As a few of you know, I installed a FAST90 / LS2 on my C5 a few weeks ago. The results were extremly disappointing to say the least Before the swap, I had a Z06 / ported TB, and it was extremly crisp off idle and at low speed, considering I have a 3500 stall. It actually drove very close to stock until you nailed it. (read;a ball to drive!) After the install, it had an extremly soggy bottom end. It had poor low speed drivability, and mid range, unless you went to WOT. It actally drove like it had one of the old, high stall, non lockup convertors in it. All or nothing!
I posted on a couple of forums looking for some suggestions, but to be quite honest, I had every intention of pulling it off and going back to the 75mm. I am not interested in a few extra hp, at the loss of ANY low speed drivability
I PM'd Tony M, a member here on the forum, and asked his advice. He told me that he could eliminate 75% of the problem by porting the TB. Since I had already done some minor porting on it, I wasn't sure how much difference it would make...Well..
Results;
After installing the TB, it is just like NIGHT and DAY! Almost all of the crispness is back (It is a 90mm after all) It has a strong low, and mid-range. The part throttle response is back, and it is once again FUN to drive. I can't really tell a lot of difference in the WOT hp, but then again, it's been 3 1/2 weeks since I drove it. I feel confident now that with a good tune, it should be stronger, yet just as drivable as before. Now to figure out whether or not to go with a speed density tune, or a good dyno tune with someone who also works on the drivability side.
Thanks for the help Tony!!

 

Great that it worked out for you

Ahmad

 

Did you disassemble your TB to port it, or do it with the throttle blade still in? I've read a couple of porting how-tos, but they're all about the LS1 type.

 

Porting done by Tony Mamo

 

Interested in your final dyno results, glad to here this is working out. The FAST is out of the box, correct?

 

I hope to get it tuned in the next couple of weeks
The FAST was straight out of the box.

 

Great, that is likely the way I would go as well. First I have to fix this code I have though

 

OK, another stupid Q.(or two) which way do you mount the TB on the FAST? I mean, with the DBWire activator on the driver's, or passenger's side? I read that the LS1-6 were one way, and the LS2-7 were the other. Oh yeah, what the hell is the name of that weird Torx fitting that only has 5 knuckles instead of the normal 6, and also has a pin in the center?

 

It's not a stupid question, just one that most people won't admit to not knowing; The LS2 activator goes toward the passenger side, just opposite the way the LS1 mounts. I found out the hard way since I was installing a LS1 N2O plate at the same time, and went ahead and moved the PS res. before I realised it.
The new Torx screws are made to be tamper proof by having the pin in the middle. For most of them there is a torx socket with a hole in the center. These however, are of a new design. I went to 3 different auto part stores and they couln't find anything that would fit

 

Bottle Fed
Thanks for the info. I have been watching and wanting to do the 90 mm mod. myself. All of this is good to know.

 

If you had to do it again......was it worth $1000+???

 

I've been thinking about the FAST 90 for my non power added car. Is the 90mm upgrade worth it on a 'natural' LS1 car? Tim, what size mass air are you using with the 90mm TB?

 

Proably not. I would proably just use the $1000 to keep my bottle filled. I had just basically done everything there was to do with the engine short of going with a blower, and decided to try the FAST. It was kind of a PITA as far as some of the minor changes I had to make swapping from the stock set-up. (I still havn't gotten my PCV setup right yet.) I haven't had it dyno tuned yet to see what it is putting down, so I'm not of the hp/$$ ratio, but it sure does make the engine look GOOD


"I've been thinking about the FAST 90 for my non power added car. Is the 90mm upgrade worth it on a 'natural' LS1 car? Tim, what size mass air are you using with the 90mm TB?"

David
As I said above, it's all in what you're willing to spend. Cost per hp, I personally don't know if it's really worth it or not. It's definitly not one of the better deals hp/$$ wise, but if you've done everything else to the car, and don't want to go "bigger" on anything (I didn't) then it's one of the last mods on a NA car to do.
As for MAF, I have a heavly ported one on the car. One of the 1st mods I did was to remove the screens and port it to make it look like the aftermarket ones. I don't know if it helps at all or not. I figured with the vararam, the ported MASS, the aftermarket air bridge, 90mm TB and FAST, I should really be moving some air through the intake system