How bad do pre-turbo exhaust leaks hurt horsepower?

[Blazer406]

I know this is probably too general to get some useful insight to..... but the search has turned up almost zero info.....

We were at the track the other night running a turbo regal..... and it just wasn't picking up any when we went from 24-25 psi to 26-27 psi..... it is like the power might have even fallen off a tad...... only thing that came up was the exhaust leak was noticed after the first pass or two..... we continued to run the car, because we couldn't fix it right there. The tuneup looked good and the car pulled clean all the way down the track......

Looking back.... I am considering the exhaust leak could've been significantly hurting overall HP..... It is a given that spoolup would suffer.....

Any thoughts?

 

[HelloBozos]

Leaks=Bad!! 3 runs back to back will make your headers "Glow",stock set's crack. Plus the more boost means awhole lot more fuel needed,don't suck your injector rail dry.. 27 psi alot boost,most stay 25 or under,unless want max output,an that's real dangerious!!...your build seems to be sneaky sneaky or could be more help..;^)

Enjoy!

 

[bison]

Cracks won't do chit once the turbo is spooled. It's the same effect as a wastegate dumping exhaust energy. If the car isn't picking up with added boost there is some other limitation.

 

[ZNix]

More information on the set-up? I am not an expert.. But maybe your springs are not stiff enough.. Valve float?

 

[Nick Micale]

... and it just wasn't picking up any when we went from 24-25 psi to 26-27 psi..... it is like the power might have even fallen off a tad...... only thing that came up was the exhaust leak was noticed after the first pass or two...........

What do you mean by "it just wasn't picking up any"?

Do you have time slips that show MPH to verify it did level out or not? You cannot guess at this using a "butt dyno".

Possibly the exhaust leak could be an issue, but there may be something else going on there like Bison stated.

 

[Blazer406]

It wasn't my car.... but basically it ran between 112 and 113 in the 1/8 at 24.9 psi or so.... and Actual AFR around 10.8:1 and 21° timing.... then cut it up a little running around 26.5 - 27 psi.... 10.5:1 (Actual AFR) and 21° timing.... ran the same MPH....... C16 fuel.

I wondered if the pre-turbo exhaust leak would effect the trap speed at all.... and when we cut it up..... basically it took more HP to drive the turbo due to the leaks... and even though the increased boost would gross more power.... the power it take to make the 27 psi boost went up making the net HP nearly the same??

Charge air temps around 110° at the end of the run in the back of the doghouse.

Just trying to figure out if that is twisted logic or what?

 

[bison]

It wasn't my car.... but basically it ran between 112 and 113 in the 1/8 at 24.9 psi or so.... and Actual AFR around 10.8:1 and 21° timing.... then cut it up a little running around 26.5 - 27 psi.... 10.5:1 (Actual AFR) and 21° timing.... ran the same MPH....... C16 fuel.

I wondered if the pre-turbo exhaust leak would effect the trap speed at all.... and when we cut it up..... basically it took more HP to drive the turbo due to the leaks... and even though the increased boost would gross more power.... the power it take to make the 27 psi boost went up making the net HP nearly the same??

Charge air temps around 110° at the end of the run in the back of the doghouse.

Just trying to figure out if that is twisted logic or what?

If you make more boost (manifold pressure)and drop ex pressure power usually goes up and it makes it easier to select a cam and time the cam so that you minimize back flow which could result in more power potential with smaller parts.

 

[Blazer406]

In the case of the exhaust leak..... it took more volume exhaust to make the same back pressure on the turbine to get the compressire wheel to spin enought to creat the more boost.

I can't see how it has zero effect after the turbo is spooled......

If the manafold all of a sudden during a run had a massive leak.... looks like the power would fall off significantly.

I guess I could see that once spooled... the exhaust leak was (in-effect) like the wastegate... taking a small amount of volume requirement from the real wastegate.....

 

[bison]

If it picked up boost then somehow the turbine got more energy (not less like in the case of an exhaust leak) from the exhaust or the inlet restriction was reduced. Power would fall if drastically if the ex energy fell off enough to drop boost. It takes more energy to spool a turbo than to maintain it's speed. The wastegate is most likely open on all your runs even with the ex leaks.

 

[tonka]

If it picked up boost then somehow the turbine got more energy (not less like in the case of an exhaust leak) from the exhaust or the inlet restriction was reduced. Power would fall if drastically if the ex energy fell off enough to drop boost. It takes more energy to spool a turbo than to maintain it's speed. The wastegate is most likely open on all your runs even with the ex leaks.

I was thinking along the same lines. In fact, I've wondered for a while now if those cars that have the wastegate plumbed off of the crossover pipe have a distinct advantage when the turbo is being run to the extent of what the exhaust side can flow.....

 

[MSDGN]

What turbo are you running...could just be out of gas...I ran a 51 and when I got to certain point
of boost it didn't matter how much I turned the wick up the car would not run any faster...it
was basically a big hair dryer at that point...went to a 62 and bam...car picked up...but exhaust
leaks do hurt the performance...they mess with the O2 sensor or wide band and in turn this effects
the fueling...what were the O2's during the run...before and after you turned up the boost?

 

[bison]

What turbo are you running...could just be out of gas...I ran a 51 and when I got to certain point
of boost it didn't matter how much I turned the wick up the car would not run any faster...it
was basically a big hair dryer at that point...went to a 62 and bam...car picked up...but exhaust
leaks do hurt the performance...they mess with the O2 sensor or wide band and in turn this effects
the fueling...what were the O2's during the run...before and after you turned up the boost?

