Time for a C-5

Ok gang I need some input on my next HP increase. I did full exhaust, ported 243s and a mild (222/226/.600/112) cam over the summer and the only obvious upgradable part hanging out there is a better intake/TB combo. I currently have an LS6 intake with a ported stock 78mm TB. One option is having the LS2 snout added to my current intake by TPIS and getting an LS2 90mm TB. Does anyone have any experience with this set up? Seems like a decent bang for the buck – I’ve read some decent reviews/threads but they seem to be 5 years old. I’m also thinking about a FAST 90 or 92 (differences?) and a LS2 or aftermarket TB. The fast is more expensive but I expect there would be bigger gains? And I could sell my current set up. The FAST 102 seems like overkill for a smallish cam, stock displacement motor that makes peak power at 6,300 RPM – plus it’s much more expensive and I’d need a different fuel rail set-up. Any other options I’m missing?

Is there 15-20+/- more horsepower possible with a new intake/TB? Doesn't seem worth while if I can't get 15+ hp. I'm at 402/379 after the tune with the heads/cam - this is an 01 6M.

Do I need to upgrade my injectors and if so to what size? Will my current MAF sensor work or do I need a larger one? I see discussions about an 85mm GM unit on forum threads with larger intakes.

Thanks guys I appreciate the input.

Sam Handwich

Budget? What do you plan to spend? I don't know much about the prices on FAST manifolds, but I do know the concept behind "Don't be penny-wise and pound foolish."
You did not mention if you have headers. Or who does your tuning.....

Time for a C-5

Yes to headers. I don't really have a budget but it's not limitless either. I guess I'm looking for the best bang for the buck - I'm not going to spend twice as much for a fast set-up if it's only modestly more effective. Dr. Phil is well known around Detroit and did my tune.

neutron82

I don't think you will get much more out of your setup with a fast intake or hacking up the ls6 to put a slightly larger tb on it... you might get a little but it may not be worth the price of parts/install/retune, the fast intakes do a better job when you get into the mid/upper 400's

warren s

Your cam and heads choice is not going to get much more out of any other intake available. I am getting about 25 hp and 10 tq more than you with a 228R cam and stock LS6 manifold, and the TB that came on my 99. I have PRC stage one heads that are pretty much just cleaned up 243s. I am running FAST 36 injectors.

Stick with what you have.

tblu92

1st about your injectors---there is NO HP advantage going to larger injectors unless you have outgrown your current ones---Industry standards dictate that you should keep your injector duty cycles at approx 80-85% max---Unless you are over that you are fine--Only way to tell is to have a tuner data log your duty cycles
As far as intake manifolds go The LS6 intake even in stock trim is plenty capable of handling up to approx 500 crank HP-----The only advantage of going to a larger intake is if you plan on running your car consistently above 6500 RPM's OR you have larger than stock Cubic Inches----Otherwise you are better spending your $$$ on something else
As far as cold air intakes go---there is NO magic here----Are CAI 's are basically created equal----The more expensive ones are just made of better quality materials and last longer and are easier to fit----basically any CAI is is worth about 8-15 RWHP Unless you are in a state that requires a SMOG legal CAI then the price doubles-----
I had your basic same set up--on my 98 and it was at about 475 crank HP and would run in the low 12's in the 1/4 mile-----
IF your car is an automatic the absolute best mod you can ever do is to add a stall converter---No less than a 3000 stall----This easy mod will gain you 1/2 second in the 1/4 mile and make your car a beast--without ever touching your engine---- If your car is a manual--- dropping the rear gear ratio from the 3.42 to a lower 3.73 will produce similar results

PS long tube headers always add approx 20-30 RWHP-----If you have No smog police where you live this should be your next mod---However a re-tune is a MUST---otherwise the gains will be minimal---If you live in a smog state then shortys are all you can do--But even those are worth approx 10-15 RWHP without tuning-----

Time for a C-5

Thanks for the replies, guys. A CAI and headers were mentioned - both are on. I think I have all of the obvious engine mods - heads/cam/longtubes/CAI and the supporting mods while in there - lifters/pushrods/timing chain/trunnions. The intake/tb were the only possible remaining components, but they don't sound worth the cost of admission based on the feedback. I kinda expected to hear there'd be some power to free up with ported heads and a cam (even a mild cam), but no one was very optimistic so ok.

tblu92 mentioned a gear change. I have a clutch going in in the spring. Maybe a 3.73 or 3.90 swap is the better use of the go fast $s while everything's apart. Time to do some gear research.

