Larger exhausts on turbos?

[rowinz]

perhaps a stupid question,
common thinking is to replace factory exhaust on diesel turbos with a larger one - helps exhaust flow and taking heat away. Fair enough. If this is such a well thought of mod/alteration, why is it not done at the factory?
Is it material savings? Exhausts are designed for the majority of users who will not need the larger exhaust? Why?
R

[safari_mulisha]

alot of car companies look at driver comfort
so they try make quiet cars

the price from 2 inch-2.3 to 3 inch just about double in price

larger exhaust increase power on turbos yes
allso reduce the exhaust and engine temp

[Steve_t647]

Larger exhausts also allow worse emissions (faster flow less complete burn at tailpipe)

In theroy all the fuel should have been burned in the expansion stroke this is fine in a perfect world but not in ours so the manufacturers increase the backpressure to allow burn in exhaust.

Also bigger is not always better all engines need some back pressure in the exhaust so if you are shortening the exhaust then a smaller size may be OK, most factory pipes are made for emission standards and cost to achieve (no need for high flow cats and mufflers).

Also in the case of the skylines there is a max HP in Japan from factory so they use the exhaust as a HP brake for the motor, prob not the issue with diesels tho.

[timotheus]

Larger exhausts also allow worse emissions (faster flow less complete burn at tailpipe)
In theroy all the fuel should have been burned in the expansion stroke this is fine in a perfect wo........

Everything he said. Some engines need heat kept in for those reasons.

If your not using it as the maker intended, change it.
Harder driving, needs harder equipment.

Im yet to hear of a turbo that doesnt benefit from looser exaust flow.

And then there is the 2L-T , Toyota should have recalled all cars running them and retrofitted a dump-pipe.

[kaney]

Im yet to hear of a turbo that doesnt benefit from looser exaust flow.

And then there is the 2L-T , Toyota should have recalled all cars running them and retrofitted a 2jz.

much better

[badnuz]

im thinking of a side dump on my 3.4t cruiser anyone tried this any pros and cons? im thinking mainly 2.5 inch with a bit of flexi pipe to allow flex.. i need to redo the exhaust as it rubs on my 35's and is stock factory all the way thru. was quoted $600 for full new system including hi-flow muffler, but as im unemployed and broke was looking at cutting costs and doin a shorter system? will it be too unrestrivite and cause more dramas? as for WOF i have been told side dumps can be certed and i want to get every certable mod done 1st so i only pay once

thoughts???

[KiwiBacon]

The tradeoff is noise. Large exhausts not only have more noise coming out the back, but the whole thing acts like a sub-woofer. Transmitting exhaust vibration and pulses to noise which is both heard and felt.

The second tradeoff is cost, manufacturers are pretty tight on that.

But the benefits of a large exhaust are often overstated. The only place they offer a benefit is at high rpm and power levels, at low rpm even a tiny exhaust has no problem removing the gas.

There is no benefit to backpressure, especially on a turbo engine. Scavenging on a non turbo engine certainly, but scavenging and backpressure are not the same thing.
Turbo engines have little to no valve overlap so cylinder fill isn't much affected by backpressure. Exhaust manifold pressure on a turbocharged engine can be more than double the boost pressure.

[Jerry]

If its for your Prado Rowinz do it... whether you have the 2L-Te or the 1kzTe the factory exaust causes too much heat which leads to the old head cracking problem....fit a 2.5" exaust and make sure there are as little bends as possible....my 2l-te is getting this mod next....I don't really care about the noise...the louder the better

[smurf182]

make sure there are as little bends as possible

Bends are no problem so long as they're mandrel bent (constant radius) not press bent, which reduces the cross sectional area (greater restriction). If a press bent system is the only option with regards to cost or whatever, then go for a bigger pipe to reduce the impact of the bent sections.

Every CT20 off a turbo L motor I've seen has had a cracked exhaust housing, evidence of the factory exhausts restrictive nature.

Bear in mind the new lower exhaust noise output rules also.

[KiwiBacon]

[
Every CT20 off a turbo L motor I've seen has had a cracked exhaust housing, evidence of the factory exhausts restrictive nature.

A cracked turbo housing is not evidence of a restrictive exhaust. It's a common occurance with many turbo housings regardless of brand and exhaust size, these things run up to 750 deg C inlet temps with rapid heating and cooling.

