engine and drivetrain M10 Build With High Compression

[kbmb02]

(testing the new forum - great work, Steve K).

Some Friday bling: The new race engine block with pistons installed. It's an exploratory high compression build, will evaulate the pros of power vs the cons of reliability/durability. Presuming it's a winner, I've designed this build to be repeatable with block, custom forged pistons, cylinder head thickness and camshaft(s) all to certain spec. I'll be lighting it up in May.

[Chamonix72]

Ye Gods! That should be fun. Going to need an auxiliary starter to crank it over?

[Harv]

What cam are you going to use? Should have a lot of overlap I would think.

John

[kbmb02]

The valve reliefs in the pistons were made to fit the Schrick 304; one of Ireland's cams and another custom cam I'm working on will also clear. The Schrick should have enough overlap, others TBD. (I'll test it with a stock starter, then move from there, if necessary.) -KB

Edited April 26, 2013 by kbmb02

[oldguy]

with a 304 it will spin over fine.  You'll need a digital MSD box to retard the ignition timing at starting speeds if you've got a locked distributor.

[Chris_B]

Valve overlap can have an significant effect on your actual dynamic compresssion. I have a motor with 9.5 pistons and a motorsport 300 cam. I was worried about preignition on street gas. I shouldn't have been, because it has never happened unless I crank the timing really up. I now wish I had gone to 12-13:1 like you. I  am running dual 45 DCOE carbs and think I am leaving a lot of power on the table.

[kbmb02]

Valve overlap can have an significant effect on your actual dynamic compresssion. I have a motor with 9.5 pistons and a motorsport 300 cam. I was worried about preignition on street gas. I shouldn't have been, because it has never happened unless I crank the timing really up. I now wish I had gone to 12-13:1 like you. I  am running dual 45 DCOE carbs and think I am leaving a lot of power on the table.

 

That's a helpful data point; we hear often there's a limit to compression ratio with street octane gas - I wonder what the 'math' formula is to determine what's safe based on static C/R, overlap, duration, etc. (on the race engines I run 110 octane ... not much concern with pre-ignition)

 

with a 304 it will spin over fine.  You'll need a digital MSD box to retard the ignition timing at starting speeds if you've got a locked distributor.

 

The Crank HI-6 has the ignition retard feature, been using that for years (and yes, I run locked-out distributor).