Author Topic: Stepside with no low end power  (Read 883 times)

Offline Chuck Step-a-side

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Stepside with no low end power
« on: May 24, 2020, 09:24:41 AM »
During my 6 years ownership of this Frankenstein '84 Stepside, there were so many thing wrong with this truck from the drilled out motor mounts pivot holes to the water pump turning in the wrong direction that it over-heated the engine and caused the rings to prematurely wore out. I have purchased the truck with the engine converted to a serpentine belt set up by use of a 90's S10 serpentine bracket assembly and they used a wrong water pump pulley to were the belt was riding half ways off the pulley. Now that I have replace the worn out engine with a used low mileage crate motor 350 and all the wrongs corrected. The motor now idle smoothly with no hesitation at WOT on a open road. I feel the truck lacks low end power as the engine just gradually get to the top speed. I don't know if the kick-down is working on the rebuilt transmission and would it make a big difference if the it did. I know the kick down cable is set to pull during WOT. The engine is a crate 350 with rebuilt TH350 transmission and a Edelbrock 1406 carb and Edelbrock Performance manifold, mechanical fuel pump, dual exhaust and 10 bolt rear end. The Edelbrock secondary has been double checked and open all the way and my total timming is set at 34 degrees.  Am I wrong to think I should be able to spin the rear tires when I floor the pedal? I want to know what would be the next step to increase my low end power? Should I work on the carb. rod and jet tuning or do I need to do major upgrades on the cam and rear end? Thanks, Chuck

Offline VileZambonie

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Re: Stepside with no low end power
« Reply #1 on: May 24, 2020, 09:30:14 AM »
First is I think you need to advance the ignition timing. If you aren't getting the downshift then check the detent cable adjustment again and make sure the vacuum modulator is hooked up and receiving a vacuum signal. If you manually shift it how does it do? What final drive gear ratio do you have?
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Offline Chuck Step-a-side

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Re: Stepside with no low end power
« Reply #2 on: May 24, 2020, 04:08:53 PM »
So I should throw the "34 to 36 degree total advance timing idea setting" out the window? Where should I set the timing?
The vacuum modulator is hooked up and getting manifold vacuum at 12 HG and no downshifting. I have the kickdown cable pulling out and ending at WOT, with a little cable play at idle before pulling. The shift will manually downshift into 2nd and 1st gear and the final drive gear ratio should be 1:1, I would need to contact the trans. re-builder to verify. Should I try adjusting the modulator or not?

Offline TB24

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Re: Stepside with no low end power
« Reply #3 on: May 24, 2020, 04:55:38 PM »
Do you know what rpm your total timing is in by?


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Offline Chuck Step-a-side

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Re: Stepside with no low end power
« Reply #4 on: May 24, 2020, 05:00:18 PM »
3000 rpm

Offline TB24

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Re: Stepside with no low end power
« Reply #5 on: May 24, 2020, 05:17:59 PM »
I would wait for VZ’s recommendation on timing. When it comes to final gear ratio I think he is meaning your final running gear ratio or your rear end ratio. If it’s a high rear end ratio mated w a cam not made for the low end you may not have a great combo


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73 K10 Custom 350/sm465/np208

84 K10 Silverado 350/sm465/np208

Offline VileZambonie

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Re: Stepside with no low end power
« Reply #6 on: May 25, 2020, 07:08:15 AM »
There are two timing pointers for SBC, 12 o'clock and 2 o'clock. Did you validate the mark at zero with the #1 piston all the way up or did you just assume the marks are correct? Also, are you running a stock vacuum advance HEI or aftermarket distributor? How do you have the vacuum advance hooked up? After you verify your marks, check the timing again with the vacuum advance hooked up at 2,800-3,000 RPM and see what you get for a reading.
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Offline VileZambonie

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Re: Stepside with no low end power
« Reply #7 on: May 25, 2020, 07:11:48 AM »
Oh and if your final drive ratio was 1:1 that would explain your problem  :D Final drive ratio is the last gear reduction in the driveline (the rear axle gearing), typically 2.73:1 - 3.73:1 was used in the C10's. If it's stock it is probably 3.08:1 for your truck
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Offline Chuck Step-a-side

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Re: Stepside with no low end power
« Reply #8 on: May 25, 2020, 09:16:43 AM »
I have replaced the 8" balance wheel with pointer at 2 o'clock and I did set the timing mark at zero and distr. pointing to spark plug one. The truck originally had a 305, but when purchased it had a center bolt 350 and now it has a standard pre-80's 350 and I believe the distributor is a aftermarket. I know that the truck has a 10 bolt rear end and so it should be a standard 3.08:1 like you say.

Offline VileZambonie

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Re: Stepside with no low end power
« Reply #9 on: May 25, 2020, 06:25:17 PM »
I have replaced the 8" balance wheel with pointer at 2 o'clock and I did set the timing mark at zero and distr. pointing to spark plug one.

Okay but this still doesn't answer the question of whether or not you physically verified #1 piston is at TDC.

I believe the distributor is a aftermarket.

Take some pics if you aren't sure so we can see
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Offline Chuck Step-a-side

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Re: Stepside with no low end power
« Reply #10 on: May 26, 2020, 07:33:07 AM »
I did verify the piston #1 was at the TDC on the power stroke and the timing pointer was on Zero while the distributor is pointing at cylinder #1.


Offline JohnnyPopper

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Re: Stepside with no low end power
« Reply #11 on: May 26, 2020, 02:10:33 PM »
Your distributor may be off a tooth?  ???

When I have set one up, the rotor is moving away from the cylinder one tab on the cap, not pointing directly at it. 
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1973 C-20, 3+3 454 4BBL TH400  Water Injection
1978 K-10, 350 4BBL TH350 NP203 M.M. Part time Kit/Hubs
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Offline Chuck Step-a-side

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Re: Stepside with no low end power
« Reply #12 on: May 26, 2020, 07:09:01 PM »
You could be right. I have one those newer clear distributor caps and pointer set up and it should be easy to verify. I'll check on that tomorrow. Thanks.