Please confirm my conclusion about overheating

[Duke W.]

Re: Please confirm my conclusion about overheating

I think it's a matter that the only spark advance requirement the typical mechanic understands is WOT at high revs.

But a road engine has to operate efficiently at nearly an infinite number of speed and load conditions. From a practical standpoint, we can break this down to idle, cruise/light acceleration, and full load acceleration (WOT).

Those who attend my seminar in San Diego next month should walk away with a good understanding of the spark advance requirement (including all the whys and wherefores) for all speed and load conditions and be able to optimize their spark advance map for maximum performance and fuel economy when they return home.

Duke

[Michael H.]

Re: Please confirm my conclusion about overheating

setting your idle at 1000 to maybe 11 or 1200 is the way to go. Especially with a 30-30 cam.
Keep us informed please. JD

I still don't understand why any 63-65 FI engine should have to idle at 1100-1200 RPM. They didn't when they were new so why now?

I've owned/driven a lot of these cars over the decades and I never had to set the idle that high.

If it won't idle properly at 850 RPM, there's most likely some other issue.

[Joe C.]

Re: Please confirm my conclusion about overheating

I still don't understand why any 63-65 FI engine should have to idle at 1100-1200 RPM. They didn't when they were new so why now?

I've owned/driven a lot of these cars over the decades and I never had to set the idle that high.

If it won't idle properly at 850 RPM, there's most likely some other issue.

1963 L84 is not at issue here, as it uses the 097 cam and develops more than adequate idle vacuum to deliver a stable idle.

John D. is a smart man. He is merely hedging his bets and protecting his business interests by recommending a "race cam" idle speed of 1100-1200 RPM. Especially if he can echo something that is stated by a certain fellow who apparently is the say-all/know-all/do-all authority around here.

We've been over and over this hundreds of times. The 1964-65 fuel injected Corvettes (which use the 30-30 cam) were the subject of TSB's detailing how to "band-aid" idle instability. I think it was by increasing the idle speed, but by no means increasing it to 1100-1200. This was the only reason that the previously recommended lash setting of .025/.025, per the engineering drawing, had almost immediately been increased to .030/.030.

[Michael H.]

Re: Please confirm my conclusion about overheating

John D. is a smart man. He is merely hedging his bets and protecting his business interests by recommending a "race cam" idle speed of 1100-1200 RPM. Especially if he can echo something that is stated by a certain fellow who apparently is the say-all/know-all/do-all authority around here.

We've been over and over this hundreds of times. The 1964-65 fuel injected Corvettes (which use the 30-30 cam) were the subject of TSB's detailing how to "band-aid" idle instability. I think it was by increasing the idle speed, but by no means increasing it to 1100-1200. This was the only reason that the previously recommended lash setting of .025/.025, per the engineering drawing, had almost immediately been increased to .030/.030.

Joe,

I vaguely remember something from GM on idle speed for 64 or 65 with FI but I don't remember the numbers. Was it something like "increase from 850 RPM to 900 or 950 RPM?

Does the engineering drawing for the 30/30 cam show .025" as the lash or the "checking clearance"?

[Joe C.]

Re: Please confirm my conclusion about overheating

Joe,

I vaguely remember something from GM on idle speed for 64 or 65 with FI but I don't remember the numbers. Was it something like "increase from 850 RPM to 900 or 950 RPM?

Does the engineering drawing for the 30/30 cam show .025" as the lash or the "checking clearance"?

Don't know, for sure, as my memory is extremely poor, but 900-950 sounds reasonable. I can say with good confidence that I can't imagine Chevrolet ever having recommended such an outrageously high "band-aid" idle speed as 1100-1200 RPM to combat an idle instability problem. I don't think customers would have stood still for that one. Do you?

On the lobe lift vs. cam angle chart for the "30-30" cam that Duke sent me some years ago, the tappet "jerk" and "acceleration" go from zero to a positive numerical value at 0.017xx" lobe lift. This denotes the end of the clearance ramp, which takes up the lash by lifting the tappet at constant velocity. Multiplying by the theoretical rocker ratio of 1.5 yields 0.0255". Multiplying by the actual rocker ratio of 1.37 yields 0.0233" which is the lash setting recommended by Hinckley/Williams in their tech paper.

I'll look for a copy of the Tech Drawing, which I know I have somewhere. Meanwhile, I believe that I've heard that a .025" lift demarcation point is shown on that drawing. It might be shown as the point at which tappet acceleration begins, or in some other fashion.

[Duke W.]

Re: Please confirm my conclusion about overheating

Does the engineering drawing for the 30/30 cam show .025" as the lash or the "checking clearance"?

Yes, the engineering drawing specifies .025/.025" lash, which is derived from the .017" clearance ramp height times the "theoretical" 1.5:1 rocker ratio.

As far as idle speed is concerned, it's always been my opinion based on experience with my own car and discussions with other owners of SHP/FI engines over the years that Chevrolet's recommended idle speeds are too low for these engines.

