Head cooling on cylinder #5 - solutions?

[Tony D]

I went away (out of the country) for the last 65 days... Left on 9/15... look at my posting date, and you see how much time I've had to do any work.

 

And it's cold now.

[Forcefed Z]

Ive read through this whole thread trying to figure out my cooling problem in my turbo l28...Basicly whats hapening is when I boost it it blows coolant out of the overflow...Ive changed the rad, tried water wetter Changed head headgasket and still the same problem. I run with a fare amount of power (480atw) so im wondering mabe its just boiling the water from top of the cylinder? Mabe someone has a different idea, But I think im going to try and tap out 4,5,6 at some point.

[TimZ]

Ive read through this whole thread trying to figure out my cooling problem in my turbo l28...Basicly whats hapening is when I boost it it blows coolant out of the overflow...Ive changed the rad, tried water wetter Changed head headgasket and still the same problem. I run with a fare amount of power (480atw) so im wondering mabe its just boiling the water from top of the cylinder? Mabe someone has a different idea, But I think im going to try and tap out 4,5,6 at some point.

 

Does the coolant literally blow out of the overflow tank, or does it seem to overflow fairly often?

 

I had a similar problem last summer that seemed to be linked to running boost/high rpm. It turned out to be due to a vacuum leak at the radiator cap outer seal. if the outer seal leaks, then the system can't pull the overflow back in on cooldown and eventually it overflows and the coolant level in the engine goes down.

[Forcefed Z]

Does the coolant literally blow out of the overflow tank, or does it seem to overflow fairly often?

 

I has a similar problem last summer that seemed to be linked to running boost/high rpm. It turned out to be due to a vacuum leak at the radiator cap outer seal. if the outer seal leaks, then the system can't pull the overflow back in on cooldown and eventually it overflows and the coolant level in the engine goes down.

 

When we were first tuning it after I put the new rad and head on I had a coke bottle on for the over flow and it would pretty much fill it up after 2 pulls....pretty violent. I have recently done a few pulls at 15 lbs and it seems not as bad but it still does it....I remember a while back on my old setup when I first got the car I would boost and watching the water temps, it would spike right up and then go back down.

 

Did you have any problems like this after fixing the problem with the vac leak on the rad? What boost you run?

[TimZ]

Did you have any problems like this after fixing the problem with the vac leak on the rad? What boost you run?

 

The problem appears to have gone away completely since I found the vacuum leak in the cap. I'm running ~28psi.

[BRAAP]

Gentlemen,

This thread, in my mind, is one of those core technical discussion addressing an issue that all L-6’s seem to be plagued with, being hyper sensitive to detonation.

As such I would like to change the title of this thread to something like;

 

“Reducing the L-6 detonation sensitivity”

“Cooling mods to reduce L-6 detonation sensitivity”

“?????....????”

 

I didn’t want to just do so without running this past the original poster, TimZ, and the core contributors in this thread first for their input.

[Forcefed Z]

Ive treid 2 different rads and still had the same problem......I think I might try and tap into 4,5,6 and see if that fixes my problems.. im curious to see what the electromotive setup tooked like? did they tap off each cylinder and then run a thermosat on the manifold and block off the one at the head?

[Tony D]

I like the second suggestion...

[Daeron]

maybe "coolant flow" rather than "cooling flow?"

[TimZ]

Gentlemen,

This thread, in my mind, is one of those core technical discussion addressing an issue that all L-6’s seem to be plagued with, being hyper sensitive to detonation.

As such I would like to change the title of this thread to something like;

 

“Reducing the L-6 detonation sensitivity”

“Cooling mods to reduce L-6 detonation sensitivity”

“?????....????”

 

I didn’t want to just do so without running this past the original poster, TimZ, and the core contributors in this thread first for their input.

 

Thanks for asking, Paul.

I guess the second one is okay, but I did make the original post to specifically talk about how to address the apparent cooling imbalances in the head in the rearmost cylinders. If we change it to talk about detonation sensitivity in general, then we open the thread up to talk about any number of things, like combustion chamber shape, ceramic coatings, fuel/timing strategies, etc., which was not the original intent.

[Tony D]

Good point. It is about he coolant flow issue, which helps decrease the detonation sensitivity as a side benefit.

From the tests KTM posted, the temperature does drop when these mods are done...and overheating on the dyno gets less acute---which was the primary goal.

 

Detonation decrease is another benefit, but secondary.

 

Cogitating on it further, after reading Tim's comment...

[BRAAP]

Thanks for asking, Paul.

I guess the second one is okay, but I did make the original post to specifically talk about how to address the apparent cooling imbalances in the head in the rearmost cylinders. If we change it to talk about detonation sensitivity in general, then we open the thread up to talk about any number of things, like combustion chamber shape, ceramic coatings, fuel/timing strategies, etc., which was not the original intent.

 

Thank you Tim. The title will remain as is.

 

Personally I would like to see one you gentleman spear head a discussion regarding the L-6 detonation sensitivity that this cooling mod addresses, including chamber coatings, possibly chamber shape etc. Maybe I’m off my rocker, but all the evidence I’ve seen points to the L-6 being hyper sensitive to detonation compared to other aluminum headed 2 valve engines. 7.5:1 comp ratio, or even 8.5:1 and 20 lbs of boost should be doable, but the L-6 seems to be more sensitive to blown head gaskets from detonation at those levels, and even 15 lbs at those levels. In N/A trim, more than 9.5:1 comp ratio with premium they rattle like a diesel. Domestic V-8's get way with 9.5: with Iron heads, and "over" 10.5:1 with aluminum heads. To me this issue points to excessive combustion chamber temps due to poor coolant flow around the chambers, (possibly other issue such chamber shape, but I feel it mostly coolant flow around the chambers related). The ZX Turbo that Paul Newman drove had revised cooling flow… OZ’s Bonneville car has revised cooling mods… I honestly feel those cooling mods either fixed the chamber temp issues or at least reduced them to the point the engine would survive at those levels. I feel that if those engines utilized the stock cooling flow, those engines would not survive. Chamber coatings should help by containing the heat in the chamber, not allowing the head to absorb as quickly and hold that heat during sprints.

