agh1889

iTrader: (1)

i just rebuilt the engine on my 87 t2. i had the car running for about 3 weeks and got tired of having no torque so i pulled the engine back out. i want to build this car for the track so i want to be able to run the least amount of boost but yet still make a good amount of power. the set up i have now chose is another s4 motor with a monster street port and n/a rotors. other components that ill be running is a t57 turbo and a heltech ecu. ive never done a high compression motor like this so if u have and suggestions it would be great.

Chris Boots

Same principal as a turbo NA in a way. Only real tips I have are to watch your A/F mix on a wideband, if you can watch the EGT temps, maybe retard the timing a couple more degrees, and don't run tooo much boost, stock boost levels of 5-8 doesn't sound too bad with those rotors and a good map. However, and I'm sure you've heard this before, rotaries aren't the torque-iest engines around. I found my nicely built 88' SE NA did maybe better on the track/autocross than my TII's maybe because the power was what it was and there's wasn't spool time and let off and back on etc etc. That being said, NA rotors aren't gunna give you that much more torque and you might not even feel the change in torque...

Of course correct me if I'm wrong guys

2slow4stock

iTrader: (18)

If you were going to do a high compression build, why not use the s5 n/a rotors? It's a .3-4 over the s4 n/a.

What kind of tracking were you planning on doing?

agh1889

iTrader: (1)

i have the s4 rotors already, im gonna be goin to lime rock most likely. not to much auto cross not really a fan of all the cones.

agh1889

iTrader: (1)

yea i kno that about the torque ill just have to wait and c if its gonna b a huge difference. the main reason y i want to do this is so i can run like 10psi and make the same power that i would make at like 15psi on a turbo rotor. so when im doing laps i can get alot less heat soaked and still make good power.

BLUE TII

iTrader: (9)

I just went FROM a monster street port to a mild street port in my race car and it helped power from 2,000rpm to 4,000rpm quite a bit.

There is a freeway on ramp that I test my various cars low end power at. Pull onto the ramp at 2,000rpm in 4th (1:1 in most cars) and accelerate until the white dotted lines end.

almost 55mph achieved in NA CSP 2400lb race car w/ 6 ports wired open.

65mph in SSM TII with monster street port and 2mm seal S5 TII rotors at 14psi.

80mph in same SSM TII with new mild street port 3mm seal S4 TII rotors at 14psi.

arghx

iTrader: (3)

if you only had the car running for 3 weeks, how did you know it had no torque? were you boosting it by then? the stock turbo spools really fast, especially the s5. Keeping that and a top mount intercooler will help spool the most. Both were designed for low end. The stock turbo has a small hotside and if you have the twin scroll system working right (s4) or just go with an s5 turbo/manifold combo you will hit boost quickly. The stock TMIC has very short intercooler piping compared to an FMIC. Keep the stock intercooler or see if you can find one of those upgraded ones that used to be sold. If you are concerned about intake temps you can spray methanol.

also, T57 turbo-- T04E 57 trim? With a T4 hotside? I think if you really want good response you should again stick with a top mount and use a small hybrid (BNR stage 1 or 2). a T3/T04E 57 trim, a common turbo on DSM's and Hondas, is too small on the hot side to be worth the trouble. I'd go with an s5 hybrid before that. You are also going to have to learn about timing curves before you attempt this. You can't run a timing map for 8.5:1 rotors on 9.4:1 rotors and then expect longevity.

From what I can see you are probably going to be limited to 280-300whp for what you want. Maybe if you dropped more money on an Aspec short runner T3 GT35R kit you'd be happy with the balance of spool and top end.

agh1889

iTrader: (1)

the motor i had was a s4 and i had a s4 turbo on it then changed it to an s5 turbo. i kno a bigger turbo is going to laggyer (if thats even a word) but im goin to in the high rpms most of the time so im not too too worried about the low end power. like i said b4 im lookin to make the most power with the least amount of boost. my buddy has a fd with the 35r kit on it and that car is an animal. im looking to make around the same power as him but just at a lower boost level.

agh1889

iTrader: (1)

how much power did u have at the wheels

BLUE TII

iTrader: (9)

It dynoed 340RWP at 12psi with the mild street port on my rough street tuned map (low 10s and high 9s for AFR), I haven't had a chance to dyno TUNE it yet.

