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Old 06-02-2011, 06:37 AM   #16 (permalink)
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Re: 351w piston question

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Originally Posted by fordmugg View Post
for 1 im not a pro engine builder, i did a lot of reading to learn how to put the one i have together, because i would rather learn to do it myself than just pay someone....2nd because 1 person says yeah it will be fine is not enough for me, i like to hear multiple inputs before i do something on a single persons opinion...i have put a lot of money and time getting this car going and all i want is to make sure things get done right.
read my first answer/reply . then ask yourself which one weighs more , the (numbers not facts) 675 gr piston you have now or a flat top you had made/modified to weigh 675gr.
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Old 06-02-2011, 07:02 AM   #17 (permalink)
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Re: 351w piston question

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Originally Posted by Tex View Post
Those replacement dish piston are killing your compression ratio and therefore leaving a lot of power on the table. You definitely want to get them out of there at some point. But don't rush.

If the cylinders are in good shape (not tapered, not gouged, and not worn out of speck) the you don't need to do anything to the cylinders. Did you have any work done to the cylinders before your recent reassembly? The proper way to check cylinder condition is with a dial bore gauge or an inside micrometer. But lacking those, if the cylinders have a mirror finish (all hatch marks have worn off) and there is a ridge at the top of the cylinder big enough to catch your fingernail on, then you likely need to recondition the cylinders. Best to take it to someone with the proper measuring tools to confirm.

If you cylinders check out (still in spec, still have hatch pattern) then you can buy the same size pistons. But just dropping in new pistons without balancing the reciprocating mass is a bad idea. Even if you don't plan on revving your engine to the moon, imbalances will rob power and decrease the life of your bearings, and if bad enough, your crankshaft. Around here a balance is about $200. Think of it as insurance money well spent. And you have to take your rods and pistons to a machine shop to have them pressed on and off anyway, so you might as well take the crank, flexplate/flywheel, and harmonic balancer along too and let them do the job right.

For the pistons themselves, don't just assume any flattop will do the job. You must also look at the compression height of the piston. If your 351W block is a true 1969/70 casting, is will have the early lower deck height of 9.48". The later 351W had a taller deck height to lower compression. Some pistons meant for those later 351W's could stick out above your deck and smack the heads. Also, do you have the original 69/70 heads? What casting # is on the underside? Early heads have small chambers meant to build compression. The stock flattops in the 69 4 barrel 351W gave 10.7:1 compression ratio. That kind of compression on today's gas could give you detonation and require you to retard the timing, which kills power and mileage. A stock 69 2 barrel piston would give 9.5:1 which is a good ratio for today's gas.

And if your engine is a true '69, those are NOT stock pistons. Those big dishes didn't come along until the first oil embargo. And that means your engine had been rebuilt before. What was done to it? Did someone overbore it already? Did they deck the heads or the block? That would have a big influence on compression ratio and what pistons to choose. And the only way to find out is to let someone with the proper measuring tools and experience inspect the block.

Hope this helps.

ok here is the story the motor is a new re manufactured motor that my brother bought for his 64 fairlane...well i got the car off him with the motor, but he had took the whole motor apart ( dont ask me why ) but he did so when i got it i put it back together with a comp cam and got the car going...the motor is +30 over and the flow chart that came with the motor said it has 9:5.1 comp ....so right now i have maybe put 300 miles on it, but i feel with upping the compression would bump up some power....
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Old 06-02-2011, 07:18 AM   #18 (permalink)
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Re: 351w piston question

Easy, kids. Personality issues aside - Dan answered it in post #5. The only item you're changing is the piston and pin assembly, and to retain your current balance, you just need to match the new ones to the old ones. Best would be to pull and match them. Close would be (if you know the exact manufacturer and part number) to find the average weight listing of the old ones, and make the new ones the same.

Those appear to be '69-'73 2v dished pistons, but in any case weights vary from maker to maker, so you can't just "toss them in". Personally, I would just weigh and match each one as I swapped them on the rods. If you are just replacing from stock 2v dish to stock 4v flat-tops, the weight will be fairly close to start with. Changing to a non-stock style (forged, or other aftermarket type) would require a full re-balance as Tex said.

David
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Old 06-02-2011, 09:36 AM   #19 (permalink)
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Re: 351w piston question

But just swapping pistons assumes the pistons that are in there are properly balanced. If it is just a reman engine as he stated, I doubt it was balanced properly to begin with. And he still doesn't know what deck height he's got.

And those are not stock '69 2 barrel pistons. Those with the oblongs deep dish are mid-70's smogger pistons. And I seriously doubt that engine is making 9.5:1 compression with them, even if it was decked and had C9OE-B 60cc heads. Probably closer to 8.5:1. Stock '69 2 barrels have a shallow round dish with 4 eyebrows, like these that came from my 351W '69 Montego:




Here you can see the 351 and 2V markings


Here you can see C9OE-D

The dish is about .13" deep, 2.56" across at bottom, 2.80 across at top, and the compression height is about 1.74-1.75.

Something along these specs with a 60cc head and a 9.48" deck height will give you a true ~9.5:1.
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Old 06-02-2011, 09:40 AM   #20 (permalink)
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Re: 351w piston question

Anyone ever use TRW or Speed Pro forged piston in a stock 351W ? Ever have one balance ? did you see the little hole that was drilled in the counter weight ? or did they charge for a few slugs of mallory ? How do you like all those questions .
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Old 06-02-2011, 11:34 PM   #21 (permalink)
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Re: 351w piston question

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... Stock '69 2 barrels have a shallow round dish with 4 eyebrows, like these that came from my 351W '69 Montego:

You are quite the lucky guy, Tex. Those are C9OE-D 351W truck pistons. Quite rare, as they were only used in export model trucks, and a very few were used to make-up for shortages in the car lines. I've only ever run across one original '69 2v with those pistons, and I kept one as a curiosity item. All other standard car engines from '69 to the end of production in '97 used bathtub dish pistons of various volumes, with the exception of the flat-top 4v, and that was only (officially) in '69 and '70. Due to low demand, they were not available for many years, but oddly enough, Badger/Manley has made a run of the truck pistons like yours. FWIW - the number for standard '69 2v 351W pistons was C9OE-H, and the 4V version was C9OE-B.

David
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Old 06-03-2011, 07:09 AM   #22 (permalink)
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Re: 351w piston question

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Originally Posted by DanH View Post
Anyone ever use TRW or Speed Pro forged piston in a stock 351W ? Ever have one balance ? did you see the little hole that was drilled in the counter weight ? or did they charge for a few slugs of mallory ? How do you like all those questions .
what nobody ever used TRW/SP pistons ? question also for 289 & 302's with TRW/SP
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Old 06-03-2011, 08:14 PM   #23 (permalink)
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Re: 351w piston question

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Originally Posted by PSIG View Post
You are quite the lucky guy, Tex. Those are C9OE-D 351W truck pistons. Quite rare, as they were only used in export model trucks, and a very few were used to make-up for shortages in the car lines. I've only ever run across one original '69 2v with those pistons, and I kept one as a curiosity item. All other standard car engines from '69 to the end of production in '97 used bathtub dish pistons of various volumes, with the exception of the flat-top 4v, and that was only (officially) in '69 and '70. Due to low demand, they were not available for many years, but oddly enough, Badger/Manley has made a run of the truck pistons like yours. FWIW - the number for standard '69 2v 351W pistons was C9OE-H, and the 4V version was C9OE-B.

David
Those also look the original pistons from 1970 351W. The new pistons have a dish shaped like the OP's, but much shallower.
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Old 06-03-2011, 09:41 PM   #24 (permalink)
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Re: 351w piston question

Those new pistons you have are later model. The C9, D2, and D3 pistons had the deep dish just shy of 1/4" deep. Then the big-chamber smog heads came out in '77 and the dish shrank to about .100" until the F4 (1994) roller blocks and small-chamber heads became standard, and the dish grew again to about 3/16" and also changed to lighter and stronger hypereutectic and thinner shallow-groove metric rings. As Tex said, you have to watch your compression height, as not only were the early blocks shorter, but the car and truck pistons were different height also. While the truck piston has a smaller shallower dish, the compression hight is shorter than the deeper dish car piston, which leaves the truck piston at a disadvantage if it allows too much room and reduced quench for detonation suppression. Or, it can save your butt if you have to cut a lot on the block to square and true the decks. The 302/5.0 has similar situations - but even more of them.

I've been through them all backwards and forwards in search of suitable pistons for forced-induction projects. Unfortunately, none of these designs has been made in a forged version that I'm aware of, though I guess that's not surprising as most folks want more squeeze - not less. The up-side is that the crowns and top lands are so thick, that racers have made nearly 1000hp on stock 2v cast pistons. Whoo!

