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Old 02-06-2008, 02:58 PM   #1
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Default A proper setup for SCCA autocross

My perfectly good 1.6 is feeling too slow right now. Specially after driving my friend's STi.

I'd planned to keep my car NA but you guys are having too much of an influence over me.

If I were going turbo it'd have to be an excellent autocross car. My goals are:

175 whp
Full boost by 2000 rpm
Flat torque curve between 2500 and 5500 rpm

Budget is a constraint of course, but I'm the kind of guy who'd spend 1500 on a DIY job than buy an off-the-shelf BEGi S cause the latter doesn't fit my needs.

I did some initial research of what's available and made a shortlist of parts based on some compressor maps and reading corky's book. In your opinions, what would be the ultimate combo. Post up in following format:

Turbo - standard T25 sufficient? Alternative is a K03 180 hp model from Audi S4. Flows really well on comp side with a very small turbine for quick spool.

Manifold - cast log style (BEGi, JGS, ebay) or equal-length tubular (custom)? How important is the latter for quick spool?

Intercooler piping size - don't know if it matters, but generic ebay IC with 2.25" ok? anything better available?

Wastegate - Internal or External. K03 has a huge internal w/g BTW.

Fuel injectors (already have MS) - Stock 1.6 with higher fuel pressure, or is there a need for anything bigger?

Exhaust - Thinking of running a 3" with cherry bomb and side exit for quickest spool.
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Old 02-06-2008, 03:05 PM   #2
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t20
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Old 02-06-2008, 03:06 PM   #3
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did someone say sr20 t25?

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Old 02-06-2008, 03:13 PM   #4
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t20? where can i find one for T25-ish prices?

brain can you direct me to a compressor map for the sr20 turbo. How is it different from the regular T25 sold on ebay?

EDIT: is it this one: http://cgi.ebay.com/ebaymotors/Nissa...spagenameZWDVW
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Old 02-06-2008, 03:21 PM   #5
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IC piping is really not a big issue, you will be ok at 2.25"
log style mani is good for quick response but can create problems with higher boost, again not an issue for you, if i was you id just build my own...
exhaust, 3" will help boost a lot
WG, either way really

what you do need is a stronger clutch and try to get a 1.8 diff in there
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Old 02-06-2008, 03:26 PM   #6
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Turbo - t25... i'll sell you a rebuildable one for 50 shipped.

Manifold - whatever you feel like paying for.

Intercooler piping size 2.25 is fine

Wastegate - might as well stick w/ the already present internal

Fuel injectors (already have MS) - I'm not sure what your "MS" is. Be safe and get the 1.8's or bigger depending on if you like head room.

Exhaust - Enthuza exhaust is cheap.. having a shop make one from a cat and muffler can be even better. Side exit is not really an option on the miata.. search it out.. its been discussed.

It looks like you missed engine management unless the MS in your fuel injector section means MeqaSquirt. Obviously if you've been lurking this site most of us choose Megasquirt.
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Old 02-06-2008, 03:34 PM   #7
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impretty sure he meant MS=megasquirt
as far as injectors go, he should at least use the supra ones, they are cheap and will do the job...
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Old 02-06-2008, 03:44 PM   #8
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There is a discussion concerning the "perfect" NA/NB SM2 Miata build going on at Scca Forums Title:SM2 NA/NB Miata Build
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Old 02-06-2008, 03:59 PM   #9
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They alluded to someone campaigning a turbo car in '05, and that it did well. Do you have any details on the car?
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Old 02-06-2008, 04:10 PM   #10
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you cant expect your car to be fast without suspension work, good alignment and tires.
My Miata and my uncle's Miata and Geoffrey Chambers Miata are faster than any STIs on street tires on our region.

My Ex-sts2 setup

-Koni revalved
-Ground Controls
-800lbs front
-500lbs rear
-15/16 RB front hollow sway bar
-Bridgestones REo1r

Alignment
-2.7 in the front
-2.9 in the back
-3/8 toe out in front
- 1/32" toe in in the back
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Old 02-06-2008, 04:11 PM   #11
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Quote:
Originally Posted by The_Pipefather View Post
t20? where can i find one for T25-ish prices?

brain can you direct me to a compressor map for the sr20 turbo. How is it different from the regular T25 sold on ebay?

