Elysian

so? how much? the previous owner told me he put a grand national turbo in my car, and people on the forums have told me its a stock S5, and i look at the intake housing, it says plainly on it HT18 and some other numbers.... so how much boost can it push reliably? cause right now, with no boost controller on it, just the regular vacuum hose, in1st its pushing 17, and in 4th it creeps all the way to 22... in the intercooler piping... any ideas?

Elysian

i've been searching for this, and most i can find is "past 12 psi the stock turbo isn't efficient" etc etc... i'll tell u what... my turbo pushing 22 psi in 4th gear, and spooling up as fast as it does... is quite efficient.... 1st and 2nd and 3rd gear if i wound it out with the previous motor, would all lose traction on dry pavement... now that i'm breaking the car in with my new motor, i'm only going to 4500 rpm, but any little amount of gas still likes to spool the turbo up fast, i'm trying to be ginger and my turbo's not letting it be

Rxmfn7

iTrader: (4)

Holy hell....
Are you sure that you are making that much boost? I assume this is a reading from a reliable aftermarket gauge? A stock FC turbo wouldnt last long at all making that much boost..much less the engine without a ton of fuel and tuning.... What fuel mods do you have? I'm a little skeptical of those boost numbers....

Elysian

yes its a reliable aftermarket guage, and the turbo's already lasted a while... i got a pillar mounted boost guage that reads to +/- 30 psi... and as for fuel... unfortunately all i have right now is 720cc secondaries... i'm not getting on it now with the new motor, i haven't let the turbo spool very much, gotta break the motor in right, when i get back from sea in july i'm buying a haltech and having the car dyno tuned... i'm also going to be running a starion intercooler as a front mount... i'd get a pic of my boost guage showing 22 psi if i could, but the car's not broken in, and theres no haltech... i don't want to blow my new motor, i'm gonna be taking it easy till i can get the haltech... u can be skeptical all u want, but i know what this turbo has done, and it scared the hell out of me...

Elysian

i didn't question 22 psi before because i didn't think it was an HT18, but when i investigated it the other day, i found it was... does the HT18 have a larger exhaust housing than intake housing?

Elysian

like this...

Rxmfn7

iTrader: (4)

I didnt mean I was skeptical to be a dick..but it just doesnt make sense. What are your mods to the car that it would boost that high? Other than a wastegate being stuck closed.. I cant see the stock turbo boosting that high. And when it did, the engine going pop or the turbo spewing oil as it shakes itself to death.. Do you have 4 720s, or just the secondaries?

Elysian

just secondaries... the setup i had with the last motor was simply this... stock porting, 3" racing beat downpipe, 3" straight pipe, port and polished upper and lower intake manifold, and a HKS hemispherical filter... the PS and AC were disconnected, and the stock fan taken off for an electric one... it had a 7lb flywheel... and thats all thats been done to the motor... the guy did a terrible job building his 12 sec rx7

Rxmfn7

iTrader: (4)

Yea...Thats a stock turbo.

2a+RoN

Yeah looks like a stock s5, but holy crap 22psi... Have you been on a dyno at all with that??? The thing about the stock turbo is not whether it can go to 22psi, but how much power is it making. That's where it's efficiency comes into play. If you get onto a dyno you might see that it makes just as much power at 14psi as it does at 22psi since it would heat up the air enough to counteract the high boost pressure. That is just hypothetical situation, I have no idea what pressure it would be comparable to. This is pretty interesting tho, the mere fact that the turbo is lasting on 22psi is astonishing by itself.

Elysian

its making enough power to push the car to a 12.4 at 121 mph... i haven't been on a dyno yet, i'd go to the dyno day we're having here but i'll be in texas when it happens, and i'm not about to go to a place and pay a premium price, i'd rather go in a group, and pay like 40 bux first run, 10 the second

Elysian

i don't know if they've internally modified the turbo or not... i know nothing about it really, i took it off, but i know this much about turbo's |-| to tell if it were modified

Elysian

the turbo has lasted longer than the 5 motors the previous owner blew with it

J-Rat

iTrader: (2)

22 PSI on a stock turbo is completely crazy (if you actually did hit it). And 22 PSI on a stock turbo with just 2x720s is insane.

Your wastegate must me totally stuck closed.

rx7lover0147

yes if you don't have a boost controller your waste gate is screwd all to crap. do you have an air/fuel on there i would definatly go get it dynod just to check air/fuel.

Elysian

yes i have an AFM, on the same gauge pillar thing as my boost guage, and it went slightly lean at 22 psi... usually it runs stoich when boosting and almost rich when not

Elysian

but thats using a stock o2 sensor

Elysian

the line for my boost guage is located in the elbow just before the throttlebody, thats where i'm getting 22 psi at

stinger

i currently run at 1bar/14.7psi for boost. i also have a fully reprogrammed Progress e.c.u., full RB race exhaust, k&n filter, act hd/6puck set up, st springs, r.c. rotors, ebc pads, kuhmos, etc.
i'm getting around 325rwhp.

i had always heard that a 'safe' boost level was 14psi and the 'max' boost level was 16psi. this would apply to a completely stock set up only.

unfortunately all my pics are too big?? i tried to attach one in the se forum and it would not load.

*** far as the turbo, he could have changed the housing, wheels, trim, etc. of the stock turbo. there's a s320 upgrade kit on ebay right now that is a 'bolt on' upgrade good for about 350hp.

NZConvertible

From that comment, you obviously don't know what turbo "efficiency" actually is. Unless you've measured the airflow rate, boost pressure and discharge temp and calculated it...

I promise you your turbo is running well past it's peak efficiency. It'll be adding crazy amounts of heat to the air, far more than the stock IC can deal with, making detonation very likely and making no more power than if you turned it down to a more sensible level. It's also spinning far faster than the bearings were designed to take, so don't expect it to last long.

Andrew

iTrader: (1)

NZConvertible is correct. You can't tell if a turbo is in it's efficeiency sweet spot by driving the car. But I promise you that the stock turbo is nowhere near efficient at that boost level, especially if the turbine wheel has been clipped which drops the efficiency. I don't have a compressor map, but I'm sure it's somewhere near 8-9 psi.

Hook up your boost gauge to the intake manifold, I'll bet there's significant pressure drop in the throttle body, so your actual boost pressure is probably a few psi lower, but still way outside of the efficiency range.

Also, get ready to bump the number of blown engines to 6 if you're running boost on a fresh engine (let alone 22 psi).

Elysian

i don't let the turbo wind out right now, especially not to 22 psi, i'm breaking it in, therefore no need to spool the turbo

Bambam7

NZ beat me to the quote... again!
There is no way you're gauging effeciency. I'd love to see you stick a temp gauge on the output pipe to the IC.
What kind of IC is it anyways??
It's waaay past it's effeiency peak. You may actually realize more power at 15psi than you do at 22, due to the air not being superheated!

Plus, running that boost on pump gas is plain dumb.
You sure your wastegate is OK? That much boost on an S5 turbo (dual wastegate!!!) is just strange... indicating to me that something is amiss.
Bottom line- I think that this next quote says it all about this setup.

Nice... I think that proves the point.

Bigretardhead

it ran a 12.4@121 mph with a stock turbo, fuel system, and ports??!! holy crap. that's not normal, is it?

maybe there's more in the motor than you think?

Terrh

iTrader: (7)

ummm are you sure that your gauge is in PSI? I didn't think that -30PSI was possible.... isn't a true vacuum -14.7 PSI?