# 300ZXT how much horsepower more per PSI



## asleepz (Feb 24, 2004)

I wanna know about how much horsepower I can expect from each PSI I add to the engine


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## morepower2 (Apr 19, 2002)

SKD_Tech said:


> I wanna know about how much horsepower I can expect from each PSI I add to the engine


The question is impossible to answer simply. It depends upon backpressure, compressor and turbine efficency as well as how well the engines tuned, fuel quality and where in the compressor map you are dwelling.

It can go from almost nothing to as much as 30-40 hp at the extremes.


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## Zen31ZR (Mar 24, 2004)

morepower2 said:


> The question is impossible to answer simply. It depends upon backpressure, compressor and turbine efficency as well as how well the engines tuned, fuel quality and where in the compressor map you are dwelling.
> 
> It can go from almost nothing to as much as 30-40 hp at the extremes.


 I read somewhere that 1 psi = about 11 Hp. Probably 10 or 9 on a dead stock car , and the 160-200 Hp difference between the non-turbo and the factory 5 psi on the turbo Zs would seem to bear this out.


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## asleepz (Feb 24, 2004)

well it can't be a factory of 5 because I am running 7. Is 5 what they ran on the baseline for the 87? If so I might be putting out up to 220 FHP... Well hmmm so if I raise it 4 psi like I want it should be about 40 horsies on the flywheel


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## JAMESZ (Mar 12, 2004)

You can't just say for every psi you will gain this much hp. It all depends on turbo efficiency. Going from stock boost to 8 psi is around 20 more RWHP.But going to 12psi will only net you another 10 rwhp. It is all related to heat and turbo efficiency. The reason you stop making so much power at a certain point is because heat increases and efficiency decreases. This is shown with the power increases from 6.7-8-12psi. Basically above 10psi the turbo is producing more heat then power. Get an intercooler though and you can turn up the boost with ample power increases as long as you can supply enough fuel. Of course at about 14.5psi your turbo is maxed out completely and after this point you will reach dangerous inlet temperatures and dangerous backpressure associated with the compressor and exhaust manifold. This is not taking in affect the exhaust system itself. Just merely the manifold and turbocharger.

Even though Ballistik will say otherwise I am adament on the fact that you will need an intercooler to sustain above 8psi for long durations. During the winter time 10psi should be safe without an intercooler but any other time of the year I would suggest only running 8psi if you do not have an intercooler. You can of course turn up the boost for short durations of time (like a race) without any issues. Also since I am on the subject without computer and fuel system upgrades I would not suggest turning the boost up beyond 14psi at any time.


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## Zen31ZR (Mar 24, 2004)

SKD_Tech said:


> well it can't be a factory of 5 because I am running 7. Is 5 what they ran on the baseline for the 87? If so I might be putting out up to 220 FHP... Well hmmm so if I raise it 4 psi like I want it should be about 40 horsies on the flywheel


 5 psi in 1985 , I beleive. At some point they switched to a T25 turbo boosting more , with a resulting 5 more Hp (In 1989 actually) .........  When I hooked my Autometer up to my car , it read 5 psi at full boost , so I'm assuming most Z31s are doing the same. Can't confirm it anywhere , however. 

I will have to disagree with what JamesZ has said about boost pressure though , Z31.com states that 14.5 psi is the efficiency limit for the T3 , so therefore me running at 15 psi is not too far out of it's range. The stock limits are fairly high on everything , you should be able to get 270-280+ whp out of everything , this with no upgrades at _ALL_.


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## asleepz (Feb 24, 2004)

so you suspect that you are running around 270-280 WHP with the boost you are running? No intercooler? Are you just using premium pump gas?


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## Zen31ZR (Mar 24, 2004)

SKD_Tech said:


> so you suspect that you are running around 270-280 WHP with the boost you are running? No intercooler? Are you just using premium pump gas?


 I'd like to think so but I haven't dynoed yet , so it's all conjecture at this point. And all I use is 91 octane , which is the highest common _street_ octane we have. You can buy up to 116 at some scattered stations , all of which are over 20 miles from me..........


