[racerboy]

I got the crank sprocket to move and removed the timing chain and then carefully pulled the cam. The reading on the back says:
COMP CAMS 2
51-224-4 911
Z0274 (I think)


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[racerboy]

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[racerboy]

Thanks Jay. There are a number of 6X-4 heads on eBay right now. Here are what my 670 heads look like. Not sure if this is good or bad.




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[racerboy]

This is what Summit has listed under the COMP CAMS 51-224-4.

How does this compare with the Crower 60423?


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[pastry_chef]

For your scenario I'd look at a Summit 2802, inexpensive but looks that it will be out of stock for some time.
https://www.summitracing.com/parts/sum-2802

[mgarblik]

Before you get too far into this engine and picking parts to lower compression/dampen detonation: If your pic in post 39 actually shows the piston at TDC, unless an optical illusion, the piston looks way down in the cylinder. Like .040-.060 down. You need to get an accurate measurement so you can calculate your compression ratio accurately. Not sure why they would be that low unless they had to cut the heck out of the rods to recondition them or the block is extremely tall for some reason.

[racerboy]

Originally Posted by mgarblik

Before you get too far into this engine and picking parts to lower compression/dampen detonation: If your pic in post 39 actually shows the piston at TDC, unless an optical illusion, the piston looks way down in the cylinder. Like .040-.060 down. You need to get an accurate measurement so you can calculate your compression ratio accurately. Not sure why they would be that low unless they had to cut the heck out of the rods to recondition them or the block is extremely tall for some reason.

Thanks. Is that something I can figure out or do I have to take it to a machine shop?


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[racerboy]

Just for the record, this isn’t the engine I was having the detonation issues. That is the 400 RA III in my ‘70 TA. This engine was in my ‘67 GTO, until I started a frame-off on that back in 2013. I don’t recall this engine pinging back then, but I do recall it having a pretty lumpy idle.


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[Jay S]

I had forgotten how big the dish is on those pistons, I think I over estimated the compression. You are probably ahead to swap to the 60243 and stay with the 670s. The dish should measure 2.3” in diameter and .126” deep, about 8.5cc. I don’t have the total cc’s with the valve releifs and the dish. Pistons mfg specs are not listed in any of my older books. Guessing the compression is in the upper 9s though.

I think the bevels on the piston perimeter give an optical illusion that it is down lower in deck. Should be about .015-020” down.

60243 should idle a little bit smoother than the xe274. Power wise there isn’t much difference, but I think the 60243 would have slightly more hp. The 60243 power band is a little broader and is more friendly for higher compression, lower compression the xe274 is better. IMO With the compression it is at with the 670 heads, I would rather run the crower. On the street the XE274 would likely feel like it is meaner, it builds more compression and has a strong mid range. If you swapped to a lower compression head I would leave it in there, as is I would swap the cams.

[racerboy]

Thanks Jay. Do I have to change valve springs if I go with the 62043 cam?


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[racerboy]

Also, do I just order a regular Fel-pro head gasket set? I see that Butler has all those different Cometic ones so I wasn’t sure if I needed something like that instead.

[steve25]

I agree with post 46 about how far down the piston is if that indeed is at TDC.

I also see that the motor was built with the early forged rods ( rubber rods) and if they are not the 421 SD forged rods made of the better and heat treated steel then I would not run them in your new build, especially with strokes over 3.750”!

And in terms of your other question about the heads , yes the chambers look pretty normal , and the coloring due to the closed semi closed design and the Cam being run.
Even the color of most of the exh valves looks ok.

[racerboy]

Steve
You are right. These are the early forged (not SD) rods. Would you also replace the pistons as well? If so, what rod/piston combo would you run? Would this require removing the crank? Sorry if that’s a dumb question. I’m also assuming that all of this will require sending everything off to a machine shop. I was trying to avoid that because I know that’s going to take multiple months.


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[wovenweb]

Do you have the 60243 camshaft in hand? I haven't called to check on my order yet, they are showing various dates out a week (Crower website/e-mail) to August(Summit) for availability. I ordered one via Crower's website a couple days ago. I've got a 428 that I'm finally assembling, Icon pistons w/10cc dish. I have '68 #16 heads and compression calculates to about 10.5

[racerboy]

I do have the 60243 kit. I bought it for my ‘70 Judge RA III motor last year, but never installed it. Then I sold the Judge to buy the Trans Am.


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[racerboy]

The #1 piston was not at TDC in that last photo. I went out to shop and rotated it a bit more.





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[racerboy]

Originally Posted by wovenweb

Do you have the 60243 camshaft in hand? I haven't called to check on my order yet, they are showing various dates out a week (Crower website/e-mail) to August(Summit) for availability. I ordered one via Crower's website a couple days ago. I've got a 428 that I'm finally assembling, Icon pistons w/10cc dish. I have '68 #16 heads and compression calculates to about 10.5

Woven - isn’t that compression a bit high for pump gas, or do you have access to AV fuel or race gas to mix?


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[wovenweb]

Originally Posted by racerboy

Woven - isn’t that compression a bit high for pump gas, or do you have access to AV fuel or race gas to mix?


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My other engines are 12.0(Pontiac w/RA II heads), 10.2(Pontiac), 9.9(Buick) and a stock '71 455HO engine. No pinging on any of them. I do run 100+ octane in the 12.0. So, this is a little higher but nothing like the 12.0. I do have ready access to 93 here in Texas.

[Jay S]

Originally Posted by racerboy

Thanks Jay. Do I have to change valve springs if I go with the 62043 cam?


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No. Springs should be good.

Just my opinion, I would leave the early rods in the engine. They are not much different strength wise than a stock cast rod. We ran some in a 455 in the stock car photo that is my avatar for for a season and a half before we broke one. It was turning 6500 at the end of the straight on a 3/4 mile track. 4000 rpm through the corners. Going through the heats, sometimes both features, that was some serious abuse. Our mistake was we shouldn’t have ran them again the second season. Lol Personally I think the strength is a toss up between a newer cast rod and those old forged rods. The other Pontiac engines we did we ran cast rods and arp bolts and thru them in the recycle bin after each season. In a street engine with stock heads I would run them an not worry about it.

[Formulajones]

Originally Posted by racerboy

The pistons have some carbon on top. Do I have to get rid of that (and how)? Also I don’t think it is at zero-deck. It looks like when it is at TDC the piston is still a little below the deck.


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Just an FYI, those are the exact same pistons I used in a 428 build I did about 25 years ago. The L2257 is an old TRW forged flat top piston for a 428 with 4 valve reliefs. Obsolete part number now I believe.

So that dish is machined in there. Here is a picture of mine after I machined a 16cc dish in that same piston. When I ran these pistons in a .030 over 428 and .004" down in the hole with a 76cc head, my compression was right around 9.7:1

Your dish is much smaller than mine, so you'll have to measure it.