I just picked up a motor and will have a few questions as I start to go through it but first I am trying to figure out more info on the pistons in this thing. Background of the motor is it is a 69 or 70 350 bored .040 with shallow dish pistons. I can not find a duplicate set any where in the web any where. What makes the unique from other dish pistons are the size of the dish 2.5 inches across and .075 inch deep. Most dish pistons I have found are .220 deep.
thanks for some insight.

 

Pictures always help.

 

That's a 2cc dish - Offhand, it doesn't ring a bell.

- Eric

 

Sounds similar to the Badger pistons in my kid's car but it's been 8 years since I've seen them so it's hazy.

 

The '68-'70 310hp 350 4bbl pistons have a 6cc dish that is .077" deep x 2.54" diameter. You likely have some replacement for those pistons, but unfortunately cast replacement pistons are typically short on compression height. Factory was 1.615" and most cast aftermarket pistons are 1.595" which reduces the compression ratio significantly.

 

I measured from block to piston at tdc and the distance from block to piston top was .060 if that helps any.

I will be disassembling the engine to freshen up the assembly lube and try to spec the camshaft- at least lift.

 

On another note, I am looking to buy head bolts for this thing. Should I buy them for the motor year or head year?

 

That is some info you will need for determining the compression ratio. You should also cc the heads to determine the true volume.

I put some numbers into a CR calculator using your .060" piston-to-deck clearance.

4.097" bore
3.385" stroke
.060" piston-to-deck
68cc heads (a guess based on the typical early SBO head volume)
.040" thick head gasket
4.23" head basket bore
6cc dish pistons

The calculator shows to 8.60:1 compression ratio.

Change the head gaskets to .028" thick and the calculator shows 8.83:1 CR.

 

Both.

If the year of the block is wrong, then the bolts won't thread in, if the year of the heads is too early, then the bolts won't fit through the holes.

- Eric

 

If it is truly 0.06 down the hole at tdc you might want to give the block decks a hair cut while it tis apart..

 

She has #8 heads going on her. They have been ported and it looks like some more cutting around the valve guides. Not sure, I can only see in through the ports- have not taken the valves out. I also know the heads have been resurfaced but again, no idea how far down.

Good news is after initial disassembly I have found that everything has been balanced but bad news is the cam shows ABOUT (keyword there) .554 life which is going to be WAY to much for what I need.

Since everything is balanced together I would hate to slap a new cam in there and through all that out the window so I have not decided what to do with it yet.

The motor is going into a Cadillac Brougham, ripping out the tired and wore out 307 and putting a 350 in its place. I don't need it to be over cammed as I still want to use the factory ccc and definitely do not want to put a stall converter in it either.

 

A mild off the shelf grind should work fine in that.

 

Without any milling and using the Rocket Racing .028" head gaskets you will be right around 8 to 1 compression, assuming those are the 6cc dish replacement pistons. I wanted to try the Lunati High Efficiency Series 207/207 .461/.461 on a 112 lsa. I went with the generic 204/214 cam on a 114 lsa, Lunati's 204/214 is on a 112 lsa. That 204/214 cam was about all the 94 TBI FI could handle, ran somewhat rough in open loop.

 

anyone know if the rocker arms off my 1989 307 will work on these #8 heads?

 

They'll bolt on but the pushrods on your 307 have 3/8" ***** on the ends so the rocker has a 3/8" socket. Also being a roller cam motor, your 307 uses shorter pushrods so you can't just swap over the pushrods/rockers as a pair. '80 350's (and '80-'84 307's, all flat tappet cam) have the 3/8" ball ends on them but a check in my Sealed Power parts book shows the length as 8.248" and the earlier '68-'79 pushrods with the 5/16" ball ends as 8.234". Either buy a set of the '80-'84 pushrods and see how the lifter preload comes out or you'll have to go with the earlier, slightly shorter components. If you deck the block you may need a non-stock length shorter pushrod anyway.

 

I found the new version of the Badger here cheap if anyone is doing a cast budget build that doesn't want to suck as much. Appears to be the correct dish and marked down cheap $166 a set
http://www.ebay.com/itm/Dynagear-P51...ZYegux&vxp=mtr

 

I just picked up a set of 72 7A heads complete so rocker problem is solved. The options I have now are a set of ported #8 heads with .015 shaved off the heads and 3 angle valve job already done or pay to have these 7A heads cleaned up and valves cut. Probably not going to port/polish these though.

