Hello all, I am building a 348 for my 1956 Belair sedan. I have always loved the 348 and 409 engines and feel like it will give it a good nostalgia feel. I have had the block machined and cleaned up. I have also picked up some NOS venolia forged pistons for it as well. One question I had is the orientation of the pistons. I have them mocked up in the first bore but don't know if I have the 180 off. Any help is appreciated.
348 assembly
- Thread starter Hods1222
- Start date
Looks correct to me.
Bigger valves are always better!
333 heads with bigger valves such as 2.07 intake,1.72 exhaust and that cam will make a spunky little engine.Those old Venola pistons are heavy and if you're using stock 348 rods,keep the revs below 6,000 for safety sake. IF you're not to far along for an upgrade a standard big block rod would be a good one
Yeah the larger valves go right in just make sure to get the throats bored to go with the new seats.And if your running stronger than stock springs you may need to eliminate the rotators on the exhaust,Comps eliminators for a BBC are the ticket your cylinder head guy may need to trim the guide OD a little to make them fit though.
So I have some forged scat 6.135 floating pin rods with 7/16" ARP fasteners that are going into the build. It looks like the pistons were lightened from venolia with some under crown milling, hopefully that shaved down some reciprocating weight. I have a gmc 6-71 that I want to put on it but I need to check the static compression to see if it is feasible. This is great, thanks for all the insights on the valves and the head work.
If you check it closely your combo should come in at around 9.1 which is good if you drive the blower at about 1-1 or 7 lbs.of boost.I know of a flat tappet hyd.grind that will work.It made 558 at 5600 on an 8.1 380 using 333's ported and big valves.Runs good,trouble free sweet running piece.
I know the crown measures 4.140 and the bores were measuring out at 4.185. I just took the pistons over to get the crank balanced so I will have to measure the skirt when I get it back. One question I had is since the pistons do not have a valve pocket and the block notch is factory will that hamper my ability to run bigger valves? Also the timing set looks to be in good shape is it best to just replace the chain or get a whole new set?
Well the clearance is measured at the skirt just below the pin. If your bore is 4.185,on these old deigns you should be seeing 4.175 [.010] at the minimum.These old design pistons aren't nearly as good as far alloy of the metal is concerned and usually are very heavy because of it.As to the valve clearance,the block clearance to block needs to be addressed only if the exhaust lifts exceed .550,the P/V clearance is limited by the cam's duration at .050.What size valve are you wanting to run and what is the casting number of the head that your planning to use? Always replace the timing chain and gears a a set..
Good choice.Make sure to do a decent bowl blend just under the valves as it will really wake that engine up.On both Brian and Nate's engines they're running 2.19 intakes but both are 380 inch engines and Nate is running aftermarket heads.The hp figures that I posted were from Brian's engine with ported 333's and big valves.
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As usual Don's right on the money about the vintage forged pistons,they were back in the days before they got the thermal expansion under control,thats not to say they're bad you just have to accommodate them clearance wise.I personally like the sounds of a loose engine,while they may not be as efficient as the newer stuff,old school has its own appeal.
If I remember correctly from my high school days,the factory spec for the forged pistons in the Max Wedge was .013 or .014 in the 1963 engines.Forged pistons such as Venola,and Forged tru expanded a lot."Black Death"from the piston getting too tight for whatever reason was not uncommon.He's going to run a blower on these parts.Now's especially the time for attention to detail so this engine can live.
So I may be getting a little ahead of myself but I mocked up the heads with the huffer on top of a 409 manifold I have. It seems a blower manifold for these engines is as scarce as proverbial hens teeth. Since I have a 3 axis VMC at my disposal and an ac tig welder I was thinking of machining/welding up my own custom manifold. Anyone have any experience in doing this? Is there a good manifold to start from? I had heard that back in the day blower manifolds were made from an offy manifold to suit the bill.