My criterion is "as low as possible commensurate with acceptable idle stability and quality", which is a subjective measure and subject to different interpretations. And it's always been my observation that most FI engines need about 100-200 revs higher idle speed to achieve the same idle quality as their carbureted SHP brothers.

When new, my '63 340 HP engine suffered significant idle stability issues. It took me a couple of years to figure out that the OE 15.5" VAC was the culprit as the engine only generated about 12" manifold vacuum. Once I installed a 236 16 VAC the idle stability and stalling issue when away, but I typically set the idle at 850 to 900. It would idle lower, but IMO was too rough. The higher idle speed also helped pulling away from a dead stop with my 3.08:1 axle.

Duke

[Michael H.]

Re: Please confirm my conclusion about overheating

Yes, the engineering drawing specifies .025/.025" lash, which is derived from the .017" clearance ramp height times the "theoretical" 1.5:1 rocker ratio.

As far as idle speed is concerned, it's always been my opinion based on experience with my own car and discussions with other owners of SHP/FI engines over the years that Chevrolet's recommended idle speeds are too low for these engines.

My criterion is "as low as possible commensurate with acceptable idle stability and quality", which is a subjective measure and subject to different interpretations. And it's always been my observation that most FI engines need about 100-200 revs higher idle speed to achieve the same idle quality as their carbureted SHP brothers.

When new, my '63 340 HP engine suffered significant idle stability issues. It took me a couple of years to figure out that the OE 15.5" VAC was the culprit as the engine only generated about 12" manifold vacuum. Once I installed a 236 16 VAC the idle stability and stalling issue when away, but I typically set the idle at 850 to 900. It would idle lower, but IMO was too rough. The higher idle speed also helped pulling away from a dead stop with my 3.08:1 axle.

Duke

Duke,

On the big GM cam prints that I have, the checking clearance is shown but not the actual lash setting. One cam is the Z28 off road and the other is the 2nd design L88. Both show a checking clearance of .020". GM typically used either .020" or .025" for the checking clearance. The actual lash spec is .024/.026 for both cams. (I think)

I also have a smaller spec sheet for both cams. Both show a "checking clearance" of .020". (below)

I don't know why GM did it that way. Other cam mfg's used a completely different system.

A 365 or 375 HP 327 would run terrible at .025/.025.

I've owned several 64-65 FI cars over the decades and all idled well around 850-900. I see no reason why the idle would have to be more than that if everything is working properly.

[Duke W.]

Re: Please confirm my conclusion about overheating

The 30-30 cam drawing specifies .025/025" lash. It does not list a "checking clearance" that was used for the racing cams. I recall that most of the racing cam "checking clearances" were less than the lash specification, so the lifter was on the clearance ramp rather than the transition point from the clearance ramp to the opening flank, so the "checking clearance" probably yielded more accurate indexing data.

The poor idle stability/quality of the 30-30 cam, especially with FI, was likely the reason the clearance spec was increased to .030"/.030" in the owner's manual and service literature, but the problem with this loose lash specification is that it jerks the valve off the seat and slams it back down at greater than clearance ramp velocity, which is tough of the valve train and valve seating surfaces.

The bottom line is that if you have to specify such loose lash to get the thing to run satisfactorily in normal road service, you have too big a cam. That's why Chevrolet replaced the 30-30 cam in both production and service with the LT-1 cam.

Duke

[Joe C.]

Re: Please confirm my conclusion about overheating

Duke,

On the big GM cam prints that I have, the checking clearance is shown but not the actual lash setting. One cam is the Z28 off road and the other is the 2nd design L88. Both show a checking clearance of .020". GM typically used either .020" or .025" for the checking clearance. The actual lash spec is .024/.026 for both cams. (I think)

I also have a smaller spec sheet for both cams. Both show a "checking clearance" of .020". (below)

I don't know why GM did it that way. Other cam mfg's used a completely different system.

A 365 or 375 HP 327 would run terrible at .025/.025.

I've owned several 64-65 FI cars over the decades and all idled well around 850-900. I see no reason why the idle would have to be more than that if everything is working properly.

Michael,

Reread the last paragraph of my post #18, above. When used with fuel injection, lash it at .030/.030 and it will idle fine as you state. Lash it at .025/.025 per the engineering drawing or .023/.023 based on the actual rocker ratio and it will need a higher idle speed.

I don't think that Chevrolet EVER recommended .025/.025 per the drawing because of anticipated idle instability issues with the Rochester cars. Even with .030/.030 lash, the fuel cars STILL need a bit more idle speed in order to get a stable idle. It would be interesting if someone could dig up an old TSB recommending a tweak to the idle speed for fuel cars whose cam is lashed per the "band-aid" spec of .030/.030.

