61 Engine Rebuilt. What to do II

[Jack A.]

I posted this question a while back on the Board to look for some suggestions on how to rebuilt my 61 315 HP FI motor. I was looking for suggestions on how to get more HP out of the motor. I got a lot of great replys but ran into a problem. Talking to Jerry and some of the other FI Gurus out there I found I pretty much have to stay with the original specs. Right now I am leaning toward stock 283 bore and Crank with 5 stage porting of my 461 X heads. Any suggestions as to Piston, Rods & Lifters selection? Would there be any advantage to using a 327 Crank with the 097 Cam. Any other thoughts

Thanks,
Jack

[Terry D.]

Re: 61 Engine Rebuilt. What to do II

Jack
What is it you are trying to do with the car? A well tuned 315hp motor will run pretty good. If you want a little more horsepower try building a 302 Z28 motor. But I agree with the FI guys, that FI unit will only handle so much. Another thing to consider is if you do go for a lot more horsepower things like axles, transmissions etc tend to start breaking cause one they are 40+ years old and two were not designed for todays high horse engines. Just my two cents
Terry

[Jack A.]

Re: 61 Engine Rebuilt. What to do II

Hi Terry,

Just basicaly some practical suggestions as to good internal parts, Pistons, Rods, Lifters etc. Brands and sources. Also, am I making a mistake in doing the porting?

Thanks,

Jack

[Duke W.]

Re: 61 Engine Rebuilt. What to do II

Talking to Jerry and some of the other FI Gurus out there I found I pretty much have to stay with the original specs.
Thanks,
Jack

Oh! You need to expand the above statement with some details.

Duke

[Jack H.]

Re: 61 Engine Rebuilt. What to do II

When we go to 'restore' these cars, the temptation to 'soup up' the motor is strong. The logic 'seems' pretty straight forward: since I'm replacing internals why not get more performance?

Well, the engine is basically an air pump. In a factory concours application, you're constrained at both ends (input and output). Judges look for correct intake manifold and factory original carb/air cleaner. So, that plugs the 'input' side of the equation.

Judges also look for correct original exhaust manifolds + exhaust system. So, that pretty much thwarts changing the output side of the system.

That leaves you with engine internal components to massage (gain efficiency). Thinking Zora and the boys were 'dumb' and they designed the engine with LOTS of designed-in inefficiency factors is naive. They DID have access to mainframe computers for modeling, gas was around $0.35/gal back then, there were few emissions restrictions and the car simply had to make it through the warranty period without undue reliability problems.

Bottom line, there are not a lot of areas for SIGNIGICANT improvement... You can easily wind up squeezing on a balloon here making performance tradeoffs. You can get a few more peak horsies out of the engine, but at the expense of low end performance (idle characteristics, low end torque off the line, Etc.).

I'd NOT encourage you to stray very far from the factory original design envelope! It's a time proven design compromise between aggressive wide open throttle response and all around drive ability...

[Duke W.]

Re: 61 Engine Rebuilt. What to do II

Jack - the biggest restriction in vintage engines is cylinder head port flow efficiency due to the constraints of low cost, high volume production. Hand working the ports yields a substantial improvement in flow efficiency, which means the engine will pump significantly more fluid.

Head massaging on any vintage engine will yield 5-10 percent more top end power and 500-1000 more useable revs without any effect on low end torque.

Corvette exhaust systems, including the OE manifolds of the era are relatively non-restrictive. Ultimately, external components such as the inlet and induction systems limit power and revs, but the facts are that significantly more power and revs are available without affecting judging appearance, without affecting low end torque in any meaningful way, and without affecting typical idle characteristics.

There are a number of examples out there that I've discussed extensively on this Board.

Duke

[Jack H.]

Re: 61 Engine Rebuilt. What to do II

Duke, I think we're saying pretty much the same thing, but from different perspectives.

The input/output constraints of a factory concours restoration severely limit what you can do with the power plant compared to what can be done for, say, a vintage race car...

Primarily, performance boost(s) come from addressing the engine efficiency profile. Yes, porting the cylinder heads to achieve better flow can/does help! So, does holding closer tolerance on moving parts, narrowing down the engine's balance profile for reciprocating & rotating parts compared to factory specs and reducing friction where possible (better bearings, roller motor/roller tipped rockers, Etc.).

