falcon

iTrader: (13)

Ok, before I get into it.. please leave the "go turbo" comments out of here. I am not at this point going turbo. I may in the future, but right now this thread is to brainstorm ideas for my current Rotrex'd set up.


So as most of you know I have a Rotrex'd 1.6L Miata. While I'm happy with where it's at right now and could realistically drive it for years on the track and be satisfied... a lot of the fun for me is the build side. I love to tinker and change things, make it better.

Now, one of the poor things about a Rotrex is the amount of torque. I make a dismal 194wtq peaking at redline (8000RPM) but silly amounts of HP (297whp @ 8000RPM). The car hauls more than any car I've built before, and up high the lack of torque is not a huge deal with the HP numbers. But on hill climbs the car bogs out of the corners a bit due to the lack of torque. I need to keep the motor above 4000RPM to really go anywhere while going up hill. This is not so much a problem on my local track since it's flat. I don't want to be lighting the tires up out of the corners, I jsut want a bit more "oomph."

What kind of things would help squeeze some more torque out of the motor? 3'' exhaust?, smaller/bigger IC? smaller/bigger IC pipes? Water injection?

I have done pretty much everything one can do to a motor so I need to think outside the box. The bottom end is build, head is ported, OS valves, cams, GotPSI intake manifold, large TB, LS2 coils, Maxim Works header (modified slightly) but only a 2.5'' exhaust. I am also running a small 2.5'' thick core IC that is 7''x 22'' or so. 2.5'' piping all around. Could going to smaller IC piping pre intercooler help? A 3'' exhaust? Should I drop my RPM limit down to say 7600RPM or so and spin the Rotrex harder to make more boost down low?

I am running 15's next year with hopefully a 6pd. I have not chosen a final drive yet but right now I have a 4.1 in the diff.

My dyno plot for reference.



Help me boost gurus.

viperormiata

iTrader: (24)

You didn't list camshafts specs, but you have "cams" in you sig. Details?

JasonC SBB

Did you go bigger or smaller cams?

falcon

iTrader: (13)

IIRC (without the spec sheet infront of me) they are 207 IN*/214 EX* duration at .050. 8.8mm in 8.9mm ex lift. Valves are 1mm OS. I don't remember the overall duration but I want to say they are in the 290*-300* for both.

Ideally I'd like to not have to touch the cams. With the solid lifters it would be impossible to find an OTS cam that works with the shim sizes available and I really don't want to go through the cam grinding process again.

Braineack

iTrader: (62)

figure out a way to get full boost at 3K.

It might mean installing a turbo.

falcon

iTrader: (13)

.

Braineack

iTrader: (62)

Savington

iTrader: (31)

Honestly, you reap what you sew. You switched to a 1.6 and used a rotrex blower. That combo does not produce torque. There is no magic tuning tweak that will suddenly add a noticeable amount of torque to your setup. Since you aren't willing to go turbo, or change the cams, this thread is pretty much pointless.

If you want torque, get new cams or (better yet) build a vvt motor. Or get a bigger rotrex and restrict the top end. It will still never make big torque at 4000rpm, though. That is not what the rotrex is good at.

I would enjoy the car as much as you can for a while, then wise up and build a vvt turbo motor.

falcon

iTrader: (13)

I hear you. I just don't want to dig into the motor any longer. Hence the reason for not wanting to touch cams. I think since my resonator is blown out on the 2.5'' exhaust now is a good time to just get a 3'', drop the RPM down a bit for reliability reasons and call it a day.

Then maybe add lightness.

JasonC SBB

With an 8000 RPM redline, why are you dropping RPMs below 5000?

What kind of torque gains are you looking for?
You need to look at power at your minimum expected RPM, which is typically 60% of redline. e.g. power at 5000 RPM when you have an 8000 RPM revlimit, or power at 4300 RPM with a 7000 RPM revlimit. And then the way to maximize torque and spread of torque when you have a centri blower is to maximize the engine's VE at the bottom of that RPM band. With a centri blower that suggests milder cams than stock - this has the same effect as "restricting" the topend, while maximizing the torque. Having said that, you can only increase VE at 4000 by ~10% compared to where you might be now.

Stock cams have a torque peak at 5500 RPM which would work well with your 8000 RPM redline.
I guess indeed the only thing left is to use a smaller pulley and restrict the top if the top end might break your motor.

falcon

iTrader: (13)

Yeah I don't really go below 5k most of the time but some corners on a few hills if i stay in 3rd i bog but if i downshift im at 6k and the motor revs so fast that im upshifting almost right away. I'm thinking i need to see how the car is with 15's over the 13's i was running.

Savington

iTrader: (31)

Or get a 6-speed, which tightens up the spacing between gears by around 30%.

falcon

iTrader: (13)

I have my eye out for one.

falcon

iTrader: (13)

How much power/torque do you think I could realistically get from moving to a 3'' exhaust and dropping the RPM down 400 or so and at the same time gearing the Rotrex a bit higher? Say 2PSI more at 4000RPM, 3PSI more at 5000RPM with the 3'' exhaust?

Worth it?

And I'd likely go 6spd if I can find one with some 15x9 6UL's

JasonC SBB

At maximum VE:

Torque (ft-lbs) ~= 72 ft-lbs * displacement_in_L * (1+boost/14.7)

Power (hp) = torque (ft-lbs) * RPM/5252

Some of that torque is used up to drive the s/c
When you're not at max VE you will have less torque than predicted
This is why with a centri s/c you want peak torque at the bottom of your powerband. i.e. stock cams show peak torque from 4000-5500. You will want to gear the car so that you never drop below 5500 rpm. As VE diminishes above 5500 rpm the centri increases boost.

Techsalvager

Tried messing with intake cam timing?

falcon

iTrader: (13)

Yeah we did a bit on the dyno. Now I don't know a lot about cams/cam timing and going from memory IIRC my motor builder said they were set at 110* something or other initially (before the motor went in the car). Maybe those of you who know, will know what he was talking about.

On the dyno both the intake and exhaust cams were tinkered with and really showed not a huge amount of gains in either direction. They seemed to like it withing 1-2* of where they were initially set up.

I also don't have a ton of room to play with for the cam gears because my motor is interference with the higher lift, OS valves and decked head/block. I can only go about 4* either way from 0* on the cam gear before getting too close for comfort.

Savington

iTrader: (31)

Probably LSA (lobe separation angle). More LSA = more overlap IIRC.

That's what I would expect. You may be able to find some low-end torque by advancing the intake cam, but you will likely sacrifice a disproportionate amount of top-end power in the process.

You've already done everything else, including all the expensive improvements - MW header, LS TB, headwork, etc. IMO, you're not going to find much more than what you have with your current motor/blower combo.

falcon

iTrader: (13)

Yeah I'm starting to agree. I think if I go back to the dyno it will be with a 3'' exhaust, RPM limit slightly lower with a smaller pulley and try to play with the cam timing some more. If I loose a bit of top end it's not the end of the world... but how " disproportionate " are we talking here?

Come to think of it, I actually only messed with cam timing on the first tune., before the got PSI intake and before the smaller pulley.

Savington

iTrader: (31)

Impossible to say. Maybe 2whp per 1wtq gained, but that is pulled straight out of my butt.