You might want to recheck your math .....85mm puts you just over 90k at 7k rpm

With the 85mm my redline is Just under 7500, not overspinning at all, I do all my logs that I send to seb and motor cuts out 74k n some change, I’ll get it on a dyno as soon as it’s retuned , spoke with techs at rotrex and kraftwerksusa where I got the pulley, said should be fine at 7k redline, guess I will find out lol

Jinxx it’s a win win either way, the pulley works And I make a little more power or I destroy the sc unit and get the c38r , don’t see the down side do you?

The down side could be contamination. If your supercharger chews itself up and metal debris and shavings get into the oil system you could have big problems. This unit is direct fed and not self contained, correct?

Just like the guys that say.. Well if my engine goes then Ill just rebuild the bottom end with new pistons and rods so Its not that bad. Well, my engine went when I was Turbo'ed back in the day and took out the crank, both heads and left a window in the block so I needed an entire new Long block. Cost went way up.

Oil system of the Retrex is usually self contained with it's own heat exchanger.

http://www.the370z.com/forced-induct...-pulley-3.html



This is a chart on impeller speed calculation...last time I talked to rotrex they confirmed the calculation as well .....and that is why GTM wouldn’t sell a pulley under 86mm

The 84mm is at 91280 at 7k rpm......a 80 mm would put you over 100k ...
Also TOPGUN is correct ..if you blow the supercharger you could damage much more than just the bottom end .. we all take that risk when boosting but ....I wouldn’t go that far over specs on a blower


I might be reading the charts wrong soooo ......im still not sure

Oh sorry forgot to mention the long block sitting on the engine stand next to my z in garage out of a crashed z

See when I do something I do it big and push the limits to see how much I can get out of whichever system, turbo, sc , etc wether it’s thought by some to Be the best or the worst, I try everything and push all parts, let’s just call it life experiences

Ya I have all that, don’t you have the 85mm installed on yours?

When is the car going to up and running

Mine is running with the 85mm pulley ...12 lbs boost

Yes the 85 mm

The 85 mm pulley is running 96k impeller speed at 7.5 k rpm and 90k at 7k rpm

Using a 80mm would be running 102k impeller speed at 7.5k rpm and 95k at 7k rpm

That might be stressing the rotrex pretty hard

Yes, I ran mine all last summer with 85mm at 7.5k with no issues as of yet, I’ll retune n try the 80mm at a 7k redline, like I said I usually don’t redline the car often I’d like to see what type of power differences there is lower in the rpm range where I like it, also may even try some different rear gear ratios as well

I think it will be a wash in difference....what you gain from smaller pulley will be lost from lower rpm
And I have different gearing as well .. the nismos came with I think. 3.96 gear...non nismo was a little lower ... 3.69 if I remember right

What are your whp/wtq numbers on 12psi? What fuel are you tuned on?

guess we will see, it sure was a big difference between the 90mm and the 85mm after installed, it brought the boost in earlier but I think a little bit earlier would be even better, but that's just me and where I like my power and boost to come in, I think roughly a 7100k redline wont bother me to much, I reviewed my logs from last summer and they show a redline of 7587k redline with the 85mm while tuning with seb, if I don like it then its only 6 bolts to put the 85mm back on.

I’m tuned with 93 octane

I agree with the boost sooner ..that’s why I went with the 85mm ....the 80mm would be another notable difference early in the boost range which is what’s we are wanting ....that’s why the c38r should be a big improvement for our platform

Ya for sure, extremely curious to see c38r results

I would expect at least 3-4 lbs increase for the whole rpm range .. which would be huge difference

C38 vs R
KgPS .065/.08= 15%
12.5psi x 1.15 = 14.375psi

Are you saying the c38 lineup is kapped at 12/13lbs on this platform? Cause its not. The c38-91/92 flows 82lbs/min thats more than a pte 6266. We prolly only see 12/13 lbs due to the restriction of a 3" intake.

No, I'm saying that if your pulley is giving you 12.5psi on the 38 then the R will make 14.4 on that same setup. I doubt you are seeing restriction from a 3" intake.

That makes more sense. Either way there has to be a restriction of air flow somehwere, no? if a pte flows 74lbs/min and can achieve 16/18lbs of boost. Shouldnt the c38-91 achieve the same boost pressure or even better? Mayb im over thinking this..

Yes, rotrex already decimates all other sc units as it is in overall performance, I have had 0 issues so far and complaints, but sure will be interesting to see what this c38r can do

I’ll get my car on a dyno with the 80mm when I can and if it’s worth it to show some results, if not I’ll be waiting in the wings on c38r results.

What size is the outlet on the c38? If it's less than 3" then a 3" intake can't bottleneck it.

All outlets are 2.5"

They haven’t released any specs for the c38r yet....how did you get that comparison ?

What boost are you seeing with your 85mm pulley

I wasn’t able to get my car on a dyno last summer, bought another car in August so I didn’t get a chance, but I will try this summer once the snow melts to get it on dyno with both pulleys,85 & 80

Seat of my pants feeling with the 85mm was great, 1st gear is absolutely useless,that’s why iam rethinking gearing, only issue is the crash bar in front of intercooler, I think it hinders our cars a lot, gonna install FI crash bar this summer.

You don’t have a boost gauge ? And I was watching intake temps in 100 degree summer day and intakes were 118 degrees ... not sure if more air will change much .... I do have a water/meth kit sitting in the garage ready to go on and tune ... that should give me a little more

No boost gauge, new car took up my parts fund but I got my parts list ready for this year, my seibon vented hood did help a lot with engine bay temps and intake piping temps, I am thinking that having half the intercooler completely blocked can’t help anything but I could be wrong. I’d install the water meth if I were you cuz then you can add more timing, I was shopping for a system to. Here in Canada where I am we see daily summer highs of only 25celius so I can make big power but then traction becomes an issue, spinning isn’t winning

See first post.

That post has inaccurate info ....our current is .63 kg/s and the c38r is .80 + preliminary and that actual final spec is unknown ... and you are factoring the pressure ratio as if it would be the same ... where is would be 3.00 or better
https://www.bimmerboost.com/content....wer-capability

Jinxx are you on the pre order list for c38r?

No I’m not .... I wanted to see the final specs before buying ... had they released the specs first I would have been... I did call Jackson racing and talked to them about it ... they said that the c38r will have 30% more output over the c38 throughout the rpm range ... all good news to hear lol

ya iam waiting on the specs to, sounds promising so far. I spoke with Jackson and kraftwerks also.

The c38r was suppose to start shipping in Apr. Did anyone purchase one to test?

I wanted to but it wasn’t quite the right time for me. I called Jackson Racing this morning and they said the pre order is closed but those units will ship in June, and then more will be available for purchase in July

Is it possible to put a rotrex supercharger and an FI twin turbo in the same vehicle?
I think that would be crazy if it lasted!

I'd do that too....just to see how it feels!!!