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## asleepz (Feb 24, 2004)

hell I would just use that octane booster stuff. That should work shouldn't it


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## Zen31ZR (Mar 24, 2004)

SKD_Tech said:


> hell I would just use that octane booster stuff. That should work shouldn't it


 Not as well as you might think. The typical bottle of octane booster will raise your octane by 1/10th of 1 point. Even the infamous _Outlaw_ brand only raises it by about 1/2 a point , if that. So , if you want 95 or higher octane........you do the math.


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## JAMESZ (Mar 12, 2004)

I would say 270-300 flywheel hp would be the max limits for the stock fuel system, turbo, and computer. I can achieve a high 13 (if not a tad bit faster) with only 230-240rwhp.


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## asleepz (Feb 24, 2004)

how much boost are you running


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## Zen31ZR (Mar 24, 2004)

JAMESZ said:


> I would say 270-300 flywheel hp would be the max limits for the stock fuel system, turbo, and computer.


 Z31.com agrees. So do I , for the most part , but I think the turbo and the ECU can handle more. But the fuel pump definitely needs to be upgraded. A Walbro 255 is sufficient , and out pumps the TT 300Z/GTR fuel pump by a few lph.


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## Marc Z31 (Jul 25, 2004)

damn, I bet you could go faster... like 12.9 @ 110 if you had a T3 and an FMU

On a T25, don't run more than about 10-12 psi. You can see about 240 rwhp if you are lucky. If you have a few bolt ons or bolt offs (exhaust and intake pieces) you could make about 260-275 rwhp and 310-340 Lb Ft.


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## Zen31ZR (Mar 24, 2004)

Marc Z31 said:


> damn, I bet you could go faster... like 12.9 @ 110 if you had a T3 and an FMU
> 
> On a T25, don't run more than about 10-12 psi. You can see about 240 rwhp if you are lucky. If you have a few bolt ons or bolt offs (exhaust and intake pieces) you could make about 260-275 rwhp and 310-340 Lb Ft.


 Actually I don't think the T25 turbos were installed til 89.


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## JAMESZ (Mar 12, 2004)

88 and 89 had the T25.


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## Zen31ZR (Mar 24, 2004)

JAMESZ said:


> 88 and 89 had the T25.


 Yeah , SKD's got an 87 , which is why I mentioned it.......


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## Marc Z31 (Jul 25, 2004)

88 and 89, yeah. 87's are really cool because it is the w series engines with the better T3 turbo. Bad part is the cars are more than 300 pounds heavier than 84's


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## asleepz (Feb 24, 2004)

what is different with the W series


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## Zen31ZR (Mar 24, 2004)

SKD_Tech said:


> what is different with the W series


 Hmm heavier rods , I think. Aka , more boost capable. Marc knows more about those than I do , though.


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## asleepz (Feb 24, 2004)

hmm more boost capable


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## Nissani (Aug 16, 2004)

SKD_Tech said:


> I wanna know about how much horsepower I can expect from each PSI I add to the engine



you can expect 12-15...and 15 is being generous...that is of course assuming you've got a motor in good condition and you don't have stock intake and exhaust...


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## hondakillerZX (Aug 16, 2004)

ive got an 87 what do you guys think is the highest boost i can safely run in everyday driving, and if the turbo heats up it will be on my guage right.


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## Zen31ZR (Mar 24, 2004)

hondakillerZX said:


> ive got an 87 what do you guys think is the highest boost i can safely run in everyday driving, and if the turbo heats up it will be on my guage right.


Nope , by the time the guages read any heat problems , it's already too late. I'd say you can run at least 10 psi with no issues.


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## Nissani (Aug 16, 2004)

with stock injectors and computer 12.5 psi...but everyday driving would not be advisable with 12.5 psi.......i agree with 10


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## JAMESZ (Mar 12, 2004)

As always I will chime in with 8psi but you don't have to listen to me or the majority of the performance world when we say 8psi is the safe everyday limit when not intercooled.


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## Nissani (Aug 16, 2004)

he's right you don't have to listen to us but don't post saying you need a new motor after reading this and ignoring it either....


