Sorta useless post, how much power per PSI of boost (at least, in my case)

[Guest bastaad525]

Hey all... well this may be a useless post for many and maybe, hopefully, at least a slightly informative post for a few... it will be a LONG post as you can always expect from me, that's for sure anyways, just an observation of my own personal experiences.

 

Now, obviously this same pattern will most likely not apply to everyone. It's probably important to keep in mind my particular setup (details in signature at bottom of post) to maybe help determine if these observations COULD apply to your car as well.

 

The reason I wanted to point this out is that I seem to remember it being a sort of 'rule of thumb' that you could expect 5-10 hp or ft lbs of torque increase for every 1 psi of boost increase, and just wanted to see how this actually played out in my own case since I've dyno tested my car SEVERAL times during the process of building it up and turning up the boost. In my case, that rule seems to be quite a ways off, same thing with the rule that power increase from boost increase with the stock T3 turbo is severely curtailed after 10psi, as I seemed to get very good power increases all the way up to 14psi.

 

Now, I'm only going to use data gathered from the times I dynoed on a Dynojet dyno (all on the same model dynojet)... if anyone wants to debate how even going to the same dyno on different days or whatever could have affected these numbers well oh well this isn't some kind of exacting science and I'm not claiming this is now the new 'rule' that all must heed, just showing my own personal experience.

 

 

Anyways, here we go.....

 

 

First, dyno of a 100% BONE STOCK 280zx turbo, 7psi of boost:

 

- 150hp @ 5500rpm

- 170ft lbs @ 3000 rpm

 

Next, stock everything with boost turned up to 10psi:

 

- 200hp @ 5300rpm (50hp from 3 psi, or about 17hp per psi)

- 230ft lbs @ 3000 rpm (a 60 ft lb increase from 3psi of boost, or 20ftlbs per psi!)

 

Next, added an intercooler and upgraded fuel pump, everything else left the same, boost turned up to 12psi, running very lean above 4k rpm, didn't rev above 5000rpm during the pulls, hence the hp didn't increase much at all:

 

- 210hp @ 5000rpm (10hp from 2 psi but again, running way too lean... it's worth nothing though that the power curve was almost perfectly flat from 4000-5500rpm and was significanly increased thru most of the powerband)

- 270ft lbs @ 3000 rpm (40 ft lbs from 2 additional psi, again, 20ft lbs per psi)

 

Next, added an adjustable FPR to raise fuel pressure and get air/fuel ratio back down to 11-12:1, boost raised to 14psi:

 

- 233hp @ 4200rpm (23hp from 2 psi, running rich enough now but on this run boost was falling off as revs increased, from 14psi at 3k to 11psi at 6k, now I've fixed it so boost stays steady to redline, estimating maybe about 240-245rwhp? I also think the falling boost is why hp peaked so much earlier than it did on the previous runs. IF my estimate is correct, that's still a 30-35hp increase from 2psi)

- 300 ft lbs @ 3000 rpm (30 ft lbs from 2 additional psi, 15fl lbs per psi... I guess this might be showing right about when the 'point of diminishing returns really starts with the stock T3 turbo?)

 

Obviously, my increases in hp were not as significant as the torque increase. Even though low end torque picked up TREMENDOUSLY with each boost increase, torque above 4000-4500 would fall off faster and faster as boost went up... at 10psi the torque curve was very flat and was almost the same at 5500rpm as it was at 3000rpm, but at 14psi the torque dropped IMMENSELY after 4000rpm, losing about 100ft lbs from 4k to 6k rpm (again, partly due to the boost falling off, but even at 12psi steady to redline the fall off was pretty severe). I dunno if this is due to a restriction or problem in my setup or what, or is just the nature of the L28 or the T3. HP started at about 150hp at 7psi, and ended at about 240hp at 14psi, so 'only' a ~90 hp increase (90 hp for 7psi, average of 13hp per psi increase, still more than the 5-10hp rule of thumb), vs. a whopping 130ft lbs increase in torque from 7 to 14psi of boost.

 

So there you have... hopefully not TOO much of a waste of anyones time to read just bored and passing time til my wife comes home. But after looking back over all those dyno results I find myself wanting to say "GO T3!!!" ~20hp/ftlbs per psi is pretty darn nice IMO

[VinhZXT]

Wow .. This makes me want to take my newly rebuild Z to the Dyno. Currently I have the stock T3 in there along with all the goodies: Good IC, 3 " exhaust, 3 angles valve jobs, RR FPR but I want to get use to the T3 before I put in the T3/T4 and see a difference. I guess the best way to find out is to go to a Dyno... I also want to go to a weight station to get the weight-in for my Z.

