MX > C6 conversion. Wide-ratio and other questions.

[66FAIRLANE]

I like the idea of the manual VB because I am used to manual trans. plus it eliminates parts which I'm oddly drawn to. I had to fabricate an adjustable kickdown linkage when I switched to the 427 MR intake manifold, so I didn't want to have to fight that again or fab up a Lokar cable.

Just on the kickdown thing. I have not had the kickdown connected to my C6 in the 26 years I have owned the car. Frankly never missed it and you wouldn't even know its not connected.

[Jackal]

Hmmmm, I could see this working out if the shift pattern was:

P-R-N-D-2-1

...and you just drop into 2 as-needed and be cautious about shifting back into D? This might be the best of both worlds. I'm not sure if mine is a "Green Dot" pattern or not. Broader said the 66 and 67 C6 is a clicker type VB.

I will re-consider it for sure. I guess with the manual, reverse it could get hairy accidently shifting from 3 to 1.

[66FAIRLANE]

I have never actually had to shift down to mimick kickdown. Maybe its just my converter, gear combo ( I have had a few too) but the governor just seems to know what to do. If I took you for a drive you would never pick its not connected. Torque is a wonderful thing

[WerbyFord]

Thanks for the calc/chart and input guys! (Though I'm confused by the shift points. Maybe this is where an auto VB would shift into that gear w/o low vacuum?)

I think I could live with a Comp 270'ish chop. I definitely know better than to over cam again.

https://youtu.be/alWXQyBhKfA

I wondered why that sounded so ROUGH. That's a Comp 270H (in a little 390).
I thought that video was the 282S or the 427-8v 324-324 cam until I looked.
IF that big Merc has a 3.00 & stock stall it's a dog off the line.

The Comp 270S is smoother than that, idles about like a 428CJ, when it's warmed up it's like there's "no cam" in it.
Solid  cams idle smoother & make more power. Downside is setting the valves, not that bad for the low miles we drive em.

ON THE KICKDOWN:
If your intake doesnt have to 2 holes to mount the "Rat Trap" (bellcrank?), you can mount it up on the firewall.
Just keep the pivot bar in the same spot in space & "swing" the Rat Trap up 90 degrees so the holes aim at the firewall.
We even just used 1 hole on our original XL, didnt want to drill another hole in the firewall & there was 1 hole already there.
Works fine, although we just us it for the kickdown, not the throttle itself.

I've also used the stock 64 PRNDDL with a 67-up C6 column trans, works fine as noted above, but kinda sloppy for manual shifting.
So I just play with the governor & modulator til I'm happy with full-throttle shift RPM & then it's done.

I suppose your plan is ok if you want to shift it every time, but that would make Werby's Wife mad if she had to shift an automatic.

EDIT_EDIT:
Oh, that's Chilly's Merc!
I like the sound of those aerochambers. Like good old glasspacks but way better flow than most of the smallish ones.

[manofmerc]

As far as a manual valve body a Transgo 67-3 shift kit installed in your valve body would work fine .It is a forward pattern full manual shift .It makes shifter selection easier .I used one of these in my drag car before I went to a trans brake .It shifts harder than most other shift kits but not to hard .It has parts and instructions so you can have automatic shifts also .With the forward pattern valve body your selection of shifters becomes much easier.Whenever I would tear down my c-6 the clutches looked like new after 5 years .Good luck Doug

[Jackal]

If the C6 shift lever engagement doesn't match well with the original console shift gates (?) then I would definitely look at going with the stock forward pattern auto VB instead. I'll try to check with those who have done the same swap to confirm so I know which way to go here. Thanks all.

I didn't realize the trans governor was "tunable". Do you have to drop the driveshaft and tail housing to get to it? Any more thoughts on going auto VB w/o the kickdown linkage? I have the original bellcrank and factory style intake to accommodate it, but I assume the linkage is quite a bit different. I already had to re-bend, cut, and thread the original FMX linkage and put a tapped section in-line for adjusting length. Maybe I'm already setup nicely for it to be adapted, but my luck doesn't usually go that way.

