Building my 427

[Nicholas M.]

I'm rebuilding my 1967 Corvette's 427. It's a 390 HP. Looking for advise on pistons ( name brand and compression, etc.) and a cam ( name brand and type.)
Thanks.

[Steven B.]

Re: Building my 427

I'm rebuilding my 1967 Corvette's 427. It's a 390 HP. Looking for advise on pistons ( name brand and compression, etc.) and a cam ( name brand and type.)
Thanks.

Nicholas, there has been alot on this topic the past few months. NAPA has OEM high quality pieces Federal Mogul.

[Dennis S.]

Re: Building my 427

Nicholas
I'm no expert, but my rebuilder is. I subcontracted him thru Dave Walters down here in Miami. For my '69 L36, he went with Federal Mogul Speed Pro .030 over forged pistons #L2300F. He also went with Comp Cams #CL11-205-3 cam & lifter kit, grind 268H. We wanted to stay as close to stock as possible. It has a slightly rougher idle now but hardly noticable. The engine pulled 408 HP at 5300 and 500 ft-lbs at 3125 rpm on the engine dyno, 93 octane pump gas. The heads were re-surfaced and I believe he used a slightly thicker head gasket to keep the compression under 10.25 to 1. I would not let him deck the block for obvious reasons and he did not have to. I've attached a graph that I created from the tabulated data given to me by the facility where the break-in and dyno runs were performed. I'm running 34 degrees total timing and haven't noticed any detonation yet, but then again I haven't put much load on it. Waiting for that 500 miles, oil and filter change. It will, however break my P235-60s loose now without using the clutch. It never did that before.

[Duke W.]

Re: Building my 427

Exact OE replacement parts including the cam and pistons. Target a CR not to exceed 10:1. You can buy everything from Federal Mogul and Dana Corp, and virtually all parts stores carry the requisite brands - like Sealed Power and Clevite.

You also need to use the second design BB valve springs, which AFAIK are only available from GMPD.

If you want "more power" massage the heads.

If you let some "engine builder" fill the engine with hot rods parts there's a very good chance you will end up with a poor configuration that won't idle, doesn't have any low end torque, and may not even make as much top end power as original.

There are plenty of horror stories in the archives, plus a lot of information on doing it right.

The engineers really knew what they were doing back then. Power was limited by cost considerations, which compromised head port flow efficiencies, but traditional head massaging techniqes will yield about 10 percent more power and another useable 500 revs at the top end of the power band.

You can also goose the top end power without too much effect on low end torque by retarding the cam 5 degrees. That's another 500 useable revs at the top end, and you can get that torque back and more with a 454 crankshaft.

Duke

[Michael G.]

Re: Building my 427

Nic, have recently went through a full rebuild of my '66 427/390 as I would best describe as a "stock" build. Keith Black hyperutectic pistons with compression around 9.5-9.7, Seal Power blue print cam for 390 hp, upgraded valve springs, guides, seals and hardened seats for the heads. Standard Melling oil pump will do the job.
No need to over build in preparing your engine for todays fuels and driving conditions.....you'll be fine.

[Joe L.]

Re: Building my 427

I'm rebuilding my 1967 Corvette's 427. It's a 390 HP. Looking for advise on pistons ( name brand and compression, etc.) and a cam ( name brand and type.)
Thanks.

Nicholas------


The original pistons for your engine were conventional cast pistons. They were not forged and I do not recommend that you used forged now.

I recommend going with Keith Black-Silvolite hypereutectic cast pistons. These pistons provide almost the same strength as forged pistons but with all the other benefits of a cast piston, including long wear, better oil control, less blow-by, and lower noise, especially on warm-up. Most modern Chevrolet engines, including the LS7, use hypereutectic cast pistons. I think Chevrolet might have used them in the 60's and early 70's except they hadn't been invented yet.

If you used a KB 176 piston, you would have near original compression ratio or just slightly higher. However, I DO NOT RECOMMEND that. I would go with a KB 360 which will give you about 9.6:1 compression ratio. Big blocks are highly susceptible to detonation and I strongly recommend keeping the compression ratio at less than 10:1. As a "clue" for you, ALL of GM's current crate big block engines with cast iron heads have a compression ratio of 8.75:1 AND require 91 octane fuel. The highest compression ratio that GM uses for any STREET big block crate engine is 9.6:1 and those engines have aluminum heads which will tolerate a little higher compression.