[COZY Z COLE]

I, for one, find it interesting and if your rule of thumb ( 5-10 hp/lbs for each 1 psi of boost increase ) is true for any type boosted engine set-up, I went from 6lbs boost to 10lbs boost in my set-up and gained 58 ftlbs of torque. This is almost 15 ftlbs per 1psi increase in boost. This is shown in the following thread. I also used the same dynojet shop for all my runs and I'm in the high 30's on pulls....

 

http://forums.hybridz.org/showthread.php?t=101200

 

 

LARRY

[materchan]

excelent post!!. i think you should invest in a 3" mandrel bent exhaust, IMHO thats where oyur restriction lies. my 3" exhust just dumps near the differential. at 8psi with a Gtech i got 200hp. not as accurate as a dyno but it might show somthing

[Z Driver]

excelent post!!. i think you should invest in a 3" mandrel bent exhaust, IMHO thats where oyur restriction lies. my 3" exhust just dumps near the differential. at 8psi with a Gtech i got 200hp. not as accurate as a dyno but it might show somthing

That seems pretty close. I've seen dyno graphs showing 180 RWHP at stock boost with a 3" exhaust on a stock motor.

[EZ-E]

That was probably on Jeffp's site about his car, he put his 3 inch system against a stock turbo ZX, and it gained 20 hp and like 18 ft lbs of torque to the wheels just from that exhaust.

 

I call that a great gain.

[Guest bastaad525]

I' date=' for one, find it interesting and if your rule of thumb ( 5-10 hp/lbs for each 1 psi of boost increase ) is true for any type boosted engine set-up, I went from 6lbs boost to 10lbs boost in my set-up and gained 58 ftlbs of torque. This is almost 15 ftlbs per 1psi increase in boost. This is shown in the following thread. I also used the same dynojet shop for all my runs and I'm in the high 30's on pulls....

 

http://forums.hybridz.org/showthread.php?t=101200

 

 

LARRY[/quote']

 

 

Nope see that was my point, it seems the usual 5-10hp 'rule of thumb' that most people spout does NOT seem to apply, in my case, and also in the case of quite a few other guys I've seen post their turbo dyno charts on here. I was gettign 15ft lbs or MORE, and hp was from 13-17hp increase per psi.

 

 

About the dyno charts posted on Jeffp's site, one thing I wonder about, is if that '100% bone stock 280zxt' had an aftermarket boost gauge or if they were even watching what the boost was doing. It's pretty common knowledge that freeing up the exhaust by a significant amount will result in an increase in boost, w/o changing the wastegate setting or boost controller setting. I"m thinking this probably accounts for part of why in that particular case he gained such a big improvement in power and torque. Of course the bigger exhaust made a difference, I'm not doubting that, just thinking it didn't make ALL of the difference.

 

 

I do agree that my exhaust is probably a part of why my torque falls off pretty badly, but even the exhaust I"m running is technically quite an improvement over the stock 280zxt exhaust, being larger in diameter, minus a cat converter, and with a straight thru short muffler vs. the stock piece. So I'm not expecting the 3" exhaust to make such a HUGE difference, maybe a few hp I dunno. I'm figuring I will get better turbo response and less lag though. Unfortunately I dont have the funds to do a proper downpipe so am stuck with the stock piece even when I do go 3" mandrel from the dp back... more reason why I think the larger pipe wont make any HUGE gains in my case.

 

More importantly is the fact that I 'fixed' my boost problem... that probably accounts for much more of the fall off in torque after 4k rpm, since by 6000rpm boost was down 3psi from where I set it to kick in at initially... and if my examples above are any indication of power gained and lost per psi, that would mean I was losing potentially 30+ ftlbs of torque by 6000rpm when last I dynoed.

[COZY Z COLE]

Nope see that was my point, it seems the usual 5-10hp 'rule of thumb' that most people spout does NOT seem to apply, in my case, and also in the case of quite a few other guys I've seen post their turbo dyno charts on here. I was gettign 15ft lbs or MORE, and hp was from 13-17hp increase per psi.

 

I guess I didn't word my statement right. I wasn't arguing with you, I was agreeing that the old rule of thumb is no longer true........

 

Also I think you would see a nice increase in power with a 3 in. mandrel bend upgrade based on my exp. after my exhaust upgrade. Forcing more air with fuel into an engine means that it's converted into power and needs to be released thru the exhaust with the least restriction......

