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Discussion Starter · #1 · (Edited)
I've been here for a long time, but if you NA guys don't look in other sub-forums, you may not have seen my car, www.midlana.com, a tube frame mid-engine interpretation of a Lotus Super Seven. I always wanted to have a turbocharged engine and it was great fun with 400-500 hp in a 1700-lb car, until I threw a rod this weekend at the track (road racing) while bothering a Porsche GT3 :)

In the several years I've run the turbo engine, I've learned like everyone else that they can be a fickle bitch without extensive support subsystems, awesome when in a good mood, a supermodel with mental problems when not. Being mid-engine made keeping it cool - especially the charge air - difficult, and with it failing in a big way this weekend, I'm left to contemplate the next step.

I'm considering switching back to NA. The turbo is great fun on the street, but the car's purpose has always been track day events, and for that, NA seems to be more reliable, which brings me here...

The rules are that it'll be run on 91 octane pump gas when it must, but E85 at all other times, especially when on-track. I've looked at the KMOD and ERL sites, plus discussing options with an engine builder. So I'll be hanging around here more, reading up on what's possible in a K-series for a track day engine.
 

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I personally think a really toned down turbo engine will be much more reliable than a strung out NA engine and make more power. First question I guess....how much power is going to satisfy you in that car?
 

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Heat management is the biggest thing you've got to combat with a turbo track car.

I agree, though, with DRAG. What are you looking to make naturally aspirated?
 

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he had it in the 500 whp ball park on a well built motor. exact cause of the engine failure has yet to be determined from what I understand but he is thinking detonation.
 

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Discussion Starter · #5 ·
I personally think a really toned down turbo engine will be much more reliable than a strung out NA engine and make more power. First question I guess....how much power is going to satisfy you in that car?
Very fair point. That is/was exactly my thinking, that high rpm is an engine killer, so a lower rpm engine on some boost should be more reliable - assuming the bonehead behind the wheel doesn't allow knocking.

The current suspicion is that the small intercooler just isn't cutting it. That said, I have the ECU dial back boost as air temp rises, so I don't know what went wrong there. Yesterday I realized that there is room for a much later intercooler, across the back of the car down low.

Anyhow, this discussing belongs elsewhere...
 

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Discussion Starter · #6 ·
Heat management is the biggest thing you've got to combat with a turbo track car.

I agree, though, with DRAG. What are you looking to make naturally aspirated?
I would "like" to make 350+ but fully realize what that takes: very expensive parts spinning very very fast. It may not be doable on E85.
 

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I think you would put more money and not be any more reliable, in an NA setup producing power numbers that would now satisfy you in this car.

Unless you wanted to get in to the transmission and play with the gearing and potentially lose some top speed.

And you would have to learn to drive it all over again. LoL
 

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How about a k23 in there? They seem to hold power reliably, and are pretty affordable. Heck you can buy a new one every season for $1500 and not worry too much about hurting the bank. Maybe this will be my nudge to get an adapter plate going.
 

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I've had a bunch of those RDX's making 370-390wtq at like 3,000rpm for a while now. No broken rods yet, surprisingly. :p
 

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Discussion Starter · #10 ·
Yeah I though briefly about the RDX - isn't it some oddball bellhousing pattern? Anyway, I'm crawling back under my rock for now - another turbo engine's in the works so we'll see how that goes. Still no smoking gun on root cause of the failure though...
 

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Have you thought about going rotrex?
 

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Sorry to hear about you losing a motor. I think your first step should be to determine the reason for your engine failure.

Loosing a rod is either excess rpm, rod clearance/lubrication or detonation. Rod clearances for road racing would be best at 0.002 to 0.0022". For oil see below. I limit RPM to 5400 Ft/Min so for a K24 that's 8400rpm.

I have been torn between NA, turbo, and SC and to some extent still am. Of the three choices there is no clear winner as each engine has advantages.

Here in Australia we ran Cosworth Serria's at 600hp for 1000klm races. The Honda K series motor is at least as good. 600hp turbo or SC can be made reliable but everything must ok.

My Quantum GP700 is a road and track car like yours and has a custom engine with Rotrex supercharging so power is like NA to drive. I have had to work through many of the same engine issues as the car is mid-engined as well.


