It's been suggested to find some 73-80 connecting rods for my 350 bottom end build. I was wondering if anyone had a spare set sitting on a shelf? The main reason for this thread is to educate me on pistons. When I rebuilt my motor back in 94. I seem to recall the stock pistons were fairly flat on top other than a little bit of a dish. My build will include decked block and heads. My question on this machine work is, how much should be taken off before the intake geometry becomes affected. I'd really like to have the combustion chamber a small as possible for the TA 212 cam to still run the motor on pump gas. 9.5 to 1 compression has been suggested as a goal for my build. I agree. So, obviously, in reality, I'm taking a stock 350 Base Skylark engine and turning it into a stage 1. Other than the obvious head parts like springs, valves and such. Were there any differences in the rotating assembly which I need to focus on to make sure it's done right like crankshaft, pistons, and such or were they basically the same as a base 350?
What pistons are in the engine now and how far down in the bore are they at TDC? The replacement TRW H522P pistons have the shallow 12cc dish and a compression height of 1.855 which puts them only .020" in the bore. You end up with 10:1 compression with an .040" head gasket. The TA 1602 10:1 compression version are identical to the TRW 522s Paul
I have been through every Buick V6, GM V6, L6, Buick, Chevy, Pontiac, Olds and many of the non GM engines looking for an off the shelf piston to work with the stock Buick 350 rod in order to get between 9 and 9.5 compression ratio without having to machine a lot of material off the block or heads. I end up with the TRW H522P Hyper pistons and the 10:1 TA 1602 with a CH of 1.855" The rest of the pistons that are around 3.800" bore have CH that put the pistons too far down in the bore. If you can find a .060" thick head gasket you can make either one of these two pistons work and have 9.5 compression without doing any block or head maching except for clean-up. Sean once had some .060" head gaskets or he would know the best supplier. Paul
Great info as usual Paul. I do not know the name of the people who made the 60 thou thick gaskets I just know I have a set here somewhere... I would not split hairs on the compression ratio.. If it is a little higher or a little lower then thats fine in my opinion. If you have not already bought the camshaft then just buy a TA 284 cam if you end up with over 10:1 compression as that would be a better match.
9.5 is okay with me after reading the responses. I already bought a TA 212 and I should have no problem getting there. If you find the gasket, would you be willing to sell it? I plan on shaving the head and the deck a bit to clean it up. How much would be too much before I run the risk of going past 0 deck with the pistons and messing up the intake geometry.
No I don't want to sell the gaskets, sorry. I would just shape 10 thou off the heads and intake and toss it together and then you dont have to use custom length or adjustable pushrods... As l;ong as you dont use a low comp piston the compression will be high enough for you. or use the low comp pistons and deck the block right down. I think the pistons sit about 70 thou in the hole if I remember right.
I could have swore TA sold gaskets for 350's and big blocks that ranged from .020 to .120. You'd have to shell out some money for them though, since they're multi-layered steel or copper (with or without fire ring for omission of block 'o' ring) G Edit: well the TA catalog says you can, but then you look at their website and it doesn't say...so I suppose the answer to that is a big fat NO.
TA can get whatever you need or you can call Cometic directly. Yes they will cost more but if you weigh the extra cost against the machine work you save you should come out ahead. Check the price between an .060" and .066" and if there is no or very little price difference go for the .066" Only deck what is needed to square the block. Try to leave the piston .020" in the bore. Paul
Looks to me like if you're going to do some block and head milling anyway, to just use 8.5 pistons, zero the block, shave .020 off the heads, and use the .040 composite head gasket. You'll have to get the intake to match up, use composite intake gaskets, and use custom push rods to get your 9.5:1. I'm kinda in your same boat, though I'm going to only shave off .010 off the heads for 9.25:1 for use with the TA rv-12 cam. No real straightforward way to it, you gotta reach around your ass to scratch your balls. Yay for no 350 aftermarket support. I may just say phuggit and get the 10:1 pistons and the .460 lift (TA 284-88H) cam, and have a nice rumpy idle. DCR with that cam with 10:1 comp would be 7.78, right about where it needs to be, so it's tempting. If I'm going the route of 3.42 gears and a 200-4r trans anyway, what the hell. The stahl in the trans can be had for about the same money, no matter if I'm at 1800 or 2800. Edit: 10.25:1 would be even better, with DCR of 7.97:1 Using TA's 10:1 pistons, .040" composite head gasket, and shaving .010" off the heads would put you there. Then like Sean said, take .010" off the intake and using stock pushrods and cost is minimized.
