Opinions on fuel tuning?

[kylemoto]

Greetings all of you DSM gurus out there!

I have a 1991 Talon with the following:
- 14b turbo set at about 15 psi
- K/N FPIK
- 2 1/2 downpipe, cat and catback exhaust
- hacked MAF (lower honeycomb out, screw backed out halfway)

The following are stock:
- clutch
- injectors
- intake system
- intercooler

In general, the car runs very well, but here in California all we can get now is 91 diet gas. Sometimes on long trips only 87 might be available for short periods. So I am looking at the following stratagy: set things such that I can run the light gas available, and keep the major components stock (keeps costs down). The plan is too keep the 14B and run only moderate bosst levels (if that means lowering, thats ok too). I want good response at the low end, even if nothing is done to the high end. Finally I notice the engine runs pretty dang rich at idle and low speeds. So, my plan of attack:
- better intake, like a Dejon. (I have heard about a 10 HP gain from better flow. Its pretty low cost too).
- is porting the exhaust manifold and turbo inlet a good idea for response? Anyone have answers on what kids of improvement is possible?
- address the fuel situation. The MAF screw is open. Can the throttle position switch be set to make the ECU think lower load, and therefore lower fuel rates?
- ignition timing. The consensus I get from the postings in here are don't mess with it - advanced timing causes all sorts of drivability problems.

Ok....thanks in advance for your opinions.


Kyle

 

[IPT]

It seems like you have a good start and good ideas where to go. As far as the 87 octane DO NOT DO IT!! I burnt up an exhaust valve running it. I needed gas, I was going on a long trip and the only gas station that was open only had 87. I figure what the hell I will just adjust for it. I richened it up 10% across the board. I did not have a datalogger, but I could feel the timing getting pulled. After the trip I pulled my plugs.... NASTY there were Gray specks all over them. That ment that there was very bad detionation going on in there. Ther car never run right after that, Low on power. I finally did a compression check and had NO compression in the #1 cylinder. Pulled the head burnt valve.

What I should have done was put in just enough to get to the next town and then full it up the rest of the way.

 

[kylemoto]

Regarding the octane.
By the way, I have a 1991 Talon, did ya know the recommended fuel is 87 octane? Of course, thats before the added boost, high flow exhaust, high flow air filter....on and on

I am going to try and do some additional tuning though. One additional thing I am going to look at is of idle response. With the compression set at 7.8:1, the engine has little pull. With the air conditioning on, forget about it - if the clutch isn't slipped a little bit then acceleration will happen tomorrow!

I will get the Pocketlogger first so I can see what happeneing. I imagine the things I will be looking at will center on knocksum and A/F ratios. I bet I can play with the throttle settings and get some improved response at the low end too!

Well, thanks again for the feedback. Anyone else want to add?


Kyle

 

[NDgsx]

Originally posted by kylemoto
I will get the Pocketlogger first so I can see what happeneing. I imagine the things I will be looking at will center on knocksum and A/F ratios. I bet I can play with the throttle settings and get some improved response at the low end too!

Good plan. A logger was the second best thing I bought for my dsm (best was a civic for a back up car ). I wouldn't do anything until you have it. With the screw out and 15psi you are probably running a little bit lean, that's been my experience.

Where does it say 87 octane on your car? On the indside of the fuel door and cap on my three DSMs it has said only premium octane, blah blah. I got my 91 for $500 off a kid who had run 87 octane, blown his headgasket, run dry of coolant, and seized the pistons in their bores. Not saying it WILL happen, but you're better safe than sorry.

You're going to want to upgrade your fuel pump, get a 190lph pump so you can keep the stock FPR.
With the 1G intake pipe I didn't notice a big difference going to metal pipe. The stock pipe isn't really that bad on a 1G. With a 2G mas on a customers car a dejon pipe did make a large difference though.