 

 

LARRY

[Sparks280zt]

If a 3 inch exhaust system gave 20 hp on a stock turbo motor, I wonder how much an open DP would give? any more? And I mean a custom mandrel 2.5", as that is what 240Hoke just made me

[Guest bastaad525]

Again I ask though, what is happening with boost after the exhaust upgrade? usually opening up the exhaust results in boost jumping up noticeably with no other changes...

 

well I'm not debating a really open exhaust will wake the car up, so to speak. I think you'll definately have much more power over a broad range of the power curve, as well as the curve starting much sooner. But I still think if boost is kept the same your PEAK power wouldn't go up 20+hp. I wish Jeffp might pitch in here and mention of boost was turned back down to 7psi on that stock 280zxt and therefore proven that power gain was FULLY due to the exaust and not extra boost.

 

an open DP is fun, I drove my car with the stock DP open for like the first week... lag is not a word in your vocabulary at that point, and the turbo makes all kinds of wonderful noises... it's loud though, very loud.

 

Cozy - sorry I misunderstood. No it seems that old rule does not apply with our L28ET's, another rule that doesn't seem to apply is that turning the boost up on the stock T3 yields less and less gain past 10psi since the turbo is supposed to be past its efficiency range at this point (not debating about the efficiency), but I was still gaining large amounts of power (well, moreso torque) even up to 14psi. So the little T3 must not be struggling just yet

[Sparks280zt]

ah well, i will be runnin atleast 10 psi, i have a front mount IC and 60 tb, I am searchin around to find how much boost I can run on stock injectors, oh and the 1g DSM BOV

[Afshin]

You're right bastaad, the 20-30 hp gain with better exhaust in turbo cars is mostly due to increase boost. More often when boost is kept constant before and after the exhaust, gains are more in the 8-10hp range, at least in the 2 tests I saw in some of the magazines. Off course that increase in efficiency has many other gains as you already pointed out.

[SHO-Z]

Try this for a calculator

 

http://www.superchargeronline.com/hp_calculator.asp

[burnedbigas]

My l28et 240z, stock EVERYTHING except a 3" mandrel bent w/ magnaflow bullet muffler runs 7psi at WOT. From what I've gathered from the forum, a stock l28et boost is around 5-6psi.

[Tony D]

What does the boos level matter on a stock test?

If you bolt on the 3" exhaust, and run the car, whatever results you achieve will be directly from bolting on the one part.

 

To understand where the power comes from you may look at boost levels and say "AHA!" but alas, in JeffP's case the increase was only....

 

8-10HP/PSI!

 

LOL

 

On another note, it looks as though this is gross hp readings. You are comparing turbo to turbo, right? Meaning you look at a stock turbo motor and say "O.K., I up the boost from 5 to 10, and then chart my total hp and divide by 10"?

 

I would think it would be a ratio, or at least compared to an N/A engine. The Dynojet says my N/A runs around 145, if the stock reading are right for turbo cars I can't figure out the disparity in HP levels, but that's beside the point.

 

So then I take the 145 I started with, put 5psi on top of it, and I get....

 

8-10, or now we are saying 13-17? So 5psi gives me almost 100 more HP over a stock N/A engine? I would think it would be closer to 200HP at the end of the day with 5psi, and not 230.

 

So I think the way you are quantifying the results of your test may be the explanation of the disparity in results.

 

Whatsay everyone?

[EZ-E]

On another note Bastaad, if you can weld a dp isnt that much to make yourself. I just bought my flange, 20 dollars, the cone 20 dollars and you would need only one J or U bend in 3 inch for another 20 dollars. Total cost plus shipping would be about 80 for a dp.

 

I bought 3 other J bends so add another 60 dollars, now just for adding some extra for the straight pieces of 3 inch that I will need, that will be about 165 total to weld up my complete 3 inch exhaust minus the cost of a good muffler.

 

http://www.performancepeddler.com sells the 3 inch J bends for a little over 20 dollars and charge no shipping at all. I got 4 J bends from them for 81.80 total.

 

If you search you can make your own system fairly cheap then again if you know how to weld.

[GrayZee]

Here is the way it was explained to me a long time ago... It is a very GENERAL formula but it does make sense. Boost is relative to atmospheric pressure, and atomospheric pressure is roughly 14psi depending on your elevation. This is what most engines have to run on, however if you take a 100hp engine and boost it to 14psi (double atmospheric pressure) you will double the HP output. Now to say you take a N/a L28 engine rated at 145hp isn't gonna give you the same value as a turbo engine because you have to remember that a true turbo engine has a lower compression ratio and will not have as much power without boost. Lets say however that a 7.3 to 1 turbo engine can produce 120hp without any boost. Then if we were to give it 7psi (stock boost levels) then we could increase power by 50%

Therefore 120hp + 50% (60HP) = 180HP @7psi

then.. 120hp + 100% (120HP) =240HP @14psi

 

Like I said, this is a very general formula, lots of things will effect HP and torque. My experience is that a bigger exhaust will give you more psi just because more exhaust gases will find it's way though the exhaust turbine because of the improved flow. I used to run 7psi steady all the time, but with the 3" exhaust my boost was reaching 9psi.

