Ted75zcar

iTrader: (2)

Pulling timing in order to reduce power drives egts through the roof, and quickly.

Ted75zcar

iTrader: (2)

Run the ewg from the outlet side if the charge cooler. Shoot, you can VTA if you want. A restrictor on the inlet doesn't change the PR across the compressor. It is the PR that drives temperature increase.

TrackHack

So if pressure ratio drives the temperature, and this ratio doesn’t change relative to volume of incoming air, then reducing the volume of incoming air shouldn’t affect the temperature at all.

ok good to know. Helps me understand my choices..

now off to read up about ewg ‘s ....
Thanks

Ted75zcar

iTrader: (2)

Right, but venting after the compressor reduces the PR, so temperature goes down.

andym

Could op just run a bigger pulley wheel on rotrex so that it produces the power he wants at a low psi so there isn't excess heat generation? I am thinking the smallest rotrex with the largest pulley he can find like their 110mm.

Ted75zcar

iTrader: (2)

Which do you think is faster?

andym

Undoubtedly the option that restricts the intake since the area between idle and redline will have more average power as that black line shows. But to answer ops question about only making 185 I suppose this is a possibility. I still think an inlet restriction is the best option at working.

Ted75zcar

iTrader: (2)

I know that an EWG on the compressor outlet will work.

TrackHack

thanks Ted. This may be my silver bullet...

HarryB

It might sound counterintuitive, but have you thought of swapping in a stock engine plus rotrex and sell your current setup to offset some of the costs? You will need some power limiting mods as well, but at least you will not have all these fancy parts in your engine doing nothing, as a stock one would be more than fine at your power level.

sixshooter

iTrader: (12)

It's a good idea to use an external wastegate and an electronic boost controller. Great suggestion.

If it's set to a particular pressure then when it opens it will prevent backpressure from rising further by bleeding it off and should prevent additional drag or heat from being too much of a problem. Some fancier EBC systems may allow you to taper the boost up or down through the RPM range to make your desired curve flat where you need it.

HarryB

I think @Satisaii had a similar setup with a WG welded on the intake manifold if I recall correctly?

Midtenn

iTrader: (15)

So I am in a similar situation as you. I had a 155-160whp 11:1 motor and looking to run a power-to-weight with a goal of 185-200whp (depending on modifiers). While a Rotrex looks like a good option because it makes lower power, that's because most kits out there advertise a compromised setup. Rotrex's really seem to work better and better with more compression. Before I committed to racing, I looked into adding a Rotrex to my 11:1 setup for fun and it would have had crazy fun.

What you might have to do is rethink how to drive the car. You keep saying you only drive at high RPM, but you can make a lot of torque down low and be faster. The route I'm taking is a low boost turbo (EFR6258) on a 9.5:1 BP4W. Great mid range torque and just cutting the boost down at the higher RPMs (and likely limiting the RPM) to keep the car under my power goals. If you look through the forum you can find some plots of low boost turbos that make plenty of great torque but limit the power. You just need to review the gearing and likely run a longer rear gear to take advantage of the torque band.

Satisaii

We did 2 of them, but never really tested them. We wanted all the power on Deviate and were disappointed with 300 hp at ~8psi. We thought the wastegate was not working right and put all the springs in it to keep it shut. It turned out that our race head flows a bit of air and it was not a problem with the setup. My personal car blew the engine (valve broke at the stem) before we could really mess with the wastegate and we sold the setup soon after. But we still have the manifolds and wastegates...

From our experience here, if your cap is merely 185 hp, then you want to make 185 hp everywhere. Gives you better options on gearing, short shifting, not shifting, etc. We outlawed this when creating our own series by using an area under the curve formula instead of a hp target.

Goingnowherefast

iTrader: (1)

Yes. Like mentioned, you're gonna run into problems if you lower the timing as much as you'll need to get down to 185 whp.

rascal

Im interested in this. We run a sprint series here in oz that runs a simple peak power cap on a couple of classes, and I’ve always wanted to find a better way to do it.

what formula do you use for the area calc? Do you just pick a few rpm points and average the hp values at these points to come up with the figure? Or is it more granular than that?

how does it work out in the real world usage?

TrackHack

Hmm, another good option.
That's get me thinking, whether to go for the -94 and use a wg to keep it under, exactly the concept you described, but obviously using the bigger Rotrex rather than a turbo. (just my personal preference)
I would have to chg my current 4.1 rear end, but 3.6s are fairly plentiful around here, as were std on NB2 in Australia.

Warpspeed

Sounds like a good idea, but the place its going to start detonating first will be around the torque peak where the cylinder pressures are highest.
A mid range torque monster will certainly be a lot easier to drive, and probably faster with less effort, but a too high initial static compression ratio is still going to limit what detonation free mid range boost increase is going to be possible.

Limiting the top end power by profiling the boost should certainly work and be quite easy to do.
But not sure that is going to really help all that much with stressing out the transmission.
Its really torque and shock loading that cumulatively adds to metal fatigue, micro cracking and then the eventual *BANG*.

Returning to the detonation issue, a centrifugal blower will have a far lower overall exhaust back pressure, and a bit of deliberate over scavenging through valve overlap can drive out the hot exhaust residuals creating a lower final temperature during the engines compression phase. Lower final compression temperature should help keep you below the detonation threshold.
Over scavenging also helps with spark plug and exhaust valve temperatures.

A turbo is the exact opposite. Turbine inlet pressure is going to be about the same or more likely a bit higher than boost pressure. Extremely hot exhaust residuals remain trapped in the combustion chamber, which heats up and dilutes the incoming mixture. Turbo engines are much more prone to detonation than supercharged engines because of this charge heating, and not much you can do about that either.

If building a high static compression mid range torque monster, I rather prefer the idea of a centrifugal blower plus a very carefully controlled boost modulating vent. It should have a much better resistance to detonation than a turbo, very likely detonation is really going to be your biggest problem.

Chilicharger665

iTrader: (2)

Why not run a C15-60? It is barely good for 200 whp, so it shouldn't be too hard to detune that. The first Rotrex set-up I ever remember seeing was a guy who ran one of those on his track car. The build thread is on m.net.

TrackHack

Another option, though my worry is that going with the 'grapefruit' rotrex might mean I don't even make it to my target which would annoy me way more, spending all this cash and not getting there.. (or more likely if it doesnt make it on the first iterations, I might have to throw some more dollars and effort changing things to get there.)

I think I've decided the easy solution is to go with a C30-84 and just run an external wastegate piped into the post-intercooler/pre throttle body pipe and vented back into the pre rotrex intake pipe, to keep the noise down as much as possible. (I'm not a fan of the wheeze!)
This means I'll definitely hit my target, wont be worrying about gearbox exploding, and can easily adjust it on the dyno when its getting tuned, without having to trial and error using restrictors, timing adjustments, or bolting/unbolting stuff, etc.

Just fit it, run it, see what it makes, and then adjust boost down accordingly, to hit my numbers.

Now to start looking on the dark web for how much I can get for one of my arms and one of my legs.... (USD- AUD exchange rate sucks atm)
I'll also need a can of lube for when Australian Customs has their way with me on duty, GST, other random charges as they see fit...

Thanks immensely to all that provided advice, and helped my confused mind formulate a plan.