61 engine rebuild. What to do?

[Jack A.]

Hello to everone out there. I'm back on the Forum after a couple of years absence. I've missed you all. I am starting to rebuild my 61, 315 H.P Fuelie. The last time I was on the forum when I asked about advice on rebuilding my motor I was told a couple of things I want to run by you again. Back then was advised to keep the compression at 10 to 1 because of the unleaded fuel (knocking).Now I am being advised by my engine rebuilder to keep it at 9 to 1 because of the newest fuel additives in the fuel. Also he advised the 327 crank instead of the stock. What do you think? I was trying to get a little more power out of it without going crazy. I was going to also use aDuntov cam, head work, 30 over, hardened valve seats, solid lifters.

Regards,

Jack

[Jim L.]

Re: 61 engine rebuild. What to do?

I am starting to rebuild my 61, 315 H.P Fuelie. Back then was advised to keep the compression at 10 to 1 because of the unleaded fuel (knocking).Now I am being advised by my engine rebuilder to keep it at 9 to 1 because of the newest fuel additives in the fuel.

My take is that your engine builder probably got to the right answer by the wrong line of reasoning. Someone with better knowledge of chemistry than I have can chime in, but I'm not aware of any additives that degrade the octane rating of modern motor fuels.

My '63 runs a 327 that has 9.2:1 compression. 99% of the time it's fine, but on a hot day, under load it will ping audibly; I use 91 octane fuel in it.

If I had it to do over, I might drop the compression slightly.

Also he advised the 327 crank instead of the stock.

That'll give you a 307 plus whatever the overbore adds. I believe you'll like it. It'll have a lot more torque down low than a 283 would have and it'll be more satisfying away from a stop.

What do you think? I was trying to get a little more power out of it without going crazy. I was going to also use aDuntov cam, head work, 30 over, hardened valve seats, solid lifters.

I'd skip the hardened valve seats. There is great risk that you'll ruin a perfectly good set of heads and that you'd do so for a benefit that is minimal, if it exists at all.

That's experience talking..... I've got a dandy set of 461 heads on my shelf that I can't use because the machine work to install hardened valve seats invaded the water jacket.

Conversely, a few years ago my son and I drove our '54 from one coast to the other. The head in its engine does NOT have hardened seats and none of the valve lash settings changed in 2700 miles of 3100 RPM driving; had there been an issue with valve seat recession, they would have.

Jim

[Jack A.]

Re: 61 engine rebuild. What to do?

Hi Jim,

Thanks for the great advice. Especailly on the hardened valve seats. Do you think the 3 angle porting is worthwhile? Also do you have a recommendation for the piston type and manufacturer? Another quandry I have is to whether I should restore it with the original Fuel Injection. It is in a box now. I know there were a lot of problems with them years ago. I'm not sure about now. I know I had a unit back in the late 60's I could not get right in our humid Florida climate. I want to drive this car.

Thanks,

Jack

[Jim L.]

Re: 61 engine rebuild. What to do?

Thanks for the great advice. Especailly on the hardened valve seats.

Jack,

You are certainly welcome. It took me a long time to come around to believing that the best strategy was to NOT install the hardened seats. What got my attention initially was that I began to hear about heads being ruined by the machining process, possibly due to thin castings. Then, came my experience with the '54. And finally, I lost a set of my own heads. The message finally became too loud to ignore.

Do you think the 3 angle porting is worthwhile?

I do and I think you'll find that any good machine shop these days can do a 3 angle valve job.

Also do you have a recommendation for the piston type and manufacturer?

As to type, unless you plan to go racing, I'd suggest a cast hypereutectic. These are strong, generally inexpensive, and can be fitted to the cylinder bore with very tight tolerances.

KB Hypereutectic pistons are very good yet inexpensive, but I don't see a catalog listing for 307 pistons. They do have 283 pistons, however.

One note about KBs, if you decide to use them to build a 283.... the top ring is located very high on the piston. This location requires that the ring gap be opened up substantially from what would be considered "normal". Your engine builder would need to file-fit a set of rings to get the correct gap.

If you don't plan regular, sustained, severe use for your engine, there are probably no bad piston choices from the manufacturers who offer hypereutectics.

Another quandry I have is to whether I should restore it with the original Fuel Injection. It is in a box now. I know there were a lot of problems with them years ago. I'm not sure about now. I know I had a unit back in the late 60's I could not get right in our humid Florida climate. I want to drive this car.

Fuel Injection is near and dear to my heart, so I can't give you unbiased advice here. I've been repairing FI units and driving fuelies for 30 years. I think they are the neatest gadgets ever put on a Corvette.

