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351v with 302 rods with acl pistons 

 

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 Post subject: 351v with 302 rods with acl pistons
Posted: Thu Jun 15, 2006 7:21 pm 
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your say on wether or not you think its any good?
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Posted: Thu Jun 15, 2006 7:22 pm 
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and power figures that youve heard of and whats mods were done to other motors built like this
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Posted: Thu Jun 15, 2006 10:31 pm 
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The bad thing about the ACL pistons is they aren't very durable. If the plan is to run anymore than 10:1 compression? Don't bother with it.

I had the same pistons but using a 351 rod. My bores looked like crap after 5 years. All scrathed up from the skirts collapsing. In the end I had 11.2:1 compression.

The pistons are only rated to a max 10:1 from ACL too. Pitty the builder of my 351 didn't know and stuck me with a 10.5:1 compression engine which destroyed the pistons. The builder ripped me off big time but thats another story. I now don't trust anyone with my engines. I supply all the parts so I know whats going in it.

As bad as it sounds? You can still do a decent engine with it.

Crane F238 solid (max rpm of 6300rpm)
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It should make around 250rwkw, be reliable and go like a cut cat :)

 

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Posted: Thu Jun 15, 2006 11:11 pm 
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Definately a good thing for the 351 Clevo running 302 rods, changing the piston to rod ratio is a big stress relief for them.
I built a couple of these years ago, but there was only 1 company making the pistons to suit back then and i can't remember the name of them.
I always wondered when another company would catch on and do it.
Next time i do a Clevo for myself i'll be running this combo, i already have the crank and a set of polished and shot peened 302 rods.

As for power figures from this alone, i wouldn't have a clue as all the ones i seen had different combo's.
I never knew anyone who actually pulled the 351 rods and pistons out and replaced with 302's without changing anything else.
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Posted: Fri Jun 16, 2006 1:48 am 
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There has been plenty of same combo's tested with 302 and 351 rods. HP difference was zero. Tests done were done on an engine dyno. I'm involved with plenty of clevo tech data etc. I find the findings interesting.

The only downfall is the rpm limitation on the pistons. Mine was limited to 7000rpm and the skirts on the pistons collapsed. I've seen some with the same issue I had that were limited to 6500rpm.

I wonder whether the Speedpro pistons are any better? I suspect they are as Chris and the guys at Speedpro actually raced. The product they sell is the product they used to race.

On the US Ford forums (the .com one) there was quite a lengthy discussion about it. I can't find it on the forum as there is no search function and google is pretty useless. The end verdict was 302 rods weren't worth it due to the extra cost on the pistons. It was peeing $ into the wind ;)

I can assure you a longer rod does nothing for torque or hp. I've seen combo's like mine doing the same power and torque. I used a 6.125' rod and they'd used a 6" rod.

 

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Posted: Fri Jun 16, 2006 1:52 am 
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Are we talking cast or Hypers?
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Posted: Fri Jun 16, 2006 2:37 am 
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the best way to install longer rod, and have no problems with pistons due to the high pin height is to use chev 6'' rods with pistons to suit (many brands are making them now) and to have you're crank ground undersize to suit, which is how stroker kits are set up by offseting the grind.
as mentioned RPM is limited by using ford rods/acl piston combo, the crown is simply too thin. kenny

 

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Posted: Fri Jun 16, 2006 11:47 am 
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I use 302c rods in my 351c(and also my 351w but that's another story) but I used the Hypatec brand Forged version. These are an excellent piston and not expensive at around $650 a set. I machined a small dish in mine to drop the comp down to 10.5:1 with the CHI heads.

Pete.
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Posted: Mon Jun 19, 2006 12:39 am 
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brenx wrote:
There has been plenty of same combo's tested with 302 and 351 rods. HP difference was zero. Tests done were done on an engine dyno. I'm involved with plenty of clevo tech data etc. I find the findings interesting.


I would be interested in seeing dyno sheets showing this, this would make the Clevos the only engine in existence to not change torque/hp and rev range in which torque/hp was produced. It would be excellent topic to show in Fordmods :D .

Changing piston speed should change something surely, other than reduced bore wear.

 

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Posted: Mon Jun 19, 2006 1:32 am 
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I think that what he is getting at is by changing the rod:stroke ratio doesnt make the massive difference that some claim that it does. Im aware of the TDC dwell differences, but they would be negligable, a bit like knife edging cranks in low revving engines

 

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Posted: Mon Jun 19, 2006 11:46 am 
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The theory is the longer dwell at TDC creates more time to increase cylinder pressure resulting in greater torque. I think the difference is negligible if any and especially since were talking about difference of 1/4" in rod length.
Ive seen tests where a 6.5" 400C rod was used in a 351w vs the stock rod(5.95") and it did make a difference.
The other benefit is rod angle and on clevelands with their thin cylinder walls 1/4" does make a difference to rod angle and therefore reduced side loads on the cylinder walls.

Pete.
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Posted: Mon Jun 19, 2006 12:02 pm 
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Spot on, and stress relief = HP.
I've pulled plenty of Clevo's down with split bores, and mainly from the skirt collapsing.
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Posted: Mon Jun 19, 2006 4:24 pm 
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Damage wrote:
brenx wrote:
There has been plenty of same combo's tested with 302 and 351 rods. HP difference was zero. Tests done were done on an engine dyno. I'm involved with plenty of clevo tech data etc. I find the findings interesting.


I would be interested in seeing dyno sheets showing this, this would make the Clevos the only engine in existence to not change torque/hp and rev range in which torque/hp was produced. It would be excellent topic to show in Fordmods :D .

Changing piston speed should change something surely, other than reduced bore wear.


Bore wear and controlling detonation is about all it changes.

 

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