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Originally Posted by 56markII
Hi Pete and thanks for reply!! Yes I see that all the time and they are TOTALLY unsuitable for street and at times the vacuum accessories don't work as well. A slight Lopey idle I can live with and my guess is the slightly more aggressive version I listed is perhaps that kind that will have a slight gallop of the idle perhaps not making the car shake?? Nope I'm most certainly not looking for massive increase but just a bit of a warming up  This would be indicated by having this car since the early 80's and using 110 hp for all those years. By some chance do you know the specs of that better Ford OEM cam and how does it compare to those Isly's? They also increased the compression to 7.5 in the latest and HP was 125 HP OEM as well and I should check my heads to be sure what I got but I'm sure I have a pair like you mentioned. 25-35+ HP shouldn't be that difficult to achieve on these and as it is I have been digging around for info on popup pistons as well. OlRon mentioned he has used 239 Pistons in the 255 as well after I was always thinking about this. He never went into much detail about using them and my future experiment that I hope to do is drag one of my cores into the shop and place a 255 crank into it with a 239 piston without rings and place a head on it doing a crush test to measure the clearance. One fellow at Isky I talked to mentioned compression is a very big factor for how the cam behaves and what it can do as well. Then there is the argument of reducing the stoke with a 239 piston but in reality the bottom of the stroke is reduced but the end result is the chamber is also reduced at TDC of compression. This is probably a bigger win win situation than worrying about a 1/4 inch reduction of BDC anyway! I have also read this is a factor for milling heads as well because yes you reduce the "squish" area on top of the piston but you also reduce the flow area above the valves as well. I have a pair of 239's and a pair of 255's laying around so I have test parts available to do simple rotational tests for seeing what goes on. Also being a higher lift cam for the slightly more aggressive Isky they mention checking valve to head clearance as well. Hopefully somebody can chime in on their experiences with popup Pistons and how high the compression is raised. Different HP heads? Well such heads and intakes are not very common up here in Canada and perhaps more can be accomplished using popup Pistons whether they be special high performance or just a stock 239 stuck in to be used, that and a better civilized camshaft. |
For cam comparison specs go to the Tilden website.
As far as pop up pistons, forget it. You can get way more compression than you need on the street by just milling and matching the dome to the pistons, with stock heads.