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## 0341TODD (Nov 15, 2003)

Im running 11- 12 everyday and I havent ever had any problems. I live in SW Fl too and its hot as hell here. This weekend I was going to try to run my hardpipes and intercooler, but Im still debating doing an aquamist instead of an intercooler. Balliztik made me a little paranoid of the top mount thing I was planning and I would really like to retain a/c ( whenever I get off my ass and send Eric money...........inside joke


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## Nissani (Aug 16, 2004)

i suppose it wouldn't be a problem... but i do know 12.5 is the limit for stock computer and injectors...


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## Zen31ZR (Mar 24, 2004)

Nissani said:


> i suppose it wouldn't be a problem... but i do know 12.5 is the limit for stock computer and injectors...


I ran a flat 15 psi for over 6 months with absolutely no issues. I don't recommend doing it for long distances , as I've stated before , but it seems as though the stated limits have been purposely kept low. The ECU didn't seem to mind the extra airflow , neither did the turbo. I'll be exploring the limits of the stock equipment later on , I think it's about time we got some real numbers on these cars true capabilities. My 13.9 was run on a severe budget and ghetto mods , I don't doubt with a little money spent in the right areas the car can hit mid-low 12s without ever touching the ECU or the turbo......


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## hondakillerZX (Aug 16, 2004)

if i get an intercooler(im thinking hks) then how much can i raise my boost on a stock turbo


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## Marc Z31 (Jul 25, 2004)

W-series engine has 8.3:1 compression (ratther than 7.8:1)
it has better cooling passages
it has larger cams (especially the japanese and euro spec)
it has floating wrist pins, rather than fixed
it is an overall stronger engine

I ran 16 psi non intercooled testing the limits and trying to blow it up (I had a better badder J-spec W-series lying around) It never flinched. I popped a radiator hose racing a 12 second fox body mustang (5.0 style) and dicided I had abused the damn thing enough.

The factory T3 turbo loses efficiency at 12.5 psi. This doesn't mean you will not make more power at a higher pressure, it just means it doesn't make as much Hp per extra pound of boost. I would recomend running 12.5 psi non intercooled, and 14-16 intercooled. If you are running more than 12 ish psi, I would recomend getting something as far as fuel goes. A Z32 twin turbo fuel pump drops right in, or you can get a walbro. AN FMU (fuel managment unit) is a ghetto cheap band-aid, but it works. A greddy AVC-R or APEXi S-AFC (electronic fuel controlling devices) and a good fuel pressure regulator will work as well, but you are still using stock injectors, it needs to be tuned, and it is an electronic band-aid. If you want more info, or want to know the RIGHT way to controll fuel, e-mail me [email protected]


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## KungFuGrandpa (Aug 23, 2004)

man i just busted both head gaskest on my Z running 14.5psi w/ 9.0 pistons. will puttng the dished pistons back in increase horsepower or decrease it. W/ the 9.0 in it has hella take off power and looses traction when the turbo spools up  i would like to keep the power but i dont want to be replacing head gaskets all the time in it


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## morepower2 (Apr 19, 2002)

[email protected] said:


> Z31.com agrees. So do I , for the most part , but I think the turbo and the ECU can handle more. But the fuel pump definitely needs to be upgraded. A Walbro 255 is sufficient , and out pumps the TT 300Z/GTR fuel pump by a few lph.


Actualy the TT pump out flows the walburo and GTR by a little. I have the flow curves if you want.


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## morepower2 (Apr 19, 2002)

Marc Z31 said:


> W-series engine has 8.3:1 compression (ratther than 7.8:1)
> it has better cooling passages
> it has larger cams (especially the japanese and euro spec)
> it has floating wrist pins, rather than fixed
> ...


I think different intake ports as well. Smaller and straighter. As far as strength, I don't think there is any difference. The cooling differences are the addtion of some stream holes in the block deck, head and head gasket.

In racing at least, there it is not considered to cool better.

You have to be careful with the AFC, if you trim fuel too much, you can end up in a more advanced cell on the spark map. This makes a AFC good for only minor tuning and you must be careful for signs of overadvanced timing.

I would tend just to tweak an FMU using a wide band to monitor the A/F ratio.

What I would really do if I had little money is JWT ECU, JWT POP, Manual boost control set to 14 psi, blocked of POV, Starion Intercooler from junkyard and a 3' exhaust, walburo fuel pump, recirculated compressor bypass valve, Nismo adjustable pressure regulator.


