Contemplating a cam change
 

I'm in the process of replacing the timing chain assembly in my 71 GTO. Right now I'm running a Lunati BMII cam, .490 lift with 290 ° (advertised) duration. I've been running this cam for over 20 years.
The engine is a stock bottom end 400, with 670 heads. The heads have Ferrea stainless valves, 1.75 installed height with Isky springs. When new the springs had 130 lbs closed and 320 open. Unsorted and only .008 taken off just to true them up. The heads were done in 1998 by a former NASCAR engine builder.
I'm also running 1.52 ratio Comp. Magnum roller tip rockers with poly locks.
I'm thinking about going to a 744 cam. With the 4 speed I won't have to worry about a converter.
I already have an Ultradyne 280-288 that I was planning on using in a future build.
All opinions appreciated. Thanks.

You didn't state your goal. But with all the flat tappet issues I consider changing to 1.6 rockers instead. Get the bump in lift without the risk of having to do a complete rebuild.

Just my opinion which along with a sawbuck will get you a steaming hot cup of Joe just about anywhere. 🙂

The specs for the Lunati Bracket Master II Cam may have changed over the years. Do you have the cam card>

This is from and older Lunati catalog.

Stan

Do you know if the pushrod guide holes in heads were enlarged?

If you're happy with the way it runs now, maybe just leave it and just swap the timing set.

If you want to change it, that cam you have on hand should work good, and if you wanted, you could change to 1.65 rockers to bump it a little. But you would have to ensure the pushrod holes have been opened up.

Since the bottom end is stock, and you are running iron heads, I probably wouldn't suggest going too crazy with it. A RA4 type cam would work, but doubt it will give you a noticeable difference over the Ultradyne you have.



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If the pushrod holes were enlarged, and you choose to keep the cam in there, you could add 1.65s on the exhaust side. You would get a bump there too.


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Here's what I found on that 280/288 cam:



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Do you have a cam card or lobe numbers?

Looking at Ultradyne's Master lobe list.

H14 280 223 132 0.3088
H5 288 231 143 0.3222

H31 280 232 143 0.3334
H33 288 240 151 0.3334

Stan

No the push rod holes have not been elongated and the springs were set for a maximum .500 lift. And according to Greg Merrick the chambers on my 670's would need to be opened up to reduce the high dynamic compression that the Ultradyne would make.

Dang. I would probably just leave it then, and continue with the timing set swap.



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The "standard" 280/288/296 lobes everyone used to use (Butler even sold them) the 288 was the 231 lobe.
A buddy has the 280/288 in a 72 455 HO with power everything and A/C and works pretty good.
Hard to beat that line of lobes! Ran a 288/296 on a 108 in a 455 and a 400 with my RAIV heads and ran real good. Even ran the A/C!

The funny thing about the semi closed chamber of the 670 heads in comparison to a later open chamber head of the same CCs is they detonate less since they need to be jetted a bit fatter especially at full throttle and depending on if headers are run open.

There cleaner burning then the pre 67 heads, but not as good as the post 67 heads .

The short lived 1967 061 casting from my experience with them is that they where the most detonation prone head Pontiacs ever had.

If you want to view it, here is the UltraDyne lobe list at Bullet....

https://www.bulletcams.com/Masters/u...nemasters.html

As already eluded to or suggested....
There are two groupings of Hydraulic Profiles. Take note of the lobe lifts.
As Stan has suggested, you need to verify which lobes are used in the cam on hand and pay attention to the distance to coil bind at net valve lift.
Presuming it has been verified that the the springs were set for a maximum .500 lift.

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I can attest to 670 heads requiring a fatter tune, and, they have a very distinctive 'smell', if you know what I mean.



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I would stick to the known good cam and lifters that are in there now. Why risk parts failure? Also, you did not state what your goal was. Why do you want to change the cam?

If everything is good except the timing set then replace that and as far everything else is concerned I’d leave well enough alone.

You stated that the current cam has been in there for 20 years but you didn’t say for how many miles.

If mileage on the cam is somewhat high it might be a good idea to pull the intake and valley pan and inspect it for wear.

If it’s looking worn or if you simply are unsatisfied with the cam then replace it with something more suitable to your needs.

b-man the engine has had numerous passes at the strip before I retired from racing. The engine has well over 135,000 miles on it and last compression check looked good. Average of 164-170ibs. While the Lunati has been a decent performer I've never really been happy with it. I've actually been saving the Ultradyne for a future build. I've been wanting to try to 744 for a long time. The GTO is a.driver and will never see the strip again.

If it has that many miles, could probably use a valve job/seals and springs.

If you choose to do that, enlarge the pushrod holes and swap the cam.

I wouldn't bother trying to open up the chambers, same money you could get a set of open chambers heads, leave the 670s as-is. Could even sell them to offset the purchase of a diff set of heads.

Then you can pick pretty much any cam, get what you want.

I know there's a couple popular 'updated' versions of the RAIV profile, the one Butler advertises has good reviews. If that's what you were looking for.

As a side note, I would say ditch the rocker arms for something better too.



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The Butler profiles I was talking about:

https://butlerperformance.com/i-3164...tegory:1459636

https://butlerperformance.com/i-3164...tegory:1459636



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As a note, I had a 455 with a roller cam that went 224k abusive miles. I did a valve job/top end around 120k miles, the rest was fine.

That's the engine that had the early SD rods, the non-rubber ones, but one did let go at 224k miles. Otherwise it probably would have gone more miles.


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What do you think the 744 will improve over the BMII?

Stan