With the type IV timing set right it's about 7.5 to 8* at idle. Has anyp0ne noticed a difference in temps if the timing is advanced at idle?

Reading the MM on the MS site, it say's, if you retard the timing at idle it will produce lower emissions by creating more heat due to the unburnt fuel left in the system.

If retarding the timing makes things hot,can advancing it make things cooler or more stable, temp wise at idle?

With MS it is possible to advance the timing at idle but still keep a 27* cap at the 3500 mark

Keith

Power has been proven with a 12* idle up to 28* full advance by 3000 rpm for most engine setups. With MS you can also pull our 3* or 4* after 4500 for smoother high RPM running.

If you tune for optimum efficiency your engine will run at its best in all respects. If you move away from those settings you are unbalancing the compromise.

But you should pick up a CHT and test things out for yourself.

Thank's Mark, I have a HTS on the way it will be here on Fri.. it's the Dakota digital Odesy II.

I will definetly do some testing once it's in place.


BTW, a while back we talked about a higher pressure fuel system. I almost have one complete. It, unfortunatly will only cater to the MS guy's(high imp. injectors). It will use all of the stock hardware with the exception of the fuel rail. It's close to being done, I have not had the time at work to finish it and have been working on my MS system in the teener. I have to pull the motor out of the car, the #3 ex. seat has to be fixed. This will give me the time I need to finish the project.

Keith

Great! Looking forward to seeing the results from the Keith!

As engine runs more advanced across the board, CHTs go up

As engine runs more retarded timing across the board, CHTs go down, but engine runs poorly.

Timing affects quality and quantity of fuel burned, more advanced timing burns more fuel.

Thats my for-real-life testing of timing.

Do you have any numbers we could look at?

When I had the 2.8L four in the race car we found out several things. As previously noted CHTs went up when timing was advanced and down when retarded. We had the timing set at 28 degrees at 3K and head temps were about 300 degrees at full power but we were over heating the exhausts valves to the point of breakage. We talked to a Union 76 race fuel engineer and he said with their 100 octane unleaded I could probably advance the timing as much as 6 degrees or so. We tried 4 then 6 degrees to a total of 34 and head temps went up to about 450 degrees but the exhaust valve overheating issue stopped and we quit breaking valves. The seat of the pants dyno seemed to bear this out as throttle response was much better. Exhaust A/F stayed the same surprisingly enough at full throttle with the difference in timing.

450* is hot and from what I understand is beyond the failure point for a alum. head. At those temps how did you not drop or damage the valvle seats and how is it that the valves stopped breaking?

Was the 100 octane fuel, more or less octane than before?


Was the car carbs or FI?

Keith, i've got the same CHT gauge in my car and it's great. Very responsive. You'll love it.

Cool, wish I would have had it before I started tuning my MS. I could have avoided a #3ex valve prob.

Oh well, time to pull the motor

We never had troubles with valve seats, I guess it was the way Tuttle's puts them in? What the Union 76 guy told us was we were buring the a/f mixture when the exhaust valve was open too much due to the slower burn rate of the 100 octane race gas as opposed to the 92 octane street gas. I also noticed that when I ran 110 leaded that the exhaust temps were even worse due to even slower burn rate. We were concerned about the 450 degrees too but never had an issue with the head overheating or distorting but then again at full throttle we had an A/F mixture of around 12:1 so it was pretty rich. He also said this was probably the highest temp we would see since we were reading the temp at the spark plug with a VDO sensor. We were using carbs, Weber 48s which had been gone over by Pierce Manafolds for me and the readings were done on a chassis dyno.

A little more background on the engine, it had flowed heads with 48 mm intakes and 38 mm exhausts (titanium), dual counter wound springs, the cam was a fairly radical road race design from Crower and had a lot of overlap so we had a huge amount of spitting back through the carbs at idle. The compression was 11:1 so race gas was all that was used in the car. It had a dry sump system with a three stage Autopower pump that drew a substantial vacuum in the case at high RPMs so oil circulation was really good.

does anyone have any data on how much higher compression pistons raise the temps?

I would imagine Jake would have some good info on this? The pistons used to raise the compression can affect the flame travel and therefor the head temps. If you raise the compression to say 10:1 you would probably then need race gas all the time which in itsself would lower the temps some. My shop told me that if you were just going to shave the heads a little to raise the compression then head temps do not go up much at all.

One thing to consider that helps lower head temps is additional oil flow into the valve cover area and using a dry sump pump to get it quicklt back to an external oil cooler. There used to be some picts of an engine with clear inserts in the valve cover and it showed at 6K RPM that the valve cover was full of oil so getting it out and cooled is a big help.

I am planning on using the stock 8:1 compression pistionsfrom a EA case motor.

I have 7:1's in it now. Going to 8:1 will probably not raise the temps. much.

I'm just looking for a bit more perf. but want to keep a reliable DD in a 1.7.

Keith