Aussie ED

Hey fellas hello from OZ. Great web site you have here, loads of information, really handy for us Osstrayliaans!

Just a quick question, fitted Comp 918s to my car a week ago. (Or rather my mechanic did), the stock valves were pretty bad! Anyhow, car is stock VX (2002) , stock cam, etc etc, tuned via ls1 edit with mafless tune (speed density tuning in your terms). Power at wheels (even with **** springs) was 237kws at the treads (317 odd hp), after spring change it DROPPED to 219kws (293 odd hp). And you could definately feel the difference on the road. The graph (sorry havent got a copy), showed that it was a lot smoother and dropped off properly, however, just not making the power it should. It has me and tuner puzzled. We agreed will let it settle down, put couple of tanks fuel through it etc, then retest.

Has been 1000ks (600miles) since done, and seems to have got the power back, however valve train has got noisy as hell. Going up tomorrow for a re-run. Could springs be too tight?? Just dont know what it could be!! Any info appreciated, and sorry if post is too long...

ED

Tom@SpeedInc

iTrader: (5)

Check vacuum, this will determine the integrity of you valvetrain. Should be at 17" idle with NO needle movement. I use the vacuum line back of the intake manifold that goes to the firewall, the little white thing is a check valve ( take vacuum line off that goes to the check valve.)

nuzee

iTrader: (2)

I noticed a drop in mph at the track after doing a 918 spring swap. I just figured that was due to the added friction from the stiffer spring rates. I was able to regain my mph by bumping up my shift point. So, that tells me that the springs helped at higher rpms. I guess stock springs don't like to turn >6200 rpm, lol.

Aussie ED

Thanks for the reply guys, youre right about the stock springs, they dont last at those revs!! Most of them were that soft you could push them by hand, and quite a few had no pressure at all!! Went back today for the recheck, and everything is in order, it picked up roughly 3-4 rwkw at peak (i didnt expect much more than that), but where it dropped off before at 5700+rpm, it has picked up more than 30 rwkw, so all good. Happy camper at the moment. However, the ticking noise was checked and engine builder/tuner I use seems to think lifters. So, Ill just not thrash it too hard for a while, and fix them next. Thanks again.

PREDATOR-Z

Aussie, I know this isoff topic but I live in the UAE and I have an export car (Not American spec) but with MAF.
Question is : My car doesn't have O2 sensors before or after cats. Are the sensors located in another area?
If no O2 sensors, how does the PCM adjust for AFR?

Aussie ED

Mate, in our cars they are in the extractors, other than that Im unsure where they would be. PCM can do all AFRs through the MAF I am led to believe. A lot of people here in the early days would put on a "performance" MAF which actually screwed the performance, as well as a lot of other things.

gun5l1ng3r

I thought that speed density was not as accurate and didnt make as much power as MAF?

MyLS1Hauls

iTrader: (2)

Its not a friction issue. 918s aren't really even very stiff. Wonder if the lifters were leaving the cam lobe with the stock springs. Some racing classes actually use special cams with weaker springs that actually launch the lifter off the cam lobe and it makes more power. Possible that there was an artificial overlap being created by the weak springs allowing the valves to stay open longer. I'd like to see the dyno overlay. Who knows, just a thought.

Aussie ED

If it is a lifter, Im not sure if they are hydraulic or solid??? If hydraulic may try a little lifter free to see if it quietens down, otherwise replace soon. How long would they last (lifters) with a bit of rattle ? Or is that more like How long is a piece of string?? Thanks fellas