The ex leaks don't do anything to the a/f at wot. There is too much pressure in the exhaust for ambient air to enter. If the fuel tables are correct you can just run without correction anyway. In your instance a pt51 which uses a to4e 60 trim compressor which might squeak out 53lbs/min in really good air compared to a 62 cea which flows upwards of 75lbs/min is like comparing a 10 sec drag car to a top fuel dragster. Which makes your question a good one. Maybe he's out of turbo. If your engine can support 75lbs/min and the turbo you have supports 53 you are going to have a huge gain in power if you dial it in.

 

[Blazer406]

supposed to be a 71 billet

 

[HelloBozos]

Could be your out of gear, i run a 71 with 72inj. ,had the same deal (1/8 mile it falls over but a Rocket till then)till lost the 3:50's (close to factory 3:42's but i run currie 9") an went 3:20's an XFI,done had the quad air mod ecm,translator,custom alky chip,professonal dyno tunes ect.etc, no help either,all factory type ecm's go lean at high mph (at 120+)an rpm (5200rpm) modified or not. The gear will give you the mph an XFI gives the ignition needed over 5000rpm for the high mph,Turbos need a pull on them,I'm hwy set-up though ,80mph is only 2100rpm in OD,my crusie speed!! top speed's a buried 160mph VDO gauge!!(200r4,non-lock,10' art carr 3500)with my 295/40-18's (28 inch tall auto cross tires) 8^)

Enjoy!

 

[bison]

supposed to be a 71 billet

Unless its up around 150mph its not out of turbo.

 

[Blazer406]

I've convinced myself.....and agree with Brian...... that the exhaust leak (pre-turbo) has no effect on HP or trap speed so long as the leak isn't so large as to let the boost drop off..... as long as the boost is there..... the pre-turbo exhaust leak is only hurting spoolup.

It's not out of gear..... or turbo....... going to look at converter slip and a few other potential issues.

 

[bison]

Could be your out of gear, i run a 71 with 72inj. ,had the same deal (1/8 mile it falls over but a Rocket till then)till lost the 3:50's (close to factory 3:42's but i run currie 9") an went 3:20's an XFI,done had the quad air mod ecm,translator,custom alky chip,professonal dyno tunes ect.etc, no help either,all factory type ecm's go lean at high mph (at 120+)an rpm (5200rpm) modified or not. The gear will give you the mph an XFI gives the ignition needed over 5000rpm for the high mph,Turbos need a pull on them,I'm hwy set-up though ,80mph is only 2100rpm in OD,my crusie speed!! top speed's a buried 160mph VDO gauge!!(200r4,non-lock,10' art carr 3500)with my 295/40-18's (28 inch tall auto cross tires) 8^)

Enjoy!

Your post has a lot of short comings. The ignition strategy the stock LC2 uses isn't enhanced with an xfi. Stock ecu's don't cause lean outs. Poor tuning does. IMO 120mph is nothing and if you are running a 71 you should be running just about that fast in the eighth. A 10" converter with a 71 isn't going to work too well either. If you think going from 3.5 to 3,2 gears is going to make the car pick up a bunch of mph you are mistaken.

 

[KevinB]

Are you crossing the line at the same rpm? Do the rpms stay in one spot going down the track? One theory could be car was making more hp but blowing through the converter. That's my guess.

 

[HelloBozos]

Your post has a lot of short comings. The ignition strategy the stock LC2 uses isn't enhanced with an xfi. Stock ecu's don't cause lean outs. Poor tuning does. IMO 120mph is nothing and if you are running a 71 you should be running just about that fast in the eighth. A 10" converter with a 71 isn't going to work too well either. If you think going from 3.5 to 3,2 gears is going to make the car pick up a bunch of mph you are mistaken.

Bison,
My postings from $30,000 of experience. Buick Specialist's plus my since 86' production owning self,How about you??? Nevermind,this thread not about you...Because Your so Wrong!!!...80's tech home computers vs the year 2000+ models, enough said there!....Turbo's need a tall gear to pull on. These cars aren't 4:56 gear small blocks..yes leave factory gears an go 26" inch tall tire,it'll be a rocket!! to the 1/8th an then fall flat on it's face!!..if your going 1/4 mile,goodbye motor!!!...All this only applys if you push over 600hp!!!...but you'll live an learn (race ya when your ready standing start to 1 mile!!!)



Blazer.. try an experiment an go up 1 or 2 inches in rear tire size...then all the next steps from there when "it works"

 

[ZNix]

Bison,
My postings from $30,000 of experience. Buick Specialist's plus my since 86' production owning self,How about you??? Nevermind,this thread not about you...Because Your so Wrong!!!...80's tech home computers vs the year 2000+ models, enough said there!....Turbo's need a tall gear to pull on. These cars aren't 4:56 gear small blocks..yes leave factory gears an go 26" inch tall tire,it'll be a rocket!! to the 1/8th an then fall flat on it's face!!..if your going 1/4 mile,goodbye motor!!!...All this only applys if you push over 600hp!!!...but you'll live an learn (race ya when your ready standing start to 1 mile!!!)



Blazer.. try an experiment an go up 1 or 2 inches in rear tire size...then all the next steps from there when "it works"

No offense.. But I put my money is on Bison winning that fight. His slow car I think pushes 600 HP.