air/fuel ratio vs cam/lifters? - S-10 Forum
 
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post #1 of 15 Old 06-17-2015, 09:18 AM Thread Starter
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air/fuel ratio vs cam/lifters?

Okay folks,
I have done my 2.8 swap. In the process I changed he stock cam to a comp cam. It had a little longer duration and slighter more lift. The truck has very little power on the bottom end and needs to have fuel pumped in(pumping the gas pedal) to get it up and running. It "appears" to be running lean.

I thought the air/fuel ratio was a constant. If you had it set to a certain mixture(altitude affecting ratio) then it was good to go. The cam and lifters would vary the amount of the mixture, but the ratio should not be changed. My truck seems to be telling me otherwise. Can anyone comment on this specifically.

On a side note, I have learned that for low end torque(which is what I really want), a cam needs to have a shorter duration, increased lobe separation, and a higher lift. As such, I ordered a crower cam and lifters for the truck. I state this because I believe the low end problems are probably due to the current configuration in my motor. I am going to goof around with the jets and fuel mixture to see what changes it will make.

Thoughts anyone?

Thanks,
mark


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post #2 of 15 Old 06-17-2015, 04:00 PM
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Re: air/fuel ratio vs cam/lifters?

I got the middle grind comp cam and I'm pleased with the torque. I just got the 1.52 rockers.
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post #3 of 15 Old 06-17-2015, 04:08 PM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

I got the 16-232-4 comp cam and used 1.6 rockers.

What cam did you get?

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post #4 of 15 Old 06-17-2015, 06:39 PM
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Re: air/fuel ratio vs cam/lifters?

That's what cam I used also. 16-232-4
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post #5 of 15 Old 06-17-2015, 07:32 PM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

What carb are you running, or is it FI?
Maybe I'll mess with it a bit and see if I can get her to run a little better.

mark

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post #6 of 15 Old 06-17-2015, 08:40 PM
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Re: air/fuel ratio vs cam/lifters?

Its a 3.4 with EFI. I put 4.3 fuel injectors in the stock 2.8 throttle body.
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post #7 of 15 Old 06-18-2015, 08:47 AM
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Re: air/fuel ratio vs cam/lifters?

Mark, IIRC - you're running a carb, yes? I thought you bought a Weber for your rig.

A few dumb questions...
1. Timing chain marks were right on the dots - true?
2. Distributor lines up with number 1 and firing order is 12345? (check it)
3. No vacuum leaks? (good idle)
4. Timing advanced enough? This may be the issue. since your engine is carbed, I usually advance the timing until the engine pings, then retard until the ping is gone. I rarely use a timing light.
5. And very important - rockers adjusted correctly? If any are tight, you won't have good power.
Best bet is to adjust them with the engine running. They will pump up and you don't have to do the "extra" 1/2 turn routine. Back off until clatter, adjust until noise is gone. Works every time.
Even at higher altitude, you should have low end power.

Hope this helps...

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post #8 of 15 Old 06-18-2015, 10:12 AM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

Quote:
Originally Posted by Mad Max View Post
Mark, IIRC - you're running a carb, yes? I thought you bought a Weber for your rig.

A few dumb questions...
1. Timing chain marks were right on the dots - true?
2. Distributor lines up with number 1 and firing order is 12345? (check it)
3. No vacuum leaks? (good idle)
4. Timing advanced enough? This may be the issue. since your engine is carbed, I usually advance the timing until the engine pings, then retard until the ping is gone. I rarely use a timing light.
5. And very important - rockers adjusted correctly? If any are tight, you won't have good power.
Best bet is to adjust them with the engine running. They will pump up and you don't have to do the "extra" 1/2 turn routine. Back off until clatter, adjust until noise is gone. Works every time.
Even at higher altitude, you should have low end power.

Hope this helps...

Confucius say: Truck who live in mountain breathe hard...
Max
Thanks for chiming in, I appreciate it.
2-4 dead on. One I hope so. Number I will redo.

I have a bad suspicion that maybe the crank/cam is one tooth off - would that cause this???

I figure since I have new cam coming and new intake, I will wait to see until I get it apart and back together.

I'll report back.
mark

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post #9 of 15 Old 06-22-2015, 10:34 AM
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maybe posting your cam card specs? if you installed the cam straight up and not degreed you may have some advance ground in. my lunati had about 5 ground in and am at about 18 degrees btdc. also had to rejet for higher lift.
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post #10 of 15 Old 06-23-2015, 10:16 AM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

Quote:
Originally Posted by greasemonkeys10 View Post
maybe posting your cam card specs? if you installed the cam straight up and not degreed you may have some advance ground in. my lunati had about 5 ground in and am at about 18 degrees btdc. also had to rejet for higher lift.

Hey GM,
What does this mean? I'll post the specs in just a few. The timing does seem to be very advanced to get it to run at any decent way. Setting the timing to factory specs seems to run pretty poorly.

Here is a link to the specs on the cam I installed.
http://www.compcams.com/Company/CC/c...x?csid=56&sb=2

thoughts??

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post #11 of 15 Old 06-23-2015, 10:47 AM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

I have started researching this, degreeing a cam. What I did was install the gears onto the cam and the crank. They only install one way. I think lined up the timing marks on the two gears. Was this wrong?

I did not use a degree wheel or anything else. Time to do more research.
mark

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post #12 of 15 Old 06-23-2015, 09:14 PM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

Okay,
Here is a pic of the cam card.

My research says that degreeing a cam is essentially checking the cam card against what the cam actually has, and if necessary, adjusting the cam with bushings or other methods. I installed my cam straight up, so as long as the came is close, I would thik this should be fine.
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85 S10 Durango 2.8L extcab rwd 36k actual miles.
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post #13 of 15 Old 06-23-2015, 09:33 PM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

here is a link to the crower cam that I am going to put in(replace the comp cam).

http://www.crower.com/camshafts/chev...u-pro-cam.html

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post #14 of 15 Old 06-25-2015, 09:44 AM
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Re: air/fuel ratio vs cam/lifters?

you degree them because some have advance ground in. you degree for true 0 for best performance. of course this is really for high performance applications where every bit of power is needed to win a race. not required for a street build. what i would do is increase your main jets up one size (.5) and run a higher ignition advance

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post #15 of 15 Old 06-25-2015, 10:36 AM Thread Starter
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Re: air/fuel ratio vs cam/lifters?

I have been thinking on those for a bit. I think you are absolutely correct.

When I put in the mods in the motor, it essentially gave it "more displacement". It is not really a bigger motor, but because it has a different cam and 1.6 rockers, it acts like a bigger motor, it breathes better, and sucks more volume. This in turn would affect the function of the carb. Hence, the need for re-jetting.

Max also mad a comment about over tightening the valves. I am going to redo them and set to zero lash. I will likely get to that this weekend.

Thanks for the input
mark

85 S10 Durango 2.8L extcab rwd 36k actual miles.
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