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How to push 20psi out of a 15g???

740Lover

New member
Joined
Nov 13, 2021
Hi! I have a ‘92 740+T with your standard 15g swap running on about 5psi to keep things safe. Everything is pretty much stock excluding a 2” exhaust and aftermarket air filter. I’d like to eventually crank things up a bit but want to do so in a reliable manner. Im already planning on getting ARP head studs and a Cometic metal head gasket to keep things nice n tight but I’m curious what sort of injectors I should run? I was considering running some Deatschwerks 650cc injectors but, this being my first turbocharged car, I’m not sure how much boost 650cc’s can handle. I read that a stock b230ft with a 13c turbo can reliably run 12-13psi so I’m not necessarily afraid of pushing my engine with this 15g but I’d rather not accidentally detonate my first 740. Since this will still be a daily driver I’m not trying to run it on 20psi all the time; but I’d like to be able to crank it up reliably when wanted. Also how much can the stock fuel rail handle? Or should I just upgrade that too while I’m at it..? If there’s anything else I’m missing please don’t be afraid to let me know! This is my still my first year owning this car and I’m trying to learn as much as possible and do this in the most correct way that I can. Thanks !
 
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I did it with E85 gasoline and 750cc injectors and 3 inch amm and straight pipe out the side and NPR intercooler and A cam and fuel and ignition chips. 5 speed manual trans 3.31 ratio rear third gear pull.

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The thing about injectors and LH 2.4 is the injector size has to match the AMM size. 550cc works good with 3 inch AMM and gasoline. 750cc works good with 3 inch AMM and E85. Other then that you can adjust the injector constants in the fuel bin instead if you can or can buy a custom chip. So your 650cc injectors would be way to rich or to much fuel as they say. Something else to consider is if you run E85 you can overfuel it and you won't loose power like you would with gasoline.

Simon
 
Hi! I have a ‘92 740+T with your standard 15g swap running on about 5psi to keep things safe. Everything is pretty much stock excluding a 2” exhaust and aftermarket air filter. I’d like to eventually crank things up a bit but want to do so in a reliable manner. Im already planning on getting ARP head studs and a Cometic metal head gasket to keep things nice n tight but I’m curious what sort of injectors I should run? I was considering running some Deatschwerks 650cc injectors but, this being my first turbocharged car, I’m not sure how much boost 650cc’s can handle. I read that a stock b230ft with a 13c turbo can reliably run 12-13psi so I’m not necessarily afraid of pushing my engine with this 15g but I’d rather not accidentally detonate my first 740. Since this will still be a daily driver I’m not trying to run it on 20psi all the time; but I’d like to be able to crank it up reliably when wanted. If there’s anything else I’m missing please don’t be afraid to let me know! This is my still my first year owning this car and I’m trying to learn as much as possible and do this in the most correct way that I can. Thanks !

Redblocks don't have the headgasket issues you'll find with a lot of motors *cough cough, m20* you don't need headstuds or MLS gaskets for a 15g.

As far as learning what supporting mods to do give turbobricks a search, there is decades of info on here that can both directly answer the question and inform you of thing you never would have thought of.
 
I did it with E85 gasoline and 750cc injectors and 3 inch amm and straight pipe out the side and NPR intercooler and A cam and fuel and ignition chips. 5 speed manual trans 3.31 ratio rear third gear pull.

<iframe width="560" height="315" src="https://www.youtube.com/embed/AS81r8c_3A8" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

<iframe width="560" height="315" src="https://www.youtube.com/embed/bawZahBJvnk" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

The thing about injectors and LH 2.4 is the injector size has to match the AMM size. 550cc works good with 3 inch AMM and gasoline. 750cc works good with 3 inch AMM and E85. Other then that you can adjust the injector constants in the fuel bin instead if you can or can buy a custom chip. So your 650cc injectors would be way to rich or to much fuel as they say. Something else to consider is if you run E85 you can overfuel it and you won't loose power like you would with gasoline.

Simon
Hmmm.. running E85? Doesn?t sound like a bad idea at all. Roughly how expensive is it to do a job like this in a 740? Sounds worth the investment if I can run richer injectors with less power loss. I kinda love a rich setup :rofl:
 
Redblocks don't have the headgasket issues you'll find with a lot of motors *cough cough, m20* you don't need headstuds or MLS gaskets for a 15g.

As far as learning what supporting mods to do give turbobricks a search, there is decades of info on here that can both directly answer the question and inform you of thing you never would have thought of.