[Thumperbird]

I have a wide ratio C6 in a heavy car with 445, 3.5 rear, 2600 stall, Brent did the cam, we were targeting a racy(ish) idle and 500HP/TQ with aluminum heads etc..
It is nice to get it moving a little quicker but yeah the 1 2 shift drops rpm's out of the power band a bit but for 90% of the driving wide ratio is nice.
Hard part for me is I keep expecting an engine to purr, just grew up that way around stockish 390's so having one that is a bit choppy makes me think my tune sucks all the time (maybe it does).
Without experience on various cammed engines I never know what a perfect tune is for my setup in terms of idle/vacuum smoothness/chop etc..

[chilly460]

I wondered why that sounded so ROUGH. That's a Comp 270H (in a little 390).
I thought that video was the 282S or the 427-8v 324-324 cam until I looked.
IF that big Merc has a 3.00 & stock stall it's a dog off the line.

I agree, always surprised it idled that rough for what's a pretty short cam at 270* advertised/224* @ .050" on a 110lsa. 

As a reference, here is same combo with the Survival Motorsports 276/282* 224/230* @ .050" hydraulic roller...fairly similar. 
https://www.youtube.com/watch?v=7auTeu_-kbU

I would say they both can pull O/D cleanly at 1600rpm, they're not "snotty". 

[Jackal]

Thanks for chiming in on the wide ratio gearing. It sounds like they still have a place on the street even with big displacement, shorter gearing, and a decent stall. I think I understand the issue with dropping out of the power band with the larger jump between 1&2. How is the 2-3 shift in comparison with its larger jump too? I'm kind of leaning toward 3.25:1 instead, assuming 2,850 cruising RPM isn't unreasonable.

It sounds like the Comp 270 doesn't typically sound so aggressive? What is initial timing? It seems as though my mild 460 is a lot more choppy @ 10 deg. vs. 14. Same w/ my H-D v-twin @ 6 deg. (stock) vs. 10-12.

[manofmerc]

Jackal A reverse pattern valve body requires its own reverse pattern shifter such as a B&M or Hurst .I wouldn't want to attempt making a factory shifter work with a reverse pattern valve body but I suppose it could be done .Doug

[frnkeore]

I added some info in my gearing chart. You can see that after the 1-2 & 2-3 shift, you are about 2000 rpm higher, in your power band, with the std gearing over the wide ratio gears.

[chilly460]

It sounds like the Comp 270 doesn't typically sound so aggressive? What is initial timing? It seems as though my mild 460 is a lot more choppy @ 10 deg. vs. 14. Same w/ my H-D v-twin @ 6 deg. (stock) vs. 10-12.

It’s setup with 16* initial

[WerbyFord]

If the C6 shift lever engagement doesn't match well with the original console shift gates (?) then I would definitely look at going with the stock forward pattern auto VB instead. I'll try to check with those who have done the same swap to confirm so I know which way to go here. Thanks all.

I didn't realize the trans governor was "tunable". Do you have to drop the driveshaft and tail housing to get to it? Any more thoughts on going auto VB w/o the kickdown linkage? I have the original bellcrank and factory style intake to accommodate it, but I assume the linkage is quite a bit different. I already had to re-bend, cut, and thread the original FMX linkage and put a tapped section in-line for adjusting length. Maybe I'm already setup nicely for it to be adapted, but my luck doesn't usually go that way.

A comp 270S will idle smoother than a comp 270H. Same specs but the solids & lash mellow out the idle.

Yes, to tune the governor you have to drain the trans somewhat, then pull the driveshaft &  tail housing off. Not that bad, you can usually re-use the gasket. The governor valve itself is made from Kryptonite so it cannot be machined by any earthly material. Machinist had to order a special tool & machine it from Apollo Moon Rock. I might have exaggerated a little but not much. Sometimes just swapping governors around will get you there, eg a 428CJ or 429SCJ or 351CJ governor.

For sure you can run the C6 without a kickdown at all, but even then you'd still need the vacuum modulator if you want any automatic shifts.

If you just disconnect the kickdown, the full-throttle shift points will drop 800-1000rpm, which is likely going in the wrong direction.

[Gaugster]

I couldn't live with a GM trans in my car, although I am running a Delco 10SI alternator. Maybe cool to stuff a massive 6R100 in there or something, but I would prefer to keep it fairly near 1967 era save the MSD and electric fan.

If you need any advice on a 6R80 swap let me know. Consider it a compromise between the C6 and the 10R80.

[Royce]

Anybody have any data on how much power a cruiso sucks up vs a C6?  Local argument.... One guy saying the cruiso. I say he is nuts, nothing uses more power than a C6