No cometic does not make any head gaskets for the 350 , no TA can not and will not offer a head gasket option. I beat that option into the ground a few years back. :spank: The only option for head gaskets is stock 40 thou fel pro or the steel shim but they only work with the early 68-71 engines. Yes we has Gaskets to go make a MLS head gasket, you could call them but I think I paid about $200 for my set of gaskets. Back to the topic of 73-80 rods I would not worry about using the 68-72 rods with a mild build as I am sure they will be fine.
For clarification purposes, I think Derek said you were the one who tested the different rods, correct? the 68-72 rods failed at 400 hp and the 73+ good to 600? Man those 73-80 rods must be gangster tough. So if the 68-72's fail at 400 hp, 375ish should be plenty within the safe zone, and the vast majority of mild-moderate 350's won't see past that anyway, so I reckon use whatever rods you got if you don't expect more than 375 hp. Edit: Jim uses '71 rods in his build here: http://www.v8buick.com/showthread.php?153248-TSP-Level-1-350-Buildup-info-and-dyno-results The engine produces 349 hp and 399 ft. lbs. and would be similar to your build with the TA 212 cam.
You are on the right track with the rods... If you are not going to be over 400 HP I would use the 68-72 rods without a worry. There is no set point where the rods break, some sets might break at 280 hp and others be good to 600 HP a lot of it is up to luck and how well the part came out from factory. The two main variables in the strength of the rods are: 1. The RPM the engine is revved to 2. The piston weight The lower the RPM and lighter the piston the higher the HP the rods will handle... Personally I would be comfortable taking my bone stock 73 Buick 350 that has 35,000 miles, removing the stock pistons off the rods, adding nice light custom Venolia or Diamond forged pistons with file to fit rings and puting the engine back together without measuring ANYTHING except piston ring gaps. Then I would trust it up to about 600 HP under boost. Maybe I am crazy but I think there is a lot to be said for keeping things simple! With heavy forged TRW slugs the limits of the 73-80 rods with ARP bolts and all smoothed out is about 580 HP and 6200 RPM... Lower the piston weight and or RPM and expect longer life. I would trust a set of 68-72 rods untill about 400 HP... I feel an all or nothing attutude towards 350 builds... Either rebuild it stock with a mild cam and head porting or go with forged rods, custom pistons, ARP everywhere and a roller cam with pro head porting...
Venolia still list the Buick 350 PN 7820 piston. I believe it was the 10:1 NHRA legal piston. I called and the pistons are $80.47 each. There is no charge for the SBC .927 pin bore or different location. With the .927 pin you now have the option of using the Eagle CRS6460H3D2000 rod (Honda 1.889" journal) so you can offset grind the crank for a 3.95" stroke or use the Callies Compstar CSC6440CS2A2AH rod (2.00" journal) with the stock stroke. Either rod is around $550 a set. In case your wondering why finding the right combination for a 9.5:1 compression is such a problem is because the 2 forged pistons that filled this gap are now hard to find. They are the Speed Pro 2232P or TRW L2343. Of coarse like Sean said they are on the heavy side but combined with the 73-80 rods made for a strong but reasonably priced combination. Paul
Yeah, Venolia will make up whatever you want also. SCE has the pattern for the head gaskets, they made my copper .050" gaskets for my 340 and if I remember correctly I sent them both the 340 and 350 sample gaskets. There are only minor differences between the two. Primarily I think, the 340 gasket had round holes for the pushrods and the 350 one had cutouts. Big damn deal. (not) Cost about a c-note. We had a huge go-around about head gaskets on here back about then, everyone wanting MLS and such. But NOBODY makes the MLS in stainless. For $200 I want it to be reusable. Cost to o-ring the deck was a hunert bucks so it was a wash. MLS vs o-ring, I went for the better seal. So the copper gaskets are available in any thickness you want, I think you can get them 1/8" thick. Just one thing, the first set they sent me were wrong, had a steam hole in some bizarre location that made absolutely no sense at all and made the gaskets unusable. Guess it was a Monday. They fixed it though. Jim
Hey guys! Thanks for all the responses. It's not until I ask questions do I discover just how ill informed I really am but now I'm beginning to get my mind wrapped around all this. I've decided to go with a forged piston so in the future if I decide to spray. It will be set up to do so. I'll install the later rods for more durability in the rod department too. The stock replacement pistons are made in a forged aluminum version. The combustion chamber in the 68 head is smaller so it will be easier to get the compression I want. I'll shave .010 off the deck and .010 off the heads just to square them up and have a metal head gasket made.
Just shave 40 thou off the block instead of 10 thou and then use a 40 thou fel pro head gasket and you will be right at the stock pushrod requirement for length.