A very small exhaust is only going to raise your backpressure by 10psi max. That's at full rpm and full noise. The resulting increase in temp is tiny.
Personally I think blaming cracked heads on a factory exhaust is stretching things a little. Expecting a big exhaust to prevent a toyota diesel cracking it's head is also a big call.

Regarding crush bends vs mandrel bends. Again I think it's way over-rated. The flow around a bend always concentrates on the outer edge, so the inner edge pulling in on a crush bend isn't a great problem. Throw in that crush bends are at a greater radius and the differences in flow become smaller.
Mandrel bends are still a good thing, but I think the differences are greatly exaggerated.

[badnuz]

The tradeoff is noise. Large exhausts not only have more noise coming out the back, but the whole thing acts like a sub-woofer. Transmitting exhaust vibration and pulses to noise which is both heard and felt.

There is no benefit to backpressure, especially on a turbo engine. Scavenging on a non turbo engine certainly, but scavenging and backpressure are not the same thing.
Turbo engines have little to no valve overlap so cylinder fill isn't much affected by backpressure. Exhaust manifold pressure on a turbocharged engine can be more than double the boost pressure.

so apart from the fact it will be loud ( im a x hoon so cool with that lol) will a side dump adversly affect the motor/performance?

[smurf182]

The tradeoff is noise. Large exhausts not only have more noise coming out the back, but the whole thing acts like a sub-woofer. Transmitting exhaust vibration and pulses to noise which is both heard and felt.

There is no benefit to backpressure, especially on a turbo engine. Scavenging on a non turbo engine certainly, but scavenging and backpressure are not the same thing.
Turbo engines have little to no valve overlap so cylinder fill isn't much affected by backpressure. Exhaust manifold pressure on a turbocharged engine can be more than double the boost pressure.

so apart from the fact it will be loud ( im a x hoon so cool with that lol) will a side dump adversly affect the motor/performance?

No, quite the opposite. You will get:

Lower exhaust gas temperature.
Faster spooling of the turbo.
Greater sound pressure level (volume, make sure it's 95dBA or less at a distance I can't recall - check out the LTNZ website).
Possibly more boost if the current exhaust is particularly restrictive.
More torque and therefore more power.

[KiwiBacon]

so apart from the fact it will be loud ( im a x hoon so cool with that lol) will a side dump adversly affect the motor/performance?

Probably not legal but it won't do anything bad for performance.

[DieselBoy]

One thing no one has mentioned is the silencers/mufflers.

Make you request they fit a "straight through" silencer, not one where it doubles back on its self inside the the box. You want a nice straight through free flowing muffler.

I have a 3" on the 80 Series, with a big straight through silencer. Its hardly louder inside, the turbo spools up to 12psi a hell of a lot quicker, almost instantly. Makes the whole truck livelier

[DJN]

Hi Badnuz
I have a bj74 with the 13bt. I have a side exhaust which exits just in front of rear wheel it is fitted with small straight muffler. It is 2.5 inch, no flexi joint [ I do have one but not got around to fitting yet] I would recommend you fit one as there is some vibration from the exhaust and has cracked once around weld it top. No problem with warrant as two door and is exiting behind it and no noise issue although it seems loud in truck when working hard on road. The change in the engine was huge,although a powerful engine it was always sluggish now it a lot more responsive, more like a petrol, holds on the hills so much better. So much more fun to drive. Best mod have done to truck.
Don.

[DJN]

Forgot to mention one downside, some of the forestry company's will not let trucks in with side exiting exhausts. Is stated on the permit. Can be a problem on some trips.
Don.

[badnuz]

DJN sounds like the answer im looking for, and yes i was planning to run flexi and a straight thru muffler, could be a concern re forrestry but not ( at this stage ) planing to do forresrty tracks apart from on ore trips ie rallwoods etc.... its the performance that im after for general 4wding and road driving etc:) cheers!

[badnuz]

well i finally got my side exit exhaust done, and man what an improvement!!! seems to spool up the turbo faster, and can pull itself from 500rpm just before stalling in 3rd low! ( albeit at a little struggle ). I didnt fit a muffler, and its not too bad at idle, bit racous at 2500 up to redline, but i enjoy the roar, and it drowns the snorkle induction noise haha!! most worthwhile on a turbo!

