Best setup for PSMCD '70/W66
 

I just perused the results for the 2015 PSMCD, and I thought that I might start a fun little thread here;

First the link:
http://www.psmcdr.com/17.html

I was wondering if anyone would chance speculating at the best manual transmission & engine setup for me.

My car was built as a 3.55:1 geared, L78/Muncie three speed car with nothing that I can think of to add weight (besides PS & PB).

I have the option for this even to run as either a L78 or a L74 car;

• L78: 067 cam, "log" manifolds, dual snorkle air cleaner (I have it all).
• L74: 068 cam, 'ram air' manifolds, 'ram air' aircleaner (functional through hood of course; again, I have it all).

I can run either a Muncie three speed, a wide ratio, or close ratio muncie four speed - all were optional (and I have them all).

• 3 speed: 2.42/1.58/1.00
• M20: 2.52/1.88/1.46/1.00
• M21/22: 2.20/1.64/1.28/1.00

(I am thinking that the Muncie three speed is a close comparison to the TH350; th350= 2.52/1.52/1.0)

Any differential gear set is permitted;
I am inclined to run 3.90:1 after a brief ride in a '68 RAI Firebird (I have the correct speedo adapter already).


My experience so far:

I have never run either of those cams;
I believe my car had a 066 cam in it when I bought it as a RAIII (less carb; YZ engine, #12 heads, ra manifolds) car;
When I rebuilt the RAIII, I went straight to the (illegal for this event) 744 cam.

I have only run a close ratio muncie in my car c/w 3.55:1 gears - which I have been told time and again is a bad match;
I have only spoken to three people who have run Muncie three speeds, and every one of them said that it was faster than a four speed.

I will likely setup my car with the numbers & date correct engine once I get the body work ect finished. Then around the time that I build a second engine purely to run at the PSMCD, I will get a second 12 bolt setup with 3.90's - so I have ample time to ponder the specifics of my combination...

I am understanding that the 067 cam is better suited for more low end torque versus the 068...

I understand that the 1970 D-port Firebird RA manifolds offer much less of an advantage than one might think...

I am seeing that the highest "hp" cars aren't necessarily the fastest - it seems to be more about setting up the car just right.

I realize that I would be at a disadvantage by keeping the manual transmission (I haven't raced much, so I will be my own worst enemy on consistency vs my dial in) - but I'm ok with that..

I am thinking that the first of these three combinations might be the best setup:
Thoughts?

cam gear trans
 

068 cam 4:10 gear and m20 will net high 12 s once you learn to drive it like you stole it

what I'm seeing is this;

L74+4.10*+M20 = lousey 60'

* = not the gear set I am inclined to run, because it makes it that much less streetable. I planned on driving there...

But, lets take your suggestion, and to simplify the variables, lets remove the differential gearing from the equation;

I would think that the L74, with slightly less low end torque teamed to a lower first gear ratio with an already low differential gear set, would essentially multiplie the torque to where I would have to either bog it off the line, or I would have a high two second 60';
I was thinking that:
A) with more torque, a lower first gear and low differential gearing, that I'd get a better lower rpm launch and avoid bogging - then hook up faster...
OR
B) with less torque, a higher first gear and low differential gearing, that I can launch at a bit higher rpm, hopefully not immediately incinerate my tires, and get up to speed faster.

I would be concerned that unlike a higher winding motor (like say a small block Ford, or a '70 LT1, putting too low differential gearing might have me need to do an extra shift just before the traps...
(it's been a while since I've really run my car, I cannot recall if one would have to be in top gear before hitting the traps, or if you would be able to remain in third while going theough the traps.)

Am I totally off here?

I have read of '70 A-bodies running L78(067) cars especially well...

The A bodies can run better because the rules allow 'hop stop' bars for them.
The leaf spring cars aren't allowed any mods except straps on springs basically.
(the 67 Firebird would work better with their radius rods)

Lots of straps on springs and possibly add the upper hole on front of spring mount, could help the launch.

The 3 speed would require the 1st shift to be the problem for it.
Getting through the 'H' part at the critical 1st shift may slow the shift and the car's acceleration.

I would probably use the TH400 with the shift kit and smallest and highest stall allowed.
Mod the governor to shift at 5500 RPM (or whatever wanted) and leave it in drive.
(with kickdown still hooked up)

This is basically a bracket race where consistency wins.

I would also use the 068 cam setup.
Not sure it said anything about 1.65 rockers?
(they probably wouldn't know the difference?)

With the right tires, moderate launch, let the Pontiac eat!

:)

i can't use 1.65 rockers.

that's some good stuff to ponder

I am going to bump this thread in the hopes for a little more help;

I may have found a decent deal on a replacement camshaft, but now I am starting to question if it really is that great of a deal.

Can someone please help me decipher who makes 067 & 068 replacement camshafts, and their part numbers?

I found this link;
http://www.pontiacpower.org/PontiacCams.htm
This page seems to have the shotgun effect on me;
there's alot of information blasted on the page - so much, that I am having a little trouble in figuring out what qualifies as a replacement 067/068 camshaft other than the (discontinued) HO-Enterprises "k" cams.

