I read your book but I had a question regarding the pre-run cylinder head temps and oil temps. I have an aluminum rod 400CI SBC turbo car with no coolant in the block. I’m measuring cylinder head temperature and oil temperature and wondering what’s a safe range to be in?
Depends on whether you are running gas or alky. With gas and real high boost and limited cooling in the engine, you may need to be real cool at the start. With methanol, you can heat or cool the engine at idle with enrichment and heat or cool after the start of the run with enrichment. In the later case, you should decide whether you want to launch your race vehicle at some oil temp over the boiling point of methanol, to boil away the methanol, or higher for more fuel vaporization. The highest I have heard that is run successfully is about 210 deg F. and sustained on the run. With no water in the block, you are susceptible to hot spots that may cause cracking, regardless of the temp you are starting with. One combo that is common is to start at around 160 to 180 and keep it there through enrichment on the run. You also have to look at the rate of idle temp rise before the run. A high rate of rise to get up to 160 before the run may be too high in that it may continue to rise fast in the event of a delay at the start. In that case if you are up over 220 or 240 after a start delay, that may be too much heat. In that case getting more idle enrichment to delay the engine heat build up would be better. Although the engine may be cool for a normal start when the delay does not occur. If you have a heat gun, check heads and block at various locations and times to develop a learning tree. The engine will tell you when it is too hot. You will see other events occurring like an overheated plug or smoke coming from the engine or bearing wear from oil break down.
At what temperature is overheating? Thanks, PT
I have heard that over 220 deg F is a bit high for a small block. Again with a dry block and high boost, hot spots can develop at lower starting temps. There are no standards. Just try it and keep an eye on cooling passage sealing. You may want to close off the cooling side of the block and pressure test it to see if it holds pressure. Then check that from time to time. If it will not hold pressure due to cracking, that is the start of a failure no matter how small the cracks.
We have run some hemi stuff with cast iron cracks and they lasted OK for a while. You just never know.
FYI: You want the oil over the boiling point of methanol to boil the methanol away. If it is gas, it does not separate from the oil, so that is not the limit. Probably not over 220 for lube failure avoidance. You want the combustion chamber temp high. And you want part of the intake passage way cool for air density and part of it hot for fuel vaporization. Unfortunately they are all tied together with the same metal parts so you have to compromise on everything.