1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

[Douglas P.]

Hello All,

I am looking for any and all advice with respect to choosing the appropriate engine components for the rebuild of my '69 L71 427/435. Specifically I would like to receive suggestions re:which components such as pistons, cam, lifters, valves, springs, etc.. to use in the rebuild. Also, any other advise would be appreciated re:setup for street use using unleaded 93 octane pump gas. My objective in the rebuild is to restore an engine that has not been run in 34 years, improve it's reliability, and maximize performance while maintaining it's originality as much as possible.

Thanks in advance,

Doug

[Joe R.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Doug,

You can get a Speed Pro (Federal Mogul) cam and lifters kit from NAPA. I think the part number is CS-165R, but don't quote me on that. I would recommend getting your heads ported and flow tested. The porting is good for a 10 % increase in HP and torque, plus a few hundred extra revs. I think the 69 may have used the first design valve springs, which are very prone to breakage. Did it detonate before the rebuild? If not, you can use the same compression ratio you have now. Check out the Duke Williams / John McRae Restorer article on managing your compression ratio.

Joe

[Duke W.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

With a couple of exceptions use all OE equivalent parts that you can buy at NAPA and other sources. Use the NAPA online catalog to get all the part numbers.

Rather than spending money qualifying the original rods, it may be cheaper to buy a set of aftermarket rods, like the Eagle SIR. You need to do some research in this area to find an economical aftermarket rod that weighs about the same as the OE rod.

Your engine, hopefully, has the second design dual valve spring. These don't seem to be available from any sources, so it might be okay use the originals. The big block community has to get together to figure out what to do about this situation. Pushrods, rockers, and balls can likely be reused if they pass visual inspection for wear or galling.

If you want "more power" massage the heads and install 1.84" exhaust valves. This will yield 7-10 percent more top end power and at least 500 more useable revs without affecting low end torque or normal driving behavior including idle behavior.

Target a true not to exceed CR of 10.3:1, which should be achievable with the OE pistons, a little chamber grinding ,and a suitable thickness head gasket. See the Fall 2009 Corvette Restorer for all the details on how to manage your CR.

Also see the Fall 2010 issue for information on head massaging. The article discussed this in the context of a SB, but the basics apply to big blocks, too.

Be wary of machine shops. Do your homework and have a definitive plan. Know exactly what you want done, and only have the machine shop perform those operations that you order. Nothing more, nothing less. It's best if you have the skills to do your own forensic teardown and assembly. In this case you can buy all the parts yourself and just have the machine shop do necessary machining operations. Boring and honing the cylinders and precilsion balancing is likely all that's needed. They will need the pistons for this operation to hone each cylinder to final dimension for a specific piston. They'll also need a ring set for precision balancing.

Many owners have deferred decisions to machine shops and so-called "engine builders" and have ended up with an expensive kluge full of aftermarket hot rod parts, a too-high overlap cam and two low compression, and ended up with an engine that has poor low end torque, poor fuel economy, and likely less top end power than the original Tonawanda build.

The L-72 is a nice piece of engine system engineering that has excellent torque bandwidth for a SHP type engine. The only issues are the rods and the valve springs, and the only other parts you'll likely need are pistons, rings, bearings and exhaust valves, camshaft, lifters, and a timing set. If the oil pump passes a simple visual inspection there is no reason not to reuse it. Even the camshaft and lifters may be reuseable, so keep track of the original lifter location. If the lifters and lobes pass inspection, they can be reused.

One question I have: Why do you think the engine needs to be rebuilt?

Duke

P. S. I see that you just joined NCRS this year. Send me an email and I'll send you pdfs of the two articles I mentioned. Also, look around and find copies of The Chevrolet Power Manual from the seventies and "How to Hot Rod Big Block Chevys from Peterson Publishing.

[Patrick H.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

One question I have: Why do you think the engine needs to be rebuilt?

Duke

Duke,

the rust in the cylinders was one of many reasons. The frame on the car is rusted out, and even the sides of the block are rusted.
I had the same question at first regarding a rebuild, but I've rarely seen a block/intake/carb combination with as much corrosion as this one did when we removed it from the car.

I'll let Doug continue to answer. It should be a nice car when he is done with it.
I told him to go ahead an post his questions here for some additional viewpoints from the rest of you.

Patrick

[Joe R.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Doug,

Don't let the machine shop deck the block on the right side. That will wipe out your broach marks & numbers.

Joe

[Ken A.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Don't forget to pitch the heavy 7/16" pushrods and get new guideplates and 3/8" STEEL pushrods from an aftermarket cam company such as Lunati. No matter what the others say I'd spring for a set of ROLLER tip rockers,
also. They good for 7-10 extra HP. The 3/8 pushrods really take a load off the valve train-plus I've never seen straight pushrods come from the General. Same with the rockers- you might go thru 40 or 50 before you found 16 that were in spec.

[Joe L.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Don't forget to pitch the heavy 7/16" pushrods and get new guideplates and 3/8" STEEL pushrods from an aftermarket cam company such as Lunati. No matter what the others say I'd spring for a set of ROLLER tip rockers,
also. They good for 7-10 extra HP. The 3/8 pushrods really take a load off the valve train-plus I've never seen straight pushrods come from the General. Same with the rockers- you might go thru 40 or 50 before you found 16 that were in spec.

