Ok so I know this topic is like beating a dead horse, but there's a slight variable to it. I have a JDM 13BT from an 87 S4 RX7, so it has 8.5:1 rotors (ideal for boost apps) Motor was torn down and inspected, everything checked out perfect. Large/monster street port job done by my friend, another friend (machinist) made me 1-piece 2mm apex seals. Atkins Rotary 1-piece corner seals (2mm) backed by FD corner seal springs from Mazda Trix. Factory stationary gears with new bearings pressed in (rotors received new bearings as well) both bearing sets OEM from Mazda Trix. Factory E-shaft with thermo pellet from Mazda Trix. Now for the variable. Reading through all the posts already made in this section of the forum, seems everyone uses fuel injection. I, on the other hand, will be running a Holley 4 barrel carburetor. I have a Jay Tech S4 manifold and have already plugged the 2 water jackets that would normally run into the EFI manifold (considering the J.T. manifold does not have channels for the coolant) Fuel will be supplied from an Aeromotive A1000 fuel pump so plenty of fuel for all the boost I'll throw at it. Ignition will be covered by individual coils (probably Crane Cams Fireballs or Mallory units), distributor in place of CAS, Mallory ignition box with 2-stage will be used, ECU will be replaced with a standalone but I've yet to fit that piece of the puzzle as well. Gauges up the wazoo to monitor everything. I'm sure I'll be questioned as to it's intended use. This is going to be a straight line car with an occasional street use, considering my gas mileage will be less than a Hummer I'm looking to push around 450 on about 20 psi, and my friend is backing his work stating I could throw more psi for track use if I wanted. Boost can kick in around 4500-5000 rpms, as I said, it'll be for 1/4's more than anything. Turbo manifold, BOV, wastegate, intercooler, dp and exhaust are not the issue, just what turbo can come close to the numbers I'm aiming for. Any and all criticism and advice is appreciated and I say criticism because I know there will be plenty of people who have been in my position before stating that I'd have better luck hitting the lottery than the numbers I want with my car so I'd love to know what your experience was and what I can do to come closer to where I want to be. Sorry for the novel, but I figured the more info, the less questions and more responses.... Thanks much for any help!

-Pedro

 

Now, I haven't much experience with carbs, so someone else running a carb'd setup could probably be of more help.... but there are a number of turbos that will put down that sort of power at that pressure, from the larger T04's...T78/88, GT40's-42's and up, and many more. As you're looking for mid 400's I would not go to a large frame turbo as its not needed, no sense in creating lag when when you can make the same numbers with more midrange...
Again, being as its carb'd, the numbers may be lower than a similar fuel injected set-up, so someone else might be a better help.
For a ballpark, you may want to check out the dyno and time slip section to see what people are making on a given setup.
Hope that helps a little....someone who has a turbo carb setup get in here!
Oh, and I would also invest in a meth/water injection system for reliability....

 

To be on the safe side I would stick with a 66+ mm turbo( To4R,T66 Etc). It can be done on a smaller turbo, but you've got to really fine tune everything for that. I wouldn't be too concentrated on a number either, you would be surprised at how many dynos give BS numbers. I have seen a lot of dyno sheets throw around on here that are physically impossible to do. There is nothing to be concerned with in running a carb; what I would be concerned with his running apex seals that a friend made...

 

eh, i've had that comment made several times by my other friends, but rest assured, these one-off apex seals are mint. the guy who machined them (friend bob) has been a machinist for 30+ yrs and in the rotary game for about 15. my good friend mike, who did my porting and rebuild, has 15 years porting and building these motors. he has the set-up i'm aiming for being carbed and such. his turbo was an ebay unit from xs engineering. now, i know many have their doubts for ebay knock-offs, but he puts 20psi through it for his daily commute with no cracking, creep, or leaks. can't really tell what size it is or the specs, but it's a decent sized turbo. he suggested a turbo with an a/r of about 1.00 or a lil more, as this car will be put for drag use more than anything else, so boost doesn't need to kick in till around 5 or 6k. so, having suggested a gt40/42 or larger, i'm safe to assume a gt45 would be a good candidate for what i'm looking for? if that's the case, another friend is looking to sell his to downsize as he wants his drag car to be a lil more streetable...

 

I would go with a GT40 or 42. For the power goals you stated, either will do the trick, and then some. On our setup, using a GT4202, we made 450 around 14-15 psi, and 519 at 18.5, and 620 at 24. A GT45 would just introduce unwanted lag in my opinion.

 

A GT40 would be the right choice. What type of exhaust manifold are you going to run? Brand, twin scroll, single scroll?

 

after doing a bit more homework, it seems as though a gt40 or 42 seems to be the more appropriate choice. a gt45 might be a bit much for me at the current moment, although it would be a dream. As for a manifold, that's also in the works of my thought process. Between twin and single scroll, is there an advantage of one over the other? I've read every thread and post in the single turbo section, and haven't come across any information in regards to scrolls. Also highly considering a water/methanol injection system as jdmfantasy had suggested, after reading up on the RR water injection helping put out about 600hp on pump gas, sounds like a promising add-on.

 

Twin scroll will give quicker spool but be a slight hinderance in the higher RPM. If youre looking for 450whp, I would say something like a twin scroll 3076R or35R, or something similar. A 42R is major overkill, Ive seen 1000+whp on those.

 

My personal choice would be a GT40 with meth injection.

 

One thing to note, I don't know if I had mentioned it but if not, my bad, is that this car will be more for drag use than anything else. So a hinderance in higher rpm's is something i'd try to avoid very much. 500 hp is more of a "just for now" setting that i'm looking for, so I can become more familiar with the output the car will make, and pass after pass, tune after tune, it will gradually increase. If 1000 hp is what a 42r is capable of, then I'll want to be there even more. The car will see an occasional sunday drive to town to give a few honda acquaintances a show. of course, i wouldn't be running 30 psi on the street, that's just stupid. 15 would be plenty enough, and that would probably still be around 400, i assume...

 

JDM, was 24 psi the most you put the GT42 through? And for curiosity reasons, what were the specs on it? And no matter which one I grab up, a w/m injection system will be employed as all i see from it are benefits to be reaped.

Guys, thanks much for all your input, it's greatly appreciated!

 

It wont be that much hinderance, but spool will be noticeably better. If you have money to upgrade later, start out with something smaller and work your way up. If you want to do it once and thats it, go big right away.