There are some design issues which never got completely sorted out before production ceased:

1. Sensitivity to heat
2. Poor cold enrichment mechanisms (chokes, in carburetor parlance)
3. Tendency to siphon fuel into the engine which can result in a bent connecting rod, or worse.
4. Unreliable engine starting mechanisms on '58 - '63 units.

Fortunately, there are ways to compensate for these problems and the end result is that an FI unit can be made to be as reliable as an anvil.

So, should you reinstall the FI unit? Well, if you are willing to thoroughly learn how to deal with some of the endearing quirks the units have and not treat it like an "appliance"..... like you would, say, a modern Honda... then, yes, I definitely think you should install the unit and then drive the wheels off your car.

Jim

[Steven B.]

Re: 61 engine rebuild. What to do?

Jack, I have a 283 and a 350 done in the past years that I took the same approach to. Balance, blueprint, .030 over, angle valve job, KB Hypereutetic pistons, stock (097) and mild (roller hydraulic) cams, advanced distributor, rejetted and metering rods, stainless valves, etc. The 283 is 100% stock on the outside but has 301 HP and 303 torque from 292 C.I. and runs both smooth and fast.

Long story short, do the mods. as the engine looks stock, if that is what you want, and the performance increases without reliability suffering. The guy I would talk to is Garry Grimes, Twister engines and Grimes Machine, Alpharetta, GA. He is a Corvette and Chevy guy who builds stock and racing engines and is logical when doing street engines that are reliable. Also, he dynos after built to extract extra power.

I would definately put the FI on!

[Steven B.]

Re: 61 engine rebuild. What to do?

I forgot; I have 9:1 compression on the rebuilds.

[Duke W.]

Re: 61 engine rebuild. What to do?

327 crank, LT-1 cam, Crower or the new Eagle small bearing cap screw rods (upgraded rods a must) pocket port/port match the heads with multiangle valve work, no hardened seat inserts, stick with the OE valve sizes - all OE equivalent replacement parts other than the rods.

Manage the compression ratio to a 10.5 not-to-exceed target, which can be done with the OE replacement forged pistons, proper head gasket selection and final chamber volume.

Do some research in the archives starting with "327 LT-1". Follow the advice and you will end up with essentially a slightly smaller bore version.

Duke

[Jim L.]

Re: 61 engine rebuild. What to do?

Jack,

Out of curiosity, I did some searching for 307 pistons and, to my surprise, there don't seem to be a lot of choices.

I checked Ross, Wiseco, SRP/JE, Federal Mogul, Mahle, and maybe one or two others. Of these, only Federal Mogul currently lists a 307 piston and it's a casting. JE can, of course, make custom forged pistons, as could Ross or Wiseco, but you would probably be looking at $600 for a set.

My search wasn't exhaustive, of course, but it seems to me that building a 283 might be the better decision.

Jim

[Jack A.]

Re: 61 engine rebuild. What to do?

Hi Steve, Duke, and Jim

Thanks guys. Sorry I did not thank you earlier. I just thought Jim had contacted me. I'm still getting used to the new Tech Discussion format. I like it though. It all sounds great. The only thing is Duke I did have the Lt 1 cam as a desireable alternative to the Duntov and the 12.5 to 1 in the compression ratio but I have been advised by several of the guys to stay around 9 to 1 to stop the knocking. The consesus a year or so ago through the board was 12.5 to 1 but lately the advice seems to be the lower ratio. Do you have experience with this ratio?

Thanks guys,

Jack

[Duke W.]

Re: 61 engine rebuild. What to do?

Who said anything about 12.5:1 compression???? I said 10.5!

There are at least two "327 LT-1" engines running around with true measured compression ratios of 10.5:1 with the OE pistons and proper head gasket selection. They operate detonation free on 92 octane unleaded premium. Due to the smaller bore a 283 might handle a little more, but why mess with success.

The later the inlet valve closes the higher the maximum tolerable compression ratio for a given octane fuel. I recommend limiting Duntov and L-79 cammed engines to 10.25, (and 9.75:1 with the base engine cam), but with its later closing inlet valve the LT-1 cam can tolerate 10.5, and keep in mind that the true as-built CR of production engines was typically one-quarter to one-half point lower than the advertised CR, which is why most remaining OE-built Corvette engines typically don't have detonation problems with today's gasoline.

By the time you do chamber relieving which adds a cc or so to chamber volume, it sometimes takes a relatively thin head gasket to achieve the target maximum with the OE replacement pistons.

A 9:1 CR with a SHP cam will result in poor torque bandwidth and poor fuel economy, but it will probably run on regular unleaded if that's what you want.

Keep in mind that you have to add 4-5 points to current PON ratings to get the approximate RON, so current 91-93 PON premium is equivalent to 95-98 RON, and typical sixties premiums were 99 RON. (Europe still uses RON and their best gasoline is 98 RON, which is equivalent to our 93 PON.)

