Piston Size

[MacQuigley]

Can anyone tell, from the numbers on the head of this piston what size it is?



From past experience Id have said +60th due to the 060 but +60 is a lot and to be honest the bore measurement doesn't support that (measures +30)

Engine is a Chevy 350SB and everything Ive read says +30 is the max recommended over bore, though I know +40 is not uncommon and +60 is I believe about the absolute max.

[Palf70Step]

I have seen plenty of engines go to .60 over, but as far as reading the numbers, no I am not much help with that. Could have it been a .60 above a 327 or 305?

[awbrown]

The only way to truly determine max bore oversize is to sonic check the block .. all blocks lack cylinder walls that are dead straight on the water jacket side ... I have bored chevy 350 blocks to .080 with no problems and have a friend that used to bore certain blocks to .125 over when he raced stockcars years ago .. so it all depends on the casting ... your piston says .060 but it would be wise to buy a caliper to double check it .. a caliper is not a precision engine building tool ,but should be able to tell you if the bore size stamped on the piston is correct ................

[MacQuigley]

Going to measure the bores tomorrow. My dad couldn't find his callipers yesterday but he has them now.

Is it possible to have a SB's cylinders lined?

[crazy longhorn]

I did the research...that piston is a .060 over/350, & yes with the short pin height. I will ask the ?....did you tear that mill down, or was it all in pcs , when you got it? Longhorn

[MacQuigley]

My Dad is rebuilding it. He has rebuilt a few small blocks over the years, where as my engine building experience is limited to British built motors, A series and Land Rover.

Thanks for the info guy's, as always. American cars are completely new to me and I find it hard to get through the multitude of different makers and suppliers of parts and for that matter options for parts. I can only dream of having so many options over here. My land Rovers are the closest thing Ive come across. There are loads of suppliers of after market parts but its still just a drop in the ocean compared with the options available for your motors.

[Bigdav160]

I say they are low compression size

[MacQuigley]

When he first took the heads off my dad thought they were high compression. But of further inspection he changed that to low.

[Marv D]

Seriously low compression!

The dish is a 9cc dish, + the 5-6cc for the eyebrow valve reliefs, AND it is a 1.54" CH which will put it 0.020 down the hole, + the standard 0.025 deck,,, on a 350 with a 76cc chamber you will have roughly 7.8:1 compression. If you can find a 64cc chamber you can squeeze that to about 8.5:1,, but with such a TERRIBLE quench distance,, I'd refrain.

http://www.summitracing.com/parts/stl-423np

[crazy longhorn]

You have to love Marv....a straight player, all the way! Talk about 'quench"....if you can set that about .038-.042, you are good many of the street bound " mills", are way looser, than .060? Bring it back Mr Marv....I will kick it with you I trust what you have....Longhorn

[68c10owner]

As already been said those are the rebuilder pistons. They dropped the compression height because they figured when you rebuild the engine you would deck the block to true it up. When you do that you lose the factory .040 quench. Yeah many engines have much more than this and survive just fine but if your going to do it, its worth doing it correctly.

If you stick with these pistons you will need to deck the block. To get some compression out of them you will need some 58cc chamber heads. There are plenty of options depending on your budget but the 416 casting 305 head is a popular head. Same runner size as the older camel hump heads and some came with a 1.84/1.5 valve set up. A little bowl work and gasket match and these heads are strong runners for a street rig. Trick flow also sells a 56cc chamber head that was designed for a 305 but will work just fine on a 350 as long sr you dont run a dome piston.

[Marshy]

Originally Posted by 68c10owner

As already been said those are the rebuilder pistons. They dropped the compression height because they figured when you rebuild the engine you would deck the block to true it up. When you do that you lose the factory .040 quench. Yeah many engines have much more than this and survive just fine but if your going to do it, its worth doing it correctly.

If you stick with these pistons you will need to deck the block. To get some compression out of them you will need some 58cc chamber heads. There are plenty of options depending on your budget but the 416 casting 305 head is a popular head. Same runner size as the older camel hump heads and some came with a 1.84/1.5 valve set up. A little bowl work and gasket match and these heads are strong runners for a street rig. Trick flow also sells a 56cc chamber head that was designed for a 305 but will work just fine on a 350 as long sr you dont run a dome piston.