BUT, we're talking about a few percentage points here/there with these approaches. You're not going to transform a basic 300 HP machine into a screaming 600+ HP pavement pounder just by going the efficiency route.

Few novice owners/drivers will detect/distinguish a power band boost of 10-20 HP. To get a significant blast index bump (smash you back into your seat to the point you really feel the difference), a decent rule of thumb is to make changes that deliver 25-50% power increases.

Yep, a step up from say a 250 HP base car to a mid-range 300 HP car IS noticeable. But, all other things held constant (gear ratio, Etc.), going from 300 to 315 HP just isn't that much of a change to the average Joe...

[Duke W.]

Re: 61 Engine Rebuilt. What to do II

Of course you're not going to get a 600 HP "racing engine", and such an animal would be useless and virtually undriveable on the street.

But few realize the potential of a "massaged" OE engine that maintains OE idle and general driving characteristics, and it doesn't cost much more than an OE rebuild, especially if the owner can do most of the labor intensive work such as the porting, matching, and relieving.

Probably more noticeable than the increase in HP alone is the extended rev range where the engine makes near peak power, which most guys just don't understand until they experience it.

An OE 327/300 makes an honest 225 net HP at 4000-4500 and is wheezing at 5000. Proper preparation can yield close to 300 net HP and extend the useable rev range to 6000+ - more power and revs than an OE L-79 and you would never know by looking at the engine or listening to it idle.

OE mechanical lifter 327s make in the range of 250-270 honest net HP and this can be increased to the range of 325 to 340 with 7200 useable revs.

Similar techniues result in similar improvements to any OE Corvette engine except the post-'74 models where the single catalyst exhaust is a show stopper for any significant increase in power or rev range.

Duke

[Jack A.]

Re: 61 Engine Rebuilt. What to do II

Hi Duke and Jack,

I appreciate what you two are saying very much and your taking your valuable time to do so. In talking to Jerry and others the bind seems to be in the FI unit itself. The actual problem is Vacume. The original internal configuration creates the desired amout of vacume to make the car not only perform at high revs but for practical driving needs at low revs as well. If you send your unit off to any of these guys to rebuild they will car test it on a car they have that is basically stock configuration. Your service warrenty will only be in force on a similar motor. Your option to that of course is to take your car a great distance to have it set up. Even then the Vacume your motor produces is critical. Despite my wanting the car to perhaps pass Judgeing someday it will be a driver and dependability is very important. This is a Novices understanding of the problem.

Thanks again,
Jack

[Bill M.]

Re: 61 Engine Rebuilt. What to do II

Probably more noticeable than the increase in HP alone is the extended rev range where the engine makes near peak power, which most guys just don't understand until they experience it.

Duke

I experienced the opposite effect when I bought a '92 LT1. It may make more SAE net horsepower than a '70 LT-1 (Chevy data), but the driving pleasure of a free-revving small block Chevy is not there. 5700 redline is a lot less fun than 6500.

[Joe M.]

Re: 61 Engine Rebuilt. What to do II

Duke,

I have a paper article from an old auto magazine on head porting that includes templates. Would you be willing to take a look at it to see if it is follows the recomendation for appropriate pocket porting?

Joe

[John M.]

Re: 61 Engine Rebuilt. What to do II

Jack,
For what it's worth I can tell you that massaging the heads, port matching, pocket porting, cam modifications and precision balancing can make a big seat of the pants difference without changing displacement, idle characteristics, etc . I've done all this with a 67 327-300 and although I won't have the dyno proof until next spring I was pleasantly surprised at the get up and go of this engine. And I had the pleasure of doing most of the work myself. Duke Williams did the engineering and I was the "hoss".
Good luck with your project.
John McRae 30025

[Tim S.]

Re: 61 Engine Rebuilt. What to do II

Jack,
It is my feeling, a little is a lot regarding port work on cylinder heads with a "stock" engine. In something smaller such as a 283 or a 327, the port velocity will be very important to retain good torque. IMO light clean up of casting flaws, massaging the bowl area of the port, and a VERY good valve job will yield the best results without making negative changes to drivabilty. It is easy to go too far. It was my understanding (someone chime in) the F.I. unit flows approx 650cfm. The F.I. unit may be your limiting factor in what route you elect to take. Care must be taken to maintain a balance in intake (F.I. unit), head prep or modifications, camshaft selection and compression as well as exhaust efficiency. I can only assume that is why Jack suggested not straying too far form the stock package.There was discussion in a previous thread about camshaft selection. At that time the LT1 cam seemed to have a good following due to torque production, RPM range, and vacuum characteristics. Has that cam been ruled out?
Tim

[Joe C.]