I've never dyno'd my car but judging by the 1/4mile trap speed vs. my car's weight, I'd guess I'm running 220HP at the rear wheels, not bad for a engine that was rated at 180hp at the flywheel. Amazing what a few bolt ons can do to a turbo. I'd say my biggest gains were from the exhaust and the modified ecu.

[Guest bastaad525]

Again... this is just my case... well it's my case but it also appears to be pretty typical among of lot of L28ET guys. For instance, I've seen more than a couple other guys up the boost to 10psi on a stock setup and end up very close to 200hp to the wheels.

 

I understand that it's all relative... for instance, adding 1psi of boost on a 5.7 liter V8 is probably going to gain a lot more power than adding 1psi of boost on a 1.8 liter four cylinder. That makes sense to me.

 

I was just... very impressed and kinda glad when I sat down and went over it and saw how much power it seemed each psi increase of boost was making, after having been told by some people that 1psi = 5hp, and stock T3 sucks at anything over 10psi, making little power and tons of extra heat (not gonna debate about the heat but at least I see it still makes great power), it was nice to see for myself that I really was gaining a lot more per psi than I thought. An average of 15 hp per psi is pretty darn nice and to get so much gain from so few mods (intercooler, RRFPR, fuel pump, manual boost controller, giving me almost 100 extra whp) really speaks a lot for the wonderful and easy potential of turbos vs. N/A motors when on my N/A motor, going high compression, full headers and exhaust, head work, mild cam, cost me a LOT more money and netted me only about 40 more whp

 

 

Grayzee - now that's another formula that seems to be way off in my case. If my poor low compression L28ET was only good for 120hp net at the flywheel (vs. N/A L28's 140ish claimed by Nissan), and adding 14psi of boost (actually you'd need closer to 15, 14.7 is atmospheric) would bring it to 240hp at the flywheel, that'd be just under 210hp to the wheels. But I made ~240hp to the wheels (approximately 280 flywheel) at 14psi (so not even fully double atmospheric pressure)... cut that in half is about 140 flywheel hp, which is what the motor would make I guess if it wasn't boosted at all...pretty close to what the N/A motor was rated for. My guess is that the lower compression doesn't hurt hp nearly as much as we think or my low CR motor just doesn't realize it's supposed to make less power than a stock N/A

 

 

Tony D - man... um... dude no offense but uh... your post just confused the heck out of me... let me read it again... um... no... fourth time thru it and I'm still scratching my head. About the exhaust thing though, yeah either way, adding the exhaust in Jeff P's case was all it took to gain that much power, but really, don't you think that the 'side effect' of boost going up from the freer exhaust is kind of 'cheating' when you say "Look my exhaust makes 20 hp!".

 

Think about a case like this. Let's say you're running a crappy exhaust, 2" diameter, very restrictive, whatever. But you've been upgrading other stuff, and have the boost way up already, where you couldn't or wouldn't want to turn it up any more. Maybe you don't have enough fuel to support any more boost, or maybe the octane fuel you can get is not high enough... whatever... something would not allow you to run any more boost. Then you go and upgrade from your crappy 2" exhaust to a nice full 3" mandrel. Now right away you see boost has gone up as a result, and immediately you have to turn it down or you'll blow your motor. So boost is returned back to your previous setting, would the exhaust have resulted in 20-30hp gain 'all by itself'? That's what I'm getting at. When I first read Jeff P's site where he talked about that exhuast, like everyone else I wen't "Wow! Exhaust alone made 20+hp!" but really, EXHAUST ALONE, didn't result in all that gain. Exhuast caused the boost to go up, and BOTH of those factors increased the HP.

 

So now I myself am finally at the point where I"m about to go have a 3" exhaust installed, and for a while, I was expecting expecting 20+hp from that mod alone. But, the problem for me is that I'm already at my 'boost limit'. I don't want boost to be any higher than it already is (13-14psi). So when I install that exhaust, and I have to turn boost back down, I'm betting I wont end up with anywhere near 20-30hp more than when I started, just from the exhaust. All I'm saying is, w/o the full info behind that incredible gain in power Jeff P saw, one might be mislead, or in this case many, as there are lots of people around here who are now convinced that a 3" exhaust upgrade over stock will instantly grant you 20+ extra hp, 'all by itself', when obviously there is more to it. I think Afshins statement is probably much more close to the truth, in that the exhaust ITSELF was probably only worth 8-10hp, if boost level was kept constant before and after the upgrade.

