65 FI Performance Issues

[Duke W.]

Re: 65 FI Performance Issues

Can you tell me what head gasket was used that resulted in the 10.2 CR? I can slide a .040 feeler guage between the block and head and I have read that a .020" shim gasket was originally used in these engines. Of course, I have also read (on these forums) that TWO .020" shim gaskets were used!

Mike

Chances are your engine was rebuilt with "low compression" pistons. Such pistons and a thick gasket will yield only about 9:1 compression, and low compression with the 30-30 cam is the worst possible configuration you can have for a road engine. It will be a dog down low.

If you can dig up a flexible tube borescope, you can look inside the cylinder to see if you have the OE type domed pistons or some aftermarket replacement with no domes.

I think the double gasketing ended in 1963. The 30-30 cam considerably reduced dynamic compression due to the much later closing inlet valve and allowed greater static compression. The OE gasket of that era was .018", but at some point it may have gone to something in the range of .022-.026".

Duke

[Mike R.]

Re: 65 FI Performance Issues

Thanks Duke, I have 145psi on my compression guage against a book number or 150psi and I am at 2100' MSL. Does this mean that I probably have the correct pistons? I will look to borrow a borescope but it is unlikely.

Mike

Chances are your engine was rebuilt with "low compression" pistons. Such pistons and a thick gasket will yield only about 9:1 compression, and low compression with the 30-30 cam is the worst possible configuration you can have for a road engine. It will be a dog down low.

If you can dig up a flexible tube borescope, you can look inside the cylinder to see if you have the OE type domed pistons or some aftermarket replacement with no domes.

I think the double gasketing ended in 1963. The 30-30 cam considerably reduced dynamic compression due to the much later closing inlet valve and allowed greater static compression. The OE gasket of that era was .018", but at some point it may have gone to something in the range of .022-.026".

Duke

[Duke W.]

Re: 65 FI Performance Issues

Cranking compression pressures can vary widely among engines and gages and are not a reliable way to estimate CR. As an engine health test, as long as all the readings are within about 20 psi, the engine is okay to run, and the narrower the spread, the better the engine's health.

If you could get some readings from other engines known to have the OE pistons and 30-30 cam, you might get a little more insight.


Duke

[George J.]

Re: 65 FI Performance Issues

Duke,
this was with the stock exhaust manifolds. There was supposedly some head work done on the heads, but I also have no flow numbers. It was supposed to be basic unshrouding of the valves. The shop was preparing Corvette C5R's at the time, so I figured they knew what they were doing.
I will try and dig out the dyno sheets, this weekend. If I remember correctly the horsepower and torque peaks occurred at the same rpm's as the factory quoted numbers.

George

[Duke W.]

Re: 65 FI Performance Issues

It would be great, too, if you were to do a chassis dyno test!

On the "327 LT-1" tested on a lab dyno, headers improved peak torque by about 8 percent, but only about 2 percent more peak power compared to the OE 2.5" manifolds and the front exhaust pipe section from the car routed into the dyno exhaust system.

Those advantages would probably be cut in half with the full vehicle exhaust system.

Duke

[Michael H.]

Re: 65 FI Performance Issues

Acceleration is OK but not startling.

There are a LOT of things that can cause less than stunning performance, as others have mentioned. Compression ratio, cam and cam timing, ignition timing etc etc.
It's also possible that someone replaced some items inside of the FI unit and did not recalibrate the unit. This can make a huge difference in performance. A little adjustment on the lean/rich stops can definitely affect the performance.
The only person that I know of that recaliberates these units is Jerry Bramlett in Alabama. (there may be others)

These cars ran strong when new and correct. I've driven quite a few that were very fast. I've also driven quite a few that wouldn't keep with a 300 HP car.

[Duke W.]

Re: 65 FI Performance Issues

A chassis dyno session with a wide-band O2 sensor is a great way to check A/F ratios both at WOT and cruise, and the nice thing about the FI system is that you can tweak it in seconds between runs with a scredriver and wrench - no need to partially disassemble a carburetor to change jets.

Duke

[Michael H.]

Re: 65 FI Performance Issues

A chassis dyno session with a wide-band O2 sensor is a great way to check A/F ratios both at WOT and cruise, and the nice thing about the FI system is that you can tweak it in seconds between runs with a scredriver and wrench - no need to partially disassemble a carburetor to change jets.

Duke

Yup. That would work.

[John D.]

Re: 65 FI Performance Issues

Hi Mike, I read your question with interest and for once I read all the replies to a post.
A 64-65 FI car with your gears should really honk on big time. How many RPM can you get out of the engine with the pedal to the metal?
You should be able to get in the high 6000 before the points give out.
I don't fully understand the .016 bushing play you are describing. If you have that much play you definitely have issues.
Nice winter project is to pull the distributor and send it out for rebuilding. As mentioned getting the right VA (can) will be a big help also. NAPA handles a good set of points and condenser. We used to use CS786P but now Standard only has the CS786 points. Others here suggest a different part number though. Have the distributor put on a nice Sun/Allen machine too.
Then go from there. If you are idling at 900 RPM with AV gas and the engine is running fairly smooth then you can suspect your engine is not stock.
I remember the 65 FI car's when they were bran d new and those babies idled extremely rough. Old antenna whipped around. LF fender was shaking. Touch of black smoke was typical also when new as the mechanics didn't know squat about calibration.
The 7380 unit is the best that RP made in the old days.
Meanwhile one of our members here runs the crap out of a 62 FI car with flat tops and it runs strong. But nothing like using the hi dome pistons with some good fuel. You should be able to burn the tires off like a NASCAR winner with that car. My 65 was only 3 weeks old when the rear tires were bald. Those bicycle tires had no traction at all in the old days. Good luck, JD

[Mike R.]

Re: 65 FI Performance Issues

Thanks John,

The car has TI and easily revs to redline. The distributor end play is minimal, there is no radial play in the bushings. If there is an ignition issue it is in the distributor boots on the spark plug cables and only occures under load. New boots will be here if a few days.

I probably wasn't clear about the idling. Without Avgas the car sometimes quit while idling, with Avgas the car idles at a constant rpm and does not quit. It is definitely a rough idle!

I realize that the car could spin the original bias ply tires. My question is whether a fuelie with 4.11s and side exhaust can be expected to spin modern *radial* tires from a *rolling* start on good flat asphalt. As others have noted, it may be unrealistic to expect this, particularly with side exhaust.

I have a friend with a 64 365hp car with 16,000 miles that he has owned since new and his car will not spin the tires from a rolling start but I have to find out what gears he has. My only recent comparison is my Ford GT with over twice the power to weight of the Corvette.

As far as I can tell so far, the remaining issue is compression, both from the currently installed .040 head gasket as well as the possiblity of non stock pistons being used. My aircraft mechanic returns in a few weeks and owns a flexible borescope to take a look the pistons.

The other thing I will try is some accelleration runs with a GPS and see how the times compare to the old magazine road tests.

Mike

Hi Mike, I read your question with interest and for once I read all the replies to a post.
A 64-65 FI car with your gears should really honk on big time. How many RPM can you get out of the engine with the pedal to the metal?
You should be able to get in the high 6000 before the points give out.
I don't fully understand the .016 bushing play you are describing. If you have that much play you definitely have issues.
Nice winter project is to pull the distributor and send it out for rebuilding. As mentioned getting the right VA (can) will be a big help also. NAPA handles a good set of points and condenser. We used to use CS786P but now Standard only has the CS786 points. Others here suggest a different part number though. Have the distributor put on a nice Sun/Allen machine too.
Then go from there. If you are idling at 900 RPM with AV gas and the engine is running fairly smooth then you can suspect your engine is not stock.
I remember the 65 FI car's when they were bran d new and those babies idled extremely rough. Old antenna whipped around. LF fender was shaking. Touch of black smoke was typical also when new as the mechanics didn't know squat about calibration.
The 7380 unit is the best that RP made in the old days.
Meanwhile one of our members here runs the crap out of a 62 FI car with flat tops and it runs strong. But nothing like using the hi dome pistons with some good fuel. You should be able to burn the tires off like a NASCAR winner with that car. My 65 was only 3 weeks old when the rear tires were bald. Those bicycle tires had no traction at all in the old days. Good luck, JD

[Michael H.]

Re: 65 FI Performance Issues

I realize that the car could spin the original bias ply tires. My question is whether a fuelie with 4.11s and side exhaust can be expected to spin modern *radial* tires from a *rolling* start on good flat asphalt.

Not likely. A good running big block will smoke the tires from a roll but a small block doesn't have that kind of low end power. Also, a small block car has a LOT more rear wheel traction than a big block car. Gobs of bite with a small block.

[James G.]

Re: 65 FI Performance Issues

A chassis dyno session with a wide-band O2 sensor is a great way to check A/F ratios both at WOT and cruise, and the nice thing about the FI system is that you can tweak it in seconds between runs with a scredriver and wrench - no need to partially disassemble a carburetor to change jets.

Duke

Right on Duke. Back in the 80's when I raced my 64 B/P Fuel car in Vintage, I used a dyno with complete gas analyse system we used for Smog Inspection. WOT at 9.00% CO worked perfect. Also you set the complete ignition system. And with valves set correcly, we showed about 200 HC at cruise.

Todays technology shows it all. Spend a few bucks at a "Power Tune-Up" shop AND YOU WILL BE VERY HAPPY.

[Michael H.]

Re: 65 FI Performance Issues

As mentioned getting the right VA (can) will be a big help also.

JD.... getting the right vacuum advance unit doesn't have anything to do with making the car faster or making more horsepower.