stage 1 Rotrex Supercharged 90 s2

[victor25]

Strapped her down on the dyno today..... 240hp at the wheels = 275 at the crank
This is a very safe, simple, inexpensive stage 1 setup with a 100mm pulley on a Rotrex C30-94. Stock injectors, Ostrich 2.0, and Gm alternator to make room instead of that bulky heavy original one.
Dyno sheet says 3.5psi, my gauge said 4, but whatever. Both runs were almost identical, even blowing the o2 sensor out of the exhaust.
The stock injectors are limiting the boost that can be used. We are pretty much maxing them at this point. Stage 2 will have 36lb injectors, an intercooler, and twice the boost

[Rasta Monsta]

Leaning out under boost. . .she's gonna blow, cap'n!

[flash968]

i'm very fond of the rotrex C30-94. i use it in my kit for the 968. i have 50 CARB certified kits using them out there running hard. i haven't messed with the 944, though the kit would bolt up, but largely because there isn't any real market for it, due to the cost.

the intercooler will suck up most of the boost you plan to increase, and so the numbers won't go up much, but it will be safer. i'll be very interested to see what you come up with in the way of an intercooler. we played with a few of them, and did not ultimately find anything that worked well enough to justify it. they all had about a 2lb restriction, which forced raising the rpms to a point of limit, and in the end, while the peak numbers went up a bit, it pushed the entire curve to the right, which made the car actually slower.

as for injectors, we also ran out of injector on the stock 28lb injectors, and had to have larger injectors made, as the ones that are out there ran like crap, due to not working well with the large piston size and chamber shape

good luck - fun stuff

[v2rocket_aka944]

nice!

[victor25]

Originally Posted by Rasta Monsta

Leaning out under boost. . .she's gonna blow, cap'n!

LOL... no she's not leaning out. Both runs it stayed solid around 11.5 on my wide band and in the data logs for both runs. They were having a problem with their o2 sniffer giving bad readings.

[victor25]

Originally Posted by flash968

i'm very fond of the rotrex C30-94. i use it in my kit for the 968. i have 50 CARB certified kits using them out there running hard. i haven't messed with the 944, though the kit would bolt up, but largely because there isn't any real market for it, due to the cost.

the intercooler will suck up most of the boost you plan to increase, and so the numbers won't go up much, but it will be safer. i'll be very interested to see what you come up with in the way of an intercooler. we played with a few of them, and did not ultimately find anything that worked well enough to justify it. they all had about a 2lb restriction, which forced raising the rpms to a point of limit, and in the end, while the peak numbers went up a bit, it pushed the entire curve to the right, which made the car actually slower.

as for injectors, we also ran out of injector on the stock 28lb injectors, and had to have larger injectors made, as the ones that are out there ran like crap, due to not working well with the large piston size and chamber shape

good luck - fun stuff

Hey Flash, How are ya. I am familiar with your kit. We get our Superchargers from the same guy, Oscar. I use the C38-90 in my 928 kits

Yeah I ran out of fuel quickly when I was at 6psi, so I had to drop back to 4 to keep things safe. I was quite surprised how well 4psi does though. For the stage 2, I have a 951 intercooler, MAF setup, and some 36lb injectors I've been testing with.

[flash968]

lol - i figured that was you.

yeah - looked at the 951 intercooler. was not impressed. didn't drop temps enough for the amount of restriction. where it had to be mounted also meant losing the cold air location for the air filter and airbox, which defeated the purpose.

i've been running 5psi on my kits, with no intercooler, and have had zero issues in 3 years. most people will tell you that an intercooler below 6psi is a mistake on a centrifugal unit. running without one also allows the curve to stay to the left. i would only add one if i were to run 7lbs or more. i'm currently at 7 and intake temps are within limits.

[9FF]

Originally Posted by flash968

lol - i figured that was you.

yeah - looked at the 951 intercooler. was not impressed. didn't drop temps enough for the amount of restriction. where it had to be mounted also meant losing the cold air location for the air filter and airbox, which defeated the purpose.

i've been running 5psi on my kits, with no intercooler, and have had zero issues in 3 years. most people will tell you that an intercooler below 6psi is a mistake on a centrifugal unit. running without one also allows the curve to stay to the left. i would only add one if i were to run 7lbs or more. i'm currently at 7 and intake temps are within limits.

What about an air-to-water intercooler, more efficient, place it were you want?

[victor25]

9ff
I use a water to air intercooler on my 928 kits with great results, but its not logical here with everything right up front. The 928 throttle body is in the back of the engine. Also those barrel style intercoolers are very restrictive.
I'm still playing and testing right now with the intercooler and bigger injectors, but Flash may well be correct and in that it's just easier keep things simple the boost down.

[flash968]

don't get me wrong, i still think the kit would be better if i could figure out an intercooler that worked, but it would require a complete retune, and a complete rework of the pulley system, so as to make up the slack due to the pulley change. not easy, given the limited belt lengths.

the only reason i didn't mess with the air to water units is the reservoir and pump needed. i have a spot, since i moved my battery, but for the "kit" it was highly problematic. the same would be said of any intercooler though, as the cost factor makes it too expensive to the customer.

it's the same reason that i don't sell the kit to 944 guys. it's not that it doesn't fit, wouldn't work, or any of that. there just aren't any 944 guys willing to pony up the money for the kit. they would rather drop in a 951 engine or a V8, and have more power for the dollar. i've been offering for years to tune a kit to a 944, as long as they would buy the kit when it was done, but so far, no takers, even knowing that it would be CARB legal.

