I have the A-spec gt40r kit with the wastegate dumped back into the downpipe. The way they did it puts the wastegate dump in at a 90 deg. angle to the main downpipe. Anybody see this setup and do you think it should be replumbed. I am thinking of running the wastgate seperate with its own muffler but do not want to go through the hassle if it won't be of much benefit. I just think incoming flow perpendicular to the exhaust stream is not the most efficient.

I am also running into a situation that once I get to target boost and therfore stay on the wastegate, my air fuels get real rich. I don't know if this is related to possible back pressure in the exhaust or not. Just starting on this. I do not think it is my fuel maps because I can be in those cell when accelerating and not be rich. It only goes rich once I am at target boost, like in 3rd or 4th gear, and accelearting. I hope that made sense.

Mike

 

It shouldn't effect airfuel readings at least not noticably. The reroute will effect overall flow to some degree the two biggest contributers are angle and distance. You are more than good on distance. Anything after 18" of the turbine is ideal. I'm not understanding you totally but it sounds like your needing to take fuel out while under boost.


-S-

 

"I do not think it is my fuel maps because I can be in those cell when accelerating and not be rich. It only goes rich once I am at target boost, like in 3rd or 4th gear, and accelearting. I hope that made sense."

I don't know what ecu you are running, but it is quite possible you are not in the same cells. For example with the PFC you can be at 5,200 rpms but at various boost levels depending on how your map is set up. Running 15 psi at 5,200 rpms is most likely not the same cell as 10psi at 5,200 rpms.

 

Sean, have you considered an upgrade 3.5" DP with a WG routed back in? Add a 3.5 MP in there and I bet you would clean up.

I like my 3.5 custom DP...WG is now dumped to air. It's a "statement" when WG opens now. Drowns out uncorked giggling Ls1's.

Mike you have a log that shows your "rich" after target boost? When is "target boost?" Mike, what RPM are you hitting 17psi in 3rd, say starting from 2500rpm?

Tony

 

Sean, how much hp do you think can be gained by rerouting the wastgate out from the exhaust? I know space constraints were a limiting factor on how you had to design the way the dump tube reintered the downpipe. Since the angle is not the best, would seperating them net a noticable increase in hp.

Also, will too much back pressure in the exhaust cause the car to run richer? I was wondeing about this due to the issue above. Would the turbulence of the two exhaust streams coming together at 90 deg angles cause an increase in back pressure. And what effect on air fuel might that have.


Books, I have a power fc. I know that the cells are different for different boost levels and rpms. It just always seems that the car runs fine untill I get to my set boost level. For example, 1st and 2 gear will pull fine and log a/r's in the 11's. I can then see on my datalogit that I went through certain cells and recorded certain air/fuel numbers in those cells. If I am in 3rd gear however and get on it, I reach my set boost level earlier and maintain that boost till redline. The car accelerates hard till it reaches my .7bar setting and then seems to flatten out. When I look at the air/fuel meter it is in the low 10's for the rest of the pull. I go back and look at the log and now see much richer numbers in the same cells that showed leaner numbers when doing a pull in 2nd gear. Same couple of cells but different readings. It seems as though a cell will put up different a/f numbers depending on what gear you are in. Maybe it has to do with how long I am in a certain cell. In 2nd gear I fly through cells and in 3rd gear I am in each cell longer.

with a 2nd gear pull I might not reach 10psi til around 5500 rpm. but from 5500 rpm to redline, I should be in the same p row moving to the right. If I get on it in 3rd gear I will hit 10psi earler in the rpm range. lets say 4500 rpm. Now from 4500 rpm to redline I will be in the same p row (boost row)as above. This means the same exact cells fromm 5500 to redline as above. So one would think the a/f numbers in those cells shold be the same but they are not. The 3rd gear pull yields richer readings in the same cells. It could be an ignition problem but I am running a crane Hi-6 with a TII coil. It doesn't seem like it's missing but just feels heavier. Like some one is pulling on the emergency brake slightly half way through the pull.

Mike

 

Tony, I just finished putting 1000 miles on the new motor. I just started putting her into boost. I have not gone past .68 bar yet. The logs that I have saved so far do not have seperate 2nd and 3rd gear pulls. I will try and save some tomorrow to document what is going on. I haven't had much time to mess around with the car. 15 min to work and 15 min home doesn't leave much time for experimenting. Hell, I am half way home before the car even reaches operating temp. other than that, I only get sundays to get any time to work on the car. Lets see what I can find out. It might just be tuning.


Mike

 

I actually offer 4" DP and MP stuff for guys who are running the GTspec and the HKS racing exhaust.

Seperating will make a diference for sure, how much exactly is hard to say. I'm not a big fan of the way rotaries sound with open wastegate. Not nearly the same as a piston motor.

-S-

 

what is the sound difference of having the wastegate routed into the downpipe, and runnin it open

 

Mike,

That was a very clear explanation of your runs and logs. I pulled up a few logs of 3rd and 2nd gear runs from a couple of days ago. There were no significant changes in AFRS between my 2nd and 3rd gear runs.

Perhaps you could perform a 4th gear run and see if those results are closer to the 3rd or 1st and 2nd gear runs.

You could still forward your logs to Tony, he can segregate the data from the 3rd and 2nd gear pulls based on the rpms vs kph data.

fwiw, I have noticed while making successive runs within seconds of each other; my AFRs seem to richen up for the same cells.