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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 02-20-2008, 05:47 PM   #1
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Default proper introduction and help me figure this out!

I ve been on this forum for a good 2 years now and never laid out what i was doing, but know i need some help. My miata , a 91 with an auto at the moment, is going to be setup as a drag car with limited street use (weekend runs). I want to start off with a solid 12 sec car (200-250hp?) and hopefully work my way into the 10 sec range(375-400hp?). I come from a dsm background and am still trying to break that way of thinking which i have seen is wrong for my miata.
I plan on running a 1.8 with a 6 speed and 4.10 torsen. The turbo I plan to use is a gt3071r with an internal wastegate, which will be an overkill for a while, but i plan to grow into it. So here is my questions, i want to start with the basics, megasquirt, intercooler, 300 something injectors, and around 8 lbs, which isnt even on the compressor map, so other than poor performance, what disadvantage is there of using a turbo at the wrong boost level. I just dont want to buy 2 turbos, and the car has been sitting for almost 2 years and im ready to drive it this summer.
Also i plan on running 3" exhaust into a muffler and 4" out the rear, pretty much straight pipe with a muffler incase im checked by a cop, but ive searched up and down and cant find a muffler with a 3" inlet and 4" outlet, anyone know?
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Old 02-20-2008, 05:55 PM   #2
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few things...if you are going with the 6speed you may want lower gearing, like a 3.6 would be much better, also you may want to go with a non torsen rear and go with a rx7 clutch type, they are supposed to be stronger...
you will need bigger injectors, get some PnP RX7 550's, those will be perfect for a 250-300 range and can idle failry well with MS...
good luck in your build, pics would be nice

also, that muffler should be easily found...but why 3in 4 out? why not just 3in 3out?
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Old 02-20-2008, 06:13 PM   #3
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yea i wanted to go 550s to start so i wouldnt have to switch injectors when i turned up the boost, but figured they would be too much for the initial setup. I want the 4 in" exhaust for 2 reasons with the boost i want to get to it wont hurt to go big, and second is strictly cosmetic, i just love the looks of a 4" straight pipe.
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Old 02-20-2008, 06:35 PM   #4
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with the MS you should be able to tune for the 550's without any problems, ask chad or someone else thats running them
as far as your pipe, its your call, it wont help if your entire exhaust is 3", post muffler will really not make a difference, but if its for looks then thats another story
ebay is full of rice mufflers that are 3" in 4" out for around $30 or so...
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Old 02-20-2008, 08:18 PM   #5
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Start by telling us every single mod currently on the car.

We'll say that a nice early goal is 250whp and the end goal being 375whp and you'd like not to purchase parts for 250 that you'd have to scrap at 375.

MS and the 3071 are good... but I don't think internal wastegate is. Talk to Corky about a T3 with appropriate turbine housing and a manifold w/external gate.

Do the math on the upper limit of 550's... I don't think they'll support 375whp.

The 6pd and the 3.6 is your friend... you'll be launching in 3rd w/4.1 due to wheelspin.

I'd think you're only going to want to build 1 engine, right.
Forged and coated everything, A LOT of headwork, and a lighweight valvetrain. There are TONS of options here, but it's not gonna be cheap. I'm thinking in the $5-$6k neighborhood for your motor.

The stock ignition system will probably be enough.

There's a really trick high-flow intake manifold out there but I can't find it to link it to you.

ACT and SPEC make clutches that will be fine for those power levels.

Since it's a drag car, the OEM automatic radiator might be adequate, but look at the Begi coolant reroute of figure out your own.

Some serious chassis stiffening is in order... start with the FM butterfly brace and do the homework on a rollcage. Depending on the eventual times you'll run, most tracks have rules on safety requirements for convertibles. You won't be running 10's anywhere with just a hard-top installed. That also means a seat and 5pt belts and a few other things.

Tires and wheels of course. You're gonna need some serious rubber, which means flares an suspension mods. Shock and spring choices will be critical with getting good launches... do some searching to make an initial good purhcase, but you'll probably end up buying a couple sets of everything before you find one you like.

