Why a different suffix code for '66 L72 w/ M22?

[Steven S.]

I guess the title says it all, what was different with an L72 that was going to be put in front of a M22 in 1966 (IF vs. IP)?

Thanks,
Steve

[Joe L.]

Re: Why a different suffix code for '66 L72 w/ M22?

I guess the title says it all, what was different with an L72 that was going to be put in front of a M22 in 1966 (IF vs. IP)?

Thanks,
Steve

Steve-----


I think you mean "IK" versus "IP"; I can't find any record of an "IF" code used for 1966.

In any event, I don't know, for sure, the answer to your question. However, I strongly suspect that the reason related to a difference in installed clutch and bellhousing between the two engine assemblies. The 1966 "IP" code used a 14" flywheel, 11" clutch, and "444" belhousing. I expect that the "IK" used a 12-3/4" flywheel, 10-1/2" clutch and "403" or "383" bellhousing (i.e a clutch and bellhousing set-up as was used for all 1965 L-78).

[Jack H.]

Re: Why a different suffix code for '66 L72 w/ M22?

Since only a handful of 'Rock crusher' trannies were built/shipped in 1965, the different suffix code may also have served the purpose of configuration validation + warranty tracking....

[Duke W.]

Re: Why a different suffix code for '66 L72 w/ M22?

Chevrolet was working on a dual disk clutch design in the mid sixties, and it may have been intended for M-22 applications.

Release was delayed until 1971, but they may have assigned a different engine code to account for the anticipated use of the dual disk clutch, which ultimately didn't materialize in '66.

Duke

[Michael H.]

Re: Why a different suffix code for '66 L72 w/ M22?

I guess the title says it all, what was different with an L72 that was going to be put in front of a M22 in 1966 (IF vs. IP)?

Thanks,
Steve

I'm a little confused on this also. As mentioned, I see no listing for an IF code for 66. (only for 65)
If it's supposed to be IK instead, I'm still confused because the IK code is supposed to be a 427, special high performance with hydraulic lifters. (a combination that never existed, at least in Corvette. Could this be an error?)
I also see no specific code for a 427 w/Sp H/Perf and M22 transmission.

All of this from the info shown in the parts book. I'll dig a little deeper and see what i can find.

Add on; The plot thickens... Just looked in some other info, including a pile of info from GM for 66. It shows IK as a 425 HP and IP as a 450 HP.
Could IK be the iron head L88 that never made it to production? In many other GM documents, especially for 66 pass car, the 425 HP 427 is indeed the L88.
Since the L88 was dropped and the HP reduced for the L72, is it possible that this is indeed what occured.

I can find no information that links the M22 with any engine code.

[Steven S.]

Re: Why a different suffix code for '66 L72 w/ M22?

Whoops, I did mean "IK", for some reason I allways want to call it "IF"

Joe, your reasoning would make sense for another reason, I've seen reference somewhere (I think perhaps it was Nolands book) that the "IK" code also used a different starter number, which would indicate to me a different flywheel was being used.

Interesting... I thought this might have been an easy one to answer

[Philip C.]

Re: Why a different suffix code for '66 L72 w/ M22?

Steve what code is on your cars engine? Phil 8063

[Duke W.]

Re: Why a different suffix code for '66 L72 w/ M22?

Steve-----


I think you mean "IK" versus "IP"; I can't find any record of an "IF" code used for 1966.

In any event, I don't know, for sure, the answer to your question. However, I strongly suspect that the reason related to a difference in installed clutch and bellhousing between the two engine assemblies. The 1966 "IP" code used a 14" flywheel, 11" clutch, and "444" belhousing. I expect that the "IK" used a 12-3/4" flywheel, 10-1/2" clutch and "403" or "383" bellhousing (i.e a clutch and bellhousing set-up as was used for all 1965 L-78).

This explanation makes sense. Does anyone know for sure if it was the case. With only 15 M-22s in 1966, finding an unmolested original would be tough.

Duke

[Michael H.]

Re: Why a different suffix code for '66 L72 w/ M22?

This explanation makes sense. Does anyone know for sure if it was the case. With only 15 M-22s in 1966, finding an unmolested original would be tough.

Duke

I have doubts about the small diameter flywheel for L72's with M22. The AIM makes no mention of a different part number for the L72 engine assembly when used with M22. There's only one part number for the L72 and that assembly had the 11" clutch assy. If the M22 option required a different flywheel, clutch, inspection cover, starter and starter brace, etc, the AIM would show a different engine assy part number.
The only flywheel listed in the parts book for L72 is the large wheel. Same for the clutch pressure plate and disc. Both are the large 11" dia. and no mention of the 10.4" for M22 or HD 4-speed.

The mysterious "IK" code never shows up in any reference material that I have dated later than November 65, just after the L88 option was canceled.

I think we need a little more research on this one.

[Steven S.]

Re: Why a different suffix code for '66 L72 w/ M22?

Steve what code is on your cars engine? Phil 8063

Philip, mine is an "IP" car.

This explanation makes sense. Does anyone know for sure if it was the case. With only 15 M-22s in 1966, finding an unmolested original would be tough.

Duke

A few weeks ago I posted a thread here asking if anyone knew of any legit examples of these cars left in existence, without pulling up that thread I recall a few being mentioned plus one guy claiming to be restoring one at the time.

This is an interesting subject to me, I'd like to learn more...

Thanks,
Steve

[Steven S.]

