[392Wrangler]

According to Rocky Rotella’s book a 70 Formula non RA should have #13 heads on it.
I’m confident mine has not been taken apart, but it has #13 heads on it.
I just pulled the motor and trans for a re-seal and it was Virgin on the long block. At one time the timing chain was replaced as I found all the nylon teeth in the oil pan and on the pick up screen.
Also this car has the M21 close ratio as is shown on the PHS. But a bulletin on Feb 9th 1970 (Again referring to Rocky’s book says you had to order the 3.73 gears set with that trans, but my PHS does not show Performance axle ratio. It does show safety trak though.
Any thoughts?
This was an early build car.

[392Wrangler]

Sorry for the typo. It should say it has #12 heads on it.

[johnta1]

I think the close-ratio would have come with that gear, so no charge?


Possibly that may have required the 12 heads?
(guess on my part if original heads)

What's the date code on heads?

[johnta1]

Should add, the 3.73 & M-21 were offered on the 400 4bbl in the Formula.
I have nothing on the heads though.

[eaglesan13]

I'm pretty sure that all the RA engines got the #12 heads. The non RA engines got #12 heads on the manual trans cars and #13 heads on the automatic cars. I don't think the trans and rear end ratios mattered.

[392Wrangler]

Both head date codes are A280

[poncho-mike]

I have seen both 12s and 13s on WT coded engines.

[Kenth]

No #12 heads on any 1970 A/T 400 cui. except RAIII.
No #13 heads on any 1970 RAIII A/T or M/T.

FWIW

[Baron Von Zeppelin]

I've never seen anything but #12 heads on 70 WT engines.
Local friend also has a #s matching 70 Formula project car.
WT -12 - 263 carb - open face alternator - yada yada
3spd M13 with AC


As to the gear ratio , your car might provide more insight to Keith_K's study about 3.73 cars.
Yours being a Firebird and showing M21 option is a great reference.
We have been dealing with TAs , that don't show that selection.

On some TA's - 3.73 cars are found with just HD Radiator - No upcharge for Perf Axle.
On other TA's - they show HD Radiator AND Perf Axle on 3.73 cars.
Seems like Keith was pointing towards an Early / Late scenario.

There could also be a factor involving whether it was the M20 or M21 alternate choice factor with 3.73 gears.
But that is getting intricate.
In that case - using your example - it would point to the TAs with just HD Radiator being M21 , and the Perf Axle cars being M20.

But Keith may have already eliminated that parameter.
I don't remember , and I can't access my files/invoices/Bsheets

[Baron Von Zeppelin]

You could get 3.73 with M20 or M21
But M21 was 3.73 only - on these cars.

[Formulas]

I was always under the impression that regardless of the ram air moniker, that if a 4 speed was optioned the higher compression heads and 068 cam went with it on 1968-1970 years

then if ram air was ordered ex manifolds and cold air induction came into play with 068 cam and high compression heads

i have never scienced it out though

[392Wrangler]

Well this car has the 12 heads but had the “P” stamped on the end of the camshaft which would indicate an 067 Cam, just to throw another curveball into the mix.
Before and after re-seal pics.

[johnta1]

'P' cam is for the WT engine I believe.

Chart of Bird stuff:

[392Wrangler]

Well yet another curveball.
It has the COX code on the rear axle tube.
Doesn’t that indicate a 3.55 posi gear set?

[Baron Von Zeppelin]

Check for the VIN on transmission , and the application stamp nearby that.

COX 3.55
COV 3.73

[giles]

I can put in a vote for’70 Formula WT, 4 speed, 3.55 axle with #12 heads. A buddy and I road raced one at Waterford Hills in 1980 (some here know of it). It was pretty clearly an unmodified engine before we broke it. We spun rod bearings as can be expected. So we took those #12 heads, bought a new 744 cam and dropped that top end on a nice 428 bottom end. That made a good runner.

[Kenth]

COX 3.55
COZ 3.73

[Kenth]

P camshaft for WT engine.

[Baron Von Zeppelin]

Originally Posted by Kenth

COX 3.55
COZ 3.73

Thanks Kenth
Old memory dies hard
I should have verified my thoughts first.

[Rocky Rotella]

Since writing the book back in 2016, we've discovered new information on a few different points. One of those is the #12/#13 cylinder head usage in 1970 Firebird. A 1970 engine assembly document that I located clarifies without question.

The #12 heads were indeed used on the WT 400 (along WS and YZ codes) engines that year. The difference between the #12 and #13 (besides chamber volume) was the inner valve spring. Both heads used 9779009 outer springs. The #13 used 9779008 inner while #12 used 9781476 inner, which contained a higher rate.

Pontiac was clearly looking to increase high rpm valvetrain stability with the manual transmission in the WT application.