[4Paws]

So who has put a larger exhaust on a 2L and was there any benefits? And anyone cracked a head after this mod?

[IcedJohnno]

So who has put a larger exhaust on a 2L and was there any benefits? And anyone cracked a head after this mod?

I have not personally done the large exhaust mod but I know a few who have.

I have however seen the dyno results from the mod below.
What some people do not know about the 2L-TE is that the outlet housing of the turbo is also quite restrictive. By putting some die-grinding work into this detachable casting coupled with a matching exhaust flange, makes for big improvements over just the standard large exhaust.

[smurf182]

So who has put a larger exhaust on a 2L and was there any benefits? And anyone cracked a head after this mod?

Cracking a head after fitting a big bore would be utterly coincidental and in no way related to the new exhaust.

Check this thread out, http://toyotasurf.asn.au/forum/viewtopic.php?p=120722&highlight=turbo+porting#120722 theres some pretty good info to be found here and in other threads on the Surf site.

[KiwiBacon]

Check this thread out, http://toyotasurf.asn.au/forum/viewtopic.php?p=120722&highlight=turbo+porting#120722 theres some pretty good info to be found here and in other threads on the Surf site.

Seems to be mostly pontificating and drumming up business porting an unnecessary part of the turbo.
The first turbo mod I'd be doing to a CT20 is ditching it for a garrett.

[tweake]

terry has been doing a bit of work on the original gear rather than just swapping it out. have a look at the boost comp mods.
swapping it for another turbo would be great but of course requires adapter or new manifold. then there is cost issue.
i think hes now looking at what some firms actually do to "hiflow" them as well.

certainly with the 2lt's big exhaust certainly helps stop the head cracking issues.

old rule of thumb.....no such thing as a to big exhaust

[KiwiBacon]

terry has been doing a bit of work on the original gear rather than just swapping it out. have a look at the boost comp mods.

His idea of porting out the transition from entry to scroll in the exhaust is a little misguided. The A/R ratio describes the geometry of the scroll right around. Hogging out one place to a bigger area will just make the gas do a shuffle on the way past.

Most "high flow" turbo mods involve a bigger trim wheel. The tradeoff with those is they surge if you want high boost at low flow. High boost at low flow is exactly what we're trying to acheive to get low end torque in a diesel. The surge can damage both your turbo and your engine when the turbo sheds it's compressor blades.

[tweake]

the CT20 is a crappy turbo, just about any mod will bring improvement even if its upsidedown and backwoud !
i thinks hes playing with just to see what does what rather than that particule mod is the thing to do.

[4Paws]

After 250,000 to 300,000K just a recon of the turbo would be worth a bit of performance gain wouldn't it? They must have a bit of slop in them after that many kays.

[KiwiBacon]

After 250,000 to 300,000K just a recon of the turbo would be worth a bit of performance gain wouldn't it? They must have a bit of slop in them after that many kays.

Nothing touches when they're running properly, so wear of the bushes isn't normally a problem. Clogging up due to oil quality issues can be a problem, otherwise I guess it's more the number of starts that matters more than hours or km's use.

[Engineer]

this will be my next mod for the skanky 2lte.
2.25" from the flange just after the flexi. the dump pipe and flange onto turbo is 2" so theres not alota point making that bigger as the main restriction is after that flange. i was quoted $260 from flange back with a turbo something something muffler, it double back on itself so it shouldnt sound like a tractor but wont be restrictive.

Ryan.

[Bulletproof]

To put it very simply . To create any boost the law of nature says you can not have pressure one way without an equal force the other way.
The heat build up is before the turbo and it does not matter if the exhaust is ten inches across the turbo has to have back pressure to create boost.

A big exhaust can actually stop flow because instead of a steady flow you can get pulsations in the exhaust that slows the release of gases. I agree with kiwibacon that the heat difference in the exhaust after the turbo is very small.

bulletproof

[tweake]

this will be my next mod for the skanky 2lte.
2.25" from the flange just after the flexi. the dump pipe and flange onto turbo is 2" so theres not alota point making that bigger as the main restriction is after that flange. i was quoted $260 from flange back with a turbo something something muffler, it double back on itself so it shouldnt sound like a tractor but wont be restrictive.

Ryan.

2.5" is proberly easier. forget any fancy mufflers, anything straight through will do. it will still be very quiet.