"Ray's AKA demonfire's XR4Ti build up"

[Ray]

Car's been feeling down on power all season. Couldn't place it. I pulled 1 degree of timing and added 3 points in fuel under low rpm high load (100kPa up, 2300-3600) but that shouldn't have taken my car's ability to melt tires away.

So after yesterday's autocross (first in class but the class was tiny), decided to dive into the motor a little bit.

Compression was good - 145-150 psi across the board, went to check cam timing, so just to fart around backed the adj. cam all the way one way, checked compression, then advanced the other, checked compression again. Picked up 5psi on full advance, figured give that a shot and nope, car would barely free rev to redline.

Backed the belt off after indexing belt to pulley location (easier than finding TDC at 9pm in the shop), adjust pulley to give 1 tooth over advance - again, not any better, go the other direction and yup.

Now, do these belts seriously stretch this early? This has at the most 1k miles on it, but granted, this isn't a street car. I have a spare on the bench. And yes, Ms. Daisy is now back to a tire melting machine. Absolutely insane what 8 degrees of cam timing can do.

[Ray]

So after a quick search, apparently it's common for the square teeth to jump time on higher powered cars. Live and learn.

Some pictures from the last event. Took home a win, but the car was probably 50-60hp and 80-90ft lbs (or more) down on power due to the cam timing being off.



A little countersteer...

[catapultkid]

That's interesting. I don't think I have this issue, but I need to look as I hit the limiter almost every event now with the 4:10s.

Made any adjustments to the suspension tuning? I'm looking to change it up in the near future.

[Ray]

I haven't touched the suspension. Currently looking into ways to lower rear roll center without lowering car any more.

I'm going to index the timing belt in reference to the distributor pulley / cam pulley with a paint pen, and just keep an eye on them both a few times a season. Easy enough.

Oh, because i'm me - going with a 3 bar MAP sensor and upping the boost to about 21-22psi (currently at 17psi), should make for a bit more fun on the straights on track days, useless for autocross but hey, why not.

[michaelb]

[cmouta]

Ray, what are you running for rear rotors? Turbocoupe? Do they feel balanced with the 300mm SVTF fronts or do you think they should be bigger?

[Ray]

Yeah, turbocoupe. The car is pretty balanced, the front will lock up before the rears but that's normal and preferable when threshold braking (at least for me).


And edit: Got my power back. Timing had indeed jumped so i changed the belt / tensioner and did index the cam to crank to aux with a paint pen so i can easily visually check timing. Of note; i did have to adjust the hell out of my tune to get the car to actually not cut spark under boost, i think my timing has been off for a while and i was "tuning around the issue". Car will now easily free rev to redline, which i have set to 6200, where before she'd only spin up to 5500 easily. Might turn the boost down a little bit, on autoX the car constantly wants to swap ends. Hilarious, but not the quickest. On road courses since i lose that gearing torque advantage of just being in 2nd (or even 1st) she's way more controllable.

[Spaldino]

What flares are you running? I'm going to be making the jump to super fat tires (at least 245 all corners) and i haven't been able to locate any flares that look like they will fit the lines well enough.

[Ray]

240sx urethane flares. Hard to find - mine were shipped over from hungary, of all places. Fiberglass ones are a bit cheaper and much more common.

[Marc]

I haven't touched the suspension. Currently looking into ways to lower rear roll center without lowering car any more.

I'm going to index the timing belt in reference to the distributor pulley / cam pulley with a paint pen, and just keep an eye on them both a few times a season. Easy enough.

Oh, because i'm me - going with a 3 bar MAP sensor and upping the boost to about 21-22psi (currently at 17psi), should make for a bit more fun on the straights on track days, useless for autocross but hey, why not.

This really is a great project! I like that you are using for autocross and keep changing things to get it faster.

Regarding the rear roll center, have you ever thought of a 6 degree beam for the rear? It lowers the roll center (which in my opinion isn't necessarily a good thing), but it also reduces the toe and camber change for the suspension travel. This gives the car less understeer and makes the rear also less snappy when it starts to slide.

[John Brennan]

The 6° rear beam has been a hot topic on FB of late. Might be worth looking into. Maybe a round tooth belt/pulley conversion, too?
Nice job winning in spite of issues.

[Marc]

With FB you mean Facebook? Is that also part of the club?

[John Brennan]

With FB you mean Facebook? Is that also part of the club?

Yep. There's an affiliation; to what formal extent, I couldn't say. I don't know the administrative details, and the Moderators are not the same as here.

[Marc]

A couple of years ago I had my own 6 degree rear beam made by a local company.





It's easy to see that with this beam the wheels drop down a lot straighter than normally.

[John Brennan]

From what I've been reading, it seems to be a major handling improvement...