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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 01-12-2013, 10:15 PM   #1
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Default Turbo setup for rally cross/autocross

This is my 1st post, so go easy ! I've done some reading about turbos but am a long way from being able to put a setup together on my own so I'm looking for some help. I have some fairly specific requirements....

My car is a 1990 miata, I have a 1.8 engine I'm planning to build up. I run rally cross and some Tsd rally's and am looking for ways to get more power. The car is driven on loose surfaces, anything from dirt, gravel, sandy loam, snow, ice etc etc, and also on the road. My ultimate goal is NOT lots and lots of hp, I will end up breaking things and just spinning the wheels excessively, so I am targeting something like 220 - 250 hp. The most important attribute is throttle response, I need to be able to adjust my throttle as near to instantaneous as possible, and decent low/mid range torque. This allows as much adjustability as possible when driving rapidly on twisty roads that you have never seen before.

Anybody have any past experience making this sort or setup ? It's a pretty low budget project in general, so advice on what bits are ok to buy used v new would be appreciated.

Thanks in advance !
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Old 01-12-2013, 10:45 PM   #2
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Well I have to say that I have build turbos for other people and am now building an EFR 99 car but, for autocross or rallycross it is difficult to beat a SC motor throttle response wise, yes SC do have their share of downs sides and that is why I am building a turbo car now but if you are looking for instant throttle response, low end torque and modest HP goal SC is the way to go in my humble opinion, take a look at my 1.6 with a tiny M45 and think of what a 1.8 M62 would do.
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Old 01-12-2013, 11:29 PM   #3
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Cannot disagree with that.
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Old 01-12-2013, 11:34 PM   #4
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get a rotrex....dead nuts reliable and stock powerband shape and response. And should hit your goals
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Old 01-12-2013, 11:43 PM   #5
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Get an SR20 T25...best turbo for your goals. Cheap and reliable too.
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Old 01-13-2013, 02:22 AM   #6
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For his stated power goals rotrex is not what he wants.
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Old 01-13-2013, 02:25 AM   #7
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220-250hp? that's like 200-230whp pretty sure a failtrex can hit that kinda oomph but tell me why not since you have one
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Old 01-13-2013, 02:54 AM   #8
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While i was originally checking out rotrex for my car pre release kits were like $3200 and the claims were very extreme. If i wanted a non choked down compressor i could make way bigger numbers and i could supposedly buy a bigger compressor for even bigger numbers. I no longer see ANY of those options available at all and no longer see these great hp numbers claims. Pre release this rotrex sounded like the cats meow. Right now they are making turbo guys look pretty smart.
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Old 01-13-2013, 03:44 AM   #9
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I can't think of anyone who is actually running a C30-74 flat out in a 1.8 Miata and has a dyno plot to go with it. Someone might get hungry and try to make it happen now that the new/revised KW kits are out, but I'd imagine its still going to be a while. If you match the blower and engine redlines, the -74 should, in theory, be able to flow enough air for something like 300hp. But again, I haven't seen anyone who has actually done/tried it and documented it.
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Old 01-13-2013, 08:03 AM   #10
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Ug, I did one rally cross and I loved it, but I would never want my car turbo'd. Every turbo'd car there had issues, it was a very muddy day however.

I'd much rather hold an N/A car at higher rpms than use a turbo.
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Old 01-13-2013, 08:51 AM   #11
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Hey - is this Mark V. from Royal Oak, MI? If so - hi again from Jon A.

I have rallycrossed a stock 1.6 miata several times, and it is apparent that they are woefully inadequate in the power and torque departments even on slippery surfaces. That being said, I think a more reasonable power goal would be 180-200hp. As mentioned earlier - a supercharger would be ideal for your targeted uses. However, it is much more difficult to piece together your own DIY supercharger kit compared to a DIY turbo setup. Which leaves you with a pre-purchased SC kit ($$$) versus a DIY turbo (cheap). I say save up the money and buy a SC kit. Used kits pop up on the classifieds here occasionally. An Eaton M62 kit would be perfect (this is the SC we are using on our rallycross Honda Civic). I don't think a Rotrex would provide enough torque boost at the lower engine speeds, so wouldn't be ideal.

Or, just swap in a late model VVT motor and see if that makes things fun enough in NA trim. It is certainly going to be a good step up from a 1.6, and you could slap a SC on it later down the road if it isn't quite enough.
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Old 01-13-2013, 12:30 PM   #12
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Quote:
Originally Posted by TheV's View Post
The most important attribute is throttle response, I need to be able to adjust my throttle as near to instantaneous as possible, and decent low/mid range torque. This allows as much adjustability as possible when driving rapidly on twisty roads that you have never seen before.
Quote:
Originally Posted by 18psi View Post
220-250hp? that's like 200-230whp pretty sure a failtrex can hit that kinda oomph but tell me why not since you have one
Because low end torque. Absolutely he can hit 200-230whp, but the low end isn't there. What he is describing is an MP62. He could put a small restrictor to limit his top end, and get somewhat close on low-midrange torque, and remain on stock internals, but it will never be as good in that range as MP62.

