Forged pistons in NA 250 engine?
- Thread starter 80Stang
- Start date
)
Hey addo, bra. Not trying to be contrary, but you know, um, I'm being analytical.(I hope!)
If it's stock US cast alloy pistons, then its probably better to go to high compression Aussie ACL +30 thou flat-tops, and track down ones for the 1966 to 1968 200 XR Falcon. Or the 15 cc or almost flat-top items designed for X-flow 3.3 sixes which reved to 5500 rpm. You will find all the strength you need in these.
I don't want to bad mouth good US Silvolite or replacement HSC or 255 pistons. They are undoubtably fit for the purpose of a stock engine tootling. However, they tend to be made for general consumption, not to be thrashed with in an inch of its life like the Australian ACL stuff.
We've seen two different sets of cracked HSC pistons on the forum, so I'd shy away from them, and reach for ACL pistons, or grin and bear it for the Ross or NOS TRW or Sealed Power forged items which pop up on ebay or garage sales every now and then.
Generally, a forged piston will hold up a lot longer than a cast piston, but stock Oz Ford XR 200 pistons with 5.5cc domes, or the newer coated ACL pistons (4.5 cc , i think) have proven there worth in some wildly turbocharged I6's in Australia. The real trick is getting a better than stock piston.
If it's stock US cast alloy pistons, then its probably better to go to high compression Aussie ACL +30 thou flat-tops, and track down ones for the 1966 to 1968 200 XR Falcon. Or the 15 cc or almost flat-top items designed for X-flow 3.3 sixes which reved to 5500 rpm. You will find all the strength you need in these.
I don't want to bad mouth good US Silvolite or replacement HSC or 255 pistons. They are undoubtably fit for the purpose of a stock engine tootling. However, they tend to be made for general consumption, not to be thrashed with in an inch of its life like the Australian ACL stuff.
We've seen two different sets of cracked HSC pistons on the forum, so I'd shy away from them, and reach for ACL pistons, or grin and bear it for the Ross or NOS TRW or Sealed Power forged items which pop up on ebay or garage sales every now and then.
Generally, a forged piston will hold up a lot longer than a cast piston, but stock Oz Ford XR 200 pistons with 5.5cc domes, or the newer coated ACL pistons (4.5 cc , i think) have proven there worth in some wildly turbocharged I6's in Australia. The real trick is getting a better than stock piston.
80Stang
Well-known member
X: if we raise the RPM, what is the first "fuse" in the lower end and when it'll blow? Let's consider pistons are forgies, I'd expect there is another fuse before those.
If I don't get the forgies I'm looking at, will the combo last well to 6K with 255s and 10.50 CR?
Sorry I'm all
: s, but...
If I don't get the forgies I'm looking at, will the combo last well to 6K with 255s and 10.50 CR?
Sorry I'm all
: s, but...8)
IMHO forged pistons are not so much a necessity for most situations as a insurance policy.
You may do everything right and take all the precautions and never need forged pistons but all it takes is a something in the fuel system to hiccup and cause a lean condition or timing to jump and a detonation and all could go asunder.
If your going to be driving in a aggressive situation like racing where aggrssive driving can lead to more breakage or high compression and high rpms are needed to SAFELY make power then I say go forged.
I guess the question is if something does go wrong can you afford another rebuild? If not then forged pistons are another level of safety to protect your investment.
IMHO forged pistons are not so much a necessity for most situations as a insurance policy.
You may do everything right and take all the precautions and never need forged pistons but all it takes is a something in the fuel system to hiccup and cause a lean condition or timing to jump and a detonation and all could go asunder.
If your going to be driving in a aggressive situation like racing where aggrssive driving can lead to more breakage or high compression and high rpms are needed to SAFELY make power then I say go forged.
I guess the question is if something does go wrong can you afford another rebuild? If not then forged pistons are another level of safety to protect your investment.
80Stang
Well-known member
These engine buildups are always multi $1000 projects. Considering that, the price I got offered for a very interesting set of forgies seem minimal.
The target vehicle (my '80) will retire as a daily year-aroud-driver and will see major overhaul, during which it'll receive load of upgrades to suspension and the new engine. It will see autoslalom 4-5 times, race track practice duty a couple of times, and one or two days at the strip per year. WOT action - yes.
The target vehicle (my '80) will retire as a daily year-aroud-driver and will see major overhaul, during which it'll receive load of upgrades to suspension and the new engine. It will see autoslalom 4-5 times, race track practice duty a couple of times, and one or two days at the strip per year. WOT action - yes.
80Stang":1nl53drk said:X: if we raise the RPM, what is the first "fuse" in the lower end and when it'll blow? Let's consider pistons are forgies, I'd expect there is another fuse before those.
If I don't get the forgies I'm looking at, will the combo last well to 6K with 255s and 10.50 CR?
Sorry I'm all
Okay, any statement needs to be qualified, with question A mapping to answer A'.
In regards to our detonation prone x-flows
Pistons first
Then rod bolts,
and consequently rods
On the Log 200. The first fuse is often pushrods, then pistons, then conrod bolts, then conrods, then crank, then the cylinder block if its a stock bore thinwall engine like everything since 1962. Detriot designed engines are the ultimate low risk economy engines.
The engine will see incipient knock often, so your best off
a) adding the best pistons
b) adding water and alcohol injection, and
c) run it on stock higher octane gasoline
We all know that even the best cast, hyper or coated cast alloy pistons can suffer piston slap, especially anything with a less than stock 1.5" compression height.
The 255's look pretty good, and are designed for a V8 reving to only 5000 rpm in a short (3") stroke engine, so I'd say 6000 rpm in a 3.126" stroke may be okay if you take care of continued incipient, wide open throllte detonation.
With forged pistons,
You will have to research the ideal piston clearance, and warm the engine up judicously before any 80 to 100% load. Since your not in Australia, and Finland has sea port closeness to the Right coast of the US, then US forged pistons are a fairlygood idea. Especially if you get them second hand when all the 'sticker shock' has gone off them.
So its still up to you. Take out of that what you will.
Shamless plug for the Antipods.
In Australiaand New Zealand, we'd never, ever go forged, because the aftermarket is satuarated with 7000 rpm, Turbo capable I6 pistons at a price that is very good, and much cheaper than forged pistons. In the old days, Duralite and Repco made the best circuit race cast pistons around, and ever since the Repco spin-off ACL and Mahale joined forces in the late 90's, the 3.3 piston selection has never been better.
80Stang
Well-known member
xctasy":169da9gy said:
Will the 250 block climb up the criteria if it is bored to 3.75? Push rods will be moly rods from Mike, bolts are ARP. If pistons are state of the art then the first fuse in this list would be the conrods. How far they go as stock?
xctasy":169da9gy said:
a) leads me towards forgies, and the knock problem to lower the target CR.
xctasy":169da9gy said:
CD would be 1.598 with the pistons I've got in sight.
xctasy":169da9gy said:
This is for 250, 3.91 stroke. Too much for the 255s?
I have a set of forged pistons for AMC 258 in sight - for an affordable price. They are 3.75, cd is 1.598 and they have a 13.636cc dish (.110 x 3.100 recess). CR would be 10.07. How about these?
Thanks X, and others. Quest continues.
