1970-W30

Rebuilding a 65 425, was running smoothly and quietly, bottom end had never been touched, my machine shop wants to used "builders pistons" but can not give me compression distance and dish size/depth. My experience has been that these cast pistons sit way to far down in the hole to get the desired 9.5 compression I want to end up with. The cost on these so called cheapy builder pistons are $431 a set. I found a set of Keith Black hypereutectic pistons (KB9907HC) with coated skirts that are only priced at $220 a set from Summit, but I'm getting pushback from my machinist, he is reluctant to use these KB pistons. Granted the Olds 425 rods will have to have custom bushings pressed in because the KB piston pins are .927 compared to the .980 Olds pins. Crower sells these bushings and I would still be under $300 total using them. I cannot see how difficult it could be to press these in and hone them to fit. Since he's going to resurface the heads anyway, and square up and mill the deck surface, I don't see why I'm getting this resistance... Any thoughts on this..... does my chart have any flaws that I don't see?

cutlassefi

That 9907 is .050 shorter than the stock 425 piston so it'll be down in the hole too. Not sure what you're going to accomplish there. And I'll bet the bushings and rehoning of the rods will cost more than the $80 you listed.
Some machinists don't understand the concept behind the hypereutectic piston so they're afraid of it. But in your case that 9907 isn't the right choice imo anyway.

therobski

1970W-30 Robski here. I have a brand new set of custom made 30 over Aries pistons with 2CC valve reliefs and 8 400-425 rods that Joe Mondello himself worked extensively over before he moved on. (The GOOD stuff) I have the complete spec sheet on the pistons giving the expected CR and so on. Never used these parts at all, nicely wrapped up and gently but on the shelve. Never considered selling until I saw your post. PM me if you want more info.

therobski

I forgot to add NOT cheap....this is good stuff.....

1970-W30

The bushings are $73 a set from Summit and would require very minimal honing work to fit. The KB pistons in my opinion are way better quality wise then the "rebuilders" pistons plus they are full floating pin design, hyper with coated skirts and over a hundred bucks a set less. Other then uber expensive custom made pistons, there isn't really any other choice that I could find.

cutlassefi

If you're ok with them sitting .080 in the hole then fine. I wouldn't even think about milling the block that much. That brings along other costs and consequences.
Jmo.

wr1970

X2 you will not get the compression you are looking for with the kb piston you posted with out more added cost . Mark is right. Sometimes cheap isn't good. If you asked cutlassefi
{Mark} he might tell you what piston to use with your set up.

joe_padavano

Setting aside the question of whether or not the KBs are the right choice anyway, the machine shop marks up the price of parts they provide. That's lost profit. On the other hand, it is difficult for the shop to guarantee work when using customer-provided parts of unknown heritage. A double whammy.

BlackGold

X2 what Joe said.

On the other hand, I would run away from any engine builder who can't (or won't) tell me the make, model, and dimensions of a piston he wants to use.

rad

what about 428 Pontiac pistons?

64Rocket

I have some TRW L2214nf same as speed pro 2184p, replacement pistons for 425 Olds. They are not floating pins, but will work just fine, if you hone the pin boss to .001 clearance.
PM me for info.

Gene

1970-W30

Update, I went with the machine shops "builder" pistons and had a choice of the high or low compression pistons. I went with the so called 10.5 pistons and was pleased that they had a nice shallow (only 6cc) dish, and they had coated skirts. After a trial mock-up assembly, sure enough the new pistons were down in the hole 20 thousands lower then the factory pistons. After some calculations, I had 14 thousands taken off the deck and combined with the .010 thousands off the heads, it will end up at 9.57 to 1, right were I want to be. This is with the common FelPro .041 head gasket. The heads ended up at 81cc.
Also discovered a oddity with the 65 425 block, the dist hole galley plug and both front plugs are all straight thread style (5/8x18) plugs with the .040 hole. I not sure what year the change was made to eliminate one of the front plugs as a squirter, this is the first Olds block I've ever seen with two squirt hole plugs up front. My shop lost one of the .040 hole plugs and I thought a pipe thread plug will screw right in, not so.... I'ts difficult working with shops that aren't familiar with Oldsmobile engines.
I wonder can anyone tell me who makes the pistons I bought? I'm not familiar with the RC logo, the number 2214 is cast inside the skirt, seems like a Sealed Power number......

70-442-W30

Those are Rebuilders Choice pistons. http://rebuilderschoice.com/

m371961

My 65 425 had both front plugs drilled, all reasons to believe engine was original and never torn down. Not knowing any different at the time it was reassembled the same way.

1970-W30

coppercutlass, my Email notification showed you posted on this thread, but it doesn't show here, anyway to answer your question, no, the pistons are cast not forged. I was charged $431 +20 shipping.

cutlassefi

I'm sorry but that's expensive for a cast piston with an archaic ring pack.
For all, you can get a waaaay better custom piston for less than $150.00 more. And the better materials and more modern ring pack are cheap hp.

1970-W30

Not as sorry as I am, wish you would have said so after my first post where I mentioned the cost of these pistons..........

cutlassefi

You make no mention of wanting a better piston though, only stating costs. It seems that was your main concern. Sorry.

coppercutlass

I was just curious what they cost and after looking at a few pics I could tell they where cast. I was curious up until I realized they where cast . The cast pistons won't be bad. They just can't take as much abuse. For a daily with the occasional blast down the strip it's fine.

cutlassefi

But that's only part of it copper. The other half is the horsepower you gain from a more modern ring and piston design.

coppercutlass

I agree. Is there much better pistons yes. But sometimes that's the way the chips fall. Research is everything.

Fun71

I'm curious to know more about this. What company, materials, rings, etc.

cutlassefi

I have an account with Racetec out of California. I do a lot with them, mostly 4032 stuff but with just about any ring pack I want. The regular street stuff I use 1.5mm, 1.5mm, 3.00mm but for more high perf stuff I go as thin as a steel 1.0mm, 1.0mm, 2.00mm ring set. That's "free" hp.

RandyS

Mark, could you expand on this a bit? Is the free hp due to less friction?

cutlassefi

Yes, from the thinner rings and a better skirt design.
MadMax's build only took a little more than 12lbft to turn the entire rotating assembly minus valvetrain.

1970-W30

After reading that, I just had to go into the shop and see what my engine requires to turn over without the valve train, since I don't have the cam in yet. It certainly wasn't anywhere near 12lbft, more like 30lbft! Is that in the normal range with my piston/ring package?

cutlassefi

A little high but yes.

1970-W30

Update on the 425 build, After filling the float bowl, she started right up and I ran it at 2000 RPM for 20 minutes or so to break in the cam. 20 minutes in the shop with the roll up door wide open meant a nice toasty 110+ degrees with the engine running. It stayed at 190 for about 15 minutes and then crept up to 200 degrees near the end of the cam break in. I was pleased it was able to stay cool in that heat with out a lot of air movement. Bringing it down to a fast idle, I noticed an exhaust leak. Waited a day so I could work on a cool engine, I repositioned the exhaust pipe, retightened it and still had a leak. I'm using the W/Z repro manifolds and had checked both of them, they were not warped. I normally don't use gaskets, but decided to use one of the FelPro gaskets that came in the set. Result, still a slight leak. Put the car back up on the lift and noticed that the ex manifold (passenger side) made contact with the block, preventing the manifold from sealing flush with the head. It's about a 1 inch length of contact. Anybody run into that problem before? I guess a bit grinding to get clearance is in order. Are the 425 blocks a bit different externally then the 455s? is that why the interference?
On a different note, what company, if any, makes an external fuel pump (60-70 psi) that will last at least 3-5 years or so? I like the FiTech fuel injection so well on my 65 that I'm thinking of putting one on the 425, but just don't have the room for their "under hood fuel delivery system". What from what I have heard about external high pressure frame mount pumps is that life expectancy is usually short and I don't want to get stranded somewhere. I prefer not to go with an expensive tank/pump setup If I can avoid it.....

joe_padavano

Nope. All BBOs are externally identical. The photo looks more like the flange of the repro manifold was excessively machined, bringing that surface closer to the block.

rad

Has anyone ever done a comparison between modern pistons with thin rings and compare the difference of like an old school trw forged piston ive seen this analogy posted a few times and i agree with it, but whats the actuall difference?

rad

ive heard about some pontiac pistons and rod combinations for 425 and 455,what are those? i have a couple of 425s id like to build up some day and might lean that direction if the piston availability is there.

cutlassefi

Easier to do it with a 455 crank and off the shelf pistons imo. Example;

4.25 stroke crank, stock rod length is 6.735, pistons are around 1.735.
If you buy the 7.00" Cadillac/Olds rod and use a stroker Pontiac piston, that has a comp distance of approx. 1.490, your overall rod and piston length is the same as the stock stuff.
HOWEVER apples to apples, if you go to the longer rod that will raise your torque peak, so make sure that's what you want.
Mahle says their new thinner ring pack (1.0, 1.0, 2.00mm) has been shown to make in excess of 14 more hp. I believe it.

lemoldsnut

I am interested in how well the 425 performs. I have a few of them myself and thinking of building one after we finish the 70 442. I thought a 425 in the 67 would be cool.
I have one that was built and then someone did not antifreeze it and it has a crack but it has what appears to be very low run time. The pistons are still shinny and clean on top and are .030 over. very small dish. it is a 66 engine with B heads that look to have had the chambers cleaned up and some porting done. I got this engine with a car from the kid of a guy who passed away and he didn't know much.

Thinking of doing a tear down past just having the heads off and checking it out. It has guide plates and roller tip Comp cams type rockers also.

Any input or advise on this?

Thanks
Larry

1970-W30

Performance is great with the 425, seems to rev just as quick as the 403 it replaced. Besides my 65, I now have installed FiTech fuel injection on the 425, the old Qjet was not jetted correctly for the 425 because the Fi made a huge difference. In the process of getting the TV cable adjusted properly, I inadvertently ran it up to 5200 RPM before I realized it. This was with it only having 250 miles on it. Also plenty of torque, way more than the 235/60-15 tires can handle. I probably left some horsepower on the table by not utilizing pistons that use the modern thin style ring pack, but I am very satisfied on the performance of the 425.

lemoldsnut

very nice

madmax442

Yup I can testify to Marks engine building!

RetroRanger

Others warned me when I did the same thing that cap on the WP heater core outlet is not that robust and should probably be replaced w something sturdier be fore it blows

1970-W30

Madmax442, well we can't give Mark credit for building this engine, I built it myself in my shop. I do take his advice seriously though.......
RetroRanger, this rubber cap is not the one that comes with purchased radiators, they are cheap rubber caps and don't last. This one is thicker walled and not likely to blow. I do know about they cheap rubber caps, and they are no good.
Another unexpected plus with the FI unit is that I can now use the factory linkage set up for the cruise control.
91 Octane gas seems to work fine with the 9.5 compression. Did have to go with a 61 amp alternator, Fi fuel pump, AC and headlights pushed the old alternator to it's limit. I found two 61 amp units from 72 98s at DVAP at $20 each, one needed nothing but a cleaning, the other a set of brushes.

madmax442

I hear you W30! I was just meaning that he definitely knows his stuff is all!