You might also want to consider aerodynamics. Trap speeds in the 10'[email protected]'ish are gonna be interesting. A hardtop I would think is mandatory to start.
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Old 02-20-2008, 08:55 PM   #6
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i bet 10's will cost you 20K by the time you're done
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Old 02-21-2008, 10:36 AM   #7
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As of now the only mods to the car are sportmax 962s, 9" in the rear with a 225 tire, which is getting ready to get a 255 drag radial, the rear of the car only will be flared. Bsp flushmount headlights with the left low beam taken out and a duct positioned right to the SOON TO BE turbo. Engine, trans and rear, I do realize the chance of having to go to a turbo 2 or a ford rear, are going to come out as soon as i get in to a new house with a garage, by the end of summer.
The build will be loosely based off racing mazdas purple miata, meaning seeing how far a stock block and head will take me with proper tuning. Act clutch just because of personal prefrence, stock flywheel because of launch, butterfly brace and solid diff mounts hopefully will cure most wheelhop. I think my exhaust is getting misconstrued, i just lost all my links, but the blue, orange and white miata from something side motorsports? has a set up like in talking about just a small magnaflow style muffler in front of the rear axle, no visible muffler, and staight pipe coming out the rear, would love to have the rear piece titanium but thats probably near impossible. By the way i do plan on showing the car sometimes, but thats not the point of the car.
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Old 02-21-2008, 10:51 AM   #8
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As for weight saving theres really not that much to do, ac and power steering are gone already, plan to get a braille 11 lb battery, and new seats. But will probably add more weight than i take out with the turbo and cage. A little carbonfiber on the hood, trunk and hardtop but no weight saving there other than the hardtop. But i want radio and carpet and i need heat. I posted in an earlier post how streetable swisscheesed from under the seats back would be still doing so research on that, dont want to do just the trunk and take needed weight from the rear of the car.
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Old 02-21-2008, 10:54 AM   #9
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and i believe between $10 and $20g's for a streetable, reliable 10 sec car is a reasonable price range.
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Old 02-21-2008, 10:58 AM   #10
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Umm, You are going to need a LOT more than 250bhp for a 12 second car. Mines running about 200bhp as are others I know of and getting mid to low 14s.
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Old 02-21-2008, 11:22 AM   #11
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most of my time figures are based off of dragtimes.com, and users like apexonyou's threads and these cars arent strictly setup for drag racing, and most miatas have bad 60 foot and wheel hop which i plan on dealing with before i go to the track, just educated guesses right now, Ill see when i get it together.
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Old 02-21-2008, 11:46 AM   #12
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This might show you how far you are off!

http://i22.photobucket.com/albums/b3...rMileTimes.jpg

244bhp, just breaks in to 13s
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Old 02-21-2008, 12:26 PM   #13
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Quote:
Originally Posted by richard_ha View Post
This might show you how far you are off!

http://i22.photobucket.com/albums/b3...rMileTimes.jpg

244bhp, just breaks in to 13s

gotta be the worst list of drivers ive ever seen.
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Old 02-21-2008, 12:36 PM   #14
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Just remember the chassis, diffmounts, wheel angles (no camber), diff bracing, dragspec shocks, good tires etc.
300 hp and in the 13's in the list, i bet that car is set up for street/mild track, and not exlusively for drag.
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Old 02-21-2008, 12:36 PM   #15
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whats the altitude of those tracks anyone know?
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Old 02-21-2008, 12:56 PM   #16
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Quote:
Originally Posted by Braineack View Post
gotta be the worst list of drivers ive ever seen.
I know a couple people making 240-250whp on their mazdaspeeds that are in the low-mid 13's and with wider rears and good tires possible 12's.

Last edited by LateralSpeed; 02-21-2008 at 01:15 PM.
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Old 02-21-2008, 01:55 PM   #17
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if it come down to me i would scratch the drag thing. miatas are made to handle the roads not just go in a straight line it defeats the purpose of one. but if you really have to do it i guess its fine. i would see much more fun with a 250hp miata at Dragons tail.
As it concerns the exhaust i would go with a 3inch all around not even bather with a 4inch i don't even see how that would fit. not sure if you have DH Griffith in your town but they got some nice scrap pipes to use i mean everything from stainless to mild steel to aluminum. good luck building it.
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Old 02-21-2008, 02:08 PM   #18
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id really like to see 12s with 250 hp on slicks if the radials arent holding, but its safe to say 8 lbs on a gt30 should be fine just a big overkill? MS should be fine even when i turn up the boost to 20lbs or so once everthing is worked out, is there a maximum pressure or max injector i can use with it? Really dont want to go full standalone.

I know im talking stock block and no standalone it gonna blow
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Old 02-21-2008, 02:21 PM   #19
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Ive been in the arguement about draggin a miata plenty of times, mostly on m.net, just because a car is made for a specific crowd doesnt mean it wont do good at other things. I ve done tons of research on this before i bought my miata and looked at plently of other cars but the miata was best for what i wanted, plus it makes it even more apealing to know it will **** some people off that i ruined a perfectly good miata with staggered wheels and turbos that are to big to use it for something it wasnt made to do, you think honda ever dreamed the civic hatchback would be the pinnacle of 4 cyl racing when they designed it in 1994. Ive tryed plenty of solo/road racing and just does nothing for me compared to running the quarter.
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Old 02-21-2008, 02:37 PM   #20
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Drag racing is a very simple form of racing and as such is very difficult to do well.

Your goal of a weekend warrior drag car, if done correctly, should net you 12s with low to mid 200whp. Its just a matter of hooking and keeping things from breaking...

The internal wastegate will be fine at the higher horsepower goal but might creep at the lower.
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