Engine Heat Issue

Melted 2-pistons.
Tore down and changed cam, pistons/rings,head gasket thickness.
Lowered cr. from 9.1 .
Now 8.86 cr.

Moly rings .025 gap./.008 piston clearance.
Gasket .098 Cometic,, Ross flat tops.

Old cam 236/241@ .050 110 c/l.
New--248/248@.050 114 c/l.

So anyway,would run 160ish 180ish all day anywhere before,now 180 to 200* and is boiling fuel in the carb. after you park and try to restart.
Timing 30* with vacuum advance just like before.
Flushed cooling system twice,no improvement.
Richened cruise AFR no improvement.
Took hood off,no improvement.

Seems to get hot driving then when you stop,idle and or shut it off the heat in the engine shows itself.
If you never stop the water temp. holds steady.

Only thing I can figure is its sealed up better/rings-pistons and is producing more heat.

Why moly rings? They are not the best for supercharged motors and do not take heat well. IMO.

I would still say your lean making all the extra heat.

I was thinking it's lean.

Another vote for it being Lean.

Fuel curve requirements will often change with a cam change.

How much time on the new motor?

About 100 miles

Are you sure something isnt tight in the motor causing more heat?

Myself cant go with the sealed up better causing the heat as that would indicate your last build didnt seal properly from day one.

Maybe run it a bit more?

Love the setup btw.

I am wondering about if the winter blend gas is in the pumps?
It would definitely boil at lower temps.
It has been usually warm in Ohio.
Not sure how it would effect what my wideband sees.
Maybe its lean any way.
Even though I have fattened it up?

How is the timing curve set up?

Off the top of my head.....if it ends up not being a lean condition.....

Longer duration cam(lower cyl pressure) with a much earlier ex opening point, in a low comp motor will tend to have increased ex temps, which will put more of that heat into the the water jackets surrounding the ex ports.

Less than optimal timing under those conditions just adds to the high ex temps.

I see a small pusher fan in front of the radiator. Is there a bigger fan behind?

If the pusher is the primary fan, its not enough and explains why it is hot when you slow down.

Timing all in about 1500.

Yes most aggressive mechanical fan I could find belt driven behind radiator.

If I get to drive it much more this see seas I think I am going to slow the supercharger down.
It is 2.72 times crank speed.
I have a pulley to get 2.32 crank s peed

Worked on a few blown engines years ago and it always seemed like they wanted more fuel. They both really responded to a fat mixture especially on the idle circuit. One had a big B&M supercharger and we always had temp issues and after we put a pair of race 750 Holley carbs it ran much cooler without changing anything else.
Gus

Well can't argue with results.
I will try more fuel and see what happens.
Thanks

The engine running temps you stated didn't melt those pistons. Nothing wrong with those operating temps. Heat soak is normal on shut down. Melted pistons came from high cylinder pressure along with a lean condition, possibly wrong heat range plugs, and crap pump gas. Got enough fuel pump to keep up with the boost? Running ported vacuum advance verses manifold vacuum? Slugs are a little loose and ring end gap is a little tight IMO.

Roots compressors get VERY HOT! The Aluminum soaks up heat like crazy, and putting a carb on top is a lousy idea, because the fuel spray vaporizes so quickly that it burns very lean.

To do it right with gas for the street, I would inject the gas directly into the intake runners. Much better.

I set a few cars back in the late '80s for hot rodders, and carbs sitting on top of a hot roots compressor never worked well, and since they pushed the issue, I went with 2 750 DP carbs, jetted VERY Rich, and the one that worked best was a mechanical enderle injected into the runners, but was not very streetable, but ran great at the track.

One idea is to buy a Holley HP and MPFI system, injecting into the intake runners, and let the ECU control the timing and fuel...that would be very cool!

My 2 cents

I did not want to go negative on my post above, but yea your right. Carbs suck for a blown engine, then the OP is wanting to run ethanol pump gas in his blown engine? WTH do you expect? 30° timing is too much, I'd go 25° max and put some decent gas in the thing. Why run pump gas in a blown engine? It's blown and needs good gas no matter what the compression is! At least straight 91 octane gas with no ethanol! Straight 91 is better than 93 ethanol for a blown engine.

Then like I said moly rings are all wrong for a blown motor, good luck with that!

Down here in Cincinnati they did away with the summer mix gas, we have the same vapor pressure gas all year long now. My god put some good gas in that thing!!

I have had several injected race engines that would have run fine on the street and we out ran EVERY carb we raced against when we were quick 8 racing.
I could have drove this 632" donovan big chief on the street it was tuned so well.


I built this motor in 1993.
Then ran this for 9 years.

I did say several above, this was a 572" BB chevy with Dart 360 heads on it. I was the 11th 4 second club member in 1991. It could have been street driven.

since no one asked, I will, how much boost you running? That will help determine how much timing you should be running. Also, I would love to see a pic of a plug.


Joe

5lbs.
Occasionally I will see 6lbs.

Have you calculated your overall CR? I run pump 93 with 4 lbs of boost that gives me an effective CR under 12:1

The harsh reality is that the blower is just to small for your engine. You can slow it down to build less heat, but I’m guessing that you want the performance of a blown big block.
I agree that you could probably get away with a bit more if it was richer, but in the end you still are limited by compressor induced temps that the blower is inevitably going to make.
I agree with others about timing and heat also. Less timing while cruising will make a lot more heat. Combine that with a constant dose of heated intake air, and you end up with undesirable results.
The easiest way out would be switch to E85.

I can tell you here in Md the winter blend will boil about 20 degrees sooner then the summer blend. I took my car out in late March and got 92 pump and when my eng hit about 185 idling in the drivethru line my fuel started to boil and the eng started to load up as it was pushing fuel out the bowl vents. I was very surprised as with the summer blend I have had it hit 195 at a long idle in traffic before I turned on my electric back-up fan and it had not boiled. And it is worse on very humid days also. Course I agree with the blower I would be thinking about better gas. Good luck with it , Ron

I think it is all better now...........

Yes,winter blend was part of the problem.Likely why it toasted a piston at the track. It runs .5 leaner on winter blend and I was WAY too close to the edge as it was.
Put some 100% "pure-gas" in it{alcohol-free},made a big difference.
Also found the vacuum advance on the dist. was not doing its job. Found that it was not returning to the same base timing every time. So I might have 30* at home and 33* another time. Found it purely by chance.
I had noticed the throttle response was different at times,probably the timing variance.
So too lean and unknown timing bit me.

So next year I am going to put some race gas in it to base line track use tune-up then wean it onto pump-gas with meth/H20 injection.
So now have the dist. out of the Cuda` in it.

Idle and response is nice. Can`t get it over 180* so far.

Live and LEARN.............