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1948 mm 08-29-2012 18:44:37 208.71.219.231 Report to Moderator	I have a 403 engine that has been bored out to 4 3/4" bore. I have also taken .050 from the blocks to raise compression and another .050" from the 10A4210 heads. I think the compression is around 11.3/1. I have the opportunity to buy a u lp which I hope has the 10A4213 heads. I also have a set of 10A4206 heads but I think that will make the compression way to high. Just wondering what you guys think. Thanks [Reply]   [No Email]
Mopower 08-30-2012 12:33:37 64.208.152.151 Report to Moderator	Re: 403 compression in reply to 1948 mm, 08-29-2012 18:44:37   Assuming you are using stock compression height on your piston, you would be correct. I am getting 11.26 after calculating the reduced chamber volume and in head volume. I think that is as much as you want to take it. A later head, manifold, and some cam work will give you a better result. 13 or 06 heads would push it especially if milled. There"s more than one way to skin a cat. [Reply]  [No Email]
1948 mm 08-30-2012 19:01:45 208.71.219.231 Report to Moderator	Re: 403 compression in reply to Mopower, 08-30-2012 12:33:37   I plan on doing some cam work but I have to raise the cylinders about an inch or so to get the cam out so I figure good time to swap heads. As far as the head and milling work go I do that myself so there is really no cost involved. I think my gtb is kind of a dog running high compression and 426 cid. We have an M&W dyno and the minny makes 76 pto hp. It seems to have good torque when I pull but I would like a little more to try a higher gear. [Reply]  [No Email]
Mopower 08-30-2012 19:25:36 174.252.241.145 Report to Moderator	Re: 403 compression in reply to 1948 mm, 08-30-2012 19:01:45   I pull a .060 over G engine with LP manifolds, a M670 venturi, 4210 heads, and an aftermarket cam. It's really nothing special. No milling, no porting, no m&w pistons. Just a mild cam. It makes 100 h.p. at 1400-1500 rpm or so. [Reply]  [No Email]
1948 mm 08-30-2012 19:41:21 208.71.219.231 Report to Moderator	Re: 403 compression in reply to Mopower, 08-30-2012 19:25:36   I did have to drill out my main jet and mixing tube in my carb to get more gas because I could remove my load screw completely and it would not load up. I do also have a set of g lp manifolds but I have never tried them. I am sure a cam would help the most. Thanks for the info 100 hp was my goal from the start. [Reply]  [No Email]
Mopower 08-30-2012 20:04:08 174.239.32.67 Report to Moderator	Re: 403 compression in reply to 1948 mm, 08-30-2012 19:41:21   Our carb needs some jet work too. Next step is a 1/8"+.060 with a ported manifold, 4231 heads, combine carb, and pierce governor. Hoping for 115-120. [Reply]  [No Email]
Moulines4breakfast 08-30-2012 06:16:43 38.123.14.49 Report to Moderator	Re: 403 compression in reply to 1948 mm, 08-29-2012 18:44:37   There are a lot of better and cheaper ways to get more horsepower than raising the compression. [Reply]  [No Email]
molineubspecial 08-30-2012 05:15:36 66.211.74.96 Report to Moderator	Re: 403 compression in reply to 1948 mm, 08-29-2012 18:44:37   the 403 engine bored to 4.75 with a 6" stroke is a 425 cu in i would use the 4210 heads but any of those will work if you get over 225 cylinder pressure run high octane gas or lp you can put the whole 403 engine in a u but you will need to grind out the bellhousing of the tractor to except the g flywheel and starter or you can put the u flywheel and starter on that g motor but i prefer the bigger starter Regards john [Reply]  [No Email]