[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.

[Cliff R]

The 60919 is a great choice for the 455 engine. We have a 455 here with 6X-8 heads and that cam, idles a bit "rough", but strong power everywhere. I would add a set of Rhoad's lifters to improve idle quality, we only have about 7" vacuum at 700rpm in gear.

I have NO idea how well it would work or how much power the XE268 cam would make in a medium compression ratio 455 engine? KRE just made 441hp with a 455 using the large chamber 4X heads and the 60919 cam. We recently built a similiar engine with 1974 #46 heads (unported) and made about the same power.....Cliff

[runningbwdog]

Hi,
I have a similiar engine , 462 cid, 9.34:1 compression and a straight up installed Comp Cam XE268 in it. You don't need Rhoades lifters with that cam. I have 15-16" vacuum at idle. Idle is fairly smooth at 750 rpm. Engine is well mannered on the street. Easy to pull away from a stop. Smooth cruise at 60 mph. Won't be the monster street engine that you read about on this forum. Mine is well balanced between traction and power. Love WOT runs. Certainly faster that the stock 400 it replaced.
CliffR did my Q-Jet and Sun-Tuned did my Dist.
Here is a thread that has a listing of most of the cams available for Pontiac Engines. Its not completely accurate, but is a good reference when trying to pick out a cam. http://216.178.81.108/forums/showthread.php?t=465125
Mike

[thefirebirdm@n]

TTT

Hey guys, still looking for more recommendations on my buildup. Esp since I will be running the TKO-500 with 3.42:1 gears in the rear. Any more comments on cam selection?

[Thumpin455_GTO]

Unless you want to port the heads, deal with less vacuum, rough idle and the associated power brake issues, I would recomend going with either the XE268 or the 60919. You dont need alot of compression to get a good running engine for the street. I have run Rhoades lifters in a couple 455s and the ticking wasnt ever that bad on them. .020 lifter preload appears to work pretty good with them. Like runningbwdog said you dont need Rhoades with the 268. Its a very mild cam for a 455 and would have more than enough vacuum and a smooth idle.

I myself am a fan of the Ultradyne cams. The 70 GTO has an UD280-288 and if I remember right it is a 230-234@.050 cam. It has a nice lope to it and makes plenty of power, I never had it dynoed but it does move the 4100lb Goat to mid 13's with highway 2.93 gears. Recently I have installed 3.42s and plan on a TKO500 as well, but since I have a set of ported 5Cs on it now, I will be moving up a bit in the cam. I dont mind a bit of rough idle and a little less vacuum. I will probably go with either the used UD 288-296 cam I have from a previous car, or a new XE274. Like I said I dont mind the lope and loss of vacuum.

[wovenweb]

Originally Posted by 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.

Jimmy! Have the 200-4R moving yet? I'm still stuck trying to figure out what to do with my floor pans as I'd like to have seats that stay in one spot. Once that gets wrapped up, I will have mine out on the road.

I did get a 60243 for a 428 build w/ '68 16 heads ported by SD Performance. Need to figure out what to put it in one of these days.

FWIW, I googled 60243 and this thread was the second hit on the list after Crower.