Forum » Practical Engine Building » High compression pistons on a methanol engine

High compression pistons on a methanol engine

Practical Engine Building

Discussion and questions related to the course Practical Engine Building

= Resolved threads

Page 1

Hi, just started my project, is a toyota starlet tube chasis drag car with a 3rzfe engine. It will be running on methanol. I measured the block as I learned in this course. My question is, is ok to use 11:1 pistons on a methanol fueled 4 cylinder engine? Whats the limit of how high I can go with compression ratio? I will like to make like 850hp .What's your thoughts based in your experience?

Short answer, as high as you can get. 11:1 will probably work well.

Just make sure you can supply enough fuel - you can be quite rich, 4:1 AFR isn't out of the question - as it will need a LOT! Staged injectors would be a smart move. It can also be difficult to get reliable ignition, so make sure you address that side of it as well.

TBH, I'd normally expect the limiting factor to be the mechanical strength of the engine and head gasket seal but, if I recall correctly, you've already pointed out the engine is rather robust and you're addressing any weaknesses.

I will be running 8 2200cc injectors, sealed block and head, fire rings on the deck and the head also and studs. I have pauter rods and I'm in the process of machining the crankshaft support braket out of 1/2 inch steel plate. The thing that I have to order now is the pistons. I can order any compression ratio I want, i was thinking in the range of 10:1 to 11:1.What do you think?

Personally, I'd go for around 11:1, as that should give a good response off boost and still allow a lot of headroom for boost - BUT I'm far from an expert where methanol is concerned. That is not a lot of power for the engine size and the spec' of your engine - any particular reason you're using that fuel instead of an ethanol/high octane fuel? You could very likely get that power with 10:1 and a little more boost on high octane petrol/gasoline or ethanol blend?

That fuel is also rather corrosive and hard on many materials, just be sure you're taking that into account when selecting your parts.

I don't be using an intercooler so methanol is the choice for fuel. I will be ordering pistons this week (hopefully) I will post the process. Thanks a lot Gord very helpful like always!!!

I'd just make sure the piston manufacturer knows it's for a high boost turbo engine running methanol, not for a NA engine, as there may be design differences required for ring position and piston crown strength.

Ok perfect thanks