 

You will have around 8.3 to 1 compression with the #8 heads with that .015" cut. The #8's should have around 75cc chambers as they currently sit. The two heads should flow similar, the 8's might have the edge slightly. Pick up the Lunati cam I mentioned. https://www.google.ca/url?sa=t&source=web&rct=j&url=http://m.ebay.com/itm/Lunati-Oldsmobile-Hydraulic-High-Efficiency-Camshaft-Cam-262-262-461-461-/291766595452&ved=0ahUKEwjI5Ja00sjUAhWE64MKHZ1PA5oQ FggqMAU&usg=AFQjCNF-sSirfHLhq3dbxIwpq0vM1tNBhA

 

Take another 0.030" - 0.050" off of the #8 heads (depending on desired compression), and you should be all set.

You'll have to confirm the right pushrod length afterward.

- Eric

 

I bought the edelbrock-3712 cam. I'm afraid if the heads are shaved to much that the intake will not Bolt on correctly. I think I am going to use the #8 as are. All the work has already been done and are ready to bolt on. I have already had enough road blocks in this build.

On a side note, I purchased a set of head bolts but noticed that they do not extend past the head very much, in fact I measured and the 8 long bolts only extend through the heads .30 of an inch. It doesn't seem like it is enough. That is on the #8 heads, it is even less (.27) on the 7A heads. On top of it, there really were not enough bolts. Stumped on this one, didn't want to have to buy ARP but feel like it is my only option but I wanted to confirm the lengthy of those but have not been able to find any where.

 

You have the wrong head bolts. You can buy a set of originals from a member of this forum, if you'd like.

The intake will still fit if the heads are decked over 0.050", but how far to go is your choice.

- Eric

 

Even with 6cc dishes, these "10.25:1 replacement pistons" will give ~8.8:1 compression ratio due to them being .020" shorter than the factory pistons:

Calculated compression ratio = 8.84:1 using the following numbers:

Bore = 4.087
Stroke = 3.385
Combustion chamber volume = 68cc
Piston dish = 6cc
Pistons down the hole = .045" (.025" Piston to deck clearance + .020" too short pistons)
Head gasket thickness = .040"
Head gasket bore = 4.2"


It would be better to use cast flat tops with everything else above being the same - losing the 6cc dish bumps the compression up to 9.39:1.

 

The Performer cam will work OK with 8.3 to 1 and the CCC. Good luck.

 

I am aware its below deck but just saying $166 for a set of pistons that are not the more common crappy .055 below deck 24 cc dish cast ones that make under 8 or even under 7:1 . A true 8.8 is not bad for a guy with a 68-72 original 350 car that still wants it to run decent and be able to support a mild cam swap on an otherwise stock rebuild and not push the limits of octane at the pump.

 

Yes, that's a good economical option for a mild daily driver. I was really trying to point out that even with the small dish pistons the compression ratio will still be much lower than the factory 6cc dish pistons.

 

yep, all those commercial rebuilders seem to direct the aftermarket to produce low cost replacement pistons way below deck from OEM so the potential for detonation is eliminated even when the smallest chambers heads are installed thus protecting the commercial engine builder from warranty failures do to 87 octane use by the potentially ignorant owner of the vehicle that needs to use 93 octane in his classic car ..or more..

 

German
Performance
5.88
R.HELM

Any idea what this means? Find on underside of block where pan mounts.

 

Looks like the machine shop, the date, and the machinist.

- Eric

 

I saved this link and they had lowered price to $122 with free shipping so I bought them. Badger box with the weight balanced set stickers on it. Probably use these down the road to swap the Speed Pro 030 ones out of my 70 mule motor that has the #4 heads currently in the wagon.

 

Wow that is cheap!

 

I have a set of this same dish pistons, only forged. Mine are standard bore and measure the compression distance to be only .010 in the hole on all of them. I am going to use them to rebuild the 400 out of a 66 442.

 

Too bad these weren't the readily available cast pistons instead of the 24cc dish variety. I can't see any application that actually needs those pistons.

 

For sure on that. Had all the rebuilders used the Badger instead of the crap Speed Pro on at least the 68-72 350's I bet there would be quite a few less that 455 or LS swapped because there 350 Olds was so Damn weak.

 

That's why I pushed to do the new Mahle piston for the 350, 400E and 425. There's a definite shortage of quality options for those engines. However not sure how many will pony up and buy a set.....

 

Fwiw i found most crappy cast after market pistons to be .050 + in the hole. The trw's or speed pros come in a .025 which is closer to where the factory pistons sit. I wouls try to find a good set of used factory pistons with the 14cc dish. I pushed a set of factory flat tops well over 6k rpm for 50 passes an 3k miles until the skirts broke off but they where old and god knows how many miles they had fatigue wise. The. 005 piston to wall clearance did help lol. Mark i plan on buyin a set of the new pistons from you to freshen up my current mill once the new one goes in.

 

I really like what you did getting that piston going as well as the new stroker option. Perhaps in a couple years if still around I will do something with those in one of my 350 blocks.