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## morepower2 (Apr 19, 2002)

KungFuGrandpa said:


> man i just busted both head gaskest on my Z running 14.5psi w/ 9.0 pistons. will puttng the dished pistons back in increase horsepower or decrease it. W/ the 9.0 in it has hella take off power and looses traction when the turbo spools up  i would like to keep the power but i dont want to be replacing head gaskets all the time in it


With proper engine managment you can. Heck with a proper everything you can have amazing power and bottom end.

Hardly anyone relalizes the pontential of the VG30ET


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## JAMESZ (Mar 12, 2004)

morepower2 said:


> Actualy the TT pump out flows the walburo and GTR by a little. I have the flow curves if you want.


This is why I have the TT pump. :cheers: It really does flow well. It is quite noisy but I don't really care about that.


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## JAMESZ (Mar 12, 2004)

I'm not so sure about the Starion intercooler; yes it will work but several people have had issues with these intercoolers down the road. I would only really trust the Supra TT intercooler (unless buying aftermarket of course). But then again the Spearco unit is my favorite even though it is quite pricy.
A Z31T with the Nismo race heads, custom schnieder cams, JWT ecu, 555cc injectors, TT fuel pump, upgraded turbo, VG30DETT crank with aftermarket VG30DE forged rods and forged pistons, custom reworked plenum, 3 inch exhaust, Cobra MAF, a good ignition, Fidanza lightweight flywheel and exedy clutch, spearco intercooler, and better valves and valve springs. Of course it needs a good radiator and the HKS exhaust manifold. Of wait I think those are the parts going on my car heh. I need to finish deciding about the cams and the turbo and start ordering parts. of course I am doing alot more work then just this I didn't list everything. I am not sure when the car will be done but it will be awhile. It is just sitting in my garage. I am in the process of getting the Nismo 350Z wheels and I am going to redo everything chasis and suspension wise and even upgrade the brakes some more.


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## morepower2 (Apr 19, 2002)

JAMESZ said:


> I'm not so sure about the Starion intercooler; yes it will work but several people have had issues with these intercoolers down the road. I would only really trust the Supra TT intercooler (unless buying aftermarket of course). But then again the Spearco unit is my favorite even though it is quite pricy.
> A Z31T with the Nismo race heads, custom schnieder cams, JWT ecu, 555cc injectors, TT fuel pump, upgraded turbo, VG30DETT crank with aftermarket VG30DE forged rods and forged pistons, custom reworked plenum, 3 inch exhaust, Cobra MAF, a good ignition, Fidanza lightweight flywheel and exedy clutch, spearco intercooler, and better valves and valve springs. Of course it needs a good radiator and the HKS exhaust manifold. Of wait I think those are the parts going on my car heh. I need to finish deciding about the cams and the turbo and start ordering parts. of course I am doing alot more work then just this I didn't list everything. I am not sure when the car will be done but it will be awhile. It is just sitting in my garage. I am in the process of getting the Nismo 350Z wheels and I am going to redo everything chasis and suspension wise and even upgrade the brakes some more.


Are Supra TT intercoolers easy to find in junkyards/used nowdays? What goes wrong with starion i/c's? I know a lot of people that use them with no issues.

Nismo does not make VG30E race heads. A ported head is avlaible through Nissan Motorsports but that is not connected to Nismo.

I would recomend a VG33 over a VG30. The torque produced when boosted is amazing.


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## Marc Z31 (Jul 25, 2004)

What I would really do if I had little money is JWT ECU, JWT POP, Manual boost control set to 14 psi, blocked of POV, Starion Intercooler from junkyard and a 3' exhaust, walburo fuel pump, recirculated compressor bypass valve, Nismo adjustable pressure regulator.[/QUOTE]
Damn, that sounds like what I have. I have the TT supra intercooler though.


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## Marc Z31 (Jul 25, 2004)

morepower2 said:


> Are Supra TT intercoolers easy to find in junkyards/used nowdays? What goes wrong with starion i/c's? I know a lot of people that use them with no issues.
> 
> Nismo does not make VG30E race heads. A ported head is avlaible through Nissan Motorsports but that is not connected to Nismo.
> 
> I would recomend a VG33 over a VG30. The torque produced when boosted is amazing.