It made a good bit over 100RWHP by 3,000rpm (55mph). I look at dyno graphs at 3,000rpm to judge a set ups low end power.

https://www.rx7club.com/2nd-generation-specific-1986-1992-17/blue-tii-09-hillclimb-build-857528/

agh1889

iTrader: (1)

how much did u pay for ur v mount

arghx

iTrader: (3)

you're going to blow the car up if you don't have the equipment or know-how to control ignition timing on a high compression turbo engine.

this contradicts the premise of the thread. If you don't care about low end torque, then you should run 8.5:1 rotors and safely crank the boost to at least 14-15 pounds while running aggressive exhaust ports. On most setups I think you'll find that 8.5:1 rotors at 15 psi is going to make more torque than 9.4:1 at 10. When you crank up the boost you are raising the effective compression ratio.

If you want torque in the upper rpm band, turn the boost high, use race fuel or alcohol injection and lower compression rotors, and at least somewhat aggressive porting. Then go with an FMIC and a largish exhaust housing (.96/1.00 or so on the turbine side, maybe bigger depending on porting).

If you want flatter torque across the rpm band consider a smaller turbo like a hybrid and a top mount intercooler (provided that you keep intake temps under control). those front mounts can really hurt torque and response compared to the stock units because of the much longer piping. Think about the factory design for a minute. A stock T2 has a flat and responsive torque curve because it has short intercooler piping, small exhaust ports, and small divided turbine housing passageways (s5) to keep exhaust velocity high. There's also the size of the wheels on the turbo but the sizing aspect plays into a larger system.

BLUE TII

iTrader: (9)

how much did u pay for ur v mount

I made it 8 years ago. $200 for 26x19 2 row Griffin radiator and about the same for an old Isuzu NPR truck intercooler, piping and shroud sheetmetal from junkyard and a sheet of CF to make it look cool.

agh1889

iTrader: (1)

Arghx its not about the torque im doing this setup to run low boost and make good power at the same time. im going to be hot lapping this car alot and im trying not to run more than 12psi so i can keep temps low. i could have stayed with the turbo rotors and either ran high boost or a bigger turbo but high boost gets hot and big turbos r too laggy.

agh1889

iTrader: (1)

im looking to do the same, V mounts seem to be the best for the track. was it a pain to get everything in.

BLUE TII

iTrader: (9)

Arghx its not about the torque im doing this setup to run low boost and make good power at the same time. im going to be hot lapping this car alot and im trying not to run more than 12psi so i can keep temps low. i could have stayed with the turbo rotors and either ran high boost or a bigger turbo but high boost gets hot and big turbos r too laggy.

Well, I understand how that seems logical, but the factors at play actually mean there is MORE heat soak with high compression rotors, it just shows up in your oil and coolant temperatures not in your intercooler temperatures.

The reason for this is the turbo compressor is more efficient at compressing the intake charge than the rotor in the engine and then you are able to also add an intercooler between the compressor and the engine to cool the intake air further increasing the difference in efficiency between the turbo compressor versus the rotor compressing the intake charge.

The only way to add an "intercooler" in for the rotor compressing the intake charge is to inject water or alcohol in with the intake air for it to change phase in an endothermic reaction. Doing this WHILE raising compression ratio and running low boost would work fine in a rotary though you will reach your limit at 10:1 C/R rotors since no one makes higher compression rotors.

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BEST thing to do for prolonged track events with a turbo is chose a turbo that will meet your horsepower goals flow demands at the lowest boost WITH that cross over point being in the highest efficiency range of the turbo and then choose the appropriate compression rotors to deal with whatever boost that ends up being.

Most flow at lowest boost will limit your turbo compressor choices to old compressor designs when high displacement engines ran at low boost.

You may end up thinking the almost 50 year old 60-1 compressor design looks damn good at 14psi and have to choose 8.5:1 compression rotors.

Then again, you may look into the effects of pre turbine exhaust back pressure at the desired boost pressure coupled with the (pre RX-8) rotary overlap phase and decide that lower boost at lower compressor efficiency is better and run two 60-1 compressors at 10psi to reach your flow demands or a single giant modern compressor at 10psi way below its best efficiency range to get the flow.

Because that is another heat soak you have to think about on the track. The more exhaust backpressure the more the EGTs are absorbed by the engine components because a peripheral exhaust port (or intake port) NEVER closes it just switches flow to another rotor face.

Efficiency is sneaky and found in odd places sometimes...

BLUE TII

iTrader: (9)

im looking to do the same, V mounts seem to be the best for the track. was it a pain to get everything in.

Yes, it all barely fits; though, I did not cut or drill the stock body at all to make it work. You can hack anything in.

Technically it is not a V mount as that term applies to the relationship between the radiator and the intercooler and in my set up they have completely different ducts and each would work just as well with the other completely removed or relocated (though the engine would preffer the latter).

I call it a Horizontal mount intercooler set up since it has its own dedicated duct and the only unconventional aspect of the design is that the intercooler is... horizontal.