[Mr. G]

Mostly stock 455 HO in a 1971 GTO with M-20 and 3.23 rear end. no a/c. I like the Crower 60240 cam but they recommend using their 84160 kit with lifters and valve springs. I have read that the cam can be used with stock springs but not sure about that. If I were to install the cam without using the 84160 kit, what would be a good flat tappet lifter to use with it? Also, if there is a better choice of cams I would be interested in hearing about it. The motor has about 30,000 miles on it since last rebuild. Thanks for the help!

[HWYSTR455]

How was it built? The heads specifically. New springs? If so, which ones? And is there info from the build for max lift?

Have the heads had the pushrod holes modified/opened up?

Do you know your static compression ratio?



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[Mr. G]

Unfortunately I don't have any stats on the previous rebuild as it was a long while back although I do know that the pushrod holes are not modified. I recall the builder saying he selected a mild cam as to be easy on the engine. Back in about 1983 I bought this as a short block with no heads and then purchased a set of bare heads that I had to buy valves and everything for to make it complete and was shooting for a stock rebuild at that time. The engine ran good but at 5,000 elevation it felt a little weak so I figured after the builder commented on the mild cam that replacing it with a more performance oriented cam would give the engine what I always thought it lacked. Maybe a stock grind for the 455 HO would be a safer bet?

[steve25]

The lift of that Crower Cam WILL work with stock springs, but if your springs are original then even if you where going to run a stock factory Cam it's high time to change them!

With what those heads flow stock it would really pay for you take advantage of those air flow numbers and run a Cam that gets you into the .480" lift range which will push you into the need for new valve springs to handle that lift.

[Formulajones]

You may have an engine that is running just fine. Just an FYI I'm sure you know. All engines will feel down on power at 5,000 feet elevation. We are at 5,000 feet as well.

General rule of thumb is that every 1,000 feet of elevation you lose about 3% power, so up here we are automatically down about 15%

To put that in perspective, a typical 500hp engine up here is roughly making about 425hp. So it's like a shot in the arm when we drive down to sea level. When driving around long enough a mile up, it's a shock and like a completely different car when at sea level.

[HWYSTR455]

Pushrod hole rule of thumb is .469 lift is where contact occurs. You might get away with a little more, but it's better to make sure and open them up.

True if the springs are old, you should replace them, it at least gives you a line in the sand going forward.

If the valves are OE, replace those too. Notorious for coming apart.


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[Bruce Meyer]

Originally Posted by HWYSTR455

Pushrod hole rule of thumb is .469 lift is where contact occurs. You might get away with a little more, but it's better to make sure and open them up.

True if the springs are old, you should replace them, it at least gives you a line in the sand going forward.

If the valves are OE, replace those too. Notorious for coming apart.


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.469 lift wont need the pushrod holes opened up unless you are using 1.65 rockers.

[Mr. G]

The Crower 60240 has lift of intake =0.422. Exhaust = 0.446.

[steve25]

The basic rule of Thumb is that is darn accurate is that for every 100 hp you want your motor to make you will need to run .100" of lift in regards to the valve sizes in these heads.

If your heads are off the motor now and with that .422"/ .446" lift Cam I would clearance the Intake push rod guide holes now so that down the road if you want to add 1.65 rockers to the heads you will be set to run the higher .464" / .490" lift that you will then have.

This again this is another reason that with the heads off get them set up to handle a tad over .500" lift , and in the process throw out the oil splash shields and also cut all 16 valve guides to accept positive .530" ID valve Viton type seals.

[Cliff R]

The 60240 cam is not nearly enough cam for a 455 engine. It's about perfect for a 400 build with low compression heads and mostly stock otherwise. For the big 455HO I'd look at more camshaft and wide LSA. The smallest cam I'd ever put in a 455 HO or Super Duty build is attached. I also attached a dyno sheet from a 455 Super Duty with stock intake and low compression that we used one in a few years ago. Even with the much larger cam it idled dead smooth clear down to 600rpm's and made over 14" vacuum at idle speed. It's a HR, but one could have a similar flat cam ground and run Rhoads lifters and high ratio rockers on it and make about the same power........Cliff

[HWYSTR455]

Originally Posted by Bruce Meyer

.469 lift wont need the pushrod holes opened up unless you are using 1.65 rockers.

This is actually a misconception, when you think of how a rocker moves, the pushrod cup sweeps in a ( path, and, even with 1.5 rockers, once you go beyond a certain lift, the pushrod will contact.

If that weren't true, you could run as much lift as you want with a 1.5 rocker, right? (until coil bind of course)

If you're using RA IV or 455 HO heads, no mod is needed.

If you're using 11/32" pushrods, with 1.5 rockers, the max lift before contact is .460 .

I may have confused the amount of lift where unported D ports start sloping off on flow, which is .469 , with the contact of pushrod hole, but, in any case, the hole should be modified, even on RA IV and 455 HO heads, especially is lift will exceed .550 .

I can seem to locate my H-O Racing book, but it I'm fairly sure its outlined in there much better.

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[Mr. G]

Wow. Thanks for all the input. Looks like I need to go back to the drawing board on this one. Good thing I didn't order parts yet.