Lowering CR is a myth that just won't go away based on the early 91 RON unleaded regular, which has about the same detonation resistance as current 87 PON regular. High octane unleaded gasoline has been available in most markets for over 20 years.

The '71-'72 LT-1 engine had a nominal advertised CR of 9:1, and it was designed to operate on that seventies vintage low octane unleaded. Is that what you want?

Duke

[Tom B.]

Re: 61 engine rebuild. What to do?

The 307 was never offered in anything other than a 2bbl grandma engine and has never been a popular engine to build for performance use. Performance pistons for this combo off the shelf are probably non-existant. If you are willing to stay with cast flat tops you should have no problem hitting your CR goal of 9.1. Decking the block and/or milling the heads and intake to set your final CR will more than likely be required though. I'd stick with the 3" stroke and spin the wee out of it with the Eagle rods and some forged flat tops in .060 over for that 292.

I also recomment polishing the chambers and piston tops (valve relief machined edges) to remove any sharp edges that can glow and cause pre ignition. A thermal berrier coating on the piston top and even in the chamber will also help reduce the possibility of pinging. Some forged pistons are coated out of the box and may also have a dry lube or anti friction coating on the skirts.

Tom

[Duke W.]

Re: 61 engine rebuild. What to do?

"Custom pistons" are not a big deal. Any of the piston houses can machine what you need from standard forged blanks. In the case of a 283 with a 327 crank what you need is essentially the 327 SHP piston in a slightly smaller diameter depending on how much you bore.

Cost is probably no more than a hundred bucks apiece, but we're talking about a 50 thousand dollar car. Even going all out for a bullet proof 7000 rev 307+ will cost a fraction of what a similar vintage Porsche engine costs to rebuild.

And other than the pistons and rods, sticking with OE equivalent parts will save a lot of money on the overall cost - like a buck apiece for Sealed Power VS677 valve springs that are the same as the '67-up 3911068 springs that I recommend for all rebuilds.

The block might need some relieving with a 327 crank.

There is a certain guy who frequents this Board who has an OE appearing "cheater 283" - an even bigger cheater than what we're discussing here - big stroker - custom pistons - custom designed camshaft - the works. It idles just like an OE base cam engine, but makes about the same top end power as a 315FI, but a thousand revs lower with a lot more torque, especially down low by design, because it's a Powerglide! We have no doubt it will pass a PV as long as he only uses about 3/4 throttle for the high rev acceleration part of the test.

Maybe he will contact you privately with some advice.

Duke

[Jack A.]

Re: 61 engine rebuild. What to do?

Duke and Tom,

You've given me a lot to think about. I will get with my Motor guy and run this by him. He is a Small Block Chevy nut. Probably knows exactly where you are coming from on all this.

Thanks again

Jack

[Jack A.]

Re: 61 engine rebuild. What to do?

Hi Guys,
Thanks again for all the great advice. Just one thing is a little confusing to me and I am undoubtedly showing my ignorance here. But how is it when I'm putting all these High Performance upgrades in this rebuild I am coming up with less HP than the claimed original 315 HP for my motor? Was that a false HP rating? Why not go back to original specs?

Regards,

Jack

[Duke W.]

Re: 61 engine rebuild. What to do?

The OE 315 HP was "SAE gross" and even this was probably overstated by a good ten percent. The numbers I quote are "SAE net" at the crankshaft (like modern engines are rated), which are derived from engine simulation software and backed up with chassis dyno testing using SAE net air density correction and .85 driveline tire/efficiency.

Whenever discussing "horsepower" the full context must be specified or the discussion/data is worthless, and, unfortunately this applies to most such discussions.

Based on simuations and test data for various SB configurations, I would estimate the SAE net horsepower of a healthy and perfectly tuned 283/315 at something close to 240, and this would yield a little over 200 on a chassis dyno with SAE air density correction as long as sufficient external cooling fans are configured to keep the OE fan clutch from "locking", which will cost about 10-15 HP if it does.

A really well done "327 LT-1" with great attention to detail - particularly cylinder head prep, valve seating, and OE valve spring setup will make 275 to 290 SAE corrected RWHP, which is in the range of 325-340 SAE net HP at the crankshaft with very little rolloff to the 7200 valve train limiting speed. Replace the OE manifold and carburetor with a FI system and the power will probably increase - at some expense to low end torque - due to the "single plane" architecture of the FI manifold.

So, if you do what we're discussing correctly with proper attention to detail, you could be looking at a 40-45 percent improvement in top end power. The larger displacement will more than make up for any lost low end torque relative to the OE 283/315 configuration, and the idle characteristics will be indistinguishable from the OE configuration as long as the exhaust system is OE equivalent.

Duke