Has anybody dyno'd their car with the same set-up and simply switched between a mid-pipe and a high flow cat? I am very curious of the exact effects of a good quality high flow cat throughout the power range on rwhp. If you have please post the results...

In the next week or two I am going to try to get my hands on a midpipe and retune the car. Afterwards I want to throw my high-flow on and see what power loss I'm seeing... I'd like to keep the cat if I can because I really don't like the smell or noise of a midpipe, but if their is a huge power difference, I might ditch it.

Just dyno'd my car last week. AFR's went to the 9's at more than 5k rpm's, using a tailpipe sniffer after the cat - so it's actually reading leaner than it really is! I have a lrage street ported motor, running 850's/1600's, and everything to support it. Engine is new with 1300 miles on it and the car is running great.

At 15 psi it only made 340 whp with a new SMB metallic high-flow cat (flows very well for a cat). I have seen other curves with a similar turbo (mine is a derivative of a GT40) and it made 390-410 whp with a midpipe at 15 psi. I figure that getting my AFR's back up will get me maybe 20-25 more hp in the upper rpm's. So in the end that would imply that the high-flow is killing about 30 rwhp or more whp at > 6k. Does this seem right? It seems high to me...

Thanks,

Matt

 

i talked with Ray down at PFS a little about this like a week ago. He said the majority of high flow cats narrow down to like 2-2.25" inches instead of being a full 2.75-3" like most midpipes. So it's basically a bottleneck.
-Austin

 

If your Air / fuels are really at 9 after the cat, you are losing a TON of power from that

The RX-7's ignition system doesn't work real well when you go under 10.

 

In the rpm range from 6,xxx rpms to 7,xxx rpms it appears you are having some ignition break up and as you noted you are also very rich. You could gain an roughly 10-20rwhp by leaning it out to 10.8 or so.

The horsepower curve at that area should have the shape of a crown (arc like). The bigger the port the further the peak of the crown shifts toward the higher rpms. I believe a stock ported engine peaks around 6,800 rpms.

A couple of years ago I switched from a high flow cat to a midpipe on stock twins. I dynoed each configuration within a month, the AFRS were close but the horspower gain was only about 10.

If you search the 3rd gen section there is a thread where a midpipe and high flow were dynoed, I know that test resulted in a much higher gain, possible 30-50 rwhp.

 

1. ditch the hi flo cat for a straight through pipe

2. get the A/F's stable around 11.0-11.5's

3. throw some timing at it



A/F's in the 9's is wayyyy to rich!


good luck!

 

Alright... thanks guys. I'll get it retuned and on the Dyno hopefully be next weekend with a midpipe.

 

I made 360 at 15psi with a metal substrate cat, Blowzilla (aka GT35R compressor with a 1.00 divided hotside/s-trim wheel and a large street port. I was disappointed to say the least. Afrs were 11.3 all the way across. Timing at 15psi was 15L with 11 deg split. I had ignition breakup starting at about 6,900, so that may have been a limiting factor to some degree.

Your numbers are consistent with my experience.

 

at what rpm was the 15L and what was the leading at 5,200 rpms?

thanks

 

Thanks for the input. Did you ever put in a midpipe and retune & dyno it?

 

Did you ever run a midpipe, retune and dyno the results??

 

Many things happened between now and then, the car now puts down 395 whp with a midpipe and gt4088 turbo with a .94 (slighly smaller because it was ground down some) hotside.

But... With just changing the midpipe and a retune, the car made 383 rwhp. The cat was actually dead (only 2k miles). The honycomb was all broken up inside when I removed it.

 

I'd be interested in seeing the new dyno results.

How's the response of the GT4088? (compared to twins, GT35R, etc)

 

I don't have the dyno sheet from the 395 whp pull. The response of the 4088 is pretty good IMO, but I have a < 0.94 hotside on it. So I gave up top end to get a better midrange. I see full boost (15-16 psi) by 4000 - 4200 rpms depending on gearing.

 

Moehler, are you running the GT4088 with the coolcharge III intercooler? that is the same setup i want to run. how is it working out for you?

 

It's an ASP large... basically the same thing as Pettit's CCIII. Set-up works great. Good temp control, good boost response.

 

For 4000-4200 full boost I would guess that is in 3rd gear for that turbo?

 

yup. same thing happened to ccarlisi's cat. clogged and dead after minimal miles. i don't think those things are suitable for our cars.

 

Yep, 4th gear is 15 psi by 3900-4000 rpms.


I was pretty disappointed about it to say the least. Oh well, now I get to shoot 3' flames at wot, lol!