EDIT: is it this one: http://cgi.ebay.com/ebaymotors/Nissan-Flanged-TD04-Turbo-T25-T28-TD40-Internally-Gated_W0QQcmdZViewItemQQcategoryZ33742QQihZ004QQit emZ140203906549QQrdZ1QQsspagenameZWDVW


no, get the real deal:

http://cgi.ebay.com/ebaymotors/Garre...spagenameZWDVW

but i wouldn't pay more than $150 for a good one, $50 for a blown one.
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Old 02-06-2008, 04:24 PM   #12
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For some reason I interpreted "SM2" as "SM". As in Spec Miata. Which made me wonder why the hell anybody would care...

But insofar as the FI system is concerned, I have to agree that, even as a die-hard turbo guy, I'd probably choose a decently sized supercharger (like a MOAB) over a turbo for a car that was going to be a dedicated autocross-only weapon. Even with my little TD04H-15G and a very loose BOV, there is some lag. It's most noticeable on courses which have a long straight section either right after the start or after a very slow corner. What the S/C sacrifices in efficiency it would more than make up for with instant boost in those situations.


Since you already have MS, ditch the stock injectors and forget about AFPRs. Just pick up a set of 330 or 440cc injectors, depending on whether you're serious about only shooting for 175HP. 175 starts sounding like child's play right about the time that the two C6's park on either side of you.
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Old 02-06-2008, 04:25 PM   #13
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Sorry, before my time.
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Old 02-06-2008, 04:43 PM   #14
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I asked very similar questions about a year ago. I did extensive homework and went out of my way to drive as many FI'd Miatas as I could get my *** in.

After it was all said and done, I decided on a SC. I drove both a 1.6 and 1.8 with nicely tuned GT2554Rs. They were both 220+rwhp and both were in boost before 2000rpms which was a rush.

But...for an autocross application I felt that I would have to adapt to a different driving style in order to be fast. Not that it couldn't be done, it was just different and a much steeper learning curve. The instant boost of the turbo was nice, but also put the car at or beyond the limit of traction and control. Now going sideways is fun, but if you have autocrossed before, you know that's not the fast way around the course.

My recommendation is to find a few different FI'd Miatas and take them for a spin. Find somewhere to simulate autocross style elements and see how each car performs. Coming out of a slow tight sweeper was the main element that pushed me toward the SC. The SC'd cars would pull strong regardless of rpm and didn't require mashing the throttle to get going. I was able to take the sweeper smoothly. When driving the turbo cars, if I maintained enough speed to stay in boost, I was able to make a smooth transition and exit in control. If the corner was slow enough for me to fall out of boost, I would mash the throttle to get going and go from lagging to sideways.

Alright enough of a novel....
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Old 02-06-2008, 04:50 PM   #15
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Quote:
Originally Posted by The_Pipefather View Post

brain can you direct me to a compressor map for the sr20 turbo.




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Old 02-06-2008, 05:07 PM   #16
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Only the S15 turbo is BB. And it's comp wheel has a 60mm exducer
http://en.wikipedia.org/wiki/Nissan_...mparison_table

http://www.turbobygarrett.com/turbob...R_466541_1.htm
"OEM turbocharger on Nissan SR20DET engine"
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Old 02-06-2008, 05:09 PM   #17
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it's the same thing just not BB....60trim. 54mm, .80 a/r. coldside 53mm 72 trim .64 a/r turbine.


the S15 is a t28. 60mm = t28 54mm = t25.


if you look at today's graphs, then it's comparable to the

GT2554 54 as in 54mm. as long as the trim is the same, the map should be the exact same as well. the wheel design hasn't change, iirc.
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Old 02-06-2008, 05:28 PM   #18
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GT2560 = 60mm exducer
GT2554 = 54.3mm exducer
http://www.turbobygarrett.com/turbob...R_471171_3.htm

Does these comp maps look the same?
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Old 02-06-2008, 05:31 PM   #19
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No Because Its A ******* 60mm Wheel.





does this look like your brain? I mean, it is a brain.


that's a bird brain btw.
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Old 02-06-2008, 05:37 PM   #20
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What's your major malfunction?
I even posted up both comp maps for you.
THE ******* MAPS ARE DIFFERENT YOU FUCKTARD.
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