joe is he streeting the car? in a track enviroment i never found my self in low rpms, even coming out of corners! at worst i was at 4000 rpms, but my redline was only 6000 in the srt-4. if he wants to track the car, and still wants decent mid range torque id do a basic street port, and t2 exhaust inserts he should still be able to make good low end torque with good tuning. he can make the torque he wants by playing with ignition timing and turbo sizing...whats is he planning for fuel and timing control anyway?

 

we talked about a turbo 3 rotor for NASA SU class (500bhpish), sprints, with some 3 hour enduros, and we figured we couldnt put enough cooling into a second gen to do it.

 

A 20b with stock twins will get very close to that figure if he's just worried about the numbers. Attila the fun over at the Rx7 club forum has stock twins on his 20b and makes more torque than hp. I think he dynoed at 390lbs and 350 rwhp with the twins running out of breath in the higher rpm's. If his twins could flow a little more, I don't see why he couldn't reach 400rwhp and more torque than what he originally got.

 

So a customer wants as much torque as possible out of the 13B Cosmo RE motor I'm putting together for him.

He's planning on using a GT35R turbo which should easily produce 400whp. But now his goal is to get around 400ft/lbs of torque.



On a turbo two rotor to gain more low rpm power without killing top end power you simply need to get the turbo spooled as soon a possible WITHOUT sacrificing intake or exhaust flow.



If you look at many dyno plots you will see engines with responsive turbos like the GT35R making 100RWHP at 3,000rpm and engines with laggy turbos making less than 100RWHP at 3,000rpm.



You have chosen the motor and the turbo so on to getting the turbo to spool faster-



1) Increase pressure differential between the engine and exhaust sides of the turbo exhaust wheel. Fit as large diameter and free flowing exhaust from the turbo back as you can fit. Bigger than 3" really does help. You can also use a rich mixture and retarded spark in varying degrees to increase exhaust gas expansion, but you have to monitor EGTs to avoid melting engine and turbo bits if you go to crazy with this. Open your exhaust ports earlier so more gas expansion happens in the exhaust manifold, contour the exhaust ports for flow so less energy is lost exiting the engine. Use a divided exhaust housing and manifold, even a wastegate per runner to avoid exhaust communication at the wastegate (I have found this helps the very low end boost response).



2) Decrease pressure drop in the intake system from the turbo compressor all the way to the engine ports. This is one most people don't think about. A turbo spools at an exponential rate becacuse of the relationship of the boost it makes increasing the exhaust volume that drives it. This means if you can cut down on the boost lost to pressure drop in the intake side it really helps spool the turbo faster. Keep the intercooler pipes as short as possible with as few bends as possible. Gradually increase pipe diameter from compressor outlet diameter to larger throttle body diameter. Spend a lot of time porting the inake manifolds modding the TB or fabricate a better one. Don't go too late closing on the intake ports or the turbo has to fight the compression reversion. Open the intake ports earlier, there are 32 degrees of intake stoke without the port open in stock configuration for emmisions purposes.

 

WOW, awesome info Blue TII. Thanks so much, that all makes sense to me!

We are building a V-mount intercooler setup so the I/C pipes will be very short.



I was thinking of opening the intake ports as far as possible without going to a bridge port and leaving the closing side stock.

Where would I get 32 degrees of intake stroke from? cutting a bridge port?

Would everyone else agree that the GT35R would be the best turbo for this application?



seanm - dont worry this motor will be quite mild compared to yours

 

Give him 500 hp and a shorter rear end gear?

 

porting does raise volumetric efficiency, IF its done right. so yes you do get more tq from porting.

a proper port will loose very little power under 2k rpm if any at all and make more tq over that rpm

turbo or na.

 

Where would I get 32 degrees of intake stroke from? cutting a bridge port?



You can get the intake to open 10-15 degrees earlier by cutting the opening edge enough that it drops the leading sideseal and keeps the trailing sideseal supported. With this porting it is best to bevel and scissor the closing edge of the port to avoid sideseal damage, so you will have a bit later closing.



It is then possible to get the port to open another 15-20 degrees earlier by beveling the rotor edge toward the sideseal.



Mazda used both these old race tricks to get the Renisis to open intake at 0 deg, but didn't properly bevel and scissor the closing edge.







Would everyone else agree that the GT35R would be the best turbo for this application?



I thought you were asking how to get as much low end as possible with the Cosmo 13B and the GT35R. If the turbo is in question, I would choose a turbo with a larger exhaust wheel (at least P trim) and put it in a small housing to get it to spool. Now that Garret T04 turbos are available w/ dual bearing centers you could choose a wheel combination that is proven to work well on rotary and still get the benifit of ball bearing center. If top end drops off too much you can swap to a larger housing. Make sure you have a large well flowing wastegate set-up and it shouldn't hurt top end power much.

 

So nobody ever really answered my question:



I want to leave the port closing time stock but then port it to open up as early as possible without going to a Bridge port. Will this work for the goal we have set?



Also as for the turbo, I was thinking of a "P trim" exhaust wheel with a .96 A/R housing ??

 

as for the turbo, thats about what seths got on his, the dyno is in the dyno section, its over 300lbs ft from 4500 to like 6500 rpms.



his port timing closes later than stock.