I have a supra IC for sale-$100
The starion cores flow very poorly, and power is limited. I'd really like a trick liquid/air IC setup... I live in texas, so ambient air is not that cool. The 33 would be the block to build, as you get 10% more power for free. I just need to find the pathfinder upper plenum and distributor.


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## morepower2 (Apr 19, 2002)

Marc Z31 said:


> I have a supra IC for sale-$100
> The starion cores flow very poorly, and power is limited. I'd really like a trick liquid/air IC setup... I live in texas, so ambient air is not that cool. The 33 would be the block to build, as you get 10% more power for free. I just need to find the pathfinder upper plenum and distributor.


Do you mostly get a supra core from supra guys who have upgraded?


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## Zen31ZR (Mar 24, 2004)

morepower2 said:


> Actualy the TT pump out flows the walburo and GTR by a little. I have the flow curves if you want.


 I'll take your word for it. Pretty sure someone here or on the net told me otherwise , but who knows.


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## morepower2 (Apr 19, 2002)

[email protected] said:


> I'll take your word for it. Pretty sure someone here or on the net told me otherwise , but who knows.


I have an engineer buddy at walburo that tested it and he sent me the data. The 255 is a lot cheaper though and the flow differences is very small between the two.


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## Zen31ZR (Mar 24, 2004)

morepower2 said:


> I have an engineer buddy at walburo that tested it and he sent me the data. The 255 is a lot cheaper though and the flow differences is very small between the two.


 Probably just stick with the Walbro idea then. It should support the Hp I have in mind anyway. Do the fuel line sizes need to be raised to get around 450-500 Hp? I know this is an issue with certain other makes of cars.


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## morepower2 (Apr 19, 2002)

[email protected] said:


> Probably just stick with the Walbro idea then. It should support the Hp I have in mind anyway. Do the fuel line sizes need to be raised to get around 450-500 Hp? I know this is an issue with certain other makes of cars.


No you can use the stock fuel line.


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## Marc Z31 (Jul 25, 2004)

If you wanted more than 500 fhp, you will need larger lines... and a better bottom end.


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## hondakillerZX (Aug 16, 2004)

do any of you know where i could get a better exhaust manifold


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## Zen31ZR (Mar 24, 2004)

Marc Z31 said:


> If you wanted more than 500 fhp, you will need larger lines... and a better bottom end.


 I know about cryoing and shot peening the crank , what else is there to do.


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## TheJackal (Aug 18, 2004)

[email protected] said:


> I know about cryoing and shot peening the crank , what else is there to do.


i think he means forged pistons and rods


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## Zen31ZR (Mar 24, 2004)

TheJackal said:


> i think he means forged pistons and rods


 That too , yep.


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## JAMESZ (Mar 12, 2004)

And a forged crank. Somewhere around 450-500RWHP the crank isn't going to be happy. Get forged, crank, rods, and pistons at about 450RWHP (pistons maybe around 400RWHP). The bottom end is strong but because of all the cast parts under high power the internals will have issues.


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## Zen31ZR (Mar 24, 2004)

JAMESZ said:


> And a forged crank. Somewhere around 450-500RWHP the crank isn't going to be happy. Get forged, crank, rods, and pistons at about 450RWHP (pistons maybe around 400RWHP). The bottom end is strong but because of all the cast parts under high power the internals will have issues.


 MarcZ31 supposedly had his stock crank shot peened and cryoed , I just want to confirm that..........


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## morepower2 (Apr 19, 2002)

Marc Z31 said:


> If you wanted more than 500 fhp, you will need larger lines... and a better bottom end.


No you don't. You can use the stock lines to over 500 whp. Stock prepped rods can work for over 500 hp for some time at least.

Prepped is beam polished and shotpeened. The stock crank is fine, just deburring and shotpeening is needed.


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## morepower2 (Apr 19, 2002)

hondakillerZX said:


> do any of you know where i could get a better exhaust manifold


Try to find an HKS with an external wastegate flange and a TO4 bolt pattern. You can only find them used.


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