High exhaust temp issues

[Howieau]

Hey,

I run a Gen 2 3SGTE with aftermarket rods, forged pistons, metal headgasket, slightly decompressed to approximately 8.5:1, head ported and polished and cams that have been welded and machined to a much bigger valve lift/duration. It has a big front mount intercooler and is controlled by an EMS computer, and has a standard intake/exhaust manifold and turbo. It also has an aftermarket homemade exhaust system which has various sizes in it.

I am just coming to the end of running the engine in for 3000kms, and am having heat issues with the car in boost. I have an experienced friend who has helped me with a tune to get me by until I can get on a dyno. We would drive the car normal doing 60km/hr (38miles/hr) in 4th gear and the exhaust temp (probe situated where the oxygen sensor used to be) would show roughly 470* celsius (878* fahrenheit) . When boosting, to give an example, doing WOT at 6800rpm in 3rd gear on 13psi of boost, the temps would go up to 720* celsius (1328* fahrenheit) before I back off the throttle. Then cruising on 60km/hr again after boosting the temps would sit on 530* celsius (986* fahrenheit), as if it had heatsoaked. With the idea that perhaps it was leaning out somehow, I upgraded to a Walbro 255lph fuel pump and 540cc injectors and we tried less boost, less timing, more timing, more fuel and nothing seemed to change the temps. I have an intake air temp sensor and the air temps were always consistently in the 30* celsius (86* fahrenheit) range, and water temps were always good aswell.

We are stumped for the moment as to what could be causing the high temperatures. I plan to do some track stuff with the car but cannot with such temps. What are some ideas that I should look into that could affect the temps like this.

I was thinking perhaps my aftermarket cam pulleys are not set correctly (done by previous owner) could this affect it? My exhaust system also has a length in it that is approx 2.25 - 2.5" and the rest is 3" so perhaps it could be back pressure, but then that doesnt explain why the temps then go higher in cruising after I have boosted, as if it has heatsoaked or something.

What other factors should I consider. Any input would be much appreciated.

[jeffro ra28]

A common wifes tail is that lean mixtures always cause high EGT's when in actuall fact they CAN cause lower egt's.
When you tuned the engine for run in did you set the timing advance very conservatively? Another common mistake. Retarded igniton timing causes hot EGT's, very hot exhaust valves and anything in the path of the exhaust gas. Fresh engines should actually be run in with a touch more then normal ignition timing to keep exhaust valve temperature and EGT's down.

Perhaps try advancing the timing a little more then you did. Obviously taking care its not detonating etc.

Note: A glowing red exhaust does not mean the mixture is lean, generally it means the air/fuel mixture is rich!

[Hen]

Note: A glowing red exhaust does not mean the mixture is lean, generally it means the air/fuel mixture is rich!

I've also heard two people tell stories of mis-timed cams causing this.

[jeffro ra28]

Yes indeed, that is also another cause!

[Howieau]

I spoke to a friend who has solely run a Motorsport workshop for 10+ years (just mentioned to give some credibility to his opinion), and he thinks the standard manifold will be what is causing the heat. Because I have such big cams and head ported/polished that my engine will be flowing alot more and wont be able expel the exhaust gases fast enough because of the restricted stock manifold.

Has anybody on here had an EGT in their car before/after putting in an aftermarket manifold - what difference did it make in the temps - a car with headwork that is.

[Hen]

The exhaust restriction sounds a little far fetched to me, though I definitely haven't run a workshop for 10 years... maybe replace "run" with "used" and "workshop" with "driveway".

But definitely the first thing I would check is your cam timing. Just make sure it is roughly dialled in correctly. I can't remember any figures off the top of my head, but I'm sure they are available.

Hen

[jeffro ra28]

Its got the stock inlet aswell tho doesnt it?

[af300e]

Has it got a cat? if so, are you sure it is clear?

[Howieau]

Standard intake and exhaust manifolds. No cat, straight through, though my exhaust system has a part that is 2.25 - 2.5" roughly which will cause restriction.

[abently]

Stock Turbo means stock exhaust Manifold is OK and not the problem. Simple as that. They are designed from Factory to flow the Turbo's max cfm due to many Racing categories restrictions on non Factory upgrades.

The only thing a lightly (Choke area non-modified) Ported Head and Cams will do is move the power-band down the rpm scale.

Look for other causes to your problem.

[sirbob]

In your original post you stated that your friend has given you a quick tune to get you by until you get the car onto a dyno. I would like to know how your friend tuned your car without a dyno, and can nearly garentee that he would have run a rich mixture to prevent undue damage to the motor duing run in.

As i undertsand it, running the car rich will cause the EGT's to skyrocket as unburnt fuel burns away in your manifold.

My advice would be to get the car onto a dyno ASAP, and get the tune right. You dont want to waste all your hard work and expense on a dodgey tune.

[rms]

What makes you think those exhaust temps are too high ????

[The Real Roadrunner]

they dont seem overly high for a turbo charged car, shit the charade had the turbine housing at 840*c on the dyno yesterday during a single dyno run with 12psi of boost.

i doubt the 2.5" section of your exhaust would be causing the problem either, try putting a port in the dump pipe and running spiralled copper line out of it to measure backpressure off, if its over about 5psi then change it but if not dont worry about it.

if its a std CT26 turbo the most restrictive part will be the exhaust wheel, they are extremely closed over and dont exactly like to flow alot of gasses thru them and create extreme temps when run above 16psi.

cheers
linden

[BlackSupra]

I will see anything from 500-700 degrees on boost depending on ambient temps with the temp probe in the exhaust housing and mine is on the rich side side of tuning.

[Howieau]

Took it on the dyno.

Only did a pull to 5200rpm as I was told it was detonating. I was never told the EGT when he backed off. AFRs showed up it jumped to 12:1 at 3200rpm then straight into the mid to low 11:1's until 4900rpm where it went into the high 10:1's then mid 10:1 where he backed off. I said to the lad there, "do you think the rich mixture could be causing the high temps?" and he said if anything it should cool them down with more fuel.

But as stated before in this thread apparently running rich can cause high EGTs from the unburnt fuel being ignited in your exhaust system, from what I understand. Maybe the lad was referring to combustions temps being cooled with more fuel.

I think next step will be fix up my exhaust system a bit, make sure its all 3" and change over that small 2.25" looking bit. Help it flow better and see if that does anything with temps.