Why do our engines keep blowing up?

[maximtaylor]

Here you go Jason (and anyone else that cares to take a read)....

Thanks in advance for the sources of information - you know who you are!!!

Three cars that I know of have blown up whilst doing a sustained high speed pull in top gear. All three at around 6000 revs /160 mph.

Detonation from high combustion temperatures is the problem. Don\'t go beyond 14 psi on 98 octane. On really hot days you are still pushing it, even at this pressure.

You cannot \'tune\' this problem out by retarding the ignition. In fact, this raises combustion temps further!

My advice: Use either or both Water Injection (with methanol) and C16 or similar race fuel over 14 psi. Mixes fine with regular SUL.

Could explain more, but the thread would be a mile long!

Regards

Max

[bill shurvinton]

Max:

Care to elucidate us on how retarding timing increases the propensity for detonation to occur, as this is a new one on me. It will increase exhaust gas temperature sure, but unless you have heated the entire chamber to the point where self igntion will occur spark or not  I\'m not seeing the mechanism.

Would also be interesting if anyone was logging coolant temperatures and AFRs when these bangs occured and if these were dyno deaths or track deaths.

But I do agree that WI is the way to go for serious HP. Just I\'d do it without the air/air intercooler getting in the way.

Bill

[JayDee]

Max
2 questions
How much ignition at that point?
where is the wideband placed and what wideband?
At that point my car is at the moment is at 11-12 my egts are under 800.
Has the timing been checked to make sure that what is in the map is what they are getting?
Intake and water temps?
Sorry more than 2 questions

more this is the stuff I love:D

Also what spark plugs are they using?

[20B_boy]

Track/strip deaths - 2 of them at TOTB2 during the high speed runs...

[bill shurvinton]

Sounds like yer basic system problem, in that the  system has not been designed to cope with that level of duty cycle.

towit: the heat is building up faster than it can be removed. Solvable anyway.

Wish I had the time or someone would pay be enough to play with this sort of gear full time...Sigh. Its horrid being an engineer but having to pay a big mortgage.

[maximtaylor]

Sorry for the delay, caught me mid Prawn Cocktail Roll

Most of this info has come via Australia, NZ and the US, and appears to solve the problems we are having now.

At the time mine went pop, my A/F ratio was 11:1.

Water temp was 95 degrees.

Timing was broadly similar to stock timing at that point, about 12-15 degrees leading?? off the top of my head - laptop is at home!

Lambda is in the midpipe. Motec Professional Lambda Meter.

Intake temps - who knows! At 160 mph I was looking at the runway, not my commander LOL!. Wasn\'t logging either, but did glance at my lambda meter (I do out of habit, along with water temp). It was a real hot day though.

No, have not checked timing, but allegedly the Apexi is fairly accurate in this department.

I was running 9 plugs leading and trailing, don\'t know about the other two. One of these cars was a single turbo as well.

Bill - I am not suggesting \'in general\' that reducing timing increase detonation risk, but that in this application in these conditions, with high boost and already high combustion temperatures, retarding the ignition will increase EGT.

Higher EGT means higher combustion temperature?, and internal components raising in temperature more also, no? I could be wrong though! Please correct me if this is the case.

I am not an expert by any means, just very inquisitive and like to research things like this. I don\'t fancy paying for another rebuild

Many engines IMO last as long as they do because the owners only give their engines short blasts of power. Drag racing is short and sweet. The sustained pulls are the problem, where the engine internals get sufficient time to get super duper hot.

Yep, yer right Bill your towit description is bang on. These engines are just not designed for the punishment we try to put then through.

Regards

Max

[bnaellis]

I know I am not a rx7 mechanic and don\'t have the technical know how of many but here\'s my take on this issue.

*Surely it\'s because the car has not been mapped properly*
Reason I say this is because a standrad rx7 will do 160mph anyway and many owners of rx7 have done this repeatedly with no problem. We\'re not dealing with a case of a car that has a top end of 145mph and it\'s been modified and blowing at 160mph, we\'re dealing with a car that does 160mph as stock. The standard twin turbo setup wth stock intercooler etc will surely produce far greater heat at 160mph than these modified cars that have blown at these speeds, so surely that would eliminate the heat issue?
Don\'t anyone take it personal or the wrong way just voicing my opinion on this topic.

[bill shurvinton]

I\'ll try and pop out a full answer tonight...

[maximtaylor]

It is impossible to offend me Brian

The one factor that differentiates a stock car doing 160 and a tuned car doing 160 is the pressure in the combustion chamber.

Running stock boost levels, does not appear to be problematic.

Regards

Max

(I\'m getting to like this thread!)

[g11ary]

I dont understand why this is not a mapping problem, I have had both my cars over 160 more times than i can remember and not just for a short spurt as at totb.

[maximtaylor]

Mine ran fine as well Gary, if it helps.

I had ran for months at one bar and done plenty of absolutely flat out runs.

I think the difference when mine went was that my car had sat in the heat with engine running and a fairly warm intercooler for a long time. This effectively moved the safety margin.

This safety margin you are going to be very close to Gary, you just need a real hot day, sit in traffic for a while etc and like the lottery used to say "it could be you"!!!

Best cure is to raise that safety margin. Many cars may run for ages close to the limit, and you\'d never know how close to popping a seal you were.

Regards

Max

[mr_tim]

A quote from the JapUKMeets Forum regarding water injection

Correct mapping does not require water to be injected. Water does not burn. Water causes corrossion. Even Water with 50% methanol alters the burn characterestics detrementally.

There does seem to be lack of rotary mapping experience/info oin the UK simply due to the investment in blown engines required to find the limits with various setups.
IMO

[maximtaylor]

AND you have those fancy ceramic seals don\'t you Gary???

They must help?

Regards

Max

[maximtaylor]

If correct mapping includes operating at lower boost, and assuming that decent fuel is used, then I kind of partly agree Tim.

The rest of the post you quoted from JapUKMeets is pants

"Water does not burn" state the obvious! - but it is very good at absorbing heat!!!

Please take this in the spirit intended

Regards

Max

[claaizy rx7]

Why did Phil Goriahs car blow up 6 times? Was that due to tuning?:confused: