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Discussion Starter · #1 ·
Hey guys,

I'm doing a mild 351c build and I was planning on running the comp 274h extreme energy cam with powerband of 2000-6000 rpms. Will my stock 351 pistons be able to rev that high without the huge possibility of a major malfunction?

Thanks,
Dustin
 

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Yes I would say it shouldn't be a problem as long as your not sustaining that rpm for long periods like in stock car racing or something like that.
 

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Discussion Starter · #3 ·
Thanks for the help frdnut,

With the CC 4v 351c heads I'm going to use the highest CR I will prob yield with the stock pistons would be near 9:1. Is this CR high enough to run the XE274h cam?
 

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The pistons aren't a problem at 6000rpm. The biggest problem you could run into is running stock valves. They are crap and if one of them breaks the whole motor is wasted. Don't run stock valves!
 

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Discussion Starter · #5 ·
I recently spent my whole wallet on getting my 4v CC heads rebuilt with hardened seats, one pc. manley valves, converted to 7/16 screw in studs. Anyone know if 9:1 is high enough to run the XE274 cam? Is a 750 DP or 750 VS too big for this cam?

Thanks,
Dustin
_________________

1972 Gran Torino 351c 4v
1995 Escort (Girlfriend's ride)

<font size=-1>[ This Message was edited by: dsfordguy on 10/22/06 3:57am ]</font>
 

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Discussion Starter · #6 ·
I recently spent my whole wallet on getting my 4v CC heads rebuilt with hardened seats, one pc. manley valves, converted to 7/16 screw in studs. Anyone know if 9:1 is high enough to run the XE274 cam? Is a 750 DP or 750 VS too big for this cam?

Thanks,
Dustin
 

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Both the 274XE cam and carb. will work well with that compression ratio.
 

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On 2006-10-21 12:57, dsfordguy wrote:
I recently spent my whole wallet on getting my 4v CC heads rebuilt with hardened seats, one pc. manley valves, converted to 7/16 screw in studs.
That's a good move.

9:1 will work. More is better. Have you concidered milling the heads?
 

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Aren't closed chamber heads the small cc ones? I mean, isn't 9:1 a bit low for closed chambers? I had a set of 2v open chambers, and with a decent flat top I think I was at like 9.5:1 or something...granted this was 15yrs ago.

Hmm...

Cris
 

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Discussion Starter · #10 ·
Yes the closed chambers are the small cc ones but the bad part is the stock pistons are dished. not sure exactly how big the dishes are...they dont look too big. Also I bought the 351c as a rebuilt short block so I'm not exactly sure what the deck height is so my best guess at CR was 9:1 according to the comp calcs.

Thanks for the help,
Dustin
 

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Not a problem! All things being equal...meaning the same compression on all three motors, dished pistons make more power than flat tops, or domed. However, that's assuming you can get a useable compression ratio!!

Assuming 62cc chambers, and a 12cc dish, which is pretty standard for small block fords I believe, your chamber volume is 74cc's. 4.1" head gasket, .039" compressed, and assuming 0 deck, you have 9.8:1 compression!. Even guessing that the pistons are in the hole .010...you're still 9.65. Not too shabby! Should make great power.

Cris

Oh by the way, I turned my stock cast 351c pistons 6500-6800rpm pretty regularly. It only took it for two years or so...but it was a rod bearing that went bad, not the pistons!

Cris
 

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Discussion Starter · #12 ·
So then I should be at a safe enough CR to run the xe274h cam?

Thanks,
Dustin
 

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Stock cast pistons will not last long. You'll crack and break the piston's skirts. Even the Boss 302s had this problem with some pistons until they improved the disign. Why do you think most of the HiPo engines how have Hyper or Forged pistons? Even the older engines used forged psitons on the HiPo engines. Save a little now and pay allot later. Even with a rebuild setup you'll probably end up with pistons slap soon enough. Anything over 5500 rpms and things get dicy. That little bit on rpms puts a much bigger load on parts. Wouldn't do it in my engine.
 

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Cast pistons are not recommended for speeds above 3200 feet per minute at 5500 RPM the piston speed is 3208. At 6000 RPM you are in the grey zone with cast pistons. The stock Ford pistons have weak skirts and are prone to cracking. Some of the after-market piston makers have cast in reinforcement ribs into the skirts to eliminate this weak point.
You might be fine for a long time or you might not - "Do you feel lucky? ... Well, do ya" Quoted from a "spagetty western's" star playing a cop with a big gun in "Dirty Harry".
Paul
 

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The stock pistons will work fine for a street/strip drag motor as long as every thing is in good condition. Just keep the tune conservitive (Avoid detonation).

I ran stock stuff years ago in a cleveland never had a piston problem always had bearing issues.........
 

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On 2006-10-23 05:34, dfree383 wrote:
The stock pistons will work fine for a street/strip drag motor as long as every thing is in good condition. Just keep the tune conservitive (Avoid detonation).

I ran stock stuff years ago in a cleveland never had a piston problem always had bearing issues.........
Same!

However, as has been said, if it were my choice to do it again, I'd use forged. But I'm older now and have learned a few lessons about money spent.

My advice? Run it.

And save for a new engine over the next year or so!

Cris
 

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Run it - but the minute you hear any bit of knock from the middle of the engine, pull it apart and repalce the pistons. Ford stock pistons are good about cracking on the skirts. USUALLY you'll get a warning with the ticking or knocking, enough that you can save the engine. The cam should be fine at that compression - assuming it's right. If the motor is already together, measure the cranking compression and that'll be a hint. Run a 750VS carb, 750DP is way overkill for that engine.
 

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Now that I looked again and remembered you have a torino and a mild build, I also agree you should run the 750VS carb.
 

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Does your question about stock pistons mean "I've rebuilt the whole engine and want to keep the stockers" or does it mean "I'm swapping heads and cam and hoping for the best?"

Putting a lot of top end (head prep, carb, cam, etc) on a 35 year old lower end is asking for it, it will run strong until you hear the 'bang'. A quality rebuild will have a lot longer lifespan, done right. Stock pistons are heavy, and typically use ring packs that were around before Elvis died. They use a lot of power simply pumping them up and down.

Modern pistons are lighter, stronger and use better ring sets that keep the pressure in the cylinder where it does the most good.

In either case, I would check piston to valve clearance, pushrod geometry and length, and installed spring height very very carefully.

Piston to valve should be a min. of .100" to allow for how everything grows when hot.

Checking pushrod geometry gets a little tricky, but is a must if you have changed hardware. You want to make sure the length is right, otherwise, you don't get all the lift, or if they are too long, you bend up a set and cause havoc on the rest of the valvetrain.

Valve springs need to be checked, too, because if you have too much lift and put the springs into coil bind, you can break rockers, pushrods, studs or on the odd occasion, valvestems.

Good luck!
 
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