69 427 rebuild

[Don W.]

I have a 69 427/390HP with auto and 3.08 rear end. I considering a rebuild and these are the suggestions I have from a local build. I have an estimated 8:1 current compression from a mechanic in AZ based on his dyno tune activities a how far he could retard the timing. Major points are:
Consider a roller cam which requires removal of the intake manifold heat shield and adds $800
Max 10:1 compression; maybe ~ 9.8:1
Add different oil system to the valve train
Heads: 3-cut valve job + venturi cut on exhaust
New pistons, rod bolts and head bolts
Keep rods; x-ray and balance full set up
Line bore and deck block except for pad
Since I have a late Nov build with 454 heads; consider a 454 crank
Have the auto trans checked and re-sealed while the engine is out

[Joe R.]

Re: 69 427 rebuild

My suggestions would be to find another builder. Some of those ideas boarder on the insane!

Such as:

Align Boring!
Deck the Block!
454 Crank!
Roller Cam!
X-ray the Rods!

What in the world are you planning on doing with this after it is finished?
What is your desire for the Corvette? What is wrong with this motor that it could require the above treatment?

JR

[Ronald L.]

Re: 69 427 rebuild

Sounds like the guy has your check book open.

"IF" you are looking to keep an original motor car stock and essentially original - none of the above.

If you have a drag strip car, you'd not have a 390 cast iron motor in there anyway so as Joe says, skip that dude.

Retarding timing? Sounds fishy but need to know more, I run my 390 HP at 8* inital timing and these things were more like 10:1 new, did they measure the 8:1 somehow?

[Michael M.]

Re: 69 427 rebuild

I agree that some of these things being recommended seem concerning but we will need to know if there is anything wrong now and what the goal is for the motor. Stock compression was 10.25:1. Possibly he's recommending lower compression to better run on todays pump gas without detonation. Currently, I am running 10.25:1 compression on Super Unleaded with little to no problem.

I run a roller cam, roller rockers, headers, and have had some other engine work performed, but my goal was to create more horsepower and torque without changing the heads, block or intake.

What's your goal?

[David B.]

Re: 69 427 rebuild

Don,

A mild decking is not unusual (.003") but can only be determined if necessary after dis-assembly and inspection and proper measurements. Align boring is not normally necessary. Adding a roller assembly is a matter of preference, depending on what your goals are. It adds HP and reduces friction wear on cam lobes, especially with today's oils. But as much as our C-3's get driven, you have to ask yourself if that matters enough to put in a roller assembly. I had my rods re-sized when I did mine years ago. It is not expensive and is worthwhile in my opinion. I would also have the crank magnafluxed while out. I had a flawed crank on a 427 that was caught this way. You may want to consider a set of forged pistons as additional defense against detonation damage with today's fuels. I have a 3.08 rear as well and still have plenty of power off the line without hefty engine mods that were suggested by your builder. If you really wanted a 1/4 mile car though, you would want to get rid of the 3.08. So, I suggest revisiting your goals first. Hope this helps.

Dave

[Michael H.]

Re: 69 427 rebuild

My suggestions would be to find another builder. Some of those ideas boarder on the insane!

Such as:

Align Boring!
Deck the Block!
454 Crank!
Roller Cam!
X-ray the Rods!

What in the world are you planning on doing with this after it is finished?
What is your desire for the Corvette? What is wrong with this motor that it could require the above treatment?

JR

I agree. I would NEVER align bore a block unless it absolutely positively needed to be align bored. If the engine shows decent bearing wear, it most likely does not need line boring. I can tell you horror stories about such a process as done by most typical machine shops.
Here's something to print and tape to the inside lid of your tool box. "IF A STRAIGHT CRANKSHAFT WILL SPIN FREELY IN MAIN BEARINGS OF .002" TO .003" CLEARANCE, THE BLOCK DOES NOT NEED TO BE ALIGN BORED".

Same for decking the block. If the engine did not experience head gasket failure, and the deck is reasonably straight without nicks/scratches, it does NOT need to be decked.

I think roller cams are a complete waste of money. There can be a bit of performance gain IF the cam profile has a more aggressive lift curve but as far as reduced friction is concerned, that's NOT going to happen. If a flat tappet cam and lifters can last for hundreds of thousands of miles, just exactly how much friction do people think there is at the lifter??? Most folks don't have any idea why manufacturers changed to roller lifters. There' absolutely zero horsepower gain, all else being equal.

Engine rebuilders usually have expensive equipment that they make payments on every month and they don't make those payments by telling people that they don't need all the services that they can provide.
Typically, they tell customers that they won't guarantee the job unless they are allowed to perform ALL of their recommended services.

Get a 2nd opinion.

[Don W.]

Re: 69 427 rebuild

All,
Thank you for your input. I'm just looking for ideas at this time. My goal is too have something fun to drive with a little bit of power. The previous owner rebuilt the engine and it seems pretty weak. It has 221 HP and 310 ft lbs torque at the rear wheels based on a dyno run. The mechanic in AZ that did the dyno runs and was jetting the carb told me that he thinks it has 8.5:1 compression based on how far he can move the timing without and an issue. I don't recall but I think he said he could take it to 12 or 16 degrees and it still ran.
Don

[David B.]

