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post #1 of (permalink) Old 06-20-2001, 11:57 AM
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351W STOCK HEAD MODIFICATIONS

I would like some advice.
I've got a 1985 Bronco with 5.8 HO

The motor is out for a rebuild due to bad oil leaks. I found a burned exhaust valve so the heads will need some work.

I see that there is a large protrusion into the exhaust ports for the air induction from the smog pump. The pump is long gone and the holes in the end of the heads are plugged. Is there any reason not to grind these off to free up the exhaust flow? Are there any water jackets or thin metal in this area. Any other minor porting that should be done?

I'm putting on an edelbrock performer intake and assume that I should at least port match the intakes.

How much can I shave the heads to bump the CR up a bit without having detonation problems?

The block is a factory rebuilt short block bored .060 over with flat tops. This was done before I bought the truck. The compression is good (125-130psi). The cylinder walls look good. I checked the rear main bearing and #8 rod and both looked good.

The rest of the setup is Holley 4160 600cfm, Comp Cams xtreme energy 4x4 cam & lifters, Summit shorty truck headers, flowmaster Y pipe and series 40 muffler.

I'm hoping to get the mileage up a bit from 10MPG but also get good power for off-road.

Thanks for you help.



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post #2 of (permalink) Old 06-20-2001, 12:13 PM
 
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Re: 351W STOCK HEAD MODIFICATIONS

Sounds like the perfect question for DRUNKEN PHAROAH. =)

The trouble with being on top...You always have to look over your shoulder. The best never rest. Fear the FORD thunder!!!
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post #3 of (permalink) Old 06-20-2001, 02:28 PM
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Re: 351W STOCK HEAD MODIFICATIONS

You're on the right track.
Dump the "thermactor" bosses in the exhaust ports. (that's what the large protrusions are called)
Be extra cafeful around the valve guides though. If you've already got the header gaskets, try to match the exhaust ports to those gasket openings, and go in as far as you dare.
Remember, it's better to take more material off the top of the port versus the bottom.
If you're getting new guides, it would be better to do the porting while those are out.
As far as the intake side goes, just a mild port match to gasket will be sufficient. The weak side is on the exhaust, so spend you're time there.
Check the new intake as well. They aren't always in the best of shape as far as port matching either.
Are you putting all new valves in? Ford Motorsport carries the entire GT-40 valve train for a not too extreme price.
You'll get larger valves, and better material.
Are you doing the port work yourself?
Reason, for the amount that a shop would charge, you're better off going with an aftermarket head. Most of the work's done, and they're a quick bolt on. Do some checking into "porting" prices.
Another thing to consider is going to studs and guide-plates, and installing roller rockers. You'll get true 1.6 ratio, and less friction. (Plus they look cool before you put the valve covers back on)
Oh, the cam you've chosen is a good one. It has a "split" profile, meaning, the exhaust has longer duration than the intake to get all the burned up stuff out where it belongs.
Which one is it though? Don't want to go too big, or you'll lose the bottom end, and your vacuum will be awful low at idle.
One thing to consider on determining your compression ratio, is that those later model heads have huge combustion chambers, so even milling off extra material won't net you that much smaller of a chamber. Someone correct me if I'm wrong here, but I think they're around 74cc?
You might look for a set of '69 4bbl heads as they already have larger ports, larger valves, and a "quench" 58-60 cc combustion chamber.
Again though, you run in to the how much $$ spent to get them as good as a new aftermarket head.
Compression ratio also is affected by the piston deck height. How far below the deck of the block is the top of the piston. That's another volume to consider when calculating the compression ratio. I think Ford Motorsport catalogue has the formulas for determining your static compression ratio. KB pistons also has a good page explaining this:
http://www.kb-silvolite.com/page56.htm
There's also a great article on "quench" distance. Hence the importance of knowing your piston deck height:
http://www.kb-silvolite.com/page07.htm
It's about half way down in the article.
Hope I'm not rambling on too much here, but as you can tell, I kinda like head and engine talk. I'm pulling an honest 400 horses out of my '69 351W, and still am managing 10mpg, and maybe 12 with a tail wind and keeping my foot out of it. And, that's with a C6, at 3000rpm at 75mph.
I'd still like to know what I'd get with an AOD, but that's a lot of bucks to convert, and I don't think they're as strong.

