Help with rpm drop when put in drive. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

grubsster · 04-02-2018, 07:02 PM

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.

*YoungPup1977* · 04-02-2018, 07:12 PM

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 ?

grubsster · 04-02-2018, 07:52 PM

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

geezer#99 · 04-02-2018, 08:09 PM

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.

**Wrenchbender Ret** · 04-02-2018, 09:11 PM

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.

**PGSigns** · 04-03-2018, 08:17 AM

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.
Jimmy

toolboxchev · 04-04-2018, 11:55 AM

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.

Dead Parrot · 04-04-2