Gears, Stall & Shift Points

[273]

Some of you may know I picked up a 68 Valiant this year. Low mileage 37,000 California car original 273. But now has a 380hp create engine less than 5,000 miles. tti headers and duels with an x pipe.
Rebuilt 727 with 2800 stall and manual shift. Here's where the original owner neuter the car 8 3/4 sure grip 2.96 gears.

Bought a bunch of parts to install this winter. Lots of suspension. But also some engine. Want an 8 month daily driver that can go to the odd autox and drag event.

For the engine I got MSD and Holley sniper to handle fuel and spark. And Rhoads lifters and airgap to help regain under 3500 power. I will install Rhoads and airgap later want to do a before and after drag and mpg test.

This a magazine dyno of a 380hp create engine. I know some will disagree with the numbers but its the dyno curves that matter.

I look at that and its pretty impressive for a truck engine with a cam.

But 1st before gearing, stall and shift points got to break down the engine curve.

1st and obvious 5000-6000 rpm is the stongest making between 97-100% so basically flat. Next 4000-5000 rpm still pretty strong the power going no less than 81%. Under that the numbers arent bad but the less time I imagine I stay there the better especially under about 2800 rpm where Im make 50% or less power.

1st up shift points. Im guessing if I can keep the engine in 80% power range when shifting the better? So shifting at 6000 rpm would drop me to about 3500 rpm or 68% of peak power. I assume the power isnt just gonna drop off after 6000 rpm. Might even be at 333 hp at 6500 rpm so if I shift about there it would drop to about 4000 rpm and still be at 333 hp in the 80%.
So again Im guessing I would have to try every 100 rpm above 6000 rpm to find the right shift point ? Plus what would a safe redline of this engine be 6500 rpm ?

2nd stall Im kind of stuck with the one I got for now and hope the guy made a decent choice. Stall is one of the areas I have least knowledge.

So Im guessing 2800 rpm would be the foot brake stall and flash would be more likely 4000 rpm or over ? Im also guessing the stall will slip a lot especially at the lower rpm. Like say at 10 mph if the engine was direct drive it would be revving 1000 rpm but the converter will slip into the 2000 rpm range, getting it into the higher hp range like 180 hp vs 80 hp even though it will lose some hp to the slippage?

If that is the case I can see why some would say stall is more important then gears.

3rd gearing. I see the advantage of more gear is to get the rpm up for any given mph. Or to get out of the trouble areas sooner (quicker) like 2800-3800 and especially under 2800 rpm.

With the 2.96 gears it will be 30 mph before i leave the 2800 rpm and under powerband.
And 41 mph before i start to get into the 80% powerband 4000 -6000 + rpm.

If I went 4.10 Id be in the 4000-6000 + powerband at 29 mph.

4.10 @ 29 mph = 333hp
2.96 @ 30 mph = 200hp about*
This is why gears are important.

Im gonna leave this to last. Haven't decided if 3.91-4.30 with OD or 5/6 speed or just 3.23 or 3.55 and 904 deep 1st and 2nd gear etc...

I know theres some questions but it is more just thinking or rambling out loud any insights or thought would be appreciate

 

[nm9stheham]

Are these questions/musings to minimize ET on the strip? For auto-x, I'd be looking at things quite differently.

 

[273]

Drag strip

 

[moper]

I think you're approaching it backwards...

1. Gearing - I would gear it to trap at 6K. It might rev there, but it won't make power or accelerate as quick. So no need to rev beyond that.
2. Stall - You want to consider a high dollar convertor because of the mixed use. This is beyond a "9.5 street strip" deal from Dynamic. Call Ultimate and talk to them about your use. The drag racing will not be the same as the autocross. So the convertor has to be a compromise to all three (daily driver, drag, and auto cross). It will be whatever they tell you.
3. Shift points - Every car will have it's own perfect shift points. That's determined by the power curve, the suspension, the driveline, etc. Your dyno curve will not be the same as the curve in the car. So don't use the published figure. I would start with a shift point of say... 5K. Then walk the 1st gear shift up 100rpm at a time while maintaining the 2-3 shift at 5K. Once you get the lowest ET, then kep that for the 1-2 point, then start moving the 2-3. A log book will be invaluable as you do this.

