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Topic Review (Newest First)
11-14-2018 08:25 AM
PHWOARchild
Quote:
Originally Posted by ericnova72 View Post
The bad news for you is that the stock 390 head casting is a closed chamber head, and that means only closed chamber pistons fit with it....and that means small domes at best, flat tops at worst.....and nobody in the aftermarket makes a closed chamber aluminum head.

Your compression ratio is going to take a hit, anywhere from a full 1 point drop to nearly 2-1/2 full points depending on what size open chamber aluminum head you were to use with closed chamber pistons.

The only two ways around that are: paying to have the heads angle milled right from the manufacturer or have a local shop do it, which is very likely to also require the intake manifold needing to be milled to fit the new milled heads....or you can replace the pistons and rings with a new set of pistons that have an open chamber sized dome.
My stock close chambered steel heads gives a CR of 10.25:1 and the pistons have a .182 high dome. I'm not going to mess with it too much. The combustion chambers are relatively small compared to an open chambered head.
11-13-2018 08:02 PM
ericnova72 Okay, gasket is the right type. Covers look like they have a decent baffle, but you could road test by putting a breather in place of the PCV valve and then plug the hose gong to the carb, and see if your smoke situation clears up.
11-13-2018 04:53 AM
Colin68 thanks for the reply! I did a little research this morning and found some info...the intake gasket # is an FEL 1210, and the valve covers appear to be Proform Parts 141813 (they were on the car when I got it).
11-12-2018 09:26 PM
ericnova72 A vast majority of aftermarket valvecovers don't even have a baffle under the PCV hole, so check on that. No baffle and it will guzzle oil.

Better yet, tell us what valvecover you have and we'll look it up and see what it has.

Not using the correct type of gaskets for aluminum intake manifolds can lead to sucking oil also. The standard replacement Fel-Pro's for iron intakes often soon leak when used with aluminum intakes. Gasket doesn't have compression and rebound characteristics to match the higher expansion rate of aluminum . The intake gets hot, expands more, crushes the gasket beyond its rebound limit, and when everything cools back off it doesn't stay tightly sealed.
Any idea what intake gasket got used??
11-12-2018 06:47 PM
lmsport Check the torque on the intake manifold bolts, Weiand is now telling folks to retorque them every 6 months in their instructions. A quart in 90 miles is alot of oil.
11-12-2018 06:19 PM
Colin68 Ok...you are taking me to school here, which I very much appreciate. So...chances are I have flat tops...domes are pretty much not possible, and if they have been replaced, who would put dish pistons in it? I do not know if the baffle under the PCV is correct, or a problem, etc. Not sure how to tell that. The valve covers are aftermarket, but I suppose that doesn't mean much. The guy that installed my cam was good....I would be surprised if there is an issue with the intake gasket, but I suppose anything is possible. The guy that did the seals and mentioned the "ears"...Probably isn't going to see the car again. So you are leaning away from piston rings?
11-12-2018 05:59 PM
ericnova72 Heavy oil smoking on Decelů.first thing is does the valvecover got a good baffle where the PCV valve is??

Second thing would be intake to head gasket seal, sucking oil from lifter valley.

Valve seals and valveguides would be third seeing how you've said the seals are new. Even on worn guides, new seals should help, even if it is only for a few weeks, but you should be able to notice it helped or didn't.

I have no idea what your mechanic meant by "broken ears"....there really aren't any "ears" on BBC heads, so I don't know what his terminology is referring to.
Maybe the top upper intake bolt location at the divider wall between the intake ports on the heads is broken through into the port, or something like that??

A 454 with a flat top piston and 98cc head, using a .041" thick x 4.370" bore head gasket is just short of 9.0:1 compression....I don't think it will be a dome as I don't recall there ever being a closed chamber dome piston made for a 454(maybe the 1970 LS-6 solid lifter 450HP 454 is the exception), they were all open chamber engines. Aftermarket doesn't sell any closed chamber dome 454 pistons unless you order custom.

The flat tops and closed chamber trick is/was a rather common "magazine hack" for building up those flat top piston 454's without touching the assembled short block other than to change the cam......wouldn't surprise me to find out that's just what you've got.