Thanks again.

Bill Curlee

If you know someone with HP-Tuners or EFI Live, have your engine/PCM data logged and send the results to someone who can look at the scans and tell you if your tune is optimized and you are getting all that you can get out of what you have.

Some things that you need to check additionally are:

- Fuel Pressure (at idle and at WOT FULL LOAD)
- Fuel Injector Duty Cycle at WOT FULL LOAD
- Knock Retard WOT FULL LOAD
- LTFT close to zero

If all of those are good, you can get a wide band hooked up and check your Power Enrichment (PE) Air Fuel Ratio at WOT FULL LOAD

If any of those are grossly wrong, you wont have all the power the engine can make.

RockyMtC5

I did basically the same as you, mild cam and heads and skipped the intake. 405/370 - I was happy but couldn't stop thinking what a FAST 90 and LS2 throttle body would get me. I bought a used Fast 90 and LS2 tb, 36# injectors and they sat in my garage for months. I ended up hand porting the Fast after researching on here and once I had it installed I gained 28 hp and 27 tq. I definitely feel the difference..... but it cost me more than I originally planned after all the extra things like new gaskets, hardware, the install labor and dyno tune. Now I feel complete though, no longer wondering what if....

If think you should go the TPSS LS6 to 90mm route.....

Time for a C-5

Thanks Matt. I checked out your set-up in your sig. Ours cam/heads are about identical. I'd be thrilled with 28/27 (or close).

vettenuts

I think I would look around for a used FAST 90 as opposed to altering the LS6. The LS6 has some value that would offset the cost of the FAST should you elect to sell it. I kept all my original parts so that whoever buys my car gets all the modifications plus all the stock parts that were replaced. Guess that's just how I roll

corvet786c

I don't think the Fast 102 would be overkill, with your cam and ported 243 heads. Actually it would be more room to grow down the road.

RockyMtC5

there are well known fitment issues with the 102 on C5's..... I'd stick with 90 or 92 or send ls6 to get opened up to 90 during the winter when the car is just parked anyways

Time for a C-5

The 102 costs more and different fuel rails are needed. I certainly have time with a long Michigan winter ahead of me to see if a used FAST 90 or 92 comes available. The modified LS6 is a simple core swap so no down time if/when I go that route. I'd like some first hand results of that set up - I found a couple old threads on the LS1Tech forum with decent results but overall not many. And they were dated.

Time for a C-5

Alright gang, I found a used ported FAST 92 with a ported LS2 TB on the LS1Tech forum that cam off a C5Z. It also came with FAST 36lb injectors and the adapter harness, an easy plug and play. I figure if I don't see reasonable gains (not sure what that number is) I'll have my tuner flash back my current tune and I'll resell the set up. So worst case I'm out the cost of some dyno time. Lots of Michigan winter left so I'll revive this thread in the spring.

Bill Curlee

Dont forget,,, You will have to have the tuner program in the new injector flow rates into the PCM or the car will not run properly.

If the PCM isnt fully optomized (VE table, WOT PE, and timing) for the new intake flow rates, you will be leaving a LOT of power & torque on the table.

I know you got them used but every injector comes with a data sheet that the tuner can use to PROPERLY set them up in the injector table.

Before you leave the tuning session, turn on your AC and make sure that your engine will still idle properly. If you dont, some time down the road you will go to use the AC and the engine will stall at idle. As me how I know?


Just saying...


Bill

RockyMtC5

Not really an easy "plug and play" unless you are super comfortable with rerouting pcv hoses and a tweaking the fitment a bit. On top of that, like user below said tuning for the intake and injectors.
That being said you should see a significant increase in hp and tq, I saw almost 30 of each and it was worth it!

Time for a C-5

Thanks, Matt. I'm open to any thoughts/specifics on the hose rerouting you may have encountered when you did yours. I have a good tuner so I'll leave that up to the pro. I was assuming I could install and drive (gingerly) to his shop untuned??? If that's not the case let me know.

RockyMtC5

I had my tuner/builder do mine so can't help much but the plumbing seems to be an issue depending on Year. I've heard some say they did the swap and limped the car to their tuner but I would only do this if your tuner is nearby. Just saying it's not an easy swap unless you really know what your doing. Good luck, it's definitely worth it for sure!