Re: Why a different suffix code for '66 L72 w/ M22?

To expand upon this, in Nolands book it states that the M22 cars received starter number 1107352, and this was referenced from "1966 Corvette production parts list". Can anyone else confirm that information?

[Joe L.]

Re: Why a different suffix code for '66 L72 w/ M22?

To expand upon this, in Nolands book it states that the M22 cars received starter number 1107352, and this was referenced from "1966 Corvette production parts list". Can anyone else confirm that information?

Steve-----

Some 1966 and 67 GM parts references indicate that the GM #1107352 was used for "1965-66 Corvette with HD 4 speed". However, parenthetically is added the qualifier "SHP, 396". Obviously, no SHP 396 was manufactured for the 1966 model year. Still, it sort of implies something "unique" about 1965-66 applications with HD 4 speed.

I can confirm, for sure, that the GM #1107352 was a starter configured for "high torque" and use with a 12-3/4" flywheel. No doubt about that, at all.

What I think the deal here probably is: the L-88 was originally supposed to be released for the 1966 model year. Of course, as far as we know, it wasn't. Since it was not released, we don't know anything regarding engine codes, horsepower ratings, etc. However, we do know that it was intended to be equipped only with M-22 4 speed. So, it may be that the "IK" engine code was the code to be used for the "stillborn" 1966 L-88. Or, it may be that it was the code used for those few 1966 L-72's equipped with M-22. If it's the former, then the 12-3/4" flywheel "fits" since all subsequent L-88's equipped with 4 speeds used a 12-3/4" flywheel. If it's the latter, then I still strongly suspect that the difference was the flywheel, clutch and bellhousing as I described previously. I just can't see any other reason for a difference in engine codes.

Finding a legitimate "IK"-coded 1966 big block that one could be reasonably sure was as originally configured would go a long way to settle this. However, whether, or not, an "IK"-coded 1966 big block could be found, it will be harder yet to find an example that one could be reasonably sure was as originally configured, especially with respect to flywheel, clutch, and bellhousing. Such a car would likely have been raced in it's earlier years and had its bellhousing replaced with a scattershield and original flywheel and clutch, whether the originals were ever used, long-since replaced.

[Michael H.]

Re: Why a different suffix code for '66 L72 w/ M22?

Steve-----

Some 1966 and 67 GM parts references indicate that the GM #1107352 was used for "1965-66 Corvette with HD 4 speed". However, parenthetically is added the qualifier "SHP, 396". Obviously, no SHP 396 was manufactured for the 1966 model year. Still, it sort of implies something "unique" about 1965-66 applications with HD 4 speed.

I can confirm, for sure, that the GM #1107352 was a starter configured for "high torque" and use with a 12-3/4" flywheel. No doubt about that, at all.

What I think the deal here probably is: the L-88 was originally supposed to be released for the 1966 model year. Of course, as far as we know, it wasn't. Since it was not released, we don't know anything regarding engine codes, horsepower ratings, etc. However, we do know that it was intended to be equipped only with M-22 4 speed. So, it may be that the "IK" engine code was the code to be used for the "stillborn" 1966 L-88. Or, it may be that it was the code used for those few 1966 L-72's equipped with M-22. If it's the former, then the 12-3/4" flywheel "fits" since all subsequent L-88's equipped with 4 speeds used a 12-3/4" flywheel. If it's the latter, then I still strongly suspect that the difference was the flywheel, clutch and bellhousing as I described previously. I just can't see any other reason for a difference in engine codes.

Finding a legitimate "IK"-coded 1966 big block that one could be reasonably sure was as originally configured would go a long way to settle this. However, whether, or not, an "IK"-coded 1966 big block could be found, it will be harder yet to find an example that one could be reasonably sure was as originally configured, especially with respect to flywheel, clutch, and bellhousing. Such a car would likely have been raced in it's earlier years and had its bellhousing replaced with a scattershield and original flywheel and clutch, whether the originals were ever used, long-since replaced.

I agree. That's an accurate assessment of the limited amount of information that's available on this subject.

One item that may tip the scales slightly more toward the L88 side of the debate is the fact that the engine stamp code, IK, was originally published in GM documentation at or near start of 66 production in 1965 and disappeared without a trace by late November 1965, about the same time the L88 option was canceled in the AIM.

Also, if IK indicated an L72/425 HP 427 with M22, why would it have been cancelled by November 65. Supposedly, there are several cars built after that date that have the M22 so the IK code would have been in later GM documentation.

I'm pretty much over on the L88 side of the fence on this.

[Steven S.]

Re: Why a different suffix code for '66 L72 w/ M22?

So what you guys are thinking is the "IK" code never actually got struck, and the L72/M22 cars still used the "IP" code? I'll try and dig up my old thread on the subject and PM the guy who was supposed to be restoring one. I'll report back.

Steve

[Joe L.]

Re: Why a different suffix code for '66 L72 w/ M22?

So what you guys are thinking is the "IK" code never actually got struck, and the L72/M22 cars still used the "IP" code? I'll try and dig up my old thread on the subject and PM the guy who was supposed to be restoring one. I'll report back.

Steve

Steve----

Yes, I think that's pretty much the way it probably is. We'll know different if a legitimate "IK" ever shows up. The problem is, assuming that happens, we'll still probably be "in the dark" as far as what bellhousing, flywheel, and clutch was ORIGINALLY installed.