when to shift?

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diymirage

diymirage

HP@idle > hondaHP@redline
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hey guys

ive noticed when I run my car in "drive" the latest it will shift is about 4000 RPM but I would like it to shift higher

so, if I drop her in first and just shift manually, 1st-2nd-drive when should I shift?

the car is a 72 duster with a 360 (stock bore, fresh heads, 268 comp cam, weiand action plus dual plane intake, eddie 600 CFM carb, dougs headers through summit 2.5 dual exhaust, ignited by a skip white distributor , sorry, I don't know the exact timing)

now, I had the carb rebuild by the person I bought it and the intake from and set up roughly for the combo im running BUT I have not had it fine tuned

where is the best spot to shift, without risking exploding the engine?

(or is there a simple adjustment I can make to the kickdown cable (running a lokar set up) that would allow it to shift later? I tightened it up about 1/8th of an inch already which made it shift harsher, but not later)

thanks for the advise, and sorry for the newby questions
 
Thinking 5300-5600 , depends on where it drops off. What gears/converter/ any head work/porting ,done?
 
Abodybomber said:
Thinking 5300-5600 , depends on where it drops off. What gears/converter/ any head work/porting ,done?
Click to expand...

stock convertor, 71/4 rear end with highway gears (I would guess 2.76s)

the heads were shaved a few thous to ensure flatness, a few new valves were installed but no porting or any other performance work was done
 
Start with 4800-5200, see how it feels. That camshaft would really wake up, with 3.55 's out back.
 
Feel it from the seat of your pants, when the cam and carb pulls good and then you should feel when it is time to move up a gear.. I have seen folks stay in a gear to long when they should have shifted sooner .. just this old farts opinion :toothy1:
 
i have been driving since 1965. ONLY chrysler car / trucks. from slant 6 to 500 inch max wedges. for me in street driving ( NOT STREET RACING) i have found no advantage going to the full RPM. i find shifting 1000 RPM short of full RPM does just fine. just my idea.
 
"The right way" to find starting shift points is to plot performance. You can do this many ways, a torque / hp dyno curve, an acceleromerter in - car, many of which are available today, or even a home-built torque cell

"What you want" is a performance curve in as many gears as you can get, both below and above max. This of course might not be possible in high gear.

If you cannot do that, plot one gear, like first, and plot the rest from calculated transmission gear ratios

Starting shift points are 'where they cross' in each gear..................

Random curves off the internet:

73345-high-revs-myth-fact-gears-jpg.jpg


Just look at this and think about it

It doesn't matter if you plot on the left, hp, torque, or acceleration

It doesn't matter on the bottom if you plot speed or RPM

Look at 1st and 2nd gear, the blue and the green.

THINK about being in first gear and revving way past the peak. The car accelerates, peaks, then slows down "in acceleration." shouldn't you shift?

DEPENDS.

Now look at the curve for second gear. "At what point" would you accelerate more quickly in 2nd gear as opposed to the "falling peak" from 1st?

EASY. "Where the curves cross in this case at about 40 mph on the bottom scale.
 
Abodybomber said:
Start with 4800-5200, see how it feels. That camshaft would really wake up, with 3.55 's out back.
Click to expand...

a bigger rear end and taller gears are definitely on the list, as soon as the budget picks back up or disaster strikes the 7.25 and forces my hand
the way the car sits now I can shift it manually into second at about 5K and 60 MPH so I think I could stand to come up on the gearing abit

AJ/FormS said:
.gtechpro.com
The only way to know. Well not only/only. But this tool will help you, in many ways.
Click to expand...

that looks pretty spiffy
I am planning on redoing the dash (in time) to get some more modern gauges and what not, I should look into that doohickey

moe7404 said:
i have been driving since 1965. ONLY chrysler car / trucks. from slant 6 to 500 inch max wedges. for me in street driving ( NOT STREET RACING) i have found no advantage going to the full RPM. i find shifting 1000 RPM short of full RPM does just fine. just my idea.
Click to expand...

most of the time I would agree
I don't mind the way the car shifts at all, but every onces in a while I would like to wring her out a bit more

SGBARRACUDA said:
I don't know but if were me, with that 7 1/4 rear I wouldn't take it above 3000 RPM!
Click to expand...

see reply to Abodybomber :D
TrailBeast said:
This will solve your WOT shift problems, if you are interested, because as you found adjusting the cable can only do so much.
Click to expand...

I read an article in hotrod magazine about those
they seem to work real well, but it is just a bit more involved then I want to get right now
though it is definitely something to consider down the road

67Dart273 said:
"The right way" to find starting shift points is to plot performance. You can do this many ways, a torque / hp dyno curve, an acceleromerter in - car, many of which are available today, or even a home-built torque cell
Click to expand...

this makes perfect sense
the duster is my first auto car (not counting the wifeys rides) and I had it pretty much down with my stick shift cars
I just figured i'd see what the consensus was here, seeing how im new to the V8s, 727s and what not


thanks for all the help guys
 
Okay, the cats outta the bag!
Now imagine that graph with a gear splitter, and more useable ratios.
Firstly, I dont have to wring it out, to catch the next gear,and secondly, more average hp gets put down,during the run,so a smaller cam goes as fast or faster,not necessarily quicker, than with a regular tranny.
Chrysler 3 speeds are pretty wide ratio which is fine with a dedicated track car. But kinda sucks on a streeter or warrior car.With %splits of 59 and 69 outshifting at 6500, means dropping into 2nd at 3800ish, well below optimum.This makes the powerband requirement 2700! Outshifting 2nd, drops into 3rd at 4500ish, reducing that powerband to 2000rpm, which is a bit better.Of course these numbers dont take into account any TC slip.
With a 4speed, things are looking up; %spits are;72-73-71. So outshifting 1st at 6500,drops into 2nd at about 4700,making the powerband requirement 1800
A gear splitter, at 78% rpm drops reduces the powerband still further to 1400.
The kicker is finding a set of factory gears to take advantage of the splitter. Both the 3.09 boxes work pretty well. Here are the ratios and splits;
The od box; 3.09-1.77-1.00-.73 O/D.,splits; 57-56-xx(cant use od), when split this works out to 3.09-2.41-1.77-1.38-1.00 and splits are 78-73-78-72-78
The direct4th box; 3.09-1.92-1.40-1.00 splits; 62-73-71. When split;3.09-2.41-1.92-1.5-1.4-1.09-1.00-78 Obviously some of those are no good; so I track-shift(qtr); 3.09-2.41-1.92-1.4-1.09, the %splits are;.78-80-73-78. and track-shifting in the 1/8 is;3.09-2.41-1.92-1.50 splits are 78-80-78.
Street shifting is 3.09-1.92-1.4-1.09-.78 splits are 62-73-78-71od.
Sounds complicated,I know. Got used to it in a hurry.
93 in the 1/8 and cruising at 2200@ 60,with a relatively small cam, made it all worthwhile.


...................So imagine that..........
 
I've always put the gear selector in 2nd and let the transmission shift 1-2 by itself and focus on the 2-3 shift yourself.
Manual 1-2 shifts hardly ever happen at the rpm-point you want them to happen.
 
Dyno the car. Start with shifting at peak HP and try 200 under and 200 over. If ET changes you know which way to proceed.
 
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