hey guys, i just wanted some opinions on this: i have an 86 gxl that has a paxton sn89 supercharger on it with the upgraded impeller (1200 cfm vs. stock 800 cfm) and pulley. although you are supposed be able to run the s/c safely on the stock NA fuel system, i wne t ahead and installed 550 cc secondaries, a walbro 255, and a vortech rising rate fpr, controlled by an S-AFC II (can never be too safe). however i recently blew the motor, although i kno it wasnt due to lean detonation because it was tuned pretty rich. (i beleive it was due to the high compression NA rotors + hot air charge due to lack of intercooler +old age of motor)) either way, while its being rebuilt i went ahead and installed TII rotors (lower compression) and plan on installing a water injection system for EXTRA safety. my question is, should i just upgrade the primaries to 550cc as well, or will this be even more overkill? either way, running too rich wouldnt be a problem since i have an safc, right? thanks in advance

 

o and for reference, the s/c is capable of about 12 psi (or at least thats how high i have pushed it), but before i *RARELY* took it even to 10. after this build i only plan to take it to 8 psi for saftey issues.

 

haha, one more thing, i have an "open" intake (cone filter) and full exhaust (headers, straight presilencer, catback) and large street port. i think that's everything that may be relevant.

 

I'd install ALL TII injectors in your case with the S-afc, or just 720 secondaries.

Also, you can blow an engine from being too rich don't rely on gobs of fuel to save you, they can do more harm then good.

I'd get it on a dyno after its run in to do the tuning. That's going to provide a much safer enviroment to get it dialed in well.

 

also i would think if you lower your compression you would still be able to run the same amount of boost, even more if you wanted. And along with the water/meth injection, with the right amount of fuel you could easily run 12psi

 

yea, i kno that the motor will take 12psi, i was more worried about the s/c! either way, to what classicauto said, i do plan on dyno tuning once the motor is broke in, but that leads me to another question, how the hell am i to break this thing in??? i know that TII arent supposed to see ANY boost before 1000 miles, but since the s/c is belt driven, its boost depends on rpm, no matter how genlty i press the gas. i start hearing the s/c whine at about 1500 rpm. i cant break the motor in by just going up to 1500! plus regular driving will be significantly uncomfortable if i shift at 1500 or before, no? sugesstions??

 

just run it with a tiny hole in the pressure manifold so that the air leaks out and never gets above one psi.

 

12 PSI is a lot for high comp rotors, and a stock NA fuel system......im running 550/720 on my T2 at 10 PSI and even then i wonder sometimes haha.

upgrade both to 550s, maybe even GSLSE 680s if youre crazy.

 

There's alot of opinion surrounding break-in and everyone is entitled to their own. If there's no new bearings in the engine all you're really doing during break in is bedding the seals into the housings. Essentially I'm saying you should be fine so long as the tune isn't monstrously off, just don't go full throttling it until its stopped pulling more vaccum and has been tuned. A new set of seals isn't going to break because it saw a little boost if the sealing surface isn't completely worn in - if it sees alot of boost with a poor tune, yeah, it'll chip.

But if you're super paranoid you could vent it as suggessted but I'm unsure if it would have any negative effects similair to over sipinning a turbo when you have aboost leak.

 

all great suggesstions! any one know of negative effects of venting boost pressure as suggested before??

 

Well, if the air you are venting has already been through the AFM, then the ECU will be injecting fuel for a measured volume of air. More air than is flowing into the combustion chambers.

IOW, you will run really rich.

 

12+ psi... you may want to start thinking about a stand alone ECU

 

no no no, i dont plan on running 12 psi, i just kno that the s/c i have is capable of at least that (thats the highest I took it to). i only plan to take it up to 8psi once the motor is back in the car

 

couple cheapie upgrades;

run the t2 ecu, its timing settings are much more turbo friendly, or even better run an rtek'd t2 ecu.

run the 550's all the way around, 4x550 is actually lean on a stock t2 @10psi...

low comp rotors are smart

also consider colder plugs for the TRAILING, as its the first and hottest spot the mixture sees; preignition

make sure the air intake isn't getting hot air off the radiator, colder air going into the s/c = colder air coming out

i think you're on the right track though

 

thanks j9fd3s, im not sure about running a TII ecu, especially if we are talking about swapping the wiring harness. i had thought about gettind my ecu chipped with the rtek before getting the S-AFC. im glad to see everyone suggesting the 550's in the primary spots as well since i was already talking to a friend about buying a pair from him

 

Find out how much heat that thing is pushing into your intake at 12 PSI. That will help make your decision.

At the very least, you will want 550 CC primary and 720CC secondary. And of course some way to control them. But if you are seeing high intake temps, then you'll need to pull timing accordingly which generally means a standalone.

 

have a look at the wiring diagram/fsm i think on an s4 you swap a few wires, but they basically plug in.

 

what if im only running 8 psi like planned?? still need 550cc pri./ 720 sec.??

 

At 8 PSI, you may only need the 550CC secondaries. As I recall those superchargers don't make much power on the 13B so consequently you won't need much fuel.

 

i guess that depends on your idea of "much power". i think that at full boost with my mods (mainly the full exhaust andport work) i can easily make more that 250hp. which is what i was originally shooting for. hopefully more tho. if im not mistaken someone (i believe it was a forum member too) made ~225 rwhp on this same super charger with similar mods (minus the port work) on 6psi. except his had the original impeller, not the upgrade like mine. even in the original paper work from the eighties that came with the s/c (came with it when i bought the blower from another forum member ) shows dyno charts with a otherwise stock s4 (exhaust, intake, fuel sys., which is actually how this setup was designed to be used per the info/install packet) making 216 hp (although im sure that was at the flywheel).

anyways, i plan on only running 8psi max, but at that level can i "get away" with running 550cc's all the way around, or just on the secondaries, or would it be a wise/safe decision to go to a 550/680 (or even 720) setup?

 

250 at engine should be fine on 550CC secondaries. You'll presumably have an FMU which will raise fuel pressure. However since I don't know the IATs you will be seeing I can only guess. 550CC on the primary and secondary would be ideal but you will need some way to control them.

Either put in too much injector now, or run the car on the dyno and then decide what you need.

 

i do already have a vortech fpr (or fmu) and an s-afc II. like i said before, when i was driving the car before i blew the motor, i was running a walbro 255 pump, a vortech rising rate fpr, an S-AFC II (which i had tuned [from highway runs, NOT dyno] a little rich) and 460/550 injectors. with this setup i the car was still running rich (the way i wanted it untill i could dyno tune it). so i kno that a 460/550 setup will be able to deliver the fuel i need. but back then i only had a catback. now the motor is ported (large streetport) and i have headers+test pipe. i didnt kno if i should go to 550 primaries for these reasons. either way, i kno that i want to do at least a 550/550 setup, but do you think 550/680 or 550/720 would just be overkill??

 

hey, how much power do you think you are putting down to the pavement with your s/c setup??

 

i know that it sounds like alot, but with my mods i dont see why 250-270rwhp wouldnt be impossible. i mean just think about it:

"cone" intake (3 in)
1200 max cfm impeller
approx. 8psi
large street port
rb header and presilencer
apex'i gt spec catback
vortech rising rate fpr
walbro 255
550ccx4 injectors (may go to 680 or 720cc depending on if i need them) (the reason i started this thread)
s-afc II
water/meth injection soon to come!!

i believe that all the mods i have power-wise

 

you think this will be pushing the 550/550 setup? need 550/680? 550/720?? 680/680??? 680/720???!!!