James-man

I have and 86.5 with chips, RMB and X pipe.

I pulled off the X pipe this evening and put back the stock catalytic converters.

The exhaust note is different - I like it! It has a more balanced, yet more complex sound. Softer in volume when the pedal goes down, but idle and mild throttle is really not much different in volume.

Anyone else find that the RMB + chip exhaust actually sounds better than RMB + chip + X?

Subjective, I know, but I was surprised.

Other general comment on the differences between the two configurations: With X pipe, the car pulls really well with low through mid RPMs (4500), but seems to weaken at upper RPMs (>5700). I nearly always upshift below 6k RPM with X pipe on at the track. Without the X, the car pulls at an increasing rate from mid through upper RPMs tempting me to upshift at closer to 6200 RPM. Does this seem strange to anyone, given this is a free-er flowing exhaust. Could it be that chips were tuned optimized for restricted exhaust and I would need custom chip to take full advantage of tuning potential with free flowing exhaust?

Note that the Dave Lomas Crossover was developed on an unchipped 86.5.

Mako 928

ON my 85 S 5 speed I first did the RMB and noticed better low end then did the chip and noticed even better low end along W/ raised 6500 rpm fuel cut off. I have been considering the X pipe and you confirmed what I have been suspecting. When I was restoring early mustangs 65-68 that was what we were doing W/ headers we called it a cross over pipe and it did pretty much the same thing you have described, the idle sounded flatter but would get better low end power. I like the sound now but if I can get better lowend power I will be happier.

James-man

Mako,

If I could improve my top end, I would be ecstatic - I may need a different chip or fuel mod. I think a tradeoff between sound and low end power is a fair one. The car has a more refined audible character with the X-less configuration, but is more driveable with the X.

If I was still in the bay area, I'd let you borrow the crossover for a couple weeks to see if accomplishes what you want it to.

Tip: unhook the battery for a while, then reconnect when ready try out the performance mods. My experience has been that the car computer learns what to do MUCH faster this way.

Good luck.

Mako 928

Thanks for the offer this is why I joined rennlist, great comradery. I guess I could always drive out to Charlotte. The chip I have is the Autothority I have been pretty happy W/ it.

Bill Ball

I couldn't stand the sound of X-pipe with an RMB. It's not that it was loud. Loud is fine. It was annoying. Sounded farty and hollow at partial throttle, like a ricer with a 5" coffee can. I hated it. I put the rear muffler back on. It made the car too quiet, but at least I could live with the x-pipe. The x-pipe brought 30HP and the rear muffler did not reduce that.

James-man

Mako,

I did my initial upgrades in opposite order of you. I started with chips, then added RMB. That was about 10 years ago. Way back when, I used to go autocrossing with the Golden Gate region PCA. I nearly always used hard, old tires so did not pull phenomenal times, but I always had a good time at it. I think I won a points series. There were some good folks there. But I digress. We don't have the plethora of engine performance parts that are available for other makes and models. Fortunately there are just enough things out there to keep our cars interesting.

Still hoping for an e-Ram system that can generate 2PSI on a 5L 32V Porsche.

James-man

I get a taste of that noise issue (tone), but the resonators on 86.5 are actually mufflers which calms things down a bit relative to yours. I get that freeway droning thing - you must have experienced it with your initial set up.

You did the right thing.

I have to admit, the X + RMB is pretty awesome to hear at full throttle going under an overpass. Sorry if your thrill is muted with your rear muffler back on. I would bet there is a solution for you that involves swapping out your mid-mufflers for something else, but I'd leave the trial and error for someone else to go through until the right combination is discovered.

Bill Ball

Yes, there was a freeway drone. Whenever I was just cruising, it was bad. Hammer down was fine, but you can't do that all day.

Mako 928

Bill the best sound I remember from your car was when you passed by on one of the Norcal fun runs, the supercharger whine when you approached then the exhaust note when you went by. Pure heaven!

Mako 928

James-man
Thats funny it sounds like we both have similar experiences. I have been Auto-Xing W/ Redwood region and Golden Gate region and agree, tires make a BIG difference. Started W/ cheap street tires and then went to Kuhmo Victor racers. Big difference. Yeah there is not as much out there for early 32 V, I have found that getting as much weight out of the car as possible helps along W/ the mods discussed.

SwayBar

Louie's and Dave's x-pipe have repeatedly shown to markedly increase rwhp throughout the entire RPM range. When Ronn did the exhaust on the GT racecar, Louie's x-pipe was worth 20 rwhp all by itself.

Without doing a before and after dyno, I would not put much faith in the ***-ometer as it's too subjective. At the very least, maybe you can GTech the differences.

I forgot. To me, an x with an RMB is too raspy and non-musical sounding. Taking off the RMB and installing the stock rear muffler gave it a very nice musical exotic-car sound, if maybe a tich too quiet.

James-man

But did Louie and Dave test with chips? On 86.5 cars, chips seem to be worth between 15 and 25 hp. X pipe (no chips) seems to be worth 20 - 25 hp.

FWIW, My RMB + Chips dynojet was peak 272RWhp. Dynojet with RMB + Chips + X was 268rwhp (HOWEVER performance was affected by a "huge" vaccum leak in the intake and exhaust leak where the X and muffler pipes come together - both resolved the following week). How much power could a couple of leaks cause? I would like to remeasure now that the car is tight again and would like to capture air/fuel ratio to see what is going on.

I haven't seen anyone else post much in the way of cumulative gains with both X and Autothority chips. I suspect that the two are optimized in two different directions so they wouldn't help each other out much. Custom chips must be the ticket.

I agree with you on the sound. I haven't tried reinstalling RMB yet - I hate to add weight back there when I am about to head down the path of lightening the car up a bit.

SwayBar

I would think an x is more sensitive to cam timing, versus chips.

The x works by sending a negative-pressure pulse up to the opposite bank which hopefully arrives at the exhaust valve just before it opens. When the exhaust valve does crack open, the hot exhaust gases escape even quicker into the exhaust pipe due to the lower pressure created due to the x.

At the very least there will be less pumping losses since the piston will not have to push as hard to clear out the cylinder, freeing up hp to be used elsewhere (..hopefully the rear wheels).

Depending upon how much additional velocity is created by the hot exhaust gases exiting out into the exhaust port, cylinder scavenging will be improved, including helping to pull in additional intake charge than before the x's installation. More intake charge in a given amount of time equals more horsepower.

So after all that thinking out loud, the x pipe will function the same, regardless of the installed chip, due to the x's dependency upon cam timing. And with a better chip, the better the results.

Shane

It works just fine for me, but I've heard S4's and GT's with the smaller mid-mufflers that were annoying with that combo.

James-man

Good comments, swaybar, thanks!
This sounds good in theory, but where is the empirical proof? Chips have been passed around like candy for a long time, and Xs have been recently added. There must be more than a couple of us that have installed both.

I would expect a chipset to enhace X performance by maybe 10 HP. You can't reasonbaly add 25hp + 25hp = 50. I would expect 25hp standalone chipgain and 25hp standalone X gain to come up to 30 or 40.

Chips were optimized holding other elements fixed such as exhaust backpressure (assume stock). Changing some of the constants, like exhaust, probably detunes what was once optimized. Same goes for X development with stock chips. I am open to the possibility that my car's fuel could use improvement on the top end with a different fuel pressure regulator, but am more inclined to believe that X and chips assume the other does not exist and there is some cancelling of benefit between them.

I believe that the only way to get 25 + 25 = 40 is with re-optimized chips with X as a constant. Sharktuner?

So the challenge goes out. 86.5 with X, Autothority variety chips, and RMB: Please post your dyno results.