my AFR 205 heads (also received minor port matching) - all done by DTE. I don't have any of the low-end or throttle response issues mentioned. Tons of torque throughout the power range. Link to dyno chart at the bottom of the page.

While this is not a true "apples-to-apples" comparision, it at least demonstrates that the Fast 90/LS2 combination should work fine. Did you have the car re-tuned after installing this combo? (sounds like it was not based on the original post) I wonder if it is getting too much air and running lean. Is it throwing any codes?

Hope that you get it worked out.

http://www.comp-soln.com/Dyno3Run.jpg

 

No, I have not had it re-tuned, I have contacted Mike Norris, who did the last tune, to ask if this is somthing he has encountered and been able to tune out or is it the charicteristics of 90mm with a stock cube engine. (I havn't heard back yet)
The reason I wanted to get some feedback first, was that it would just compound the spiraling cost issue if I spent $400 bucks on a dyno tune and it STILL has a crappy mid range. Then I would have to change the Intake out and have it tuned again
As I mentioned before, I am trying to enlist Tony's help since he has a lot of experience in this combos.
ChipN,
it's encoraging to hear that this combo can work on a med. hp, stock cube street car.

 

I am obviously interested in your results as you blaze the trail I may follow later

 

I have done a few 90/90 combos and it's all in the tuning. It acts just as you described before the tune. Idle and part throttle are completely different. It is easy to get a car to idle good. A dyno tune is not necessarily needed, the airflow tables need to be dialed in. If this is done I'm confident you will get your crisp throttle response back. PACE HER has given good advice as well.

 

Well, the TBs on it's way to Tony; I'll post to let you know how it does in a couple weeks.

 

Uh-Oh....The pressure is on now....LOL

Ive stated this on another board but just to recap quickly here....I think Bottle's problem is two fold (possibly three), with the major culprit being the TB which I will have my hands on shortly. The other issue at play is that a FAST intake with it's larger runners and plenum volume will hurt some low speed performance somewhat but of course a properly modified FAST will not and make better peak #'s (one of the key benefits of the additional hand work is the low speed gains). Obviously money is always an issue and where every one draws the line in the sand on the spending is different....its all about priorities. I would sooner eat mac and cheese than know I gave up a little airflow in one of my engine combinations....LOL The good news is that I feel reasonably confident that most of what Bottle's complaints are based on will be eliminated when I rework his TB....at the very least made a lot less pronounced. The last potential piece of this puzzle could lie in the tune as others had mentioned and certainly any change that are significantly airflow related in nature should be tuned if you expect to extract the most power from the swap.

Hopefully the TB makes a big difference....I'm looking foward to the results as much as you guys.

Have a good weekend all....

Tony