Good to know ! So you believe the stock gasket and head bolts will handle 20psi alright? Also I most definitely will. I?ve been trying to here and there, there?s just so much that I feel like I?m in a storm of info ! Slowly getting more acquainted with how to navigate through the site though :D
 
Good to know ! So you believe the stock gasket and head bolts will handle 20psi alright? Also I most definitely will. I’ve been trying to here and there, there’s just so much that I feel like I’m in a storm of info ! Slowly getting more acquainted with how to navigate through the site though :D
It's not about the boost but cylinder pressure. Stock gasket and bolts can handle more than 400hp.
 
That turbo is too small for 20 psi. It'll do it, but won't really make more power. You need to keep the intake air cold, add fuel or meth injection to over spin that little turbo.
 
Having played with the small Mitsu turbos in the past, there is little point in running over 1 bar boost - they just are not efficient for that use. Running even 7-8psi on the 15g should make for a good ride!

As sbabbs has illustrated, it can be done, but on a NA that was +T'd that you don't want to break?? Not a great idea.
 
You don't really need bigger injectors to run up to 15psi on a 15G. Even on a 16T (which isn't that much bigger than a 15G) stock injectors are fine to 0.9 bar (about 14psi).

If you go to bigger injectors then you're best off chipping the ecu to suit (and resistor mod required might be required too). Rather than dicking about with a 3" MAF or trying to hack it.
 
650's on a 4 cyl are good for 380hp on gas with a .52 BSFC @ 80% d/c.

I agree that the turbo size is small for 20# boost, exhaust back pressure will likely tip it over.

I had to switch to a .60 AR turbine housing.
 
You don't really need bigger injectors to run up to 15psi on a 15G. Even on a 16T (which isn't that much bigger than a 15G) stock injectors are fine to 0.9 bar (about 14psi).

I too can confirm that stock injectors are plenty with a 16T at 12psi.
I'm running this very setup on my 940 + chips and a KL Racing Intercooler.
 
My sons 240 we are running, 15g- TLAO chips- B cam- 3 inch ex. and aftermarket i.c. We went to the track. Runs 13.80s @ 102. We tried 16-20lbs of boost. Ran its best times at 16lbs never gained any mph with 18 or 20.
 
I always ran my 16T with a kl racing intercooler, bigger injectors (470cc) and a chip. I plugged the hose coming from the turbo to the wastegate so it never opened. 3 inch exhaust also helps spool up that turbo, let it breathe! Pretty sure 21 psi was the max I could get out of that turbo. But the HG blew so guess I should've turned it down to 20 psi:lol:

I started at around 0.8 bar (11.6 psi) but I gradually increased, 15-16 psi was the most reliable though. If you run it at max boost the car also becomes very slow on a warm day compared to a colder day.
 
Five star post! ^ That is the boost addicts progression. :cool: It's so much fun to do keep trying more boost. Then I old man copped out and keep it around 12psi or so. :oops:
 
I was curious as to whether I would benefit from water/meth injection at higher boost levels so I purchased four of those cheap Chinese Temp sensors. Put one just after the air filter, another after the turbo, one after the intercooler and one in the inlet manifold. Even if they aren't super accurate I can get a comparative idea of what's going on.
However, one question I haven't been able to answer is how hot is too hot? - at what inlet temp would water/meth be beneficial?
Tim
 
I don't know what number to give you. But you don't want air temps after the intercooler to be too much higher than ambient.

The water/meth injection is mainly going to be used to bring down combustion chamber temps not air intake temps.
 
Here is the information you need:
http://www.turbobricks.org/forums/showthread.php?t=271886&styleid=1.

Don't upgrade things you don't have too.

The most important things you need too think about are:
How much power do you want?
What compression ratio does your motor have?(I would recommend using 9.3:1 or lower and use orginal squish or 3mm squish nothing between like 2 mm for example).
What camshaft do you have?(I recommend k or kg004
How much power does your fuel pump support?
How much power do your injectors support?
Do your current injectors have uneven flow?
Do you want 250 hp that 15G supplies with

Things you probably have to do:
Get a big and cheap intercooler from klracing if you don't have an intercooler.
Get a chip that fits your final setup or setup a megasquirt 2 standalone ECU(I personally don't understand why anyone has a custom setup with OEM ECU).
Setup a 2.5 inch exhaust system minimum.

You can get up to 500hp with this block and internals if you want(if it has 13mm rods).

If you want better information on these engines go to savarturbo.se and read what jens gustavson writes about red blocks.
 
Far as I know Greg Ervin holds the 15g quarter mile world record at 12.60 and I am right behind him at 12.61 done 10 years ago at PIR when he came up one friday and I helped him swap out his 13c for a 15g and then we went drag racing. So anybody else go any quicker or faster? Any more advice on how to beat that? Ha ah hah ha har har. I ain't telling til you beat that time..
 
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