3" vs 2.5" exhaust

Sorry my ignorance, but why in the earth I would need back pressure with turbo-diesel?

KSV,
as the guys have mentioned below. The correct Exhaust Gas Temp is critical for the turbo to operate at its peak performance. I think, and I stress THINK, the 2.5 with the little extra back pressure helps maintain the correct temp.

Anyone that knows what they are doing will tune the engine utilising the EGT.

All engines need some back pressure, how much..........I wouldn't have a clue:-)

Toytruck

I agree with your statement about EGT, but still found strange that less restriction make things worse. Mind you two physical facts. First – more gas expand cooler it became. Therefore exhaust directly in atmosphere (after turbo) appears to be the best option. And secondly - pressure in exhaust manifold (before turbo) is significantly higher then after turbo - this difference in pressure actually make turbo works. Thus extra pressure after turbo has very little to do to pressure immediately after exhaust valves, as least when load is high. Mystery indeed.

Seems the smaller exhaust helps keep the EGT higher. The point about a larger exhaust being you get the gas out quicker and you don't need back pressure, you are trying to reduce it. There was a good comment by Ian of Thermoguard Instruments about it Site Link
Suggest you read it!

"Seems the smaller exhaust helps keep the EGT higher." - Exactelly my believing. Thus it automatically means bigger is better. Also I agree with you that back pressure is nonesence in relation to diesels. Thus again bigger is better. Thanks for link BTW.

I would think that heat issue related to turbo rather then to exhaust. Why do you recon bigger pipe would cause more heat in engine bay? Sound funny to me.

As mentioned previously its something to do with the back pressure and exhaust gas temperatures being higher when completely unrestricted, which is why blokes like Roachie monitor their engines EGT pretty carefully.

Best to talk to the experts, but they will all say the same I think you will find.

I certainly can tell you from experience that the coolant temp is now a bit touchy since the new exhaust was fitted and too much right boot over a sustained period will cause high engine temps. Have checked engine completely including compressions, injectors, radiators, thermostats the lot and problem remains tho it wasn't there before.

How about your turbo boost? Has it increased since you upgrade your exhaust? If your bust regulator does not work properly (or simply can not cope with such low-restriction system), then I would expect your boost became higher. If this is the case then I would understand everything - temperature problem related to higher boost pressure rather then to 3" pipe itself.

Following the install of the 3" system it spent two days at Bunbury Diesel Injection who are agents for Safari - same as mine and who have dyno facilities.

They did the lot including dyno testing, fuel metering, turbo boost, injectors etc etc until the client was proven broke so to speak.

Made stuff all difference in the end and the problem still persists especially if its working hard as mine often is with the weight I carry around tho grunt is no longer a problem for this truck anymore. Noticed it most on hills like the one up to Collie and if I sink the boot in with a bit of weight on board, this is soon reflected in high temps. I know a few blokes in Collie who have had the same problem as mine in similar specced vehicles, spent heaps chasing the problem and no one really seems to know the answer and we all have 3" exhausts in common.

My son tho has a 100 series IHZ Safari and Intercooled which has significantly more radiator exposed to fresh air compared to the 75 series and he has no problems-bit like the wide mouthed frog methinks.

Thanks to follow. Is your son has 3" in his 100? And do you have intercooler in your 75? Thanks.

My son has a Safari turbo + Safrari intercooler and 3" exhaust. His intercooler is a radiator/intercooler style mounted behind the grill and in front of the main water radiator. He has had no heating issues and has also installed gas. His truck seems to be a bit of a one off - one of these vehicles made when the factory was in happy mode as it has buckets of grunt, is super quiet and v8 petrol like in its driveability. It's a 100GXL Live axle for the bush type and a serious offroader with all the bells and whistles.

The Old Plodder has Safari turbo - no intercooler - 3 " exhaust. The 75 series does not have enough room behind the grill in terms of area to install a similar type of radiatior/intercooler. "Denco" however make a fluid cooled intercooler which sits over the top of the motor where the normal induction pipe crosses from the air filter to the induction manifold

I am currently seriously considering the "Denco" as an option to cool down the inlet gases and thus hopefully the entire combustion process.

