Anybody Built a 10.5:1 Type 1 or 4 Engine?, Do they explode? Options

[Series9]

I build 10.5:1 /6 engines pretty regularly. 93 octane and single plug. That's about the limit without going twin-plug, but all of them on the road have been fine.


Why don't I see this in Type 1 or Type 4 engines?

Some rough math suggests a 2.0 @ 8.5:1 is an 85hp engine, while the same engine at 10.5:1 would give almost 120hp.



Just thinking out loud..... (IMG:style_emoticons/default/beerchug.gif)

[a914622]

If you real want the 12-1 comp. motor to run you need to change the cam so the engine runs on an Milliner cycle, Like some of the Mazda's. Basically the intake stays open until the crank hits bottom dead center. As the piston starts up the vale slams shut= giving you a running compression of 8.5-9.0 ish but with a much smaller quench area.

Best designed for the "pen head" intake exhaust systems(16 valves).

I had a 12-1 type1 1300 that broke 2 trannys on pump gas. That little motor only lived about 4k miles before it pulled all the exhaust valves thru there keepers. it was like a 2 stroke, rev until it quits pulling and shift!

But really would i do it again? no because i would probably have a ton of hours getting the subaru heads to fit a T4 or T1 or start form billet and make my own using the single over head cam 16 valve design.

jcl

[Series9]

I had a 12-1 type1 1300 that broke 2 trannys on pump gas.
jcl

I'd love to see that.

In Florida, 93 octane is readily available. For my 10.5:1 /6 customers, that makes all the difference. They are told when they take delivery that 93 octane is mandatory. 91 octane won't do it.



My question isn't about cams. It's simply about reliability. I had assumed the 911 heads are better at getting rid of heat than T1 or T4 heads. So heat dissipation is the real issue? What's the failure mode?


I'm always keeping my eyes open for a fiberglass-style street buggy. If I find one, I may build up a 10.5:1 T1 engine and see how long it takes to make it go boom.

It would have Megasquirt and EDIS, so it would be fully programmable.

Should be fun.