Logo
FULL SITE MENU

427 fe comp ratio.???

G

glenn der

Contributing Member
Hi new guy here I'll try to keep it short I have a lot of qs I took the top off my 427 int 300 hp my heads cop chambers have a stright eage with sqare corners on one side and my pistons have about a qarter inch deep dish the same shape as the chambers. I fould another 427 and pulled the heads thay are d heads mine are c s the d s have. A roulded corner in the chambers and the pistns are fully dished both are saying 300 hp? ? What do u think the comp ratio would be in these to set ups and what if I put the d heads on my engine? Eney help would be nice thanks.
 
glenn der said:
Hi new guy here I'll try to keep it short I have a lot of qs I took the top off my 427 int 300 hp my heads cop chambers have a stright eage with sqare corners on one side and my pistons have about a qarter inch deep dish the same shape as the chambers. I fould another 427 and pulled the heads thay are d heads mine are c s the d s have. A roulded corner in the chambers and the pistns are fully dished both are saying 300 hp? ? What do u think the comp ratio would be in these to set ups and what if I put the d heads on my engine? Eney help would be nice thanks.
Click to expand...

Hi Glenn,

Compression is listed in July 1968 Chris-Craft 427 engine manual as 8.9:1 with 160 psi cranking to max of 190 psi. They also say DO NOT RUN @ 4000 RPM Top cruising RPM is 3600.

Mike
 
Hay thank you that took a bit yea I fould some old c c sales books but I have a old trojan wood 42 foot rear cabin the engine / trans are set up way different I can find no original info on the boat or engines only c c info but maybe its the same .
 
Todays gasoilne being what it is I would make sure piston to head clearance is between min .035" -.055" max. This will will get you more out of the gasoilne that you burn even if the compression is lower than the 8.9:1 say 8.5:1. Quench/Squish area (piston to cylinder clearance) is most important for completely burning the air/fuel mixture in the combustion space. The difference in boat engine that I have seen over the last 45 years is when correct it will reduce the time trying to get the boat on plane and better fuel mileage.
Mike
 
I glad to talk to somebody that knows the big thing is I have to fix my engines if at all posible in the boat as thay will not come out with out cuting the boat open and looking at a old abandent c c with 427 that I can get cheep thay turn way smaller props than I have I have 24-12 wide 4 bladed props the c c has smaller 3 bladed props I'm thinking that mine must be set up for more power/tork somehow the origal sales flyer only thing I can get says 100 gal fuel and 2 poeple no cargo ext my boat will run 28 mph max and its a big boat so what do you think. Plz
 
Mike you still thare if you can think of eneything let me know iv been arould. And messing with engines most of my life and I'm a littel stumped on this one
 
Yea that's ezer said than done its not just that its parts and knowing what I realy have and like I said I would have to cut the boat open for that the bottom ends are good and most shops have there own ideas but thank you for the info.
 
427 Compression for CC and Interceptor 300-horse engines is as noted, 8.9:1

Regarding the props, if you have (for instance) 23x25 3-blade like I do on a 38 Commander, then you must go to a 23x23 in a 4-blade or you will be grossly over-propped and will not be able to reach max rated engine speed. The rule of thumb I use is to deduct two inches of pitch if you go from 3 to 4-blades, but you can always check with the nice people at Michigan Wheel.

regards,

DS
 
Back
Top