Re: 61 Engine Rebuilt. What to do II

Jack,

I agree that porting the heads will increase torque across the entire rev range, and give you an additional few hundred USABLE revs. If you do it yourself, and do it correctly, and then have the extremely CRITICAL valve job done by a pro, with 3, 4, or 5 angles, you can save yourself anywhere from 700 to 1500 bucks! Remember, that you must first have the heads flow tested before you touch them. Then, have them flow tested again after completion, to verify the quality of the porting job. The above applies to any engine, in any configuration. 30 degree intake valve seats provide better flow at low lift (to match your 097 cam), if done properly. YOU MUST build the engine with the properly matched compression ratio for its camshaft. Anything less, and done without understanding of dynamic compression ratio, is foolhardy. It will produce a boat anchor, easily beaten by your grandmother's Nash Rambler.

You are restricted with your 283 block. I do not believe that stroking the 283 is a viable option. Also, from what I understand, some desirable camshafts such as the 30-30, LT1, and L82 are not a good match for 283 cubes.......although the 30-30 was used in the 4x3 302 Z28.

From this point onward, your main consideration is "bang for the buck". Are you willing to spend an additional 2000-3000 to equip your engine with all the tricks, to minimize friction, windage, and inlet/exhaust manifold flow restriction....................which, when all combined, might provide an additional 40-50 horsepower? You can have your exhaust manifolds "extrude honed", and your intake plenum ported and the internals reworked to increase its original 650 cfm capacity somewhat. You can use low tension rings for a few horses, but at the expense of reliability and oil consumption. You can have your bores honed using deck plates, at additional expense.......good for a few horses. As Duke likes to say here :" it's all in the details". There is a certain amount of satisfaction to be gained in having a so called "sleeper" motor....................a more potent-than-stock motor residing in a stock appearing exterior, but this is obtained at a relatively high cost.

Now, if you start with a 400 block, and bore it over to 406, install a modern, mild hydraulic roller, a good set of AFR aluminum heads, with relatively cheap, hypereutectic pistons, with low compression, you can have your 500 plus horsepower along with a tire-burning flat torque curve.

Your choice! And, as Jack alluded to, if you start "exploring" the middle-ground, you are only looking for trouble.

[Duke W.]

Re: 61 Engine Rebuilt. What to do II

Duke,

I have a paper article from an old auto magazine on head porting that includes templates. Would you be willing to take a look at it to see if it is follows the recomendation for appropriate pocket porting?

Joe

If you want to send it to me I will look at it. The usual sources I recommend are "How to Hot Rot SB Chevys", the Chevrolet Power Manual, and David Vizard's books. These have been in publication for up to over 30 years, so there is nothing new here - just tried and true methods.

"Pocket porting" just involves work on the first inch or so above the valve and a little work on the on the head-manifold interface (both sides). The exhaust manifolds do not need to be Extrude Honed - just matched at the head-manifold interface.

This work doesn't increase peak torque significantly, but it moves the torque peak up a few hundred revs and keeps it from falling off rapidly at high revs, which is what gives the signficant boost in top end power and useable rev range.

I recommend the LT-1 cam for 3.25" and greater stroke engines. It has about the same effective overlap as the Duntov cam, so it produces about the same manifold vacuum at idle.

Modest cam and stroke changes usually don't require any major carburetor retuning - just conducting the normal idle speed/mixture procedure, which is essentially the same on both carburators and FI.

Dyno testing with a wideband O2 sensor might indicate a slight jet change to fully optimize the cruise and WOT A/F ratio. With FI this can be done on the spot with changes to the power and economy stops.

Assuming the owner does his own disassembly/assembly and the required port/manifold grinding, the cost of a precision/massaged engine restoration is not much more than a "stock" rebuild, but it does take much more hobby time.

There is no need to flow test the OE heads. Their flow characteristics are well known. I do recommend flow testing after the work to ensure that the work was done correctly, and in cases where I've developed specific valve timing, a flow test was necessary to properly tune the valve timing to the flow characteristics.

Duke