You can get some pretty good low cost borescopes that connect to a smart phone on Ebay, that might be a simple way for you to see what piston you have without removing a head.
11-12-2018 05:33 PM
Colin68 well....that is very bad news. unraveling this is frustrating. Is it possible that the pistons in the car (whether they are stock dish, which I think may have been put in some of these blocks depending on the year) or whatever pistons they put in don't match the heads currently? Certainly what this seems to be coming down to is the pistons themselves. In the short run, if I can get it to stop smoking with some type of head solution, and maybe that means another set of rebuilt heads like the ones I have (I believe there is an issue with mine, as the mechanic that did the seals told me there were "ears"---whatever those are----broken off, which may be allowing oil to be pulled in to the cylinders), then I would be OK with it for a while. Ultimately, I want it to be RIGHT. While I am learning more about it, it is becoming more complicated. If this thing is smoking ONLY on deceleration and otherwise it runs fine, what would your gut tell you? Another note...when I pulled the valve cover off to check the number, there was quite a bit of oil pooling in the head.
11-12-2018 04:21 PM
ericnova72 The bad news for you is that the stock 390 head casting is a closed chamber head, and that means only closed chamber pistons fit with it....and that means small domes at best, flat tops at worst.....and nobody in the aftermarket makes a closed chamber aluminum head.

Your compression ratio is going to take a hit, anywhere from a full 1 point drop to nearly 2-1/2 full points depending on what size open chamber aluminum head you were to use with closed chamber pistons.

The only two ways around that are: paying to have the heads angle milled right from the manufacturer or have a local shop do it, which is very likely to also require the intake manifold needing to be milled to fit the new milled heads....or you can replace the pistons and rings with a new set of pistons that have an open chamber sized dome.
11-12-2018 01:49 PM
Colin68 sorry I am just getting back, but I appreciate the response! The valve guides and seal are new. I checked the PCV system, and all seems well as far as I can tell. The valve itself is new. the heads are 3904390 (66-68 2.06/1.72)....no idea what work has been done to them, but it appears they were worked on at some point in the last 50ish years. when I took the valve covers off it appeared that there was more oil than should have been sitting on top of the head. It would appear that after the seals were replaced I am using less oil, but it is still a lot....and it only smokes (gray) on deceleration. thanks again for the reply!
11-12-2018 09:07 AM
lmsport 90 miles a quart is alot, either bad rings or sucking oil into the intake manifold at the intake to head flange.
I built a 454 for myself using low tension oil rings, used about that much oil after just a few thousand miles, and it too only had visible smoke on hard acceleration or decel, cruising produced no smoke.
11-12-2018 08:29 AM
Colin68
picking aluminum heads for my BB chevy

thank you for the responses to my aluminum head question.....I have been out of the country and have just gotten back to my laptop. I did a little research...the Muncie I have my eye on to replace my Saginaw is actually an M20 with 2.52 1st gear ratio that I want to match to my 3:53 rear end. The head casting number is 3904390....2.06/1.72 valves, and a 98.4cc chamber. Again, no idea what the pistons are....I guess I will find out when I get the heads off, but hopefully the info above is at least a start. The PCV system seems to be working OK, and the valve seals have been replaced. It is still smoking quite a bit on decceleration...its a little embarasing. Since the valve seals were replaced I don't seem to be using as much oil, but still about 1 quart down after about 90 miles of driving (concerning that it is actually an improvement over where I was). My goal is to have a strong streetable car. I am not going to race it, but I would like it to perform well enough that I don't feel like I only have a nice looking motor with no real performance behind it. if that makes any sense at all.
11-08-2018 01:09 PM
PHWOARchild Run the numbers on your existing heads, see how good they might be. I have a pair on my 396 that are great for what I'm planning on doing. When that is up for a rebuild, I'm using the same heads with a freshen up.


I'm with Autogear, you don't want a doggy engine that lugs at 30 or 40 mph around town. My M20 has a 2.52 1st gear (blew up the 2.56 gear set back in May..) and 3.89 gears out back.
11-07-2018 03:39 PM
AutoGear Muncies don't have vacuum modulators or use ATF though.

Check your Muncie before you screw humptydumpty back together again. I'd hate to see you put an M21 in front of a 3.55:1 axle. It'll seem doggie in 1st gear, and have nothing to do with the engine.

Turn the OUTput (back) of the transmission 10-times while its in 1st gear (the right-hand lever in the side cover turned to its RIGHT)
Have a friend count the number of times the INput (front of the trans) turns.
25 times is an M20 wide ratio
22 times is an M21/22 close ratio

If you do have a close ratio, you can easily swap the input and cluster to make it an M20 for a couple hundred bucks, it could probably use a new 1-2 slider, new forks, bronze synchro rings and bearings anyway. Better to do it now than making a special weekend of pulling the trans again, probably when you have much better things to do.
11-07-2018 09:34 AM
55 Tony
Quote:
Originally Posted by Excellenceautosoluti View Post
If your car is automatic tranny it may be pulling atf through a bad modulator.

Good thought! ATF burns with a white smoke.
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