David
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Old 06-04-2011, 05:47 AM   #25 (permalink)
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Re: 351w piston question

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Originally Posted by PSIG View Post
Those new pistons you have are later model. The C9, D2, and D3 pistons had the deep dish just shy of 1/4" deep. Then the big-chamber smog heads came out in '77 and the dish shrank to about .100" until the F4 (1994) roller blocks and small-chamber heads became standard, and the dish grew again to about 3/16" and also changed to lighter and stronger hypereutectic and thinner shallow-groove metric rings. As Tex said, you have to watch your compression height, as not only were the early blocks shorter, but the car and truck pistons were different height also. While the truck piston has a smaller shallower dish, the compression hight is shorter than the deeper dish car piston, which leaves the truck piston at a disadvantage if it allows too much room and reduced quench for detonation suppression. Or, it can save your butt if you have to cut a lot on the block to square and true the decks. The 302/5.0 has similar situations - but even more of them.

I've been through them all backwards and forwards in search of suitable pistons for forced-induction projects. Unfortunately, none of these designs has been made in a forged version that I'm aware of, though I guess that's not surprising as most folks want more squeeze - not less. The up-side is that the crowns and top lands are so thick, that racers have made nearly 1000hp on stock 2v cast pistons. Whoo!

David
TRW had both style forged dish pistons . exact match to dish shape , that I don't remember . Any type of piston (dish shape/size) can be had , custom pistons , but not cheap

Last edited by DanH; 06-04-2011 at 06:00 AM.
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Old 06-04-2011, 10:21 AM   #26 (permalink)
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Re: 351w piston question

Still no answer to the balance question...well no definite answer. Let's beat around the bush some more!

Here's the deal. Typically the engines are balanced when reassembled...if it's a reman engine, and a good one, it was balanced more than likely. Maybe only to +/- 10g but it probably was.

Now...we get into over and under balancing. Some performance shops like to use over and under balancing technique...which more or less rather than using the formula of 100% of the rotating weight + 50% of the reciprocating weight to calc the bobweight....let's say they over balance. Then they'd use 55% or more of the reciprocating weight to calc the bob. Or if under balanced maybe 40-45%.

So you can see that typically the piston weight is not absolutely critical. It is but it's one of those things where a lot of people make a bigger deal out of it than it needs to be. Where the issue arises is when you swap a stock set of pistons-which are typically 5-10g either way and the engine was balanced with that in mind originally...even with the +/- 5-10g. TRW and speedpro are notorious for haivng them off that much too and it makes it a real pain to remove weight to match a set. Especially forged pistons because theres less ways to remove weight on them. Now say you have a set of factory pistons that vary 10g. And you wanted to drop in a set of JE's or SRP's or something (might as well go that route...lighter is better) and they're usually within .5g or 1g at most. Just dropping them in might throw the balance off depending on how much the original set varied. But again it's not a huge issue. Especially from a lower performance application that won't be running 9000 RPM all day long. I've had many 302's that were never balanced at all...one shook pretty good at about 2000 RPM and again at 5500, but I put over 100,000 miles on that turd without any issues other than an oil leak or two. and we've swapped light pistons into engines that were not rebalanced and they were always fine.

For those who are not in the know...balancing a V8 is not an exact science. It's an educated guess based on years of experience. It's not possible to get all orders of imbalance 100% perfect on a 90 V8. Close but not perfect. Therefore, there is some lee-way, so to speak.
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Old 06-04-2011, 11:25 AM   #27 (permalink)
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Re: 351w piston question

mavman , you coverd a good deal of it . My questions were trying to make other think what the oem engine balance tolerances are . when TRW forged are used and then balanced , heavy metal most likely will never be used . IMO , balancing does not make any more power , not just an opinion I seen several times where it doent . The point is an engine must be way way way off before it's noticed .
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Old 06-04-2011, 12:55 PM   #28 (permalink)
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Re: 351w piston question

Fordmugg,

You still haven't said what head castings you have. If you do indeed have C9 or other small chamber heads, then replacing the pistons is pretty much your only option. But if you've got D8 or other large chamber heads, then swapping for a set of heads with small chambers might yield the piston question moot.

Also do you know where the reman engine came from?

PSIG,

Hmm. Never thought those pistons were anything but regular '69 2V. Only other early 351W I've worked on was from a 1970 Mustang and it had the same pistons. I had never even seen the oblong dished ones until I tore down a 1978 351W about five years ago. I was horrified by the Grand Canyon carved into them. I had only seen that on 460 pistons.

Good thing about that '78 351W was that it had football head rods while my '69 had the original broach cut with the oil squirters. So I combined the best of both.