I had run my 346 cam at .023/.023 and later .025/.025 when it was still installed in my 327. I liked it. I liked the rougher idle but did have to raise the speed to about 900 with the Holley 2818. Damn thing came on like gangbusters at around 4000 RPM and pulled like crazy to 6500-7000.

[Michael H.]

Re: Please confirm my conclusion about overheating

The 30-30 cam drawing specifies .025/025" lash. It does not list a "checking clearance" that was used for the racing cams. I recall that most of the racing cam "checking clearances" were less than the lash specification, so the lifter was on the clearance ramp rather than the transition point from the clearance ramp to the opening flank, so the "checking clearance" probably yielded more accurate indexing data.

The poor idle stability/quality of the 30-30 cam, especially with FI, was likely the reason the clearance spec was increased to .030"/.030" in the owner's manual and service literature, but the problem with this loose lash specification is that it jerks the valve off the seat and slams it back down at greater than clearance ramp velocity, which is tough of the valve train and valve seating surfaces.

The bottom line is that if you have to specify such loose lash to get the thing to run satisfactorily in normal road service, you have too big a cam. That's why Chevrolet replaced the 30-30 cam in both production and service with the LT-1 cam.

Duke

Duke,

Hopefully, I'll have a copy of the original large 3849346 cam blueprint, and a few others, within a week.

I looked through every bit of old GM info that I have going back to summer of 1963 for the new 64 model and there's no mention of a lash setting of .025/.025" for the 3849346 cam. I'll keep looking.

[Michael H.]

Re: Please confirm my conclusion about overheating

Michael,

Reread the last paragraph of my post #18, above. When used with fuel injection, lash it at .030/.030 and it will idle fine as you state. Lash it at .025/.025 per the engineering drawing or .023/.023 based on the actual rocker ratio and it will need a higher idle speed.

I don't think that Chevrolet EVER recommended .025/.025 per the drawing because of anticipated idle instability issues with the Rochester cars. Even with .030/.030 lash, the fuel cars STILL need a bit more idle speed in order to get a stable idle. It would be interesting if someone could dig up an old TSB recommending a tweak to the idle speed for fuel cars whose cam is lashed per the "band-aid" spec of .030/.030.

I had run my 346 cam at .023/.023 and later .025/.025 when it was still installed in my 327. I liked it. I liked the rougher idle but did have to raise the speed to about 900 with the Holley 2818. Damn thing came on like gangbusters at around 4000 RPM and pulled like crazy to 6500-7000.

Bet it sounded nasty at those lash settings. Probably giving away HP though.

My new 64 with that cam always seemed to run best when the lash was a bit loose and needed adjusting. Same for my new 68 Z28 Camaro. (same 346 cam)

[John D.]

Re: Please confirm my conclusion about overheating

HI Doug, I see this post was hijacked by cam talk. But it's all relative.
Story: In 1965 I had a 365HP glen green convertible with horrible paint job. It also idled horrible and the mechanics solution was to do the following. He disconnected the vacuum advance. Now that wasn't bad enough but he also tach welded/brazed the point plate to the distributor body. The car ran like crap and overheated. Now I blamed it on the hot summer weather.
So I took my 65 to another Chevy dealer and the service manual said the warranty was voided as someone butchered the distributor.
This car was only 6 months old. Well my Dad got involved and he had a fit. So he complained to the selling dealer and they installed a new distributor for free.
The heating problem went away but the car still idled crappy. The left front fender shook bigh time and the car was no fun to drive in heavy traffic.
All I did was turn the idle up to 1000 and it was like a whole new car. Remember this was a carb car and not an FI car.

[Joe C.]

Re: Please confirm my conclusion about overheating

Bet it sounded nasty at those lash settings. Probably giving away HP though.

My new 64 with that cam always seemed to run best when the lash was a bit loose and needed adjusting. Same for my new 68 Z28 Camaro. (same 346 cam)

Actually, just the opposite is true. The tighter lash increases lift and duration, making the cam "bigger". This increases torque at high speeds (horsepower), at the expense of low speed torque.

[Joe C.]

Re: Please confirm my conclusion about overheating

HI Doug, I see this post was hijacked by cam talk. But it's all relative.
Story: In 1965 I had a 365HP glen green convertible with horrible paint job. It also idled horrible and the mechanics solution was to do the following. He disconnected the vacuum advance. Now that wasn't bad enough but he also tach welded/brazed the point plate to the distributor body. The car ran like crap and overheated. Now I blamed it on the hot summer weather.
So I took my 65 to another Chevy dealer and the service manual said the warranty was voided as someone butchered the distributor.
This car was only 6 months old. Well my Dad got involved and he had a fit. So he complained to the selling dealer and they installed a new distributor for free.
The heating problem went away but the car still idled crappy. The left front fender shook bigh time and the car was no fun to drive in heavy traffic.
All I did was turn the idle up to 1000 and it was like a whole new car. Remember this was a carb car and not an FI car.

You should have left the idle speed alone and tightened the left front fender bolts.