<font color=green>**Question for "the board"..
Is it that tough to swap in a AOD (not electronic E40D)?
I suppose I can still buy a lot of gas for the conversion cost and trouble.
Plus, this C6 has got 270,000 on it and I'll bet I'd have gone through 3 AOD's in that time the way I drive.**<font color=black>

The most important thing though, is to have fun while you're doing the build-up. Because it's kind of a Tim Taylor thing!
Hope you aren't coming up with more questions than I answered, but at least you've got a little more information to go with.

Oops, one more thing, if you haven't picked up the performer yet, I'd seriously think about the performer "rpm".
The performer is basically a stock manifold that's aluminum with a little smoother runners.
The "rpm" is much more performance oriented, and would match your cam better.







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85 Bronco XLT, '69 351W, C6-Shift Kit, 9"-Detroit, Dana 44-Tru Trac, 2" Lift, 33X12.5s
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post #4 of (permalink) Old 07-05-2001, 08:03 PM
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Re: 351W STOCK HEAD MODIFICATIONS

MY2ND78,
thanks man [img]/wwwthreads_images/icons/laugh.gif[/img] I haven't been around lately. Vacationing in northern Australia at my brother's [img]/wwwthreads_images/icons/wink.gif[/img]


WD40,
I agree on everything. I personally prefer to work my own intakes from stock, but I have the means with which to do this. Most people don't. By the way, nice full roller rockers in your pic. Bet that cost a pretty penny.


85bronc,
listen to what WD40 has said. As far as grinding heads for more compression goes, don't waste your money. The biggest compression gain from shaving your stock heads is to grind them more on the outside of the head than the inside. By doing this you remove more of the combustion chamber without cutting through the deck. Several serious problems arise from this, including the need for spacers between your intake and heads, bad valve geometry, and generally speaking a much weaker head. The cost of all the machining will be at least as much if not more than the cost of better heads. Shaving heads IMO should only be used for making them flat. Compression can be gained in other ways.

Another way to increase compression is to use a cam profile that opens and closes the valves much quicker than traditional profiles do. Comp Cams seems to use this concept in most of their grinds (the other companies are doing it too). This allows for a heavier charge of air to be drawn in for combustion, while maintaining the stock combustion chamber shape (prevents detonation). You can typically run higher compression this way without having to buy really expensive fuel (like the cheap stuff is cheap anyways, right?). Running longer connecting rods also dramatically increases power. You will require new pistons with a lower compression height, so use flat tops and put a very mild dish in them to keep your compression from going throught the roof. This will be more expensive than just head work, but also much more reliable.

<font color=red>Pharaoh
Yah baby, That's right! [img]/wwwthreads_images/icons/cool.gif[/img]</font color=red>
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post #5 of (permalink) Old 07-10-2001, 01:49 PM
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Re: 351W STOCK HEAD MODIFICATIONS

Thanks <font color=red>Drunken Pharaoh</font color=red>.
The rockers were $160.
Same part as Ford Motorsport, just cheaper from a different supplier.
(don't ask, too much paperwork to throttle through to find the answer...but if you really insisted...)
However, guideplates, studs, and machining for studs came to $100.
The required hardened pushrods from Ford Motorsport were about $60 if I remember correctly.
After building a couple of off-shore boat engines, I wouldn't run without 'rollers on anything other than stock.
Too much to lose.
Some day the ole shop will have a drill press, so I could do my own cutting on the stud bosses and save some bucks.
I do have the facilities to do the port work on the heads and intake myself, so that does save quite a bit.



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85 Bronco XLT, '69 351W, C6-Shift Kit, 9"-Detroit, Dana 44-Tru Trac, 2" Lift, 33X12.5s
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