J Chen

Brent,
I suspect your rough running issue is due to the
fact that the APE chips are not compatable to the
72lbs injectors. You can massage the A/F but you
can't control the injector pulse width.

Brent951

Thanks for the reply, hopefully that's it, I'm going to try to have John make me some chips.


Brent

special tool

That's the end of that problem

Brent951

That's the end of that problem
__________________
Jim


I have my doubts that it's that simple but I'll report back. If anyone has some tests for me to try before I get my chips I'm all for trying them out. Thanks for everyone's input.

Brent

TurboTommy

Brent,
I couldn't comment on your PB setup, partly because I'm not a big fan of PB.
You'll definitely be on the right track with a custom chip.
You'll find with big injectors, however, that the idle, and especially the transition "tip in throttle" won't be as smooth as the stock injector/chip combo.
Maybe others here have solved the problem 100%, but I can't seem to get it just right.


sl951,
I guess we're kinda guilty of OT to this thread, but:
at first glance it seems to make sense what you're saying, but it's still not correct.
You can do your own research, but just quickly:
longer strokes are always accelerating/deccelerating more quickly than shorter strokes to get to/from their highest midpoint speed. Therefore, at any given point in time they will always be further from TDC than a shorter stroke.

Ski

it was said earlier, get the Vitesse 2.8 chips, not only does the timing need to be adjusted but with regards to the air metering, the APE chips were set for a VE of 2.5L - just think of it as an air pump. The new chips and the piggyback, I think you'll be set.

Tommy - why not a fan of piggybacks? How many custom sets of chips would you have to go through + dyno time to get all the data that you need? It certianly doesn't seem to fit to me even in the financial point of view with the SMT6 and Mafterburner coming in under 1 dyno session and a custom set of chips. The right set of chips for the engine size and timing and the you take control of the fuel to set up your own version of the perfect A/F ratio.

MySwiss

I can certainly vouch for the Vitesse 2.8L(stroker) chips, since I have a customer running with these in his 951, with fantastic results. John's chips combined with a decent fuel controller, will yiel reliable results.

As I said earlier..It's very easy to melt down a 2.8 stroker. I speak from experience...

APE chips are not the best.....for any application. As John stated, the timming is way to agressive and they tend to lean out to much(13.3to1) on the top end. So it's definitly a combination for desaster in the 2.8L.The power curve and torque curvs are different and simply adjusting the fuels isn't enough....

FSAEracer03

I didn't read all the posts, but whatever you're tuning with, I'd question the instrumentation as well as the chips. X-brand chips will only hurt you so far as how much you modify them with the piggyback. If that 14-14.7 reading you referred to was at idle, then you really shouldn't be worrying. Idle air/fuel is sporadic at best, and it will wander high without a problem. Tune only off full-load.

If your readings are jumping to 14-14.7 at WOT... wow, well we need to work on that

Good luck!

Brent951

FSAEracer03,

It's not so much that the O2 reading is jumping around, it's the idle that's not very stable, 900 to 1000RPM and if I try to maintain say 3k RPM it varies somewhat as though the fuel or air delivery isn't constant, although I yet to find any leaks in the system.

Thanks for the input, Brent

FSAEracer03

How much does it vary? If it's jumping 14-15, that's wild, but if it's 14-14.1 or something, that's only gauge error (in this case, sending error, but you get the point).

How does the engine sound? Does it rev crisply or sound like it's getting an odd fuel load? We'll get this worked out and have that sick monster ready sooner or later

Brent951

FSAEracer03,

How much does it vary? If it's jumping 14-15,
It can vary quite a bit when the idle is jumping from 900-1000 it goes from 14-14.7 although if the idle is stable then the O2 is stable as well. It's pretty erratic though, one second it will be stable then get rough again.


How does the engine sound?
At idle it sounds like it has some kind of racing cam, at higher RPM for the most part it's pretty smooth all the way up to 5k. On the other hand if you try to maintain say 3k you can tell it's not running perfectly smooth.

Thanks, Brent

sl951

Brent951: At 3000-3200 revs are you getting rough vibrations. I seem to have these on my engine with a lighten crank with balance shafts.



TurboTommy:
TDC and BDC Dwell Time is dependent on crank stroke and the rod Length. The crank stroke length is only part of equation for dwell Time. The rod length is the other key factor. I'm guilty of not talking about the rod length in my orginal post.

Brent951

SL951,

It's not so much a vibration it's more of a slight change in RPM or a really mild miss if that makes any sense. So far I left me balance shaft belt off to see how it's going to run without one, does anyone else have an comment on running 2.8 without a balance shaft belt?

Thanks, Brent

dupeds

Brent , I am not qualified to respond to your current posting. I would very much appreciate being able to purchase at World Pac quality and prices. I have two 1987 951s. I did have access to World Pac in Florida but now no longer help out in a shop and am spending this winter in NY. Thanks, Ben

Brent951

Ben,

Not a problem, just let me know the part number you're looking for and I'll get you a price. Here's a link to the 951 manuals and PET5, I think the PET6 that's on there is corrupt.

944/951 manuals, complete PDF's and PET 5 app for all years I'm sure everyone already has that though.

http://www.cannell.co.uk/944%20Reference.htm

One quick question for the group:

In the mean time I'm still trying to figure out this problem, I got some new chips from John at Vitesse and it changed the fuel curve but I'm still having to really lean out the car at idle and then add a ton of fuel at RPM, someone that knows how to troubleshoot better than me will hopefully be here soon to help out. Can anyone else confirm the amount of vacuum at idle when cold and at idle after warm-up. At higher RPM I'm getting about 20psi of vacuum (No load of course) I've noticed that at startup I'm only making about 5psi of Vacuum and then 10-12psi after warm-up. I assume that's the idle stablizer closing after the DME senses that the engine is warm?? I'm using webcams #274 cam as well if that changes anything.

Thanks, Brent