 

And another thing a lot of people don't keep in mind, is Jeffp's 20+ hp gain was going from a bone stock 280zxt exhaust with catalytic converter and so-so stock muffler. And isn't stock 280zxt pipe 2" in diameter? Most of us who put L28ET's into S30's, as a matter of course, forego the catalytic converter, and if we don't go with 3" mandrel right off the bat, we usually end up with 2.5" press bent and an at least half decent muffler to start with. So we are already in a far better position than the stock 280zxt setup, and hence, won't get as big a gain when we finally do go with the 3" mandrel. In my case I've got mostly 3" pipe with maybe 1/3 of it being 2.5", all pressbent, and a good straight thru muffler. This is one reason why I haven't prioritized upgrading from my current exhaust setup, as I don't expect I'll gain a whole heck of a lot from it, especially since I can't afford to go all the way and get a custom downpipe as well (and no unfortunately I can't weld one myself). I'd honestly be surprised if I gained more than 5 peak hp, and others from these boards have thought the same thing when I discussed it with them, that just upgrading the pipe but being stuck with the stock DP is just not going to net me a lot of noticeable improvement.

[Tony D]

actually no, the industry standard currently is to bolt parts on and see what they produce.

 

JeffP bolted his pipe on, and got a bump of 20hp. That is "bolt on HP" in the purest sense of the word. We are not talking about some crappy restrictive exhaust cobbled up by joe on the corner, we are talking about a functioning as designed OEM unit that someone did a fair and comparative test on. And it was done on a stock car. It was a test to determine "first step" capabilities. I think it succeeded. This modification alone on a stock ZXT will be the basis on which to build further---which was Jeff's goal. How many people stupidly turn up the boost FIRST? We all did it, admit it! But then later we go and screw with the exhaust, and then our boost numbers go everywhere, or the engine overboosts and we go lean---boom! If the exhaust was done first which was the point of Jeff's test and philosophy, yhou are much better off. Thusfar he has supported 450+hp on that pipe, so you know it will work on a wide range of applications. A piece you buy ONCE, and not replace again in a few years because you "outgrow it"!

 

People many times say "oh this part added this much"---well show me the dyno sheet. JeffP did, because he was curious and did ONE mod to see what would happen.

 

You are all assuming his boost went up 1 psi, and it may well have. Fact of the matter is it was because of the exhaust so the claim is valid!

 

I mean we are hearing over and over that one vendor's intake setup is better that stock. Yet there are no dyno charts to prove it, only subjective opinions. That smells to me. When someone can do an before an after comparo, then it has a bit more credibility.

 

But like I said earlier, the 1psi may explain why the 20 hp is there, but the fact still remains the modification that made it possible was the exhaust.

 

I personally am running a 2.5" mandrel bent MSA system on my wife's car. I am curious to see what it runs the dyno at when it finally makes it over there. It's quiet, that's all she cares about, and it FIT right on the stock turbo downpipe right after the double layered section, so I was happy too!

 

I know the gain is probably not going to be that great if I replace the whole exhaust with 3". But I believe my gains from a replaced downpipe (Scottie GNZ Style) will be more fruitful than a total exhaust swap anyway. And when that mod gets done I can put the electric cutout on the downpipe, and scare the hell out of little kids and old ladies as I see fit.

 

3" Exhaust? We don't need no stinkin' exhaust!

[Guest JAMIE T]

I'm going to point out(it way have already been said, but the other posts have been too long to hold my attention), that you can have less boost pressure and still make more power. Improving the intake side of a boosted system will reduce boost pressure, while still making more power.

 

Say, you don't change the boost settings on your fancy boost controller.(for grins your running 12psi)

You get yourself a 70mm throttle body, a real expensive sheet metal intake, and you prot and polish and install ginormous valves in your P90 head, and you got this special cam from Electormotive R&D. You've reduced the RESTRICTION on the intake tract. Now your 12 psi is 10 psi, but your making 50 more HP. Boost pressure in reality is a function of restriction. I hate the way people try to estimate power gains by how much boost they have.

 

I built a 3" exhaust for a friends turbo charged SE-R(B13). After the exhaust, it made more HP at 15psi than it had previously at 17 psi Like almost 50hp. No kidding. The 17psi was with an HKS exhaust!