Hi Stephen,

I have a 3.8 Liter twin turbo road race only Bob Holcombe Motorsport Design Zytek full blown race engine. It is a true 760HP best of everything engine.

The engine only has 20 hours and the leakdowns are mostly 8% except 1 cylinder is 14%.

I am being told by several people that run these engines, that on this engine that is fine to run for another entire season. 14% seems very high to me. What do you think ? I am used to numbers on my other water cooled race engine of 2% leakdown.

What do you think ? I do not want to risk hurting anything. The car is used for PCA, SCCA, and NASA Pro racing.


At a minimum, I was going to borosope it and make sure the cylinders/pistons, valves all look good...

Thanks,
Stewart

 

I thought my ears were burning

Generally a leak down that gets into the teens is an issue. I often tell people now is the time you need to plan your budget and map out the route you want to take with a rebuild. These conversations exist with people that use their cars as a weekend toy. My concern with you is the track usage. Nothing is harder, period, than tracked use. There are several factors involved such as what degree will you be running it? If you run very little boost such as a half bar then the car might live. At full tilt I would be reluctant to say it could make a half of season. The 14% is an issue. Especially when you look at the surrounding numbers of 8%. This cylinder has probably either seen audible or subsonic detonation in its short life.

Keep in mind I am a bit conservative and would rather face an issue now rather than prolong what is inevitable. Prolonging normally only creates a bigger hole

 

Not that I'm second guessing Stephen, But what does Bob think you should do. After all, he should know the average life span of his engines.

ps, What boost did you make that power at? What boost do you normally run at the track, and what power does it make at that boost setting.

 

I would ask about that leakdown test,......

Was the air leakage noted coming from the oil tank breather? Intake? Exhaust?

If you heard air escaping from the oil tank filler, then I'd take it all apart and look. Might be time for pistons & rings.

 

Thanks for the replies. I do have a call in for Bob.

Stephen, I run 1.0-1.3 bar continuosly and always have for 1-3 hour enuro races. Which is why I always play it safe. I will recheck the leakdown and also check the cylider walls, piston tops, valves and heads with my 2 way articulating fiber boroscope. I will also check to see if I hear the escaping pressure from the oil tank, intake or exhaust..

Thanks again for the info.

Stewart

 

I talked with Bob and he did indeed say it was fine to run an entire system with the 14% leakdown. He said on this special configuration of very high hp race engine he has seen over 20%.

For safety I will be boroscoping the engine and looking at the cylinder walls, piston top, head, and valves.

Plus I will check if the leak is at the oil tank, intake or exhaust.
Depending on what I find, I still may freshen the engine. I dont like taking any risks especially since I push a race car to its limits.

Thanks for everyone's input.

Stewart

 

Bob builds a heck of a motor. I personally would be jittery about the 14%. I consider that high by any standard. Like I said though, I would rather be safe than sorry.

 

Okay,

So here's the real scoop -

It is very good that I am **** retentive engineering type. I did indeed do my own leakdown and use a 2 way articulating fiber boroscope and checked out the engine....

It would not have lasted a weekend.

Leakdowns :
cyl
1=1%
2=3%
3=25%
4=1%
5=1%
6=4%

So it was not 14% (as I was told) it was 25% on a properly warmed engine checked with 2 gauges...

Small little smiley faces on the intake & exhaust. Cyl 2,3,6 exhaust valves slightly bent.

1 broken intake spring.

Running it would have definitely burnt a valve, and maybe even dropped the valve on the one with the broken spring.

The engine is already apart, new parts already here, and will be completed in 2 days.

So my initial worry, plus all of your valuable insights were correct.
No matter how good of a top notch race engine you have, the basics still apply, you need to have a good leakdown to run properly.

Everything else looked like brand new. All new 3.8 race valves, race springs, titanium retainers, clips, and the like will be used. The pistons were barely touched and are fine.

Thanks everyone - especially Stephen for all the input.

Regards,
Stewart