weedman

It is time to have my 327/340 rebuilt. My question is whether I should stick with the pop up pistons or go with the flat. I have always been told that with the high compression of the pop ups I need to run pure racing fuel and with the flat pistons 92 or 93 octane works great. I just hate to lose the horsepower. It is a numbers matching engine. HELP!

MikeM

Rebuild your engine to the stock specs, including the domed stock replacement pistons and the 097 Duntov camshaft. You'll be fine on 93 octane. Maybe even get away with 91 octane. I do. Mine is a fuelie but otherwise it's the same engine.

I would even use the stock type forged pistons just to make it sound right but that will just about double your cost on the pistons. But, it'll sound like it's supposed to.

Seaside63

Stick with the pop-ups and just use a thicker head gasket. Use a replacement "stock" cam and you should be fine.

How is it running now? It shouldn't be worse after the rebuild.

kenba

I would go with 9:50 pistons. You will need hardened valve guides & seats. Your not going to beat on the car & race it with the original motor so the little HP loss will not matter.
KEN

weedman

It was running great until I lost the #8 rod bearings.

MikeM

So, if it was running great as an original 340 hp engine, why not rebuild it as original? I didn't mention it before but you should be able to use the domed pistons and make the ignition advance curve a little more aggressive than stock. If you do, you will probably have to use the 93 octane.

The high compression, forged pistons and the 097 all go together to make a distinctive sound of a SHP engine. I wouldn't deviate from the stock configuration if that's what you're after.

Ironcross

Leave it alone, build it back to 340 standards. There is not any hardened seat issue that you should be concerned with. If you do install flat tops, just dont tell any one. Car shows dont tear engines down as a requirement to win..

claf

I redid a stock 1966 300 HP engine to 340 HP specs for my '62 last summer with the original stock pop-up pistons and the Speed-pro replacement mechanical cam. Zero problems at 1500 miles using Premium fuel, no audible pings or knocks. More than satisfied with the sound and performance. Bob

Mark Lovejoy

Are new pistons absolutely required for this rebuild?

I would measure the original pieces before discarding them, they may be servicable. Especially if the block is not bored.

Seaside63

I would recommend that you use new Crower rods though.

If you're going to go through it you might as well strengthen it. The original rods are notorious for weakness.

LouieM

Scott Marzahl and SWCDuke pounded into our heads that early 327 rods are weak and should be replaced. I participated in the Forum group buy of the Crower Sportsman rods, I'm happy to say.

RoadKing96

Any one have opinions about a need to strengthening the Crack as well?

And if so, what are some suggestions?

RK

MikeM

The crack (crank?) is fine as is. You would be better off with '66-'67 rods if you can find a set. The early 327 rods should be okay if they pass magnaflux and you don't wind it to the moon. I thnk it's better said that instead of being "notoriously weak", they will not stand as much abuse as aftermarket, high dollar rods or the improved, later '67 Z/28/327 rod.

Scott Marzahl

The crank should be fine even if it has been turned once before. You don't mention if you like to spin it up to 7K or not. If it is still at original specs, hopefully a polishing is all that is needed for the rebuild. One can have the crank nitrided after turning to harden the surface again. Forged steel doesn't work harded quickly like cast iron does so that is one reason to have it nitrided.

As for rods, it is an insurance thing. After 40 years, originals have seen plenty of fatigue. The Crowers are top notch, Duke has found that the Eagle cap screw SIRs are nice for the money and aren't nearly as heavy as the SCAT rods are.

Pistons, definately stick with the Speed Pro L-2166NFs if you want the original design, they have a newer skirt design along with the black coating.

64_365

Eagle or Scat rods are a good buy, the Crowers are so expensive that you could get light weight H-beams for the same price.

Scott Marzahl

He couldn't use the cheap offshore H beams with the stock type pistons UNLESS he sends the pistons to Arias and spends another $200 to have them cut for retainers since the Speed Pros are press pin fit only. UNLESS something has changed in the last several months, the last time I looked the cheap H beams were only available in the floating pin configuration.

stevens03

Hi there,
Im looking at a old post you did about rebuilding your 300hp to a 340hp stock.
I am researching in doing the same project.
I would love to know and have all the specs for the 340hp if you have them. Cam, heads , balancer anything would help me with my project.
Let me know if you can help. Thanks

MiguelsC2

A Forum archaeologist.

Heads are 461s with 1.94 and 1.50 valves
Cam is the 097 'Duntov"
Compression 11.25 to 1
Intake 461
Carb Holley 2810
Exhaust-cast iron 2 1/2 inch
8 inch harmonic balancer

Try starting a fresh thread.

You may also want to use the Forum search feature. There should be lots of info on the 340hp.

Westlotorn

A note on turning Cranks, if the crank is properly radiused you will have no issue turning it .010, 20,30,40 or .050 undersize. I have heard many say they won't run more than a 10-10 crank. Properly turned a crank can go very far under with no negative affect on the strength. Racer's and Nascar engines run Honda journal size in Chevy V8's at 9,500 RPM with no issue. Hot Rodders turn the 400 GM cast crank down to 350 journal mains and beat them hard. It is OK. If you need to go deeper in your undersize do it and don't worry. If you break a crankshaft you probably had a balance issue, bad harmonic balancer or very hard abuse. If you need to turn it .010 under on each rebuild to keep it perfect you have 5 sizes available for future rebuilds. Hope that helps.

UberLegend

The 340 does have it's own sound, and it's terrific at WOT.