Great advice but for what it's worth I wouldn't stop there. If you need the small chamber 305 heads it would be of benefit to seek out the 059 vortec heads. They have 58 or 59cc chambers just like the 416 heads you mentioned. The only down side is the vortecs need a vortec style intake manifold. Might be worth it if he's getting an aftermarket manifold anyways but at that point I wouldn't be messing with any 305 heads. Deck the block proper and get the 062 or 906 vortec heads with 64cc chambers. The intake runner on the 305 heads is small and will limit the power in the upper RPM range (I'm probably not telling you anything you don't already know).

[68c10owner]

Originally Posted by Marshy

Great advice but for what it's worth I wouldn't stop there. If you need the small chamber 305 heads it would be of benefit to seek out the 059 vortec heads. They have 58 or 59cc chambers just like the 416 heads you mentioned. The only down side is the vortecs need a vortec style intake manifold. Might be worth it if he's getting an aftermarket manifold anyways but at that point I wouldn't be messing with any 305 heads. Deck the block proper and get the 062 or 906 vortec heads with 64cc chambers. The intake runner on the 305 heads is small and will limit the power in the upper RPM range (I'm probably not telling you anything you don't already know).

Well good luck trying to locate a set of 305 vortec heads. They are not near as common as the 350 vortec heads and I dont know that the 305 vortec heads flow as good as the 062/906 heads. And they would require the vortec specific intake manifold and rocker covers.

The intake runner on a 416 and the 601 head is 160cc stock which is the same size as the old camel hump heads. A little porting can get them in the 170cc range. These would not limit the upper rpm power over any other GM head. Do a google search on the 416 or 601 HO heads and you will find plenty of info on them and how well they work.

Decking the block is a must with these pistons regardless of chamber size used but with a 64cc head its still going to be about 9:1 at best. This may be fine though because the OP has not mentioned the intended use of the engine.

[MacQuigley]

So we measured the bores this evening and they have been bored out +60. So I'll see if I can contact a local machine shop tomorrow and see what they can do for it.

I must thank you all for all the info and time you have taken to reply. But, can I ask a question. What is decking and quench?

In the context that decking is being used Id guess you are talking about skimming/machining the top of each bank on the block.

Really not sure what quench is!

[Marshy]

Decking the block is a term used to describe the machining of the block where the heads mate to the block. Basically shortening the length of the bores. When you deck a block, the result is the pistons at TDC are closer to the heads. The distances between the piston at TDC and the head surface is the quench. There is an optional quench distance and the thickness of the head gasket is included in the quench distance.

[MacQuigley]

Thanks Marshy.

Essentially decking and skimming are the same then. I had never heard of quenching before but I understand what it means now.

[GASoline71]

Originally Posted by MacQuigley

Going to measure the bores tomorrow. My dad couldn't find his callipers yesterday but he has them now.

Is it possible to have a SB's cylinders lined?

You can have cylinders sleeved.

But it is expensive and to try to do it to all bores probably can't even be done. I know you're across the pond and 350's aren't a dime a dozen over there. But a new 350 block will probably still be cheaper than trying to sleeve an old one.

The only time I've seen anybody sleeve a SBC, is in a rare numbers matching block in say a Corvette.

Gary

[MacQuigley]

Ive not looked extensively yet but so far the only block I can find is £1100, thats about $1500. Thats just for the block, nothing else.

Sleeves are about £22 each ($28 roughly) plus the machine shops time, which Im still trying to get.

I need to find a bit of time to have a good look about to see whats available.

A better option may be the Ebay list for a complete 350 short engine at about $1500. I could possibly get it shopped here for very little if I can piggy back on a friends shipment (which shouldnt be an issue).

But first up I need to figure out whats available.

[GASoline71]

Good luck to you dude! Gotta be hard finding stuff available over there that we take for granted over here.

Will be curious on your progress. Keep us updated!

Gary

[MacQuigley]

I'll keep you updated.

My dad, who has worked with US motors many times still has some contacts. He is making some enquiries. If they can come up with something it may be best just getting a replacement and possibly selling what I have as a project to someone.