Bellwilliam's car (unopened junkyard VVT motor), back when it had a rotrex + custom (flowed more than the one in the kit) restrictor, compared to an MP62 setup, both on E85:


Now, Brainie got involved in the original discussion that spawned the above dyno plot comparison, and put 2560 results onto it:


But for the sweet sweet torquez, and the moar flows to redline, go EFR:


All of the WRC cars are turbocharged. In my opinion OP should go either MP62, or EFR and limit his boost to keep him at 200wtq or so.
Attached Thumbnails
Turbo setup for rally cross/autocross-e85rotrex_vs_e85mp62.jpg   Turbo setup for rally cross/autocross-begi_e85rotrex_vs_e85ffs.jpg   Turbo setup for rally cross/autocross-efr_6258_dynodataplot.jpg  
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Old 01-13-2013, 12:50 PM   #13
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Quote:
Originally Posted by Mobius View Post
Because low end torque. Absolutely he can hit 200-230whp, but the low end isn't there. What he is describing is an MP62. He could put a small restrictor to limit his top end, and get somewhat close on low-midrange torque, and remain on stock internals, but it will never be as good in that range as MP62.

Bellwilliam's car (unopened junkyard VVT motor), back when it had a rotrex + custom (flowed more than the one in the kit) restrictor, compared to an MP62 setup, both on E85:


Now, Brainie got involved in the original discussion that spawned the above dyno plot comparison, and put 2560 results onto it:


But for the sweet sweet torquez, and the moar flows to redline, go EFR:


All of the WRC cars are turbocharged. In my opinion OP should go either MP62, or EFR and limit his boost to keep him at 200wtq or so.
You need to keep in mind that one thing that those dyno plots don't show is power at transient TPS values. At 4,000 RPM after being at TPS=0 for a second or more while slowing down for entry to a tight transitiion, going to TPS =100 for 2 seconds to dig out of that transition to the entry of a slalom and then back to TPS = 0. That is the ONE(and possibly only) area where a belt driven positive displacement supercharger is superior to a Turbo. And in Autocross there are A LOT of those situations. A turbo sized with this in mind would be my second choice for this application but would be power limited. I centrifugal supercharger would be my last resort for this specific application as it is literally the worst of both worlds. Just MHO...but what the hell do I know.
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Old 01-13-2013, 12:52 PM   #14
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Get a 2554 and run ALL OF IT?
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Old 01-13-2013, 12:53 PM   #15
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gt2554 or equivalent. Instant torque because instant spool. 200whp attainable.
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Old 01-13-2013, 01:00 PM   #16
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Looking at the rotrex Dyno plot I'm surprised that the kit does not have a dual path intake system where it the air has a large opening with a buterfly open for low speed that closes at the boost limit pressure forcing the intake air to flow through the path with the restrictor, seems like that would give you the best of both worlds when using a large compressor.
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Old 01-13-2013, 01:03 PM   #17
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lol ANY boost with the rotex kit will be welcome.

With a centrifugal setup you need rpms. Thats the flaw of rotex. At low rpm you dont have enough rpm to turn the compressor to where it makes some boost, if you add too big of a pulley then you have too much rpm at the top end.
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Old 01-13-2013, 01:15 PM   #18
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Quote:
Originally Posted by sixshooter View Post
gt2554 or equivalent. Instant torque because instant spool. 200whp attainable.
+1, Mazda's factory turbo bp rally cars came with a turbo approx this size ('90-'94 323 GTX, GTR's turbo was larger). They give great low and mid range then peter off in the upper rpm range.

It makes a good street / autox set up, not so much a highway king.
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Old 01-13-2013, 04:11 PM   #19
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Wow, thanks everybody for your thoughts, Frank and Beans, yes, it's Mark V ! - I still have front fenders for you if you want them ??

So it looks like either a M62 SC or some small turbo would be a good way to go. Jon, I can't tell if 180-200 is a good recommended goal or if you just don't want me to beat you ?? ..... But you are right, I'm not too hung up on peak HP anyways, lots of instant usable torque with fast throttle response is what I need.

So if I look at the Turbo recommendations for a minute it looks like they are all small ball bearing turbos - since I don't have an endless budget which one gives me the best smiles/dollar factor ?
- and is there a theory on what of the components to spend your money on - for instance is it better to spend it on engine management v turbo v manifolds v BOV's etc etc ?

Thanks again for the many responses, this is a great forum !
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Old 01-13-2013, 04:18 PM   #20
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Can't Megasquirt run anti-lag? That'd be sick.
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