Valve clearence Info
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From: Minnesota
Valve clearence Info
Does anybody know what the limits are on 351M for lift? also, will there be any problems with running the larger 4v valve size (2.19 and 1.71) and stock pistons? Thanks
Jerry
Jerry
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From: PacNW
Valve clearence Info
All of the stock 351M and 400 pistons I've seen have valve reliefs milled into them but If I were rebuilding an engine I wouldn't necessarily trust them with the larger valves. I'm not sure what you mean by 'limits on 351m for lift". Are you talking about with stock springs or is it just a valve clearance question?
Valve/piston clearance is also affected by duration. You want to open the valves as much as possible to get maximum A/F mixture in and exh. out so a longer duration is best but the higher you lift the valves the longer it takes to open & close them so you can run into interference problems. Flat tappet cams are limited in this regard which is why the lobes have a much "sharper" profile whereas on a roller cam you can open & close the valves much quicker allowing the engine to breathe better and make more power.
Valve/piston clearance is also affected by duration. You want to open the valves as much as possible to get maximum A/F mixture in and exh. out so a longer duration is best but the higher you lift the valves the longer it takes to open & close them so you can run into interference problems. Flat tappet cams are limited in this regard which is why the lobes have a much "sharper" profile whereas on a roller cam you can open & close the valves much quicker allowing the engine to breathe better and make more power.
Last edited by Bill_Beyer; Sep 3, 2003 at 01:50 PM.
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From: Minnesota
Valve clearence Info
Thanks for the reply. I guess what I was wondering was, with a stock truck cam in a 351m, with stock pistons, will I have any problem running 351c heads with the larger valves? The engine is going to need a rebuild soon, and I can buy a pair of heads already done cheaper than I can rebuild the ones I have, but I don't want to have any valve/piston issues.
This is the first 351m I've had. I know some engines are close, while others, like a 302 have a lot of room, as far as valve clearance goes.
Will a edelbrock performer cam give me any trouble? the duration is still pretty short, but they do have more lift. Thanks,
Jerry
This is the first 351m I've had. I know some engines are close, while others, like a 302 have a lot of room, as far as valve clearance goes.
Will a edelbrock performer cam give me any trouble? the duration is still pretty short, but they do have more lift. Thanks,
Jerry
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From: PacNW
Valve clearence Info
The 351C heads which came with the larger valves were the 4V version which also had much larger ports and while they would physically fit on your 351M the port mis-match would not be a good thing. 351M heads are essentially the same as 351C 2V heads, both have the smaller valves and ports. Both can be machined to accept the larger 4V valves but still have the smaller ports. I would still check very carefully when putting the larger valves in a stock engine although I don't think you'd have a problem.
The E'brock camshaft would require different springs but the lift shouldn't cause any valve/piston interference problems.
The E'brock camshaft would require different springs but the lift shouldn't cause any valve/piston interference problems.
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From: Minnesota
Valve clearence Info
Thank you, that was what I was looking for. I'll probably get out the clay and make sure everything will be ok, but as long as most agree that it "should" work (I know there are no garentees) I feel better about buying the heads.
Thanks again,
Jerry
Thanks again,
Jerry
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Joined: Jun 2003
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From: Houston/Hope BC
Valve clearence Info
Works fine for me in my 400. Using stock cast pistons (dished) and a RV cam 272 advertised (212 @ .050) and .510 lift. Am VERY pleased with mid and big end, no noticable deterioration of off-idle response. Very expensive though, lots of work at before porting and then again at the head shop.... you must get the hardended seats put in the exhaust. I also recall the machine shop guys telling me that I would not get into coil bind until over .700 lift. (No opinion here on valve to piston clearance at that number.) Stainless is the only way to go if you are going to this kind of expense. Am also pleased with the Speed-pro S/S valve. Best of luck to you.
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From: PacNW
Valve clearence Info
The 400 has much more deck clearance than the 351M (.06" vs. .02") however which is why I would be especially careful about checking the clearance before running the engine.
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Cross-Country
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Valve clearence Info
Jerry,
I know I'm coming into this a little late, but what you are proposing to do is very close to what I've done already. The difference is that I have a 2V Cleveland. With that said, I have a Comp Cams 270H with .519" lift on intake and exhaust. My pistons are about .005 below the deck and I have aussie closed chamber heads. Absolutely no problems with valve to piston clearance. If you are going to use a mild RV cam with just over .500 lift you should be fine. Also similarities between our engines is that I had 4V valves cut into my Aussie 2Vs. Tight fit and a little scary to look at, but they also work fine. In all reality, I should have only opened up the exhaust to 1.74" and left the intake alone... It's big enough.
If you get Cleveland heads you might gain some flow on the exhaust side because they don't have the bump. As far as hardened seats, I remember reading on here or another related forum that about 1972 and later the seats were hardened anyway. If the seats are in good shape, save your money or spend it somewhere else.
Check ebay for 2V cleveland heads if that is what you really want to do, they are dirt cheap and always available.
Good luck,
Steve
I know I'm coming into this a little late, but what you are proposing to do is very close to what I've done already. The difference is that I have a 2V Cleveland. With that said, I have a Comp Cams 270H with .519" lift on intake and exhaust. My pistons are about .005 below the deck and I have aussie closed chamber heads. Absolutely no problems with valve to piston clearance. If you are going to use a mild RV cam with just over .500 lift you should be fine. Also similarities between our engines is that I had 4V valves cut into my Aussie 2Vs. Tight fit and a little scary to look at, but they also work fine. In all reality, I should have only opened up the exhaust to 1.74" and left the intake alone... It's big enough.
If you get Cleveland heads you might gain some flow on the exhaust side because they don't have the bump. As far as hardened seats, I remember reading on here or another related forum that about 1972 and later the seats were hardened anyway. If the seats are in good shape, save your money or spend it somewhere else.
Check ebay for 2V cleveland heads if that is what you really want to do, they are dirt cheap and always available.
Good luck,
Steve
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From: Minnesota
Valve clearence Info
Thanks for all the replies. It will probably be winter before I tear into it, but I'll try to post the results. This message board has been very helpful, so I want to try to give back as much info as I can.
Jerry
Jerry
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From: Delaware
Valve clearence Info
If they are 351C-4V heads, you will need a new intake manifold. You will need a 4V intake for a 351C, then you will need adapter plates to make the manifold fit the 351M. Then you will have to change or modify the distributor so it will clear the manifold.
That is a lot of work and expense just to get larger valves. In addition any improvement in peak horsepower will be offset by a loss at low RPMs.
You would be much better off putting those Cleveland valves into your heads and doing some porting work.
Better yet get Aussie 2V heads. Check Ebay, there were a set there the last time that I looked.
That is a lot of work and expense just to get larger valves. In addition any improvement in peak horsepower will be offset by a loss at low RPMs.
You would be much better off putting those Cleveland valves into your heads and doing some porting work.
Better yet get Aussie 2V heads. Check Ebay, there were a set there the last time that I looked.
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