 

[roccodart440]

I agree with Mopar on all 3 points, gear it to trap at 6k or really close to it in 3rd gear. Mine makes peak power at 5,800 and traps at 6,200. I run 4.56 gears and a 28" tire. It traps 11.70@114mph.

I've tried shifting into OD and I lose nearly half a second of ET. I'd like to play around with tire height, but the car is fast and very consistent, so chasing whatever little bit of time might be in it isn't worth the added cost. I'd actually be most interested in trying a taller tire which would effectively drop my gear ratio down a tad on the street. Right now I turn 2500@60mph in OD.

If you want more convertor, and that car can happily use more convertor. Again, get a high quality convertor. They aren't cheap, but you'll be happy with the money spent. Ideally that car would have a 5k convertor but for street use you'll have to compromise and a vert in the 3500 to 4k range set up for your use wil most likely fit the build nicely and really wake the car up at the strip. You'll never know there is a higher stall under normal use if you get a good convertor.

 

[nm9stheham]

The drag racing will not be the same as the autocross. So the convertor has to be a compromise to all three (daily driver, drag, and auto cross).

That is my mindset.... auto-x, road race, rally is not about max HP or torque all the time... in the corners, it is about using the throttle to get exactly the torque for the right forward thrust and rear tire drift angle through each segment of each corner throttle steering, if you prefer, and which is important to a higher degree in RWD than in FWD or AWD. With the variety of corner speeds and only 3 gears, you're gonna need a wide usable torque band, and your engine looks fairly decent for that. But then, with an auto trans, the torque converter can ruin it .... a high stall one will leave you with constant hunting with the throttle in the lock up RPM range to get to that exactly right rear wheel torque. And when you achieve it for one 0.1 sec segment, the best wheel torque will change in the next 0.1 sec segment as the turn radius changes. (It'll be kinda like driving with the driveshaft made of rubber erasers that twists and winds up LOL)

If I was gonna do auto-x only, I'd be looking at a stall speed in the stock to 2200 RPM range, to get rid of the 'torque ambiguity' that a high stall TC will have in the RPM ranges below lock-up.

Which leads to the point made above: drag race is a whole 'nother story where you are looking for max torque all the time, not variable torque, and hence the compromise in the TC for this multi-use.

Time for a 4 speed for anyone wanting to be serious in auto-x and such....

 

[273]

I would love to swap a TKO 600 but dont have the coin. Even if I saved for it, we're talking years.

Might be able to do a 500 or 518 swap next winter or so.

I might still decam I'm seeing how the Rhoads lifters and airgap play out. If i do plan on over drive I'll probably swap in 3.73-4.10 this summer if not 3.23-3.55. Right now have 2.96 sure grip.

Stall I'll have to live with what I got for now.
If I do decam or the Rhoads work enough. So I could run less stall I probably would.
Mileage is somewhat important to me closer to 15 mpg intown would be good.

I dont plan on it to be a track star on either track drag or autox. I just want a decent powered car thats a daily 8 months out of the year driver. Thats able to go to the odd autox and drag events. Now who knows I might get the racing bug and everything goes out the window.

As far as stall is concerned for the drag track. I assume even a farily high stall can help et's even if the cam don't require one ??
What I mean by that if I were to put in a cam that works with stock stall. Still some more stall over stock would help et's ??

Like said not looking for Max performance but do want the best compromise. Less stall seems the way to go for daily driver and autox even if I have to drop a cam step or two to do it.

Im in no rush. See how what I got plays out and go from there.

Just trying to come up with a game plan.

 

[Inertia]

Shift-point. - As mentioned, all engine shift points vary as to vehicle. I've found and recommended downloading a G-meter app to most smart phones. Tape, or secure the G-meter/phone near the tach, establish when g's. start to drop, then start experimenting at 200rpm below G drop-off.

 

[nm9stheham]

I would love to swap a TKO 600 but dont have the coin. Even if I saved for it, we're talking years.

Might be able to do a 500 or 518 swap next winter or so.

I might still decam I'm seeing how the Rhoads lifters and airgap play out. If i do plan on over drive I'll probably swap in 3.73-4.10 this summer if not 3.23-3.55. Right now have 2.96 sure grip.

