Hmm, well started the car up tonight and it's smoking a little. :\ Checked the oil, and it's a little discolored. Pulled the radiator cap, and it's bubbling. Seems like the head gasket might have let go. I think I'm going to go ahead and pull the engine and make sure the block isn't cracked also. Oh well, I can't expect too much, i've put this engine through hell and back, even before I put the turbo on it.

 

Have you still been running the following conditions as per your first post:

Also, what head gasket, fasteners, and torque did you use and plan to use next?

 

The last time at the track during the 10.56 run, it was on 14 psi, and 110 mix instead of 114. The engine was all stock inside, including head gaskets and fasteners. I haven't decided for sure what i'll do next. I may throw some arp rod bolts in it, and possibly ROL head gaskets.

 

Dude, I am WIDE awake.
Again, I ask:
"What makes you think excessive backpressure will break a block?"

And please, this time.......instead of just going off without answering the question, I would like some FACTS.

 

OK, I read through again.
I see NO NEED for you to be insulting, so get off your box.
You still haven't said "why" a too-small housing is going to break an engine.
You say what you are implying is what *may* happen or what *might* cause the block to break, but NO FACTS.
So far you have only spouted hearsay.

OK, that makes sense to a point.
I can see high temps adding to the problem, but residual exhaust gases have been proven to reduce octane needs. (slows the burn rate)
Folks who have spent time around EFI engines with the EGR blocked often find the engine pings when it hadn't before.

 

If the .68 were too small wouldn't there be problems controlling the boost? 46mm wastegate looks like it is dumping enough of the exhaust pressure to control the boost and bleed off any excessive backpressure. Am I missing something here?

Nice job with your project!!! Hope you didn't break your block or anything serious.

 

That makes sense to me.

I just wanted to say I'm not trying to stir up any mud, I just want to know facts only and no rumors (and the "why" behind the facts).

I can see there being headgasket problems with too much backpressure, but I'm not seeing how it could break a block.

 

If it is too small then you can have difficulty actually obtaining the a boost setpoint. This would be due of the turbine wheel simply not being able to supply enough power to accerate the compressor to sufficiently high a RPM to obtain the desired boost target. Since this is not happening, this is not an issue.

Another thing that can happen, which I believe is currently happening with my 0.4 Bar wastegate spring, is that if the pre turbine pressure is sufficiently high it can force open the wastegate prior to it receiving a signal to open. This will bleed off exhaust flow and can also prevent the turbine wheel from reaching a sufficiently high RPM to obtain the boost target.

 

If he did have excessive backpressure he would know very quickly. Boost would bleed off (if only pushing up on the wg valve, not down) and he'd blow header gaskets left and right. If he doesn't have those symptoms, the only problem he'll have is being octane limited at a certain power level. That is, being less efficient.

 

Guys even "IF" his .68 housing is too small, the wastegate is before the exhaust pressure hit the turbine and wouldn't show any negatives effects from that housing since you say it has a 46mm on it. I do think that is he changed his housing out, that it would free up some power and you'd be surprised that the spool up may not even change at all. You are taking an 8 cylinder motor and cramming all 8 exhaust ports together and bottle necking to a .68 housing which would be more geared towards a 4-6 cylinder motor. The bigger housing would free some of that up.

My personal experince with my R302 motor that made a honest 770 RWHP and 836 RWTQ with a .96 "ON-CENTER" turbine housing with a PT-74 GTQ was that the turbine housing was too restrictive for my power level at the time at 18 psi of boost. I added a gauge on the turbine housing and saw 40 psi at the housing and just 18 at the intake.............way too much backpressure at the turbine and it caused head gasket problems, header gasket problems and it even started to warp my header ball/socket flanges. That 770 RWHP was only up to 4900 engine RPM's too as the motor was starting to go real lean. No matter how much fuel I threw at it, it went lean and that was because of the restrictive on-center housing. I change that housing to a .96 "TANGENTIAL" housing and pressure at the turbine now was 34 psi and just 27 psi at the intake. What a huge difference and I ended up making 888 RWHP and 917 RWTQ. That housing was "STILL" a restriction but better than the on-center .96 housing. I then changed to a 88mm with a tangential .96 housing and at 32 psi of boost at the intake, I get 30 psi at the turbine. Also I now make way more RWHP than I do making more RWTQ. The smaller turbine housings always showed a significant amount more RWTQ over HP whereas the 88mm with the bigger housing although the A/R is the same .96, it is a bigger housing, it now makes 1177 RWHP and 1097 RWTQ which I found later is a clear indication that your turbine housing is a restriciton if you make way more TQ than HP.

Everyone knows who Big Daddy Dwayne Guthridge is. He even has a article in 5.0 Mustang magazine where he said they kept blowing head gaskets, breaking pistons and couldn't figure out why until they did a pressure check comparison from the turbine housing to intake. He was then using a Turbonetics T-76 with a tangential .96 housing. THAT was the culprit and they have since changed and you see all of those guys running big turbine housings.

 

WOW, that's some hardcore info right there.
TOTALLY blowing away the theory that many "efficent" turbo systems run 2:1 ratio exhaust/intake pressure.

 

dude, I'm not saying that the .68 is going to break his motor or cause additional backpressure.. whatever the case. What I was stating, and which someone did figure out, other than you is that I would like to see what the car would do with a larger turbin housing on it period.

he's at the power level now, to split the block before he does, regardless of the turbin housing I was asking for results with the .81 or .96..

Ya know, before regardless of HOUSING the block has just been beat on too much and cracks. . .

jesus your hardheaded.. .. I'm not getting into technical jargon I never posed a question or concern about "excessive pressure" really.. I would like to see his combo maximized before he doesn't have a combo

 

BUMP for Linc!!

Understand? This this guy got it. results with the larger housing before, at the power he's making now something happens. . . IE: Headgasket etc..

 

I never said excessive backpressure would break a block, someone else stated that. I asked for results, if MadBeems didn't mind with another turbin housing before his motor has enough from his time of n20 abuse and now with the turbo before it has enough overall.. .

turbo or no turbo... nitrous or no nitrous.....

you got me?

 

Very similar results compared to what we see and saw on several setups. Guess folks don't take our word for it .

 

Now hold on, now.

I never ONCE, ever called you names, or called you a liar or called you stupid or anything.
So just relax a little, will ya? Jeez, go drink a beer or something.


I'll admit I got confused, and I understand that what you are saying is he should try to see if some changes will affect power,
and that he should play with some changes now to find what is best before the block breaks from too much power.


Damn, that was easy to say, if said right.
But you had to be an ass about it.

I'm not dense. But you are not very good with answering questions clearly.

 

then my nice 1.15 a/r should breath rather nicely

 

You have no worries my friend....hehe

 

Excellent info! However, I would like you to explain the logic behind the part of your statement that I have bolded. I am looking to learn here; I am not challenging your info.

In my case, going from a 0.81 A/R p-trim to a 0.68 A/R p-trim allowed a 300 RPM quicker spool from a 4th gear roll. However, this is on my specific application. I am curious what other info you have .

Thanks.

 

Excellent info Brent. Thank you very much for it. You pretty much confirmed, and added to, my thoughts from this post that I put up last week. https://www.theturboforums.com/smf/index.php?topic=58058.0