JD Heads on 78 Vader

[Truder78]

Rebuilding my 78 vader engine I will be putting on a pair of nos JD 440 heads and was wondering if the jetting and timing will stay the same due to the increased area of the head dome? (squish area)
Thx... Site Still looks Great

[gixxer6]

Jetting and timing should be the same. 

Why are you changing to the JD heads?  This will decrease the performance due to the lower compression ratio...

[rminier]

 The Liquifire's heads reduce the effective compression ratio from the Invaders 7.3 to 1 down to 6.9 to 1...not a huge deal.....but sacrificing 3-4 ?? HP.
 The Liquifire's stock jetting (at sea level to 4000 feet) is 150 Main jets, 110 (PTO) and 105 (MAG) power jets.....awfully close to the Invaders  stock 150 Mains, and 120 power jets.
 That small difference in jetting may, or may not, be due to the slightly different compression.
 It could also be due to the slightly different air box design and exhaust system that John Deere engineered to fit in their Liquifire chassis., and the way all of those components work together.
 I could find only find one reference for timing in my John Deere manual, and that was to "Align Stator Marks".
 One would think you could advance the timing a couple degrees when you reduce the compression ratio, but I wouldn't even attempt it.. unless....maybe.... I could do all of this with the engine on a dynamometer.
 I second gixxer6..... leave the timing as is, and run the stock Invader jetting.

[gixxer6]

I run shaved heads on my 440 Invader.  Stock timing and stock jetting with premium (92) gas without issues.  These old piston port motors make good power up top, but have very little low end/mid range.  I find the bump in compression helps in these areas.  For what it's worth, I advise against using the Deere heads. 

[Lloyd (ljm)]

 You won't notice any difference when you switch to the JD heads. Liquifire's base timing is actually retarded a little bit compared to an Invader. Deere did this to try to add to the life of the engine. I don't think it helped much.

[Truder78]

Thx for the input
My sled had shaved heads when I got it and did not know... they were not sure of the correct number but it was something like .3 .030 .003 what ever the max was I was told after it blew up using low octane gas. I have the JD heads on hand as well as nos cylinders and will only use it around the lake for short rides and ice fishing and if jim is still active in the club...  ;)YES CRANKSEALS ... and don't care about top speeds anymore ...age has taken its toll. Tried to post some pics of the heads that came off it but site kept freezing images were to large I guess

[Truder78]

The heads are not nos my mistake but the cylinders are
Nasty looking

[Truder78]

PS. You have done a Great Job with the site Bob hope all is well with you and your family

[Interceptor398]

Thanks!!!!!!  Currently keeping it alive with hopes of better things to come!!

[Truder78]

Luck!!!