Re: 69 427 rebuild

Don,

I imagine those were the peak dyno values? If so, I think you are about 50HP below where you should be at the rear wheels. I think the three biggest results you can get for the buck would be:

1. making a good cam selection. There are some cam experts on here who can suggest a good cam (Duke, others, chime in here if you like).
I really like GM#14096209 for the 427. Here are the specs.
14096209 flat tappet Hydraulic "502" I: 328
E: 324 I: 220
E: 220 I: .500"
E: .500" 0
0 115 Good street high-performance and marine cam. Use spring P/N 3970627. Use in Gen V 502 HO engine P/N 10185058.

2. designing for a good static compression ratio. For this, the heads can be cc'd to determine the actual current volume (in case they may have been worked or milled in the past).

3. consider switching to a 1970 2-1/2" exhaust setup (manifolds, and pipes) if you are not concerned about judging. The BB will breath a lot better!

The rest of the exotic stuff I would leave out.

Dave

[David B.]

Re: 69 427 rebuild

Don,

This might be easier to read:

14096209 - Hydraulic Flat Tappet "502"

This hydraulic flat tappet "502" is a good street high-performance and marine cam used in the Gen V 502 H.O. engine P/N 10185085. (Use spring P/N 3970627.) The duration at lash point in degrees (intake/exhaust) is 328/324; duration at .050" tappet lift (intake/exhaust) is 220/220; and maximum lift with 1.7:1 rocker ratio (intake/exhaust) is 500/500. Valve lash is zero/zero and lobe centerline is 115 degrees.
Dave

[Curt S.]

Re: 69 427 rebuild

Don, This is a little tough , not knowing your driving style and performance needs. I firmly believe that a good oem type rebuild will suffice. Possibly a cam upgrade as suggested will work. The turbo 400 is a great auto transmission. I have concern with your 3:08 gears. In my opinion , it will take so long to get the engine to its peak power curve that you may be going dangerously fast just when things are beginning to rock and roll. I believe 3:55 or 3:70 gears might surprise you with your current engine. Also, back in the day, a good distributor advance curve starting at about 2000 with full advance around 3500 woke up alot of sleepy engines. Hopefully, someone still has and uses a Sun distributor machine in your area. They work. Hope this helps. Curt

[Don W.]

Re: 69 427 rebuild

Hi David, Chuck and All,
Yes the rear wheel HP I quoted was peak HP. Any Joe Reno of Reno Racing in Mesa, AZ performed the dyno runs. He also rebuilt the distributor and optimized the set-up on a Sun Distributor Machine.
I'll skip the roller cam set up and continue to look for a good cam.
Any suggestions on the type of head work I should have? I have 454 heads; part number [FONT='Times New Roman','serif']GM8T; J 25 9 (= Oct 25, 1969); 3964290; PASS. [/FONT]
[FONT='Times New Roman','serif']I will not be changing the exhaust system as this is a 2nd flight car and I plan to get it to top flight some day.[/FONT]
[FONT='Times New Roman','serif']Thanks,[/FONT]
[FONT='Times New Roman','serif']Don[/FONT]

[Don W.]

Re: 69 427 rebuild

I searched the archives and here is some information I found...Don

[FONT='Verdana','sans-serif']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.[/FONT]

[FONT='Verdana','sans-serif'][FONT='Verdana','sans-serif']As far as the camshaft goes use the original camshaft that was installed in your engine. You won't find this part number in ANY GM Parts & Accessories Catalog 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.[/FONT]
[FONT='Verdana','sans-serif']The CS1093M is an exact duplicate of the OE cam. It is built to the GM print.[/FONT]
[/FONT]

[Don W.]

Re: 69 427 rebuild

If I google Keith Black 360 pistons and federal mogal 1093M; I don't get any results. Any suggestions?

[Joe L.]

Re: 69 427 rebuild

If I google Keith Black 360 pistons and federal mogal 1093M; I don't get any results. Any suggestions?

Don------


Keith Black KB 360 pistons will produce a compression ratio of about 9.6:1 in your engine. These are what I would consider the ideal pistons for your application.

You could also use KB 176 which would produce a compression ratio of about 10.5:1. I wouldn't use these but you can "roll the dice" and hope you don't end up with detonation problems.

You can easily obtain KB pistons from sources like Summit Racing.

[James G.]

Re: 69 427 rebuild

Don------


Keith Black KB 360 pistons will produce a compression ratio of about 9.6:1 in your engine. These are what I would consider the ideal pistons for your application.

You could also use KB 176 which would produce a compression ratio of about 10.5:1. I wouldn't use these but you can "roll the dice" and hope you don't end up with detonation problems.

You can easily obtain KB pistons from sources like Summit Racing.

Back in 1989, I used the same style KB 360 piston from TRW. It was a 9.0 compression unit.

Then we did a super 3 angle valve job and ported and cc'ed each chamber.

Finally, I left the dated 3:55 positraction, that per tank sticker was a 3:08. Could never figure that out as the casting number and date were correct to the car and it sure looked like it had never been removed.

Final result, a 67 air conditioned 427/390 Powergide car that turned 14.4 @98.15 quarter mile times WITHOUT the AC belt installed.

If your car is original, just clean it up and enjoy it. With these $4.50 gas prices, you won't drive it that much anyway.

Tell Joe Reno I said HI !!