CK5
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Offsetting rear end gears with power?
- Thread starter mark84k5
- Start date
As it sits I have both sides new inner and outer rockers, kickpanels, I had to cut out and replace some metal on the trans hump flange and mating surface flange, and also a peice out of the door jam which gave me a chance to spray rust treatment in the roof. And I did both cab mounts and on just the drivers side the floor and the floor support that goes from the front of the cab to under the seat not sure what it’s called. Ow yeah and inner and out cab corner on passenger side and tomorrow drivers side.
Looking at the pics and reading the thread your engine may not be stock now. What year is truck ? long or short bed ?
I think @Bent77 cam specs are 210°/220° are at .050 lifter rise.
@folkenheath gear calc says 3.42 for gear ratio me I wouldn't go below 3.73 and probably do 4.1, even with 31's
I think @Bent77 cam specs are 210°/220° are at .050 lifter rise.
@folkenheath gear calc says 3.42 for gear ratio me I wouldn't go below 3.73 and probably do 4.1, even with 31's
So the engine is a tbi 350 and it has swirl port heads.it’s carbed now obviously. The truck originally from the factory had a 400sbc. It’s a 1977 k10 shortbed midwestern rust bucket edition. I tried the spicer rpm calculator and with 3.42 at 80mph I would be spinning 3000rpm. Seems high. I’m gonna need an od trans
How often and long are you realistically driving at 80 mph?
At 70 mph I’m at 3069 RPM, don’t be afraid to let her sing….I think OD transmissions have made everyone forget that 2700-3k rpm was normal when these trucks came out
At 70 mph I’m at 3069 RPM, don’t be afraid to let her sing….I think OD transmissions have made everyone forget that 2700-3k rpm was normal when these trucks came out
So here in Michigan the speed limit on most major highways is 75mph, most people in the fast lane do 80-85 mph. I typically cruise at 80mph for hours at a time. A good example is I live near detroit and head mid way up the state for like 3hrs doing 75-85 mph. This may sound crazy but here in Michigan this is standard operating procedure. My expectations may be unreasonable. You also have to figure we don’t have any rocks to climb and the land here is flat. You would have to go out of your way to find a hill climb or go to an off road park to find rocks to crawl over. We have mud.
More cubes has an ability to deal with crappy gearing.
I know that don’t help much but it works for me.
I know that don’t help much but it works for me.
Yes you would probably be at @3k. An overdrive would be the best.
Your truck probably weighs a bit less than most previous posters were thinking.
My situation. 77 k20 burb, balanced 355, high compression, cam similar to @Bent77 specs, q jet, single 3" exhaust.
I installed a 700r4, 4.1 and 33"s,
From 45 to 60 something it wouldn't pass a micro bus without down shift to 3rd.
At 4.1 in overdrive final gear ratio is 2.87.
I up the gear to 4.88, which is 3.42 in OD. 80 is about 3k, my engine thou is making great power there. Our speed limits here are 75, I normally hang at 70-73, my best mpg to date is 9.7
Worst has been 5.6. even with a 40 gal tank that's only 200ish mile range.
Your 350 will do 3k all day no issues.
Your truck probably weighs a bit less than most previous posters were thinking.
My situation. 77 k20 burb, balanced 355, high compression, cam similar to @Bent77 specs, q jet, single 3" exhaust.
I installed a 700r4, 4.1 and 33"s,
From 45 to 60 something it wouldn't pass a micro bus without down shift to 3rd.
At 4.1 in overdrive final gear ratio is 2.87.
I up the gear to 4.88, which is 3.42 in OD. 80 is about 3k, my engine thou is making great power there. Our speed limits here are 75, I normally hang at 70-73, my best mpg to date is 9.7
Worst has been 5.6. even with a 40 gal tank that's only 200ish mile range.
Your 350 will do 3k all day no issues.
Back when I bought Chloe, (74 K10, 350,350,205. 1/2tons.)
She was kind of a dog driving her.
After a she started running poorly, I punted.
New cam and Lifters, new HEI dizzy.
I used the 1973, L88 Corvette cam, with 222° duration, both intake and exhaust, plus the HEI.
She was a new truck then!
Zippy and loud, fun to drive, you had better have your thunderwear on above 5K rpms.
Then the transfercase fell off, going down the hiway, and my build thread is the result...
So, yes a new cam, Lifters, and dizzy(electronic ignition) willfix a bunch of power problems, if that's what I you're after.
She was kind of a dog driving her.
After a she started running poorly, I punted.
New cam and Lifters, new HEI dizzy.
I used the 1973, L88 Corvette cam, with 222° duration, both intake and exhaust, plus the HEI.
She was a new truck then!
Zippy and loud, fun to drive, you had better have your thunderwear on above 5K rpms.
Then the transfercase fell off, going down the hiway, and my build thread is the result...
So, yes a new cam, Lifters, and dizzy(electronic ignition) willfix a bunch of power problems, if that's what I you're after.
Timing chain maybe used up high lighting the highway gears.
SOP, when doing a cam, new chain & gears
Parts for SBC are cheap, incomparison, to most other engines
Another reason to gear it right.
The SBC will be able to keep it moving. No reason for a big motor with big, expensive parts.
The SBC will be able to keep it moving. No reason for a big motor with big, expensive parts.
More power can over ride crappy gears, but if you swap the gears the more power will be even faster.