I chased maximum supercharged power for many years but have for now detuned to around 600whp on E85 and my focus shifted to chassis and aero development. This power level appears to be sustainable in 10 lap bursts with an ambient temperature up to 36degs C. I haven't run on a hotter day. The problems I have had have been mostly heat related and I will go through them as it may help.

At 600whp road racing we needed these basic things:

Low Compression: Short bursts on the dyno or drag racing can run much higher static compression like 11/1 with boost. Try Sustaining this at high hp for 30 minutes and it will knock as the oil temperature and heat soak climbs. The static CR needs to be a lot lower at 8.9 to 9.2. I have run 11/1, 10.4/1, 9.2/1 combinations and would recommend 9.2/1 on E85. Water injection would help but adds more complexity and more things to go wrong.


Plugs: -10. I use R5672A - 10. Do them up tight as if they loosen the earth tip will melt. (yes I had one fail and NGK said it was too loose) This probably will take the engine through detonation.

Oil: 10w 60. I use Nulon ful synthetic with Moly DTC and PTFE engine Treatments. Log oil temperature and oil pressure and stop when the oil temperature goes over 125deg C and I use a massive oil cooler (For every 10deg C operating temperature increase you need a 10w oil increase. My oil temperature operates from 110 to 125degs.)


Intercooler: needs massive air ducting and is huge. My air to air is 500mm x 450mm. IAT is now 12 degs above ambient. With a smaller intercooler I was chasing detonation as IAT's climbed over 50deg C.


Water Temperature: Try and keep it under 90degs if possible. Higher water temperatures are more knock prone.

Engine Tune: Be conservative. Add 3D ignition retard tables (and boost reduction) based on IAT and ones based on the oil temperature or the number of laps. As heat soak increases the knock window gets closer. At 600whp on E85 a knock event tends to be an avalanche. If I get one knock I retard the timing. If I get 2 knock events I activate the rev limiter for safety for 1 second to alert the driver and flash a message.

Take away the boost and you will 1/2 the torque and 1/2 the acceleration. To get that acceleration back NA needs huge rpm holding lower gearing. It is possible but not as cheap as boosted.

I still believe SC is the best road race solution for a given budget up to 600hp. If you want more power then it's not an option. With low exhaust back pressure a SC engine's blow-through on overlap cools the combustion chamber, piston and valves. This makes tuning a hot engine much easier and safer than turbo.

I just wish we had 5 cylinders so the loading on each cylinder was 20% less.
 

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Discussion Starter · #13 ·
Thank you very much for your input.

The engine was built to handle 9300 rpm and I have long been running a 7700 rpm redline.

Cylinder walls were in perfect condition, so the piston had not seized or galled.

All bearings were in great condition so it wasn't oil pressure related (it runs a dry sump).

Oil and coolant time stayed between 85-90C.

That leaves detonation, though timing was extremely conservative at about 11 degrees when it let loose at 220 kpa and 6000 rpm (running E85).

Air intake temperature... maybe. At the previous event, ambient was 18C and peak air temp was 63C, so there's room for improvement. A much larger intercooler will be added.

What sucks is that the ECU was supposedly set up (by me...) to detect knock and dial out timing. As mentioned earlier though, for some reason the ECU didn't record a log for that session - very frustrating. The values above were either from previous events or were deduced from the GoPro video.

I've had three experts look at the plugs and got three answers: lots of detonation, some detonation, and no detonation.... great.

The surface of the piston... I don't know enough to say what I'm looking at, but here it is. What looks like pitting is actually a thin layer of carbon. Note the dings from the valves. Fortunately they're slight, and the head is in great condition, as is the turbo.

All in all, I still don't have a smoking gun, which isn't a good feeling. The injectors are being sent out for cleaning and to check whether one was plugged. The dry sump pump is also going out for cleaning and check-out in case any grit made its way into it.

 

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Contact Drag with that picture of your piston and get ready for a wave of good insights as to why the issue happened. Seriously talk to 4Piston and let us know what they think. Send them a high res of that piston
 

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Discussion Starter · #15 · (Edited)
I did exactly that and Jeremy said - to quote him exactly - "Heat heat heat wowzer."

I'm too dumb to know what on the piston indicates that. (Another engine builder took me to task about the sharp corners on the valve pockets. I get his point, but it wasn't like I made them...).

I'd like to try and move this thread back to my main thread in the "kit car" sub-forum, http://www.k20a.org/forum/showthread.php?t=47373

I don't like polluting forums with unrelated topics.
 
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