Header leak causing HIGH egt's???

[Spooled]

I'm seeing EGT's WELL over 1700. The guage stops at 1600 and it's well past that. I'd estimate 1750 or more. The actual AF ratio is right on at 11.4. Timing is around 25 degrees on 110 ocatane. I've got some header leaks (those damn copper SCE gaskets dont' seal worth ****). I know air leaking into the header can cause flames on a NA motor. Could that cause these HIGH egt's? Thanks for the thoughts

 

[Craig Smith]

I am no turbo expert but I have heard of many people whose EGTs are comparable to yours on a high-powered turbo setup. The header leak isn't helping you a bit, but that fact aside, you may not be doing that bad. Those with knowledge of turbos, please chime in and educate me if you would be so kind. THX

 

[Spooled]

More info here...

Well i have more problems than just my high EGT's. I make no more power on 19 lbs than i do on 13 lbs. I use the same VE of about 75 to keep an AF ratio of 11.4 on both 13 lbs and 19 lbs. it seems like i get a rise in PSI but there is no more actual VOLUME of air getting into the motor. My BOV doesn't leak, and i don't think my intercooler is restricting too much b/c i took it off and there wasn't much of an improvement. I really dont' know what the problem is. I did a compression check and everything looked ok. I've exhausted all posibilites i can think of. I think i'm using enough fuel for about 530 HP. I think that's about the right number at 13 lbs but at 19 i should be pushing much more. It's just not getting the air for some reason. It went 124 mph on 13 lbs at the track and then went 123 on 19 lbs. Somethings not right obviously. It feels exactly the same on either amount of boost. Duteweiller picked out the cam...it's 228/228 at .050 on a 114 (hyd flat tappet). I wouldnt' think he'd pick out a bad cam. I'm checking it tomorrow to make sure i haven't wore a lobe flat or something. I'm really stumped as to what it is. I dont 'think i'll ever figure it out. I've done all the simple things...verified timing, checked for leaks, etc. If anyone has any suggestions, I would be glad to look into them. I'm totally OUT! Thanks for all the help fellas.

 

[NoSlix]

Valve springs letting the valves to float a bit at the higher boost level, maybe?

Shane

 

[bobc455]

Just thinking a bit here-

I would guess that a header leak would allow fresh air into the exhaust pipes (on the low pressure side of the exhaust pulse). So your O2 sensor would then be seeing more fresh air than what is coming through the motor, so it will think you are lean. Then it will richen up your fuel (causing extra fuel consumption).

However I would think that running richer would bring your EGT's down. If it weren't for that, I'd tell you to fix your exhaust leak and be happy.

So I have nothing useful to add (but I would still fix the leak).

Valvesprings are also a good thing to consider- 19# of boost doesn't do you any good if you are not closing the valves.

-Bob Cunningham
bobc@gnttype.org

 

[nightdiver]

What Turbo bo you have ?
Small turbines makes high exhaust pressures thas high temps

 

[Spooled]

Those are good thoughts fellas. I have 120 lbs on seat on a hyd flat tappet cam. Dutweiller said taht was the max he'd recommend. I have a T-72, P trim, with a .82 turbine. I'd think that should be ok for my application. I checked the cam last night for a flat lobe. The only thing I saw was one rocker that was loose. I'm still stumped...

 

[nightdiver]

I got a T74 with a 0.84 turbine P trim. 1250*F WOT & 1350 when i travel

 

[bobc455]

I just read another thread where the author insists that running rich *or* lean can give high EGTs- if that's true, then I think as soon as you fix your header leak your EGTs will come down and you'll be making power again.

I am guessing that your actual A/F is pretty close to your target A/F, but you are seeing some O2 sensor correction to get there. That's because the O2 sensor is not reading what's actually coming out of the engine- it's reading some engine exhaust + some fresh air that comes in through the header leak.

If you have a header leak, you should disregard the reading from the O2 sensor.

-Bob Cunningham
bobc@gnttype.org

 

[ChrisCairns]

Originally posted by bobc455
it's reading some engine exhaust + some fresh air that comes in through the header leak.

If you have a header leak, you should disregard the reading from the O2 sensor.

-Bob Cunningham
bobc@gnttype.org

I've never understood this. I can understand how, through the venturi principle, air is taken in at idle, no backpressure but not at WOT with tons of backpressure.

How can air from the outside get into a pressurized header? If you're running 20 psi at the intake then you're going to have 25+ psi in the header...

Am I missing something?

Chris

 

[Craig Smith]

120 pounds on the seat? With 19 psi boost? There's your problem.

Multiply 19 psi times the surface area of the back of your intake valve. Now subtract that number from the 120 lbs seat pressure. That's how much seat pressure you have at that boost level.

I think the final seat pressure numbers you will come up with will scare you.

 

[lazaris]

Craig,

Dont you have to include the cyl pressures acting in the opp direction tring to keep the valve closed as well?

 

[10SV6]

What's the rest of your combo ? Is this a V-6 or V-8 ?

I ran 105 lbs of seat pressure last year with a hydraulic flat tappet last year @ 24 lbs boost. 1.9" intake valve.

You might be out of turbo.

 

[Spooled]

Craig, Dutweiller said 120 was the max he's run on my cam. I dont' know if he remember that i was running that level of boost or not. I'll call him back tomorrow.

10SV6, it's a 383, with 8.33:1 CR, 190cc AFR heads, 228/228 cam .492, T72. I thought this turbo was good to about 800 HP or so. I'm not there. It will run high 10s at 124 on 13 lbs. That turbo should be able to do more than that. And if it was the turbo, i wo uldn't think I would see in increase in PSI. With my blitz controller set at 45 (which is suppose to be a percentage of full boost), i'm at 18 lbs. So i think the turbo has more to give. I'll see what kenny says tomorrow about valve spring pressure.

Any other thoughts on what it could be?

 

[RealFastV6]

Have you verified your timing/crankrefangle with a timing gun?

 

[Spooled]

I sure have....it's right on.

 

[10SV6]

I'm wondering if the exhaust side of the turbo is too restrictive. You'd see the high EGT's, lack of increase in MPH with higher boost.

I've gotten higher boost and not seen any gains MPH wise. The turbo has gotten out of it's efficency area.

 

[Spooled]

10SV6, do you mean the turbine housing or the exhuast after the turbo? My exhaust after the turbo is this: 3" mandrel bent piping, about 4 ft. in total pipe, and a 3" dynomax bullet muffler. I would think this would be adequate. Or if your saying my .82 is too small, can anyone else chime in on this. Would you think it's too small for my combo? Should I step up to a .96? I'm not too hot on reading compressor maps. I'm not sure where i'm falling in the map.

 

[nightdiver]

I dont think that the 0.82 is small .When does the T 72 wake up ?
3400 to 3600 full boost ?
Id say its some kind of spark plug /wires problem
I saw once on the dyno 1800 F but it was substracting advance due to deto of high intake temps

 

[Spooled]

I get full boost i'd say at about 4000 rpm. I just bought brand new moroso blue max plug wires. And I run the accel plugs, gapped usually at .032 but i just narrowed them to about .28 and it didn't help.