Its noteworthy that the 3" exhaust does not use a muffler but then I don't know if the 2.5" does either. Apparently most of the noise is stopped at the turbo making the muffler pretty much superfluous.

Load weights in the 75 crew cab are pretty significant when loaded for trips as she becomes the chuck wagon and fuel supply for both vehicles when in the bush.

Hope all this helps.

PS

The sons 100 does not have a snorkel wheras the 75 series does....

Thanks a lot for such extensive information. I recon main difference b/w yours 100 and 75 is intercooler - this is key issue. I recon 3" better, but it kind of "too good" and as result engine breath much easier and turbo spins much happier - this is probably why you have light (if I understood correctly) temp problem. BTW where fluid from this fluid-cooled intercooler get cooled? (Cool sentence - is not it :-)

I think the Denco IC still has a small radiator behind the grill but because it is fluid to air rather than air to air as in the Safari, the size is distinctively smaller and thus able to fit in a limited space.

I think the jury is still out regards how effective it is as an intercooler in this type of truck.

Hmmm... Have a look and it sems to be very attractive set-up. Would be nice to find out if anyone uses them amd what they think.

Follow that to the logical conclusion, would you actualy need an exhaust?

"More back pressure = more low-down torque. "
Sorry - found this statement incredibly strange. If follow this logic then 1" pipe would be just right for low RPM torque (although will struggle at high RPM) IMHO it is nonsense. I recon quicker removing exhaust gases means more torque. And BTW as far as I understand consensus came to the point that bigger exhaust make noticeable difference at low RPM increasing torque and do not so much at higher RPM.

"More back pressure = more low-down torque."

Yes, for a petrol engine, but it's the opposite for a diesel.
Diesels don’t have optimum mixture requirements like a petrol eg. more air needs more fuel. With a diesel you can’t run too lean, you’ll just loose power, but you can run rich. Having a free flowing exhaust just allows the turbo to spool up quicker without the restriction, but does increase the risk of turbo surge.
Manufacturers go to great lengths to quieten diesels to make them more car like, but check out the exhaust on a tractor or stationary diesel gen set, and you won’t see much of an exhaust system. It’s only there to direct the gasses away from car.

Illogical conclusion John.

Actually Chaz is the most correct of all of us (me included).

Site Link

Off-track,
A good article, but again it refers to a petrol engine situation.
The two are vastly different.

Actually the article referrs mostly to carburettored motors so is hardly any use at all. Where it referrs to injected motors, it talks about the compensation by modern engine management systems giving more fuel.

The question above is about forced induction diesels and as more force goes into the turbo, there is more gas to be dealt with, generating more exhaust. there are undoubtedly going to be more restrictions to overcome, including how much the air cleaner will allow. The turbo will also restrict as the boost potentially goes up. The question is the boost after the turbo and the answer is that it should be as little as you can afford.

Your point above led it's own fallacy

Off-track, I should have just said you were offtrack

The 1HZ hardly has a modern fuel management system even though it is injected, and is quite common for them to be over fuelling.

I think you may be travelling a little offtrack in the other direction :-)

As far as I understand physicals going on in internal combustion engine all this back pressure is total BS. It is only applicable for carburetors engine and yet mainly to two stroke one where proper exhaust flow absolutely critical. It is total nonsense for diesels and hardly has any effect in modern petrol fuel injected engine. Even abovementioned article flawed because presence of extra exhaust gases in cylinder (i.e. bigger back pressure) lead to *REDUCING* oxygen because more oxygen-free exhaust gases occupied space instead of fresh air thus leading to *RICH* mixture. But because EFI engines relay on oxygen sensor to judge fuel mixture quality they can self-adjust to bigger or smaller back pressure efficiently. Flow speed of exhaust gases only can make sense to oxygen sensor itself (it *MAY* read incorrectly if flow too quick) and catalytic converters (they *MAY* not be able to cope with higher flow). But again all this gibberish utterly inapplicable to diesels and in particular to torboed one. Just my $0.02 of understanding this problem not pretending on absolute truth.