Stall I'll have to live with what I got for now.
If I do decam or the Rhoads work enough. So I could run less stall I probably would.
Mileage is somewhat important to me closer to 15 mpg intown would be good.

I dont plan on it to be a track star on either track drag or autox. I just want a decent powered car thats a daily 8 months out of the year driver. Thats able to go to the odd autox and drag events. Now who knows I might get the racing bug and everything goes out the window.

As far as stall is concerned for the drag track. I assume even a farily high stall can help et's even if the cam don't require one ??
What I mean by that if I were to put in a cam that works with stock stall. Still some more stall over stock would help et's ??

Like said not looking for Max performance but do want the best compromise. Less stall seems the way to go for daily driver and autox even if I have to drop a cam step or two to do it.

Im in no rush. See how what I got plays out and go from there.

Just trying to come up with a game plan.

That is where we went with my son's 'cuda with the 340; we live in the mountains and we both have rallied a lot and love to 'run' the twisty roads.
- Mild Crane 268 cam with slow ramps to get the engine well up on the torque curve by 2000 RPM or so
- Higher CR to enhance that low end torque
- Good head breathing, 1.6 rockers, and headers are there to extend the top of the RPM range; we have not determined the top end where the torque falls off (my son is cautious) but I expect it to be 6000 or a bit more and so we should have a nearly 3:1 RPM range engine with solid, usable torque
- 2200 RPM stall to get it locked up early so you have that predictable torque control to the rear wheels

The first time we wrung it out a bit, I headed into a 60-70 MPH corner aggressively, braked hard, then put the throttle where I thought it ought to be... the torque response to the rear wheel was instantaneous and on the money, and with the Biltsteins and suspension bits, it 'set' the car just right with the prefect amount of rear drift and the car powered through the corner just right; the torque modulation via the throttle through and out of the corner was excellent.

It is a beautiful thing when the combo is right. (And 3.55's in the rear help! The GearVendors unit is there for economy.) That' is just one case to think about as you plan.

 

[273]

This engine is very strong from about 2000-2500 to 6000 rpm. Under 2000 rpm I have to drive in 2nd gear intown or it lugs.

I wouldn't went with this cam or intake. The cam seems model after a thumper type cam. I kind of like the idle, sounds nasty but Id rather have under 2500 rpm power.
I figure Rhoads and airgap will help a lot.
Seen an M1 vs airgap shootout and engine picked up around 30 lbs-ft peak and 20 bs-ft average down low. And no loss of peak power.

 

[Abodybomber]

I would love to swap a TKO 600 but dont have the coin. Even if I saved for it, we're talking years.

Might be able to do a 500 or 518 swap next winter or so.

I might still decam I'm seeing how the Rhoads lifters and airgap play out. If i do plan on over drive I'll probably swap in 3.73-4.10 this summer if not 3.23-3.55. Right now have 2.96 sure grip.

Stall I'll have to live with what I got for now.
If I do decam or the Rhoads work enough. So I could run less stall I probably would.
Mileage is somewhat important to me closer to 15 mpg intown would be good.

I dont plan on it to be a track star on either track drag or autox. I just want a decent powered car thats a daily 8 months out of the year driver. Thats able to go to the odd autox and drag events. Now who knows I might get the racing bug and everything goes out the window.

As far as stall is concerned for the drag track. I assume even a farily high stall can help et's even if the cam don't require one ??
What I mean by that if I were to put in a cam that works with stock stall. Still some more stall over stock would help et's ??

Like said not looking for Max performance but do want the best compromise. Less stall seems the way to go for daily driver and autox even if I have to drop a cam step or two to do it.

Im in no rush. See how what I got plays out and go from there.

Just trying to come up with a game plan.

Rhodes should mellow it , a bunch ....
What's idle vacuum, on that big stick?

 

[Abodybomber]

This engine is very strong from about 2000-2500 to 6000 rpm. Under 2000 rpm I have to drive in 2nd gear intown or it lugs.

I wouldn't went with this cam or intake. The cam seems model after a thumper type cam. I kind of like the idle, sounds nasty but Id rather have under 2500 rpm power.
I figure Rhoads and airgap will help a lot.
Seen an M1 vs airgap shootout and engine picked up around 30 lbs-ft peak and 20 bs-ft average down low. And no loss of peak power.

Ironically, I am headed the other way. Have the air gap ,and a Howard's similar at .050 " ,quicker ramps..." supposedly "
Picked up a single plane from here ,and a torque converter that stalls tight @ 3200..,with 2.2 torque multiplication. (old Turbo Action converter . )
Just a basic rule : Taller the tire , or lower numerical gears..raises the converter stall speed ,and puts more load on the drive train ..
A , couple of known old school knowledge , and you need,to start thinking how this may effect your suspension needs ..straight line racing.

 

[273]

Rhodes should mellow it , a bunch ....
What's idle vacuum, on that big stick?

Not sure but it feels like it wants to vibrate every bolt loose at red lights probably less then 10

 

[Abodybomber]

Not sure but it feels like it wants to vibrate every bolt loose at red lights probably less then 10

That's, usually about right... 8 " inch is the norm...I have 10-11 " inch ,with a smaller advertising cam . With the air gap RPM ..

 

[273]

That's, usually about right... 8 " inch is the norm...I have 10-11 " inch ,with a smaller advertising cam . With the air gap RPM ..

Id like to see the valve opening and closing points on this cam, probably similar to the thumper cams out there.

If I was you Id stick with airgap, single plain probably won't gain anything up top and just lose bottom end. Unless traction is a real problem than losing some bottom might be whats best.

 

[nm9stheham]

This engine is very strong from about 2000-2500 to 6000 rpm. Under 2000 rpm I have to drive in 2nd gear intown or it lugs.

I wouldn't went with this cam or intake. The cam seems model after a thumper type cam. I kind of like the idle, sounds nasty but Id rather have under 2500 rpm power. I figure Rhoads and airgap will help a lot.

With that description of the cam operation around town, I would go straight to another cam. (And I would say you have made the right type of comparison with the thumpr.) The intake is not going to fix too much overlap which is what is causing the low speed suffering; the Rhoads lifters may fix it some but it may not do enough so then you will spend $$ again. But they are on the right track IMHO. If you do use the Rhoads, let us know how it turns out.

BTW, my son's 340 is at 14-15" vacuum at 850-900 RPM idle. So your a loooong way from there, cam wise.....

For comparative purposes, his cam is a Crane Z-268-2, 212 duration at .050" lift, 268 advertised (intake duration numbers), 112 LSA, 5 degree ground-in advance, installed at 106 ICL. SCR is 10.0:1. Smokes tires from stop sign at a bit over half throttle with those 3.55 rear gears.... gobs of low RPM torque.

Again, we are geared towards road race/rally type of use.

 

[roccodart440]

I would love to swap a TKO 600 but dont have the coin. Even if I saved for it, we're talking years.

Might be able to do a 500 or 518 swap next winter or so.

I might still decam I'm seeing how the Rhoads lifters and airgap play out. If i do plan on over drive I'll probably swap in 3.73-4.10 this summer if not 3.23-3.55. Right now have 2.96 sure grip.

Stall I'll have to live with what I got for now.
If I do decam or the Rhoads work enough. So I could run less stall I probably would.
Mileage is somewhat important to me closer to 15 mpg intown would be good.

I dont plan on it to be a track star on either track drag or autox. I just want a decent powered car thats a daily 8 months out of the year driver. Thats able to go to the odd autox and drag events. Now who knows I might get the racing bug and everything goes out the window.

As far as stall is concerned for the drag track. I assume even a farily high stall can help et's even if the cam don't require one ??
What I mean by that if I were to put in a cam that works with stock stall. Still some more stall over stock would help et's ??

Like said not looking for Max performance but do want the best compromise. Less stall seems the way to go for daily driver and autox even if I have to drop a cam step or two to do it.

Im in no rush. See how what I got plays out and go from there.

Just trying to come up with a game plan.

Spend your money once.

An OD transmission is virtually invaluable in a street driven car.

This is mild crate engine. You don't' need Rhoades lifters. I'd buy a new cam before I bought them for any engine.

Even without an OD trans you can comfortably run more than 2.90 gears.

As far as flash stall. Ideally it's 500rpm over where the engine makes peak torque. FOr a street car, usually that means you compromise a little bit. Like I said a mild 3500-4000 stall will make you plenty happy and wake that thing right up.