As far as the camshaft goes, the attached photos show the EXACT original camshaft that was installed in your engine. You won't find this part number in ANY GM Parts & Accessories Catalog but, trust me, this is the one. Since it's not found in any GM P&A Catalog EVER, that might lead one to conclude it was never available. But, it was. Here's the "living proof".

This one's not for sale and you can't get it from GM anymore. But, you can get a very respectable copy as manufactured by Federal Mogul and that's what I recommend you use. This cam was probably the best STREET big block, flat tappet cam EVER devised.

[Duke W.]

Re: Building my 427

That's the '67-up 390 HP cam. It's exactly the same as the 3883986 used in the '66 version, except for the lack of the rear journal groove. Either can be used in a '67-up engine. The OE replacment Clevite number I have in my notes for the 359 is 229-1953, and you can use the napaonline cross reference to get the Sealed Power number.

As far as CR goes, the early closed chamber heads will tolerate more compression than later open chamber heads, because of the small chamber and two large quench zones. Based on anecdotal evidence I have, up to 10:1 is okay for the 390 HP engine and 10.25:1 for the SHP version.

The only way to know what the CR is on any specific engine is to MEASURE IT. This requires accurate dimensions for deck height, chamber volume, head gasket thickness, and piston compression height and volume.

Piston catalog specified CRs are based on assumptions regarding deck clearance, gasket thickness, and chamber volume. As built, the CR could vary by up to a point either way depending on actual dimensions for a specific engine.

All this has been discussed in detail in the archives, and a detailed article on the subject was in a recent issue of the Corvette Restorer.

Duke

[Michael G.]

Re: Building my 427

Nicholas....I used the Keith Black KB360 pistons and the Speed Pro/Sealed Power cam CS 1093M which has virtually the same specs as the orginal L-36 cam. These pistons has the CR below 10:1 with the factory orginal heads.

[Duke W.]

Re: Building my 427

The CS1093M is an exact duplicate of the OE cam. It is built to the GM print.

Duke

[Don W.]

Re: Building my 427

So for a 69 427 rebuild is the target at 10:1? I have a 390 hp; is it the same for 435 Hp as I had I had in 1974 as a senior in high school?

[Joe L.]

Re: Building my 427

So for a 69 427 rebuild is the target at 10:1? I have a 390 hp; is it the same for 435 Hp as I had I had in 1974 as a senior in high school?

Don------


Personally, I would not go above 9.5:1 for any big block.

By the way, I have heard lots of folks say that reducing compression "emasculates" the sound of the engines. However, the 1971 LS-6 had 9.0:1 compression and it's one of the, if not THE, best sounding engine I ever heard. They also run real well, too.

[Don W.]

Re: Building my 427

So 11:1 and 10.25:1 out with gas we have?

[Joe L.]

Re: Building my 427

So 11:1 and 10.25:1 out with gas we have?

Don------


All I can say is that I would not do it. It's also the strong advice I got from a long conversation I once had with John Erb, chief engineer for Keith Black-Silvolite. In fact, he advised no higher than 9.0:1 with any STREET big block. And, John is no stranger to hot-rodding and performance cars; he owns a lot of 60's "muscle cars".

As I've pointed out many times before, ALL GM crate big block engines with cast iron heads have a maximum compression of 8.75:1 and still require 91 octane minimum fuel. The highest compression for a STREET big block crate engine with aluminum heads is 9.6:1. I feel very confident that if a higher compression ratio was practical, the GM engineers would be using it. After all, it doesn't cost much more to build an engine with higher compression than with lower compression and these are CRATE engines, not PRODUCTION engines so there's no emission requirements to be concerned with

[Tommy J.]

Re: Building my 427

can someone verify if a jan 69 427 should have a 8" dampener?thanks tommy

[Joel F.]

Re: Building my 427

can someone verify if a jan 69 427 should have a 8" dampener?thanks tommy

I believe it will depend on what HP engine. 7" for hydraulic lifter engines and 8" for solids.