[victor25]

Originally Posted by flash968

don't get me wrong, i still think the kit would be better if i could figure out an intercooler that worked, but it would require a complete retune, and a complete rework of the pulley system, so as to make up the slack due to the pulley change. not easy, given the limited belt lengths.

the only reason i didn't mess with the air to water units is the reservoir and pump needed. i have a spot, since i moved my battery, but for the "kit" it was highly problematic. the same would be said of any intercooler though, as the cost factor makes it too expensive to the customer.

it's the same reason that i don't sell the kit to 944 guys. it's not that it doesn't fit, wouldn't work, or any of that. there just aren't any 944 guys willing to pony up the money for the kit. they would rather drop in a 951 engine or a V8, and have more power for the dollar. i've been offering for years to tune a kit to a 944, as long as they would buy the kit when it was done, but so far, no takers, even knowing that it would be CARB legal.

My setup is completely different than yours. I run the supercharger facing the other way, so I have an unlimited supply of belt lengths. Also I designed it with a full wrap and can use the A/C to tighten the belt. With this setup you get to keep the A/C and the big heavy stock alternator is replaced by a much smaller GM unit.
This picture was taken a while ago, so the blue piece is gone and it's a one piece silicone unit coming out of the supercharger now

[flash968]

i get to keep the AC too, and use a similar adjuster (i just improved on the porsche design)

i couldn't change the alternator, as the 968 requires too much current. it needs the 115amps the unit produces, and any other alternator that would fit was actually larger than the bosch.

i couldn't fit the unit where yours is either. the 968 intake manifold is shaped very differently, and that space is filled.

it's hard to see from the pic, one thing i may see as a problem in your setup though is the reservoir height relative the head unit. rotrex is very clear about the reservoir outlet needing to be BELOW the head unit inlet. failure to do that results in front seal leaks. it looks like you are above that. is it just the pic?

we should probably hook up at some point.

[victor25]

Yeah the reservoir is higher than the supercharger, and I will have to relocate it at some point, but for now it's an easy spot out of the way while I'm testing, changing parts, playing with intercoolers etc...

[flash968]

lol - boy do i know that one.

[v2rocket_aka944]

Originally Posted by flash968

i get to keep the AC too, and use a similar adjuster (i just improved on the porsche design)

i couldn't change the alternator, as the 968 requires too much current. it needs the 115amps the unit produces, and any other alternator that would fit was actually larger than the bosch.

i couldn't fit the unit where yours is either. the 968 intake manifold is shaped very differently, and that space is filled.

it's hard to see from the pic, one thing i may see as a problem in your setup though is the reservoir height relative the head unit. rotrex is very clear about the reservoir outlet needing to be BELOW the head unit inlet. failure to do that results in front seal leaks. it looks like you are above that. is it just the pic?

we should probably hook up at some point.

bob,
have you seen the nissan alternator mod? the alternator from a nissan quest van more or less bolts on (some people needed to grind the bracket a little under the alternator to clear a screw) and its rated 130 amps, and is significantly smaller/lighter than the 944/968 beast.

[flash968]

i don't see the real advantage. victor had to change for reasons of size. i didn't have that problem. the bosch unit just isn't all that heavy. are there lighter ones out there? sure, but the couple of pounds loss doesn't justify the cost to me. for the purposes of a kit, you have to include such things. you can't tell the customer "go out and get this to complete your kit". it makes it increasingly difficult to provide reliability when you do that. that means that you have to take into account all of the variables. on the 968, even keeping the OEM AC compressor proved to be an issue, as bosch changed the unit slightly during production. it still fit the stock application, but changed how it mounted enough that i have to provide a different part to make it work with my kit. having to have people make a modification to a part brings in its own problems too. it opens the door for somebody to mess up and blame you for insufficient instructions. when that happens, no matter how much it was their fault, due to the internet, you get badmouthed.

the ironic thing is that the guys who tend to gripe the most, are the ones with the least money. i could easily make my kit fit the 944. it would take me maybe 3 days to work out the small items i would need to make for it to fit, and a day to tune it. it would make 30% more power than stock, across the board, and be CARB certified. it would also be nice to look at. all of that would be a waste though, if there is nobody to buy it, or worse, somebody on a shoestring budget that is going to be more trouble than i am prepared to deal with. even with the 968 guys, there were guys who had no business installing the kit, either for reasons of qualifications as a wrench, or for reasons of installing it on a raggedy or modified car that was bound to have problems. i've had to hand hold a few guys through the process. with the 944, i fear that would only be magnified.

that's why i haven't put any energy into making the kit for the car. 944 guys tend to focus on peak numbers. that will never be the strong suit of a centrifugal unit. the centrifugal unit will run better, and make more drivable power, but the numbers will be lower than what can easily be done with a 951 motor. that's a hard sell.

so, i wish victor the best of luck with his project. it's certainly going to be a long road, and having gone down that road, i don't envy the scenery. he knows the deal though, and is obviously either a die hard 944 guy, or a complete loon. lol - we'll see how that goes.

[victor25]

"A complete loon" Hey now be nice... I just may resemble that remark, lol

As you know I already make a kit for the 928s4, so I am familiar with the scenery. This is a simple project compared to that one, and I intend to keep it that way. Simple and inexpensive!! I hope haha

[flash968]

lol - yeah - join the club - having jackets made next week

simple - yeah - funny how they start out that way, but never seem to end up that way

[JD159]

Oh boy. This sounds so tempting while I do my rebuild. With the mods I have and the s2 intake, this sounds feasable. Will follow...

[guru944]

Victor25;
Could you post more pics of the modification parts and specs needed to duplicate your success forced induction setup? I'm know many 16v 2.6 and 3.0L (non 968) guys would like to see more applicable power with a bolt on setup like yours before they hit 4k or more rpm band. How much did it set you back $$? Have you considered also a MAF conversion? I'm very interested aswell and considering it as a backup to my K27 turbo conversion.
PM me about the intercooler upgrade i offer, later...