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Old 04-02-2018, 07:02 PM   #1
grubsster
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Help with rpm drop when put in drive.

Hi all. I recently installed my 283 engine and had a major issue with driveability. Contacted Comp cams, B&M and Summit. All recommended a 2,000 stall converter. I swapped in a B&M 20400 which is a 2k stall. My issue is better but I'm dropping from 900 rpm to right around 500 rpm in drive. I would prefer to set my idle around 800 and have my in gear idle around 600. Where should I start? Timing is @12 degrees initial which is what the engine builder recommended but I think since the cam is a mild performance cam I could go higher. Any help is appreciated.

283, vortec heads ,edelbrock 600 ,and rpm intake comp cam with a 218 duration@ .050 ,th350 ,3:08 gear on rear end 1966 c10 long bed, cam comes in at 1300 rpm.
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Old 04-02-2018, 07:12 PM   #2
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Re: Help with rpm drop when put in drive.

Who is your engine builder ?

With any good engine builder, when he degreed the camshaft, what exactly did he end up with ? I am assuming the cam is a 12-210 comp.....

This is the same engine that was sparking at the base of the dizzy right ?

Last edited by YoungPup1977; 04-02-2018 at 07:22 PM.
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Old 04-02-2018, 07:52 PM   #3
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Re: Help with rpm drop when put in drive.

Yes but I'm having no issues with the sparking now. Performs great. Just having the rpm drop .

Boyettes in Raleigh built the engine. Cam is a comp XE262H-10

Last edited by grubsster; 04-02-2018 at 07:55 PM. Reason: Clarification
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Old 04-02-2018, 08:09 PM   #4
geezer#99
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Re: Help with rpm drop when put in drive.

Check your timing when it’s in gear. You might be surprised how low it is.
Then reset it at 16, put it back in park and turn the idle down to 600.

At 900 rpm in park your mechanical timing is kicking in.

With a small motor and bigger cam you need lots of initial.
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Old 04-02-2018, 09:11 PM   #5
Wrenchbender Ret
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Re: Help with rpm drop when put in drive.

If you have the vacuum advance hooked to full manifold vacuum, try hooking it to ported vacuum. You may have to readjust the idle speed.
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Old 04-03-2018, 08:17 AM   #6
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Re: Help with rpm drop when put in drive.

Have you looked at the fuel pressure? If it is higher than about 4 or 4 1/2 psi the carb will go fat at idle and you will see what you have going on.
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Old 04-04-2018, 11:55 AM   #7
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Re: Help with rpm drop when put in drive.

On my older engine with Edelbrock, Hei, I have about a 300 rpm drop when I put into gear. Friend of mine and I were talking transmissions one day and he mentions if you have anything over that amount that the transmission is old and worn. We were looking at the problem from a mileage standpoint.

Good pointers from the other posters.
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Old 04-04-2018, 04:02 PM   #8
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Re: Help with rpm drop when put in drive.

If the motor was rebuilt, is it broke in yet? It can make a difference. Some motors behave from first start, other seem to need a 1000 miles or more before they want to settle down.

What is your vacuum at idle? Both in drive and neutral.

Have you set/checked the float level in the carb? They are often set wrong from the factory.
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Old 04-14-2018, 11:43 PM   #9
grubsster
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Re: Help with rpm drop when put in drive.

Thanks all for the help. After much head scratching found one of the weights on the distributor to be partially deployed. I believe this was causing my timing to begin to advance way early. The springs and weight setup in this distributor are set to begin to come in at 800 rpm. I think the one being already deployed created an effect that would start about half that. So my timing was so far off and when I would set the idle and fuel air mixture all would end up out of whack. At any rate you can see in the pictures what I saw. Replaced the distributor. I also think this was causing my timing fluctuation some of you tried to help me with also. I only lose about 200 rpm when i go in gear now and the truck is happy.

Last edited by grubsster; 04-14-2018 at 11:52 PM.
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Old 04-14-2018, 11:51 PM   #10
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Re: Help with rpm drop when put in drive.

Updated with pictures...
Attached Images
  

Last edited by grubsster; 04-15-2018 at 01:19 AM.
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Old 04-25-2018, 07:22 PM   #11
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Re: Help with rpm drop when put in drive.

Quote:
Originally Posted by grubsster View Post
Thanks all for the help. After much head scratching found one of the weights on the distributor to be partially deployed. I believe this was causing my timing to begin to advance way early. The springs and weight setup in this distributor are set to begin to come in at 800 rpm. I think the one being already deployed created an effect that would start about half that. So my timing was so far off and when I would set the idle and fuel air mixture all would end up out of whack. At any rate you can see in the pictures what I saw. Replaced the distributor. I also think this was causing my timing fluctuation some of you tried to help me with also. I only lose about 200 rpm when i go in gear now and the truck is happy.
Nice work. Glad you got it figured out and fixed.
BTW, it sounds like a nice combination. Let us know how your driveability and fuel economy are after a few months.
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