Sameer

I had the Zork tube on and with not uch pressure, it did'nt make any difference in low end but pulled stronger on the mid range upwards. Same for the Fabspeed muffler.

Peter Carroll/Toronto

I'm currently running a K29-7006 but I've gone through a few turbos too. I've been told it's a big one even for a K29. The K27s, even HF, also seemed to have been a restriction on my engine. My current headers are a custom set that look like B&B but use larger tubing. I have some lag but it goes like a bat out of hell now. The EFI got rid of a lot of lag. I have pretty much immediate torque everywhere.

As for losing torque with an open exhaust, I think that argument only works for normally aspirated. I'm not really a great expert here, but a turbo derives its energy by the pressure differential between the high and low pressure sides. Back pressure in the muffler would only reduce the spinning potential of the turbine. How can that ever be good?

As for flames, I get quite a lot. Four feet or so I'm told. I believe they only come from the turbo as they only occur when I lift off the gas. The wastegate would be closed in that situation. When the throttle closes, ignition cuts and the unspent fuel is ignited in the exhaust system. Since the headers and straight pipe account for less than 24 inches, the flame lasts well beyond the end of the exhaust system.

The other benefit of a straight pipe is that you are removing a great deal of heat from the engine bay. The muffler used to arrest the flames in the engine bay. My rear reflector was melting from the heat. Now the engine runs much cooler.

DonE

Flames are from a lean condition.

For proper or quick spool, back pressure in the header should be between 12 and 15 psi, before the turbo at idle. A local tuner uses a pressure probe in the header to match the engine with the correct turbo, and tunes using temp and pressure in the pipes.

PT

Peter, with your 3.6 if you don't have immediate torque anywhere anytime, we must be driving a chevette then

kens911

Peter you have any good pics of how it's routed under the car?

38D

I disagree. Flames typically come from unburnt fuel hitting the turbo and igniting in the exhaust, normally when you lift off the gas at max boost.

sand_man

Correct. I get the feeling the animal in this picture (and in countless others that I've admired) is NOT running lean!

911rudy

DonE,
I live in Peachtree City and would like to talk to you about your tuner and car. I know you don't want to receive e-mails but maybe you could talk to me one time. My phone is 770-487-6055 and my e-mail is yarbros@comcast.net
Thanks, Rudy

DonE

If you are comfortable in tuning your car, lean it out a bit and tell me what happens. Then fatten it up and see if you get.

Slightly lean will significant heat the entire exhaust system as to burn any unused fuel (typically on decel or between shifts). WIth a rich condition, you cool the system (after all, thats the idea in order to reduce detonation) and there is just too much fuel to lite.

Its not fair to show a pic of a race car and compare with with ours. That car is tuned on the raged edge, but for longevity (at least a race). It is not in a lean condition, but it is at WOT most of the time. Therefore the exhaust system in always cherry red, so you could dump a bucket of fuel through the system and get great fireworks.

I can tune my car to produce flames on the go. It typically happens between 15.5 and 16.0:1 AFR on decel or between shifts. To get rid of it, I set the min injector pulse width for that RPM/MAP cell to provide 13.0:1.

DonE

Send me an email at 930turbo@mindspring.com and let me know when you want to hook up

38D

My car is used 95% of the time on the track, hence my comment. Street use may be different as you have said.

sand_man

Peter Carroll/Toronto

Cars have followed me into service centres along the autoroute just to express to me how spectacular the flames are. So I suppose it flames in everyday driving too.

For sure the car is not running lean. Engine temps and EGT remain low when it's happening. When I had the O2 sensor in there the AF meter was off the scale (rich) under boost. The car is running a Tec3 and when I lift, a little fuel dumps during the overrun.

BTW: If you want an engine like this, try leaning out yours. It's one of the fastest ways to kill an engine. My old 3.3 ran lean under boost due to a deteriorating fuel head. The car made impressive power right up to the point where it didn't... Now I would like my new motor to last.

Sameer

Seeing flames are signs of running lean? Thats something new to me but thanks for the info anyway.

DonE

OK guys, I did not mean lean your car out to the point of destruction....

My engine, under boost, sees 12.1 - 12.5 AFR. At cruise, it is at 13.9 - 14.3. At decel, it is no more than 15.0.

When I lean the cruise to 14.7 - 14.9, and lean the decel to 16.0, it will shoot flame and back fire and so on. The car will not be damaged in this condition. Hell, there are a bunch of CIS cars running around like this, and even worse, they are showing low to mid 13's under boost. That will provide a hell of a flame.

That being said, every engine is different, especially when they are modified. For example, my engine would not run (black smoke, slow response, fouled plugs, etc) with AFR's under 11. Peter says that his car goes off the scale rich under throttle and it runs. So who is right? Both are right if they deliver the expected results.

So when I said lean it out, it DID NOT mean run at dangerous lean conditions. It only takes about a half a point on the AFR for my car to produce flames. For a turbo car, I can not see how this could not hurt the turbo after a certain amount of time. The turbine blades are fairly fragile, so popping and mild explosions in the turbo can't be good.

Peter - you have a tec3 -so do I. How do you get the fuel to stay on when you lift the pedal under accel? As soon as my unit senses both MP and TPS change, it adjusts the injectors immed. Do you keep fueling for cooling or to wash the cylinders? I can get the injectors to fire AFTER decel for a specific pulse width.