Mavman,

Can't say I agree with your outlook on reman engines or balancing. Most mass-produced remans out there are thrown together from a bin of used parts. Only a bare minimum of new parts and machining is employed. I would be very surprised if any reman engine from Autozoo, O'reillys, et al are balanced. And I know the ones from Advance aren't (I used to work there). Nor City Motors. Jasper, yes. That's one reason why I recommended that the OP balance when he gets new pistons.
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Old 06-04-2011, 02:47 PM   #29 (permalink)
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Re: 351w piston question

Yeah, they make the bathtub in forged, just not the early deep one. The forged versions match the '94-'97 piston volume, and of course I'm after the max volume in a production cheapo version. No biggie, as the current hyper dished versions are inexpensive and have better shape anyway.
-
I'll disagree about the balancing issue. Two reasons - all side loads require power to make, and out-of-balance needs energy to make the side load. Not huge power, but it's a parasite. For example, a 160 gr. imbalance (about the same as adding H-beam rods to your small block) will create a side load of over 380 pounds at 6000 rpm. Hard on parts and bearings, and obviously it's taking energy to make that load away from the rear wheels.

Second, the stress in the parts is increased, leading to failure sooner or at lower rpms. So, although balancing won't make huge power, it extends the power you can make before exceeding your safety factor or simply blowing it up. Even the parts wear in increased. For example, all engines certifying for 100,000 miles minimum service life (your car) must be balanced to ISO1940 minimums to qualify. That tells us that an engine not balanced to at least those factory specs will not likely last that long. Performance balancing is half that error or less - generally 3 grams/inch or better - to reduce stress, failures, and extend engine life. I vote for fine balancing every time.
-
BTW - sorry to the OP we hijacked this thread. At least it's relevant - sort-of. Since two more found the round-dish pistons (Tex & 70XL), I called a friend who was a big-cheese at one of the Ford engine plants during that era, and he had some interesting comments. In a nutshell, the export truck engines and parts never made it to export, as it's hard enough to get spare parts overseas without it also being a "new design" and it was rejected. So they went into regular car production as 'fill-ins'. Although they are a smaller percentage, some car lines (mostly full-size it seems) had a much larger percentage and are not uncommon. The famous C9 and later "truck rods" that performance builders prefer got their nickname from the same original source. So, it's possible one area of the country near that plant or certain model lines saw a lot of these pistons and/or rods, and others didn't. Interesting. To me, anyway.

David
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Old 06-04-2011, 10:13 PM   #30 (permalink)
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Re: 351w piston question

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Yeah, they make the bathtub in forged, just not the early deep one. The forged versions match the '94-'97 piston volume, and of course I'm after the max volume in a production cheapo version. No biggie, as the current hyper dished versions are inexpensive and have better shape anyway.
-
I'll disagree about the balancing issue. Two reasons - all side loads require power to make, and out-of-balance needs energy to make the side load. Not huge power, but it's a parasite. For example, a 160 gr. imbalance (about the same as adding H-beam rods to your small block) will create a side load of over 380 pounds at 6000 rpm. Hard on parts and bearings, and obviously it's taking energy to make that load away from the rear wheels.

Second, the stress in the parts is increased, leading to failure sooner or at lower rpms. So, although balancing won't make huge power, it extends the power you can make before exceeding your safety factor or simply blowing it up. Even the parts wear in increased. For example, all engines certifying for 100,000 miles minimum service life (your car) must be balanced to ISO1940 minimums to qualify. That tells us that an engine not balanced to at least those factory specs will not likely last that long. Performance balancing is half that error or less - generally 3 grams/inch or better - to reduce stress, failures, and extend engine life. I vote for fine balancing every time.
-
BTW - sorry to the OP we hijacked this thread. At least it's relevant - sort-of. Since two more found the round-dish pistons (Tex & 70XL), I called a friend who was a big-cheese at one of the Ford engine plants during that era, and he had some interesting comments. In a nutshell, the export truck engines and parts never made it to export, as it's hard enough to get spare parts overseas without it also being a "new design" and it was rejected. So they went into regular car production as 'fill-ins'. Although they are a smaller percentage, some car lines (mostly full-size it seems) had a much larger percentage and are not uncommon. The famous C9 and later "truck rods" that performance builders prefer got their nickname from the same original source. So, it's possible one area of the country near that plant or certain model lines saw a lot of these pistons and/or rods, and others didn't. Interesting. To me, anyway.

David
Factory ISO specs and 100,000 miles . Thats all well and fine , BUT who runs their stock engine up to 6K rpm for extended time and gets 100K mi. life .
ever do the 2.3 OHC with the 5.7 H beams ? they would sell well at a adult store . Problem isn't the engine , it's what bolts to it . (trans for 1) what about that external imbalance weight hanging out front on it's own ? 2.3 had one of those , I know how long it would last
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