[thefirebirdm@n]

Last week I posted and asked about a cam choice for a low compression 8:1 455. I have since completed removing the heads and cam and have learned a lot about the current engine configuration so I am again asking for feedback, recommendations, or inputs.

First I was positively able to ID the heads as 4X-7H heads, which have a chamber volume of 98cc (measured in article in June 05 HPP). The heads have been outfitted with 7/16" screw-in studs and upon visual inspection appear to have previously underwent a good valve job and have had some bowl work performed. The heads are at the machine shop now. They are going to clean them up, install new seals, refresh all the angle cuts and try to improve the bowl work a bit. They're also going to fill up the open passage over the exhaust heat crossover.

The engine has been bored 0.030. The piston to deck clearance measured at 0.022" and Fel-Pro 8518PT gaskets were used, which I have read crush to 0.040". Pistons are flat tops with valve reliefs (4). I measured cylinder volume without valve reliefs at 5.1cc and added 4cc as an estimate for a total of 9.1cc including the valve reliefs. Does 4cc extra sound right to you guys? I haven't had the chance to measure the actual cylinder volume with fluid so I am trying to approximate as closely as possible.

Plugging all the numbers into the Performance Trends compression ratio calculator I come up with about 9.2:1. So now that low compression is no longer a factor I can consider some of the previous recommendations made. The final discovery was the cam. Turns out it had a Comp Cams XE268H cam in it with the following specs: 268/280 224/230 .477/.480 110

A couple of recommendations were made if I could get to a higher compression ratio such as the Crower 60919 and 60423. If I went with a slightly thinner head gasket such as the Cometic gasket that compresses to .024 I could get to around 9.4:1 pretty easy. I am really leaning towards the 60919 (or other 041 equivalent) cam based on all the feedback I've gotten in the past about using it in a high compression 455. Comparing it with the cam the engine had in it previously it looks like I'd get a longer duration but lower lift and a higher LSA (60919 specs: 231/240 .470/.470 112). What do the differences in the specs between the XE268H cam and 60919 cam tell me? How would the 455 perform if I put another XE268H back in it vs. the 60919?

Also several people recommended the Rhoads lifters. I've heard the benefits but I've also heard they are noisy and make an annoying clacking sound. Anyone have opinions on this?

Any other considerations I should keep in mind? I plan to put the Edelbrock Performer RPM back on with this combo and I removed the old Hooker headers to install a set of Tri-Ys from Ram Air Ron. I also have a 7043262 Q-Jet to bolt on that has been cleaned up and gone through (looks new!!!) and I am installing a Tremec TKO-500 5-Speed behind it. Rear gears will remain 3.42:1 unless someone has modified them in the past and I'm not aware of it yet.

Thanks everyone for comments and feedback.