Piston recommendations?

[lewtot184]

with old bores i wouldn't use a piston with a straight pin. without getting the dial bore gauge out you'll never know exactly where your at. a piston with an off set pin will "cover" used bores better. think your stuck with the old trw clones. i'd look at a 2266 (think that's the right number) with a .022 steel shim gasket. shouldn't be a big deal to get compression in the 9's. may need a little off the heads, but should run on pump gas.

 

[Portagee]

Thanks for all the replies!

I suppose some more background info would help. My (original) goal is to get a drivetrain in my super bee so I don't have to push it around my driveway. I'm not trying to build a monster engine, but I would like to have a good bottom end for a head swap down the road (ideally would like Trick Flow 240's).

I bought the shortblock on CL, and it was assembled when I picked it up. I also got a pair of ported 906 heads (see pic below), and another pair of 516 heads (which I think were original to the short block) with the deal. I disassembled everything, had the block hot tanked and fluxed, and mic'd the bores to verify that they were not overbored. I then flex honed the cylinders myself, and I thought they turned out pretty good. There was no ring ridge at all in any of the cylinders.

I then had the crank, rods, pistons, and flywheel balanced to within 1 gram (machine shop said they were ~28g out of balance...). So the rotating assembly is now internally balanced (flywheel was neutral balanced).

I knew I was going to need to calculate the CR once the bottom end was installed, and that's when I ran into my issue with the pistons being so far in the hole.

My plan for the build is/was:

• 1974 440 block, standard bore (fluxed, and flex honed)
• Forged crank, six pack rods, standard flat top pistons (balanced within 1g)
• Comp Cams Hydraulic Flat Tappet Camshaft (247/254 @ 0.050, 0.509 lift, 108 LSA, suggested 10:1 CR)
• Ported 906 heads (original seats/non-hardened, at-home valve lap with lapping compound and a drill)
• Trick Flow Track Heat single plane intake
• Holley 750 double pumper
• MSD 6AL with MSD Pro Billet Distributor

Started as a budget build, but definitely have some nice parts there (I already have purchased all of those parts listed). The shortblock is currently assembled, and now I need to figure out how to get my CR up.

I would really like to not have to bore the block, but it's sounding like a 30 overbore with aftermarket forged pistons is the recommendation? Would most likely need to get it all rebalanced at that point...

Thanks again for the help and suggestions.

Mike

 

[BSB67]

This is the tough spot so many folks get into.

Consider what Lew suggested in post #13. That's the simplest and probably least expensive in the end. What you'll give up in compression will probably be a wash with what you gain in a better head.

Or take it back to the shop and get actual measurement of all the bores in several locations to see if: 1) the bore/ridge is good enough to swap in 2235s, 2) he can or would consider honing out the bores ridge, out of round, and taper to get you close enough to use the 2235s, or 3) bore it and put in the 2235s.

FWIW, generally speaking, unless you paid really good money for the heads and have documentation to go with them, consider them marginal at best no matter what you were told. Just my opinion.

 

[PRHeads]

I didn’t look very hard, but Summit shows std bore 2355’s or 2266’s as “not available”.
Silvolite 1263’s (1.969”ch) are shown as “in stock”.

We recently swapped some 1276’s(1.912”ch) out for some 1263’s in a 440 with good bores.
That was a 13.7cc improvement.

https://www.forabodiesonly.com/mopar/threads/another-very-mild-440-build.482202/

 

[Curiousyellow71]

Really need to measure the bores. It is a possiblity that someone used a ring groove reamer to remove the groove at the top of the bores. Sometimes it's hard to tell if someone did a good job with it. If you are good to go w a std bore I don't think you have many options other then speed pro.
For speedpros like 2355s beware that you will likely have to shop around. There prices have gone up to where it's cheaper to get a Icon, wiseco or DSS for less...and they are all better lighter pistons then speed pros but require balancing and boring. There has been some more reasonably priced old stock speed pro pistons if you shop around...Ebay or Amazon. Summit more then doubled there price for pistons from speed pro last time I looked (after they were out of stock for months).. Hoping the prices come back down eventually.

 

[Portagee]

Thanks everyone for all of the help! It's sounding like the 2355s are the best bet. And will probably look into getting the 030 oversize pistons, and use the savings to have the bock bored and maybe even clean up the deck a little. Will be nice to have the bores fresh anyways for the new pistons.


Thanks again!

 

[Babyblue66]

I also agree, the old 2355 speed pros work well. There are lighter, better, and more expensive pistons. But these do just fine.

 

[Babyblue66]

Thanks everyone for all of the help! It's sounding like the 2355s are the best bet. And will probably look into getting the 030 oversize pistons, and use the savings to have the bock bored and maybe even clean up the deck a little. Will be nice to have the bores fresh anyways for the new pistons.


Thanks again!

Also get it balanced. You'll be glad you did.

 

[1 Wild R/T]

Also get it balanced. You'll be glad you did.

The whole point of using the 2235 is the pistons weight is virtually the same as stock pistons & he's already had it balanced to stock... If he's spending money to balance my recommendation is gonna be a better/lighter piston.....

 

[Curiousyellow71]

The lighter pistons also have a narrower ring and will make a little more power. If your .030 over and balancing I'd spend a little more( they may even be less???) and get a nicer lighter piston w 1/16 rings. They also usually have 2 eyebrows...2355s have 4.
If you can do std icon also has a 4.32 forged piston.
https://www.summitracing.com/search...ne-family/mopar-big-block-rb/bore-in/4-320-in

 

[Wing It]

For my 440 build I used 2355 Speed Pro forged pistons, stock forged crankshaft, LY rods, 906 heads, Edelbrock RPM Performer intake, 1407 750cfm Edelbrock carb, and a
298/303 Duration 0.466/0.488 Lift Summit 6401 cam. 440'

I was wondering what clearance you ran your L2355F pistons at. I am building a 440 and I have the same pistons. The box says minimum clearance is .001" but an old Speed Pro catalog says minimum is .0015". I know the pistons are VMS-75 alloy and do not expand as much as other alloys but .0015" still seems awful tight. One other application for the same Speed Pro pistons with the same alloy show the clearance at .004" (Chevy 4.250"). Other piston manufacturers who make pistons with the same alloy also specify a little looser clearance (.0025" - .0055") What clearance did you run and has it been ok? Thank you for your help!

 

[BSB67]

I was wondering what clearance you ran your L2355F pistons at. I am building a 440 and I have the same pistons. The box says minimum clearance is .001" but an old Speed Pro catalog says minimum is .0015". I know the pistons are VMS-75 alloy and do not expand as much as other alloys but .0015" still seems awful tight. One other application for the same Speed Pro pistons with the same alloy show the clearance at .004" (Chevy 4.250"). Other piston manufacturers who make pistons with the same alloy also specify a little looser clearance (.0025" - .0055") What clearance did you run and has it been ok? Thank you for your help!

Some of us believe that the Speed Pro recommended clearance is too tight. It is not uncommon to find badly scuffed Speed Pros that were installed at 0.0015-0.0020. I put mine in at 0.0035". There is a little slap. You could go 0.003" and maybe 0.0025", but that is probably on the edge IMO.

My Speed Pro piston after about 30,000 miles

https://imagizer.imageshack.com/img538/2750/mSckbZ.jpg

 

[TN Mopar]

I ran into the same problem with my engine (L2355f)
My machine shop didn't like it at all
We ended up at 0.0030

 

[Challenger340]

ICON IC9953's..... really good Pistons for the 440