engine upgrade

[FLEA]

im slowly puting together my parts for a major rebuild (rephase,5th gear late model transmission etc) but still undiecided about the 700 from hoos or a 750 kit what are the pros and cons for both with performance and relibility in mind.the motor is a tx 74,thanks

 

[650Skull]

hey Flea, 700 kit is a max bore out on your cylinders, if you have to rebuild down the track you will have to resleve

750 kit can be oversized to 81mm

Heiden tuning has a 6th oversize 680cc, a bit xy but you can rebore for a 700 kit later.

 

[FLEA]

the motor is siezed solid would most probably have to resleeve any way as it was on 2nd o/s years ago and with un siezing it ?? 1 bloke reckoned he did the 2 upgrades to 2 fairly identical motors and for some strange reason he said the 700 seemed to pull harder.could it be from being a heavier piston as some people say the 750 pistons are lighter (which seem to cause more vibration) and cut different or are they just being purests.to be able to o/s the 750 further down the track is a plus

 

[650Skull]

Put in some barrels to take a 700 that can be taken out to 750 later. Have to kill the 700 before you can compare the

Are these available???

 

[Hamos]

I think the advantages of the 700cc big bore is that you can do it on stock liners. The high compression (10.5:1) is where the main performance benefit comes from. This compares to Mikes big fin 750 kit with a 9.5 compression ratio.

If you get a weisco/JE 750 kit, then you resleve. These kits are higher compression, again 10.5:1, so even more oomph, but cost more than the 700.

 

[XSLeo]

I don't know about the piston weights between mike's kit and others. When I put Mike's 750 kit in my 75 the vibes did change, the idle to 3500 rpms the vibes a bit more but no increase in the 3500 up rpms. The vibes feel the same at any rpms.
Other may or may not feel the difference but that's what I found.
It might be that others did other changes at the same time as the 750 kit. That's all I did at that time. I did most of my changes during the 650 rebuild, headwork, exhaust work, carbs, all that stuff.
Leo