 

At any rate, I just don’t have the time to devote to this topic with all my other projects, though I would like to see it discussed by you guys that are at the fore front testing and successfully running above and beyond where everyone else seems to be blowing their head gaskets and busting pistons etc.

[Forcefed Z]

Does anyone have photos of different ways this has been done over the years, besides whats been posted up here allready..Just like to see some different options so I can get an idea how I want to do this.

[HowlerMonkey]

I'm working on a flattop f54 with p90 that will be boosted to the point of encountering this problem.

 

Since this engine is full of old and high mileage parts, I may substitute one or two dished pistons in 5 and/or 6 for kicks and post dyno and damage results..........might take a month or so though.

 

It's not the solution but more of a workaround if it works and doesn't kill power/balance.......etc.

 

You guys doing the research on this thread are heros and should get mucho credit (and money) if you find the fix.

[jgkurz]

I'm working on a flattop f54 with p90 that will be boosted to the point of encountering this problem.

 

Since this engine is full of old and high mileage parts, I may substitute one or two dished pistons in 5 and/or 6 for kicks and post dyno and damage results..........might take a month or so though.

 

It's not the solution but more of a workaround if it works and doesn't kill power/balance.......etc.

 

You guys doing the research on this thread are heros and should get mucho credit (and money) if you find the fix.

 

My personal opinion is that the coolant flow fixes that are being recommended in this thread are for a extremely modified L28's (turbo and n/a) that are subject to extended loads on the track or on the dyno. There are many people on this forum with over 500bhp that have not seen a need for the coolant flow mod. Again, this is my opinion, but if your car is street driven, under 500bhp and only goes the track occasionally you probably have nothing to worry about. Just make sure your cooling system is in good shape and you should have no issues. If you are still worried, bump up the pressure of your cap and add Water Wetter.

 

Tony D and TimZ... flame away.

[Daeron]

detonaton hurts every motor when it happens. IMHO, my family's Z-cars have run into this issue in the past (I am diagnosing wayyyy after the fact, hence the "opinion") and we have never been anywhere near 300 horsepower, and the only turbo'd car we have owned was a bone stock 83ZXT. FWIW I don't think the turbo car ever had the issue, and I think a good deal of our issues cropped up as a side effect of inefficient cooling due to aero concerns. (The whole airdam/ductwork/seal the radiator off thing)

 

The way I see it, this modification is an insurance policy in any L-6 that gets driven hard.

[jgkurz]

 

The way I see it, this modification is an insurance policy in any L-6 that gets driven hard.

 

I agree that the coolant flow mod is good insurance and allows enhanced coolant flow through the back cylinders. The questions is whether it's necessary. My belief is that it's a waste of money on most street driven Z's. If people want to go through the hassle to modify their head and plumb in the coolant lines then more power to them.

 

Essentially I think we agree, it's just a matter of deciding when the mod offers the most benefit.

[Tony D]

No flames from me, but remember both KTM and I live where only 91 octane pump gas is the best commonly available, and radiator level airflow temperatures can routinely exceed 120F on a sunny 85F day...

 

When you have 120F COLD water back into the engine with at best a 190 degree thermostat in it... (I have seen air inlet temperatures to the radiator of 160F on a 90-100 degree days!)

 

85F on a clear day in SoCal is more demanding on a cooling system than 105F in Iowa on a clear day (from personal observation!) due to Aerosols blocking so much of the heat inducing radiation that causes that hot asphalt thermal layer our S30's travel through.

 

heck, on winter gas last wednesday, my 260 started vapor locking in 85 degree weather. A quick check of my pre-radiator RTD (oh don't EVEN ask!) found my air temperature into the radiator was close to 120F!!!

 

So for many, the cooling mods aren't anything to worry about. But 'while you're at it' for a head that is off to get porting done...

Or 'while I'm in there' for a valve job...

 

Having some holes tapped and ready for down the road may not be that much of an expenditure...

[ktm]

The way I see it, this modification is an insurance policy in any L-6 that gets driven hard.

 

Exactly. I typed up a response last night that basically stated the same thing, just a bit more verbose.

 

I agree that the coolant flow mod is good insurance and allows enhanced coolant flow through the back cylinders. The questions is whether it's necessary. My belief is that it's a waste of money on most street driven Z's. If people want to go through the hassle to modify their head and plumb in the coolant lines then more power to them.

 

If your head is getting rebuilt, it takes all of $15 to $20 to drill and tap the holes by the shop. Add another $30 for SS hose and AN fittings and you are done.

 

I would not remove the head just to do this modification. However, if the head is off for any reason, it is a good "while I am at it" modification.

[Z_Maggio]

Forcedfed Z...With that nuch power,you must be running pretty high boost.You may be lifting the head off the block.Are you running head bolts or studs?To pressurize the cooling system,compression has to be "leaking"into the cooling system.That can only be a bad gasket,crack in the block or head.

Maybe I'm just a lucky guy but I roadraced a 2.8na(300hp)12.8 to 1 compression ratio with none of these problems described here.In road racing,the races were 30-45 min and I routinely shifted at 7800-8000rpm.I also had a z car shop in New Orleans for 25 years.Maybe I'll learn something new here.Thanks,Bob