How to make it drivable?

[Nick H.]

Hi Nick....that's awesome that you are keeping the car in the family. I suspect that your Dad wished it that way.

I'd love to see a photo of the car.

Cheers,

Larry

 

Here's a couple pics and a video:

 

 

 

 

Pic of Dad with the engine back in '96 when he started the tear-down:

 

 

 

And here's a link to the YouTube Video of me driving it out of the garage after doing some work in January 2010, getting the car ready to be driven to Dad's funeral.

 

[Nick H.]

Nick - the drawbacks to iron heads is the weight and detonation. If you truly have 12.5 pistons, not sure you can throw on the iron heads and not ping. You will have to do the math. Aluminum heads will allow you almost a full point higher compression, without pinging - so you would be able to keep your bottom end.

 

Thanks for the information, I will continue looking for a set of aluminum heads then. I didn't know the head composition could cause pinging. . . I'm still rather new to all of this, I've only helped rebuild engines before, when it comes to choosing parts, I've always had to ask for help.

 

Should I go with a hydraulic roller cam instead of the mechanical that's in it? Maybe something a little more mild?

 

Anyone know where I can find a decent deal on a set of long-tube headers? Hopefully something ceramic coated or stainless, as the mild steel headers that went on when the engine was installed have rusted through.

[wallaby]

Ok, I have to chime in here. My dad had a Corvette with an L-88 in it...factory 427 with aluminum open-chambered heads and 12.5:1 compression. We went through the same process when they took the lead out of gasoline and the airport stopped selling us fuel. LOL

 

The problem is that the high compression creates a lot of pressure in the cylinders and the gasoline becomes very volatile. Low octane fuels ignite easier than high octane fuels, so high octane levels are required to keep the fuel from igniting before the spark is delivered. This is called pre-ignition, or ping, or detonation. It is destructive for the engine to run it under this condition. During the compression stroke, a lot of heat is generated just compressing the mixture and it can ignite on its own...aluminum heads are better at transferring heat to the cooling system, so they help to keep the combustion temps down and reduce the pre-ignition effect.

 

Something to consider is the cylinder pressures in your engine. The compression ratio has something to do with this, and so does engine load and throttle opening. You are trying to reduce the cylinder pressures so you can run a lesser octane fuel. Going to an open-chamber head will drop the compression ratio 1 or 2 points, and the aluminum heads will reduce the temperatures a bit. A thicker head gasket won't change the compression hardly at all, and may make matters worse by removing "quench" which is a complicated dynamic that helps deter pre-ignition.

 

Now the problem with your idea of using a milder cam is that it will boost low-speed performance and economy by building higher cylinder pressures at low speed. This is a recipe for pre-ignition. The same goes for the overdrive idea; it slows down the engine speed and you compensate with more throttle opening. All this is like lugging the engine under load all the time, and high compression engines don't like it.

 

If it were me, I'd consider new pistons to get it right, but if you are set on what you have, I'd go with an open-chamber aluminum head and cross my fingers. You want to keep the engine running as freely as possible without putting load on it...the high stall converter, low rear end gears and non-overdrive trans are good here. So is the radical camshaft, as it bleeds off cylinder pressures with some valve overlap. Put a 160 degree thermostat in it and make sure the cooling system is in good shape. None of this is good for fuel mileage, but it might get you back to buying normal pump gas. This is all considering normal street driving...heavy load or full throttle use may still require the pricey race fuel.

Good luck with this.

[MCfan]

Thanks for your detailed post, Mark. It's great to be reminded of the major causes and contributors of detonation in the higher compression engines. I've been fighting this problem ever since I bought my 402 4-speed Monte over three years ago and it seems I haven't made much progress at all.

 

I am loathe to mess with the bottom end of this rebuilt engine so that means living with the .060 over TRW domed pistons that are spec'd at 11.9:1 CR. Of course, the .010" decked block and milled heads also add a bit. Davey has recommeded replacing the whole top end with aluminum open chamber 122 cc heads, a Straub cam, new intake manifold and larger carb so that is the direction I am leaning.

 

In the meantime, your post triggered a thought - relative to keeping the engine running cooler. Last winter I replaced the fixed 7-blade fan with a 772 clutch fan (reasoning that it might improve performance and/or mileage). That may have actually exacerbated my exposure to detonation because the engine does not ping under load until it warms up. I also need to confirm my memory that I have a 160 degree thermostat installed. The original heavy duty radiator was leaking when I bought the car so I replaced it right away. I also need to confrim that it is up spec. Then I added A/C, although I seldom use it because I prefer windows-down cruising. Any or all of these things could be contributors or opportunities for improvement.

 

My primary focus has been on timing and I've spent a lot of time and energy studying and trying various settings and component combinations including HEI and variable vacuum cans with some improvement but no breakthroughs.

 

I can see now that I need to try getting and keeping the engine running cooler so that will be my immediate focus when I return to Florida in November. Thanks again for your helpful and thought-provoking post!

[wallaby]

I mainly focused on the mechanical aspects, but tuning can have a great deal to do with it also. The HEI has a poor advance curve if it's stock, and the vacuum can will pull in more advance than you need. You should limit your vacuum can so it pulls a max of 10 degrees, and run it from a manifold vacuum source. (Not ported. Holley often has a fitting labeled "dist" and it's a ported supply...use the other fitting that comes out of the baseplate, or some other manifold fitting).

I set my timing with vacuum unhooked and revved the engine to 3000+ rpm and at that speed locked the distributor down at 35 degrees. Reconnect the vacuum supply to the dist, and set your idle mixture. All done.

 

When your engine is cold it is less likely to ping because it's cooler in the chambers, or because it's running rich with some choke still on...or both. Having a richer mixture will help with the pinging after it's fully warm.

 

When you do a thermostat, use a full-flow type. Sometimes they are called a reverse poppet type. Looks like this: