FINALLY - have custom RaceTek pistons, can calc final CR

[62Ranchero200]

Greetings Ford Six Fans,

As a reminder, I'm building a 250 with the 55 cc CI aluminum head. It's going to use early 300 rods and custom RaceTek pistons to move the piston much farther up the bore and achieve better quench. The pistons are forgings with a 15 CC dish (to keep compression reasonable after moving the piston about .118 up the bore). The pin bores have been moved far up the piston towards the ring lands, compared with a stock 250 piston. Photos of the pistons are attached. Please check my CR calcs. Looks like I'll have around 9.5:1 SCR, which should be fine even with 87 octane gas once the Clay Smith 274/274/108 cam lowers the dynamic compression. I can achieve a bit more CR if I use a Victor gasket with .045 compressed thickness.

http://imageshack.com/i/j61mnzj

http://imageshack.com/i/jo3npoj

http://imageshack.com/i/eh0i8vj

Thanks
Bob

 

[JackFish]

What do you have to do to the 300 rods to use them in the small block?

 

[bubba22349]

excellent looks like a good combo

 

[rocklord]

What's the CH and pin diameter of the pistons?
How much did they cost?

I've been looking at stock pistons from other engines that would either have to have work done on the small rod end to accommodate their pins, or have the tops milled to keep zero deck. A custom set would take care of all of my problems. One piston I was looking at came from a motorcycle, had a smaller pin than the 200/250, and cost almost $140 apiece ($840 a set), so a custom set may not be that unreasonable.

 

[62Ranchero200]

@Jackfish,

I don't think you have to do anything to the rods. If you use the early 300 rods, which have a smaller pin diameter, you can use the same diameter pins as are used for the 250 piston. If you use the late 300 rods, the pin diameter is larger. Journal diameters are almost an exact match. The 300 rod is .3297" longer than the 250 rod, which requires the custom piston.

@Rocklord,

CH = 1.300, pin diameter = .912, the same as the pin diameter from a 200. A set of six forged pistons cost $575 + freight from RaceTek Pistons (owned by the former owner of JE Pistons).

Thanks
Bob

 

[rocklord]

Thanks 62Ranchero200. Custom forged pistons with the specs you need for around $95 apiece is a decent deal.

The 300 rods are almost the same length as the AU 200 Crossflow rods (6.21 vs 6.27), giving a rod-stroke ratio of 1.588.
The Aussies figure that RS ratio gives the 4.1 xflow another 500rpms to play with.