cbrock

iTrader: (1)

I have a question about my setup on my 10AE.

I've got a completely stock keg with a GT3574. Currently it is pushing 426 RWHP at 16psi. Aspec has my rev limiter set at 7,000.

The problem is that the turbo comes on around 3200-3500 and then the fun is over at the rev limiter. With stock ports I realize my power band is some what limited but being able to get up to 7500 or 8000 should help my turbo stay spooled up better as I shift to the next gear.

I plan to have the RX7store or Banzi tune the microtech's matrix maps for better part throttle/around town drivability, but I'm curious what to do about boost/red line.

Questions:
1) I hear the end plates can crack on S4's (maybe all). What is the limiting factor here? Boost or RPM? Both? Street/strip motor (3-10 seconds of WOT) vs road race (long periods of WOT)

2) If I lower boost could I take the RPM higher with a similar risk that I have now 426 rwhp and 7000rpm. So less boost, more RPM for similar peak HP.

3) What are some of the ranges people are taking their stock blocks with a big single turbo?

peejay

If it has 2mm seals that have been clearanced properly, and oil pressure is bumped up, you can run it to 9000rpm safely with occasional mis-shifts to five figures at zero boost. I don't see the factors that limit RPM to be related to power output.

Dowel pin cracking seems to be a result of misfires, not really boost and definitely not RPM. Misfiring leads to detonation which breaks the dowel land. So: Don't misfire and don't detonate.

arghx

iTrader: (3)

I don't know if it's luck or what, but my old s4 block was a tank. I severely detonated that thing multiple times. I never cracked an iron and only switched s5 irons because I wanted the bigger ports and some peace of mind from the thicker casting.

I take s4 rotors up to 8500 rpm but usually shift around 7500. Now clearly that doesn't do you any favors as far as wear goes, but it's not like a piston engine where you have to worry about high revving causing problems with the top of the motor. That's with an s4 rotating assembly, stationary gears, etc.

cbrock

iTrader: (1)

I would have imagined that combustion pressures could cause the motor to want to separate and hence cause cracking.

The motor has never been opened so stock oil pressure, seals, corner seals...etc. 49k miles on the original mill.

rotatrix

the s4 motors that ive built here i ask them to limit boost to 14/15psi and revs to 8500,depending on porting/turbo combo we are seeing about 410-420 rwhp,a couble of these engines have been street driven for just over 10000kms without issuses as yet(they are internaly stock exept ports),the pump fuel quality here limits the amount of safe boost as the octane can change alot(nz petrol+lots of boost=bang!)id rather see a few more revs than more boost as the motor should handle that safely without geting closer to detonation!(a good tuner realy helps this too!)

cbrock

iTrader: (1)

Got it. Well around here I can get 93 octane anywhere and 94 at some sonoco stations. I will talk with Banzi and RX7store since it'll be one of those shops doing the work. Sounds like 7500 to 8 should be no problem. Seems like my stock ports will be more of a problem then the motor holding together.

Zero R

iTrader: (1)

1) The thinner castings can be prone to cracking around the rear plate even mazda realized this and made the castings thicker. Detonation is usually what cracks a rear plate but not always. I have had S4's rear plates crack with no signs of any issue either physical or logged, just plain HP most times it was over 460whp.

2) Yes potentially, 8k on stock setup should be ok. Keep in mind lower boost will mean slightly less response. You may be able to offset this a little with the tune though.

3)I can tell you I've seen very few last for very long* over 500whp, drag setups are a different thing they don't put miles on them. Example would be unbreakable seals, some shops will tell you they see no wear with their seals yet few ever put more than 50 miles on a engine in one season so of course there is no wear to see (* more than 10k miles, most people aren't wanting to rebuild so often)

Stock ports wont be a issue at all unless you're referring to needing to run more boost than you would on a ported motor, at your level that's not a major concern.

~S~

bumpstart

i agree with just about everything posted above
,, and have personally cracked up a few s4 rear plates at the dowel while drags racing them at street meets

at 350 rwhp and up,, there is no "small" detonation event

twisting from detonation is also potentially compounded by twisting of the driveline

you see mazda scramble to revise the webbing at top of the oil dowel and also to revise the area around the inspection cover at that end to more metal and 1 less bolt
- done mid production as there is 2 and 1 bolt inspection cover versions in both the G ( s4 ) and D ( s5 ) plate variations

the running baindaid for the oil dowel to the engine occurs in the "D" stamped turbo plates part way into the production cycle
,, i have examples with and without the web on the dowel