I downloaded the comp cams catalog, but I can't make heads or tails of their offerings...
I have also perused summit (LINK), but again, am havign a tough go at it.

Thanks!

I was under the impression the 067 was no longer made. Seems like there is always some cam suggested which is "close to" or "like" an 067. FWIW, I've used both the 067 and 068 in 350's and 400's and definitely like the 067 more in the 350.

I know that for a while it was NLA... it appears to now be available.

He's already figured out how to drive it like that. :drive:

/\ /\ well, thank you very much :D

Normally I only get ridicule for this - I'll take compliments any day of the week.

Yes, they do :-)

scrap the idea of a replacement 067/068 cam. Get a custom designed cam near those specs. work with someone who knows cams. They cost the same as those replacements and will work much better.

for years I've really been thinking of a RAIII bird. I could just find a donor car, swap in my engine/trans setup (with RA manifolds of course), at least 3.90s, or maybe 4.33s and run mid 12s. However, I have enough projects as it is

Get yourself a back copy of HPP Aug 2008 issue the article is Pure stock Prep school. It goes into drivetrain and suspension and what makes them run.

/\ /\ I have that issue - there are not many from the last fifteen or so years that I do not have;
But setups like that aside, I haven't yet totally nailed down my actual configuration that I should be running - which is why I'm looking for any advice that can be offered.

:D

3.90 with what tire height?
I would choose a 3.73 gear with the 3 speed stick if the tires are under 25 inches...
Just my opinion.....
You are on the right track!

according to the information I found;
F70-14 or 225/70/14 are a 26.5" tire - who knows if that's based on a 6" rim or not - and my car having 7" rims might shorten up that diameter a smidgeon.
I believe that 235/60/14 are permissible, but they offer an extra 1" of tread width, at the cost of over an inch shorter tire (25.1") - so I am inclined to run either a repop bias ply F70/14 or a 225/70/14.
(aren't first gen Firebirds running on a tire at least as skinny as an F70/14?)
http://www.psmcdr.com/7.html

My choice of 3.90's is based on the 67-69 RA cars all(?) coming standard with that gear set;
I had one brief shotgun ride in a legit '68 RAI car;
(It had headers, and an unknown cam, but the factory 3.90's, with the #'s M21 - and that gear set REALLY made the thing launch!)
I figure if I'm going to try to replicate early RA car performance, I need to start with an even playing field - and that necessitates at least 3.90's. :D
Also, 3.90's are still a little more driver friendly than the 4.30's that I was strongly encouraged to go with from a Pontiac racer I respect.

Now, 3 speed versus 4 speed(s) comes down to opinion/consensus;
I am inclined to believe that the guys who are having positive results from using lower gears with the wide ratio stick does point to the Muncie three speed being a winner (less shifts, and the few I have spoken to with this gear box say it seemed noticeably quicker than the four speed they had to compare it against);
I understand that not everyone goes through the traps in fourth gear - and that might be a matter of gearing & delays from shifting ect - but combine this with the Muncie three speed being geared similar to the TH350, and I am thinking that with a little more gear that factory, that I should be in top gear by the time I hit the lights at the end of the track...

Two possible strikes against running the Muncie three speed are:
1) very hard to find parts - if it needs servicing/repairs, I'd be better off running a four speed.
2) if I get some good info that suggests I shouldn't run the Muncie three speed...

:beerchug:

hmm...
It looks as though I misinterpreted the rules regarding tires;
If I show up running either a 14x7" steelie, or a 14x7" rally, my OE tire size is F70-14;
The rules allow me to go up one size - but they require that I retain the aspect ratio - which means I can run a G70-14.

I found this:
F70-14
Dia: 26.45"
Tread: 6.55"
Sect: 8.75"

225/70R14
Dia: 26.4"
Tread: 6.7"
Sect: 9"

I just found this (same link as F70-14):
G70-14
Dia: 26.81"
Tread: 6.9"
Sect: 8.9"

I am guessing that a 235/70R14 is the equivalent size, but these appear to no longer be manufactured.

Just came to this thread from your other link. I don't race Pure Stock, but I do run on the little tires…

Best combo in my mind, especially if you're intent on keeping a clutch pedal, is one that would have less torque and more top end power. Any 400 is going to have enough torque to get you off the line smoothly. Too much torque, though, and you're fighting wheel spin all the way through first gear.

Also- I'd set it up with log manifolds. They weigh a good 20 pounds less than RA manifolds and run just as good if you use mandrel bent 2 1/2" down pipes. Look at Chris (gloryrestoparts) results in his signature.

I would go with the G70-14 tires. The bias ply works way better than a modern radial off the line.

thanks for offering your thoughts!

std manifolds = 'L78' trim = 067 cam = 430tq @ 3,000 rpm
RA manifolds = 'L74' trim = 068 cam = 430tq @ 3,400 rpm

http://i303.photobucket.com/albums/n...irebird-15.jpg

I don't recall the exact rule, but they do allow you a little room on cam design at the PSMCDR. Use that leeway to your advantage.

there is a tiny bit of leaway, it is a rule which was created to accomidate people who cannot get an original pattern camshaft any longer.

I did get one lead, and reached out to it, but never got a reply.

http://www.psmcdr.com/12.html