69' amx

[Paul Ceasrine]

Jeff,
Wasn't the issue, that the 70 'dog-leg' exhaust port design flowed
better than the 69' exhaust port design, and AMC wanted to get them out there (supposedly an additional 25+ HP) over the 69' heads.
And that the 70' heads were to be prepped by Crane (ported and tricked-up).
AMC wasn't about to build 50 more 1970 Super/Stockers, so they
offered the 70' upgrade kit for the 69 S/S cars, so they could utilize the newer and better flowing Crane-prepped 70' heads.
The 70' 'dog-leg' Crane heads would not be legal for the 69 s/s cars, but would be legal for 70' S/S cars
Of course, NHRA put the 'kibosh' on the up-grade kit.
Paul

[Jeff Lee]

Originally Posted by Paul Ceasrine

Jeff,
Wasn't the issue, that the 70 'dog-leg' exhaust port design flowed
better than the 69' exhaust port design, and AMC wanted to get them out there (supposedly an additional 25+ HP) over the 69' heads.
And that the 70' heads were to be prepped by Crane (ported and tricked-up).
AMC wasn't about to build 50 more 1970 Super/Stockers, so they
offered the 70' upgrade kit for the 69 S/S cars, so they could utilize the newer and better flowing Crane-prepped 70' heads.
The 70' 'dog-leg' Crane heads would not be legal for the 69 s/s cars, but would be legal for 70' S/S cars
Of course, NHRA put the 'kibosh' on the up-grade kit.
Paul

There are no communications I am aware of between NHRA or the racers to upgrade to the -291 or dog leg heads. FYI the 1969 Crane heads have a significantly larger combustion chamber volume than the 1970 passenger car -291 head volume; something around 12cc's or so. That would have required a different piston (1969 SS piston is domed) to go with the new heads if that was what AMC wanted.
The cheap / easy way out for AMC was to just change out the sheetmetal parts and carry over the engine parts.

Tom,
Yes, the front suspension on the 1970 AMC is substantially different than the 1969 AMC. I know of at least one racer that converted his '69 AMX to a '70 AMX with all the sheetmetal parts and was later advised he had to change his suspension (which he did).

[Paul Ceasrine]

Jeff,
I thought the cylinder heads were the same casting.
Don't the 69' S/S "Crane' heads have slightly larger combustion chambers, due to machining for valve schrouding, and not casting.
I think Kaplan Engineering has something discussed about exhaust flow
and the major incease in flow developed at higher rpms, with the 'dog-leg' design.
Just read my old 68' Drag Performance Mag
1968 AMX 390/315,,E/S
With Doug Headers, 4.44 gears, 7' slicks, Schieffer clutch package, and dyno-tuned.
13.07 @ 108mph
PC

[Jeff Lee]

The original 1969 SS head was based on the production head, ending with -558 and had rectangular exhaust ports. The standard -558 production head in 1969 shows 49.10 cc chambers while the SS only -558 head shows 57.00 cc chambers. So yes, the chambers were somehow modified on the 1969 SS only head.
1970 production cylinder head started with -291 castings which had the dog-leg exhaust ports and still retained the 49.10 cc chambers.

In Stock the 343 is rated at 275 HP and the 390 is rated @ 315 HP. They both look better in SS with 265 and 290 HP ratings.

[Tom Goldman]

The 558 S/S head had the chambers completely opened up to unshroud the larger valves, accounting for much of the increased volume. The heads I had were completely polished , and came from the S/K Performance car . .........Kenny Freeman was instrumental in getting the 558 superceeded by the 291 casting ........AMC by that time could have cared less. ..........Tom

[Jeff Lee]

I have a SS/AMX owner looking or an original pair of Crane heads for his restoration. Anybody have a good pair (no cracks or ported beyond recognition), let me know!

[Paul Ceasrine]

I think I got it.
1969 AMX S/S cars. Engines with 390 Cross-Ram.
69' heads, modified by Crane, ported out, with Mopar 440 valves.
Combustion chamber (49 cc) hogged out to (57 cc) to reduce valve schrouding.
Cars were running in SS/D for 70', versus the Street Hemi cars
(primary competition).
Kaplan Engineering discovers more flow and 25+ HP at higher RPM's in the new 70' dog-leg ("L"-shaped exhaust port heads). Approximate gain of 3/10's off the E.T.
AMC wants to utilize these heads on the 69' S/S cars as a replacement head. NHRA says "No Way'.
Since they are a 70' design, they can only be accepted on a 70' car.
AMC, not interested in building an additional 50+ 70' AMX S/S cars
Decide to produce 70' up-grade kits for the 69' AMX cars. Front grille, fender extensions, light hardware and dashboard. With the 70' conversion, the newer 70' Crane 'dog-leg' heads can be used, to help
dominate SS/D.
NHRA gets wind of this, and says 'no way'. The 70' car is actually longer than the 69' car, and is not the same car The 70' heads cannot be utilized on the 69' car for Super/Stock, but Modified Production would be fine.
AMC was not about to spend another $250,000 building 50+ 70' AMX Super/Stockers.
PC

[Jeff Lee]

You have it right except I really don't think the -291 head for 1970 was a part of the equation. If it were, AMC would have sent a pair of heads out with the body parts. I have a LOT of AMC correspondence on the conversion issue and have never seen even a hint about newer heads on the horizon.
I think the only deal was to have a fresh face for the 1970 model year.

[Paul Ceasrine]

Jeff,
Your probably right. Maybe it was just the 70' nose looked better than the 69'.
From an AMC marketing stand-point, the new-style was the way to go.
The new 'dog-leg' heads would only work, if they went through 'Crane' for
modifications.
Maybe AMC's original thought was to try to back door the newer heads
on to the 69' S/S cars, after they were converted to 70' cars.
Greg Long of AMC (Elmsford HQ), said, he thought that AMC would be willing to build (7) 70' AMX S/S cars (in January 70') with the new style heads. Once out there, they would push the 70' conversion kits for the 69' S/S racers.
PC

[tbenvie]

AMC sent the upgraded 70 kit to the SS/AMX owners purely as a marketing idea. The 70 AMX had a big facelift-nose, taillights, interior, and wanted to promote the new 70 model line. The heads were also much better, and larger head bolts as well, but this was never part of the upgrade. Didn't other manufacturers change grills/taillights as well to upgrade to a newer model year?

The improvement of the heads was not done by Kaplan, but rather in-house by the engineers that ran the flow bench and other testing equipment. They tried to sell the idea to AMC when the 390 came out-and improvement that actually cost no extra money, just a redesign casting. One of the engineers actually raced an original SS/AMX at the Nationals-the purple one shown in the staging lanes. he later helped write Performance American Style, a early "bible" for AMC enthusiasts sold at the dealers parts counters. AMC and Hurst redid the original set of heads used on the prototype Super Stock car, but did not have the time/facilities to do a run for all the cars, so sent them to Crane.

Spoke to the original owner of an SS/AMX yesterday. He also swapped the parts to an upgrade 70, but as he only raced at a local track he did not have to change them back.