Dangers of 7200rpm+ ?

[kitkat]

After reading another thread which lead me to another thread which lead me to jaycar which finally led me to an open ecu and a soldering iron... i now have a raised rev limit (approx 8000rpms).
Note: Crystal used=4.43MHz

Engine:
~90' 1.6L Automatic engine (new engine(short-nose)apparently slightly lower compression than manuals due to different pistons)... exhaust/intake/timing mods

First impressions are... engine noise at 7500rpm+ is PHWOAR, AWESOME. 5000rpm+ feels stronger, possibly due to the 10% leaning that is meant to occur with this mod which *should* result in a better mixture. Slowing down in 2nd gear from 4000rpms (no throttle) the engine backfires/crackles which would suggest it runs richer down there. 8000rpms is very high and im to scared to hit the limiter... yet.

Questions:
- Has anyone else done this... what are your opinions?
- At what rpm will vavle float occur on a stock head... will i be right with 8000rmp?
- Apart from decreased engine life, can i expect any other problems to now occur?
- Does anyone really know if it leans out the mixture by 10% and will that be ok for the engine?

Notes:
I will only be venturing into the red section on the very odd occasion...
Mod cost $5 and 30mins of time.
Yes, i am a hoon and i like to make lots of noise!
Seeing the needle go past 7000rpm and into the red section is cool but scary!!!

[Babalouie]

As for leaning question....well obviously you should get it checked on a dyno, etc but on my NA8 I am running 12% leaner above 4500rpm to get to 12.5:1 AFR. From what I understand, the NA6s are even richer than the NA8s so that should prolly be ok then....but yeah, spend the $50 on a dyno pull to be sure!

As for valve float, I think that the HLAs will run out of oil pressure before the valves will float, and the guys on miata.net reckon that will occur at 7600rpm. That said, Slammer has been running his car out to 7800rpm for years....

[Boags]

I sat in Sean's car on Saturday morning and watched him pull to 8000rpm with 15ish PSI... That was cool.

I just thought I'd brag.

Boags

PS - nice work! Glad to see you had the minimals to just do it. If I didn't have other things in the pipeline, I'd get you to come round and do mine!

[Li7hium]

I sat in Sean's car on Saturday morning

Who let you back out of Queensland again?



Matt

[StanTheMan]

why don't you replace it with the 4.19 crystal......brings the rpm to 7550

gotta get my act together.

[Sheck]

i think Nissan GTR valve springs are supposed to be a great upgrade for our cars. I've seen heaps of jap demo cars run them (in there spec sheets).

Isn't it a big strain on the crank and rods to be doing those kind of rpm? I've always heard/read its rpm that kills engines not cylinder pressure (ie boost).

I'd love to do this mod, but i think i'll build an engine for it rather than put another strain on my current one. Plus i'd prolly hit the limiter way too much on track!! (good old rev limiter bouncing while drifting!!)

Dave

[StanTheMan]

this mod doesnt add a whole lot of power to the engine. Most worked engine would have a seperate ECU where you can alter the rev limiter anyway.
if you are going to build an engine around the crystal.....don't waste your time.

To me personally the benefit of the crystal is so you don't need to change gears in certain high pressure situations just a few exta RPM is all you may need.

leaning your fuel can also be achieved by tightening your AFM spring.

[kitkat]

To me personally the benefit of the crystal is so you don't need to change gears in certain high pressure situations just a few exta RPM is all you may need.

Thats the reason why i did it... i dont think there is any power increase in this mod tho as i said, 5000+ felt very strong... cant say there was much after 7300rpm and going up that high would only be done when theres no point going to 3rd cause of the next corner, it will just be great to have that extra 15km/h to play with.

My main concern is will it be safe, provided im sensible.

[Boags]

I think the extra go you feel above 5000rpm is because your engine is now not drowning in fuel like it was before!

Leaning out an MX5 gives you more horsies, and who could say no to horsies?

I can think of a few corners at QR where that would help!

Boags

[kitkat]

but then again, my suggestions are a little more costly

Yup

No need to go all out just yet....

We're planning on going turbo later this year so ill be making the megasquirt which might end up completely replacing the standard ecu.

This mod is just to fill in the gap and to keep my right foot satisfied

[CT]

At 8000rpm, you need solid lifters and better valve springs.

[rjr666]

At 8000rpm, you need solid lifters and better valve springs.

CT can you recommend some solid lifters and valve springs? And where to get them from?

So gtr springs fit eyyy???

[kitkat]

At 8000rpm, you need solid lifters and better valve springs.

What about the crank and other parts in that area, will they suffice?

rjr666 Clicky

[irwin83r]

can this be done on an NB8A??

how far can you take a NB8A before it gets the same problems you've all pointed out for the NA's? or is it the same poop differnt smell?

[kitkat]

can this be done on an NB8A??

how far can you take a NB8A before it gets the same problems you've all pointed out for the NA's? or is it the same poop differnt smell?

Pretty sure i read somewhere here you could do it... there is an NB model that you cant but thinking about it that was the SVT model.

clicky here

Beware ~ 10 pages long ~