Ken-----

L-71 never originally used 7/16" pushrods. The only engines that originally used 7/16" pushrods were 1969 L-88 and ZL-1.

[Richard M.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

How many miles are on the engine? How will the car be driven? If the engine will not be subjected to multiple high rpm runs, I would keep the stock rods but rebuild with ARP bolts, on the heads rebuild with hardened valve seats, 1.88 exhaust valves, and a multi-angle valve job also some pocket porting but nothing
radical. Most important find the machine shop with the best reputation in your area.


Best Wishes, Richard

PS. If avaliable have it broken-in on an engine dyno.

[Timothy B.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Duke,

the rust in the cylinders was one of many reasons. The frame on the car is rusted out, and even the sides of the block are rusted.
I had the same question at first regarding a rebuild, but I've rarely seen a block/intake/carb combination with as much corrosion as this one did when we removed it from the car.

I'll let Doug continue to answer. It should be a nice car when he is done with it.
I told him to go ahead an post his questions here for some additional viewpoints from the rest of you.

Patrick

Patrick,

Can those cylinders be cleaned and lightly honed and reuse the original bore and pistons.. And with low miles what's wrong with the bearings, camshaft etc..

[Joe R.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Richard,

You don't need hardened seats unless you plan to tow a boat over the Rockies.

Joe

[Douglas P.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Joe,

I will defenitly replace the valve springs in the rebuild, re-using the original springs is a risk I'm not willing to take.

My engine has never been run on modern gas, as it has been out of service since 1978. So I am unsure of it's performance with currently available fuel. Compression ratio for the L71 was originally spec'ed at 11:1, which is higher than what most are recommending for use with modern fuel to avoid detonation. This is where I'm looking for advise on specific pistons brand/part # to achieve the goal of performance w/today's fuel w/o additives.

Thanks for your input.

Doug

[Douglas P.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Patrick,

Can those cylinders be cleaned and lightly honed and reuse the original bore and pistons.. And with low miles what's wrong with the bearings, camshaft etc..

Tim,

Based on the condition that the block is in, it is highly unlikely that a cleaning and light hone will allow use of the original bores and pistons. Yes, the car only has ~43K miles, but it has been sitting idle for a little more than 34 years & this hasn't helped the situation. While I have things apart, I want to do what is necessary to ensure a smooth running engine that can be enjoyed for many years to come.

Doug

[Douglas P.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

How many miles are on the engine? How will the car be driven? If the engine will not be subjected to multiple high rpm runs, I would keep the stock rods but rebuild with ARP bolts, on the heads rebuild with hardened valve seats, 1.88 exhaust valves, and a multi-angle valve job also some pocket porting but nothing radical. Most important find the machine shop with the best reputation in your area.

Best Wishes, Richard

PS. If avaliable have it broken-in on an engine dyno.

Richard,

The car has ~43K miles on the ODO. This car will not be raced, but certainly will be enjoyed on the street. Of course I may want to prove it's performance on the 1/4 mile at some point, but this would not be a typical application. Overall, the engine rebuild objective is to maintain originality while improving reliability (smooth operation/balanced) and maximizing performance.

I am working with a highly repuatable machine shop in my area. They understand the significance of Corvette engines and will not do anything that I do not specifically request or authorize. I posted my question here because the shop is looking to me to make the decisions about what parts to use in the rebuild. They have suggested some of the basic components, but looking to me to provide direction on some of the majors (piston, cam, etc..).

The stock rods have already been reassembled with ARP bolts and have been balanced. Hardened valve seats are on the list, but head work and valves are still to be discussed.

Engine dyno is planned.

Thanks,

Doug

[Douglas P.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Doug,

Don't let the machine shop deck the block on the right side. That will wipe out your broach marks & numbers.

Joe

Joe,

The decks will not be surfaced. It is however necessary to have the block shot tumbled to remove the rust as Patrick mentioned is present in an earlier reply. Steel deck covers will be fabricated and bolted on to protect the decks/stamp pad from damage during the tumbling process. The deck surfaces checked out OK; there is no concern about deck flatness, so no machining is necessary.

Doug

[Patrick H.]

Re: 1969 L71 427/435 Engine Rebuild; Which Pistons, Cam, Etc.. To Use?

Joe,

I will defenitly replace the valve springs in the rebuild, re-using the original springs is a risk I'm not willing to take.

My engine has never been run on modern gas, as it has been out of service since 1978. So I am unsure of it's performance with currently available fuel. Compression ratio for the L71 was originally spec'ed at 11:1, which is higher than what most are recommending for use with modern fuel to avoid detonation. This is where I'm looking for advise on specific pistons brand/part # to achieve the goal of performance w/today's fuel w/o additives.

Thanks for your input.

Doug

Doug,

Read the papers Duke sent.
What the compression spec was and what the actual compression ratio were did not match. You need to measure the TRUE compression ratio, which will probably end up at 10.3 or so. Don't be scared of that with 93 octane fuel.

Also, as mentioned elsewhere, skip the hardened valve seats.

Patrick