Also, typically when you add more power it also raises the peak RPM, which wants more gear, unless you boost the engine with a roots or screw blower for down low boost, but then you would want forged pistons, etc.
Some things can be done to improve power throughout the RPM range, like more compression, a good exhaust, proper tuning with timing and fuel, etc. But these are limited, especially with pump gas. More cubes and boost are the really only "major" things to up the power all the time. You can always add nitrous, that works really well, for short bursts of power at the track, etc. But not for anything other than drag racing, whether it be asphalt, mud, sand, dirt, etc. That can work well, and it's off the rest of the time.
I can help you select parts if you tell me what your goals are, and I can probably get most of them for you.
Also, typically when you add more power it also raises the peak RPM, which wants more gear, unless you boost the engine with a roots or screw blower for down low boost, but then you would want forged pistons, etc.
Some things can be done to improve power throughout the RPM range, like more compression, a good exhaust, proper tuning with timing and fuel, etc. But these are limited, especially with pump gas. More cubes and boost are the really only "major" things to up the power all the time. You can always add nitrous, that works really well, for short bursts of power at the track, etc. But not for anything other than drag racing, whether it be asphalt, mud, sand, dirt, etc. That can work well, and it's off the rest of the time.
I can help you select parts if you tell me what your goals are, and I can probably get most of them for you.
88Silverado
1/2 ton status
Gears are Torque multipliers. To me, this is the cheaper/better way to make things move.
Lots of power/torque on stock drivetrain with crappy gears puts additional potentially damaging power into the Trans, u-joints, differential, etc. Learned that back when I was 16. Built strong engine to make my 62 Chevy utility body truck a sleeper and shortly after was replacing clutches, transmissions and differential/axles. It sounds like there's going to be a compromise somewhere in your build.
I didnt catch what trans you are running but if its not a lockup type in drive you need to take into account the additional slippage of the torque converter and its impact on RPMs. If its lockup or OD, the standard gear/RPM equations work fine. Few calculators include torque converter slippage percentage in the calcs.
In addition, dont bet your tires are exactly the size they say. Most tires are at least 1/2" or more smaller in diameter new so 31s are probably 30.5" and the will wear down from there increasing RPM/torque over time.
Just for comparisons I have 31s on my TJ and re-geared it from factory 3:73 to 4:10. Since the new tires are actually 30.5", with 1:1 lockup final drive im doing slightly over 3000RPM at 70. With a non-lockup trans it would be higher.
Now my K5 was re-geared from 3:73 to 4:56, 35" tires (34.5") lockup/with 0.7:1 OD (700R4) trans, im taching around 2200RPM at 70. At least now I can run it in OD without it kicking out too often. Kinda wish I went with 4:88 with the stock TBI engine.
No matter what you decide the question comes down to "How much gas/mileage can you afford"? Building an engine for more power or re-gearing for more torque increasing RPM "might" cause your mileage to go down and driving/fuel expense go up. Here in CA, with average ~$5.45/gal its something to think about.
Lots of power/torque on stock drivetrain with crappy gears puts additional potentially damaging power into the Trans, u-joints, differential, etc. Learned that back when I was 16. Built strong engine to make my 62 Chevy utility body truck a sleeper and shortly after was replacing clutches, transmissions and differential/axles. It sounds like there's going to be a compromise somewhere in your build.
I didnt catch what trans you are running but if its not a lockup type in drive you need to take into account the additional slippage of the torque converter and its impact on RPMs. If its lockup or OD, the standard gear/RPM equations work fine. Few calculators include torque converter slippage percentage in the calcs.
In addition, dont bet your tires are exactly the size they say. Most tires are at least 1/2" or more smaller in diameter new so 31s are probably 30.5" and the will wear down from there increasing RPM/torque over time.
Just for comparisons I have 31s on my TJ and re-geared it from factory 3:73 to 4:10. Since the new tires are actually 30.5", with 1:1 lockup final drive im doing slightly over 3000RPM at 70. With a non-lockup trans it would be higher.
Now my K5 was re-geared from 3:73 to 4:56, 35" tires (34.5") lockup/with 0.7:1 OD (700R4) trans, im taching around 2200RPM at 70. At least now I can run it in OD without it kicking out too often. Kinda wish I went with 4:88 with the stock TBI engine.
No matter what you decide the question comes down to "How much gas/mileage can you afford"? Building an engine for more power or re-gearing for more torque increasing RPM "might" cause your mileage to go down and driving/fuel expense go up. Here in CA, with average ~$5.45/gal its something to think about.
Hell, I once regeared a '96 Ford Ranger I had from 3.27's to 4.56's. Went from 31's to 33's. I also went from 13mpg to 15mpg all day long. It was so high geared with the 31's that it was always lugging. With the 4.56's and 33's it just revved and was so much happier.
My 392 charger, my Infiniti G37, and my k5 all gained mileage around town and stayed the same on the highway with lower gears than factory. 3.27 to 3.73, 3.54 to 4.08, and 3.55 to 4.88. Load is more of a factor in mileage than rpm in my experience.
Imo you need gear. Modern trans with more gears will keep you in optimal torque band so you can get away with less power.
before you get to far down the rabbit hole whether you gear swap or change the engine build/tune you need to make sure the rest of the parts support the combo. For example does the torque converter have enough stall speed to help the engine build enough rpms to where the motor is in the power range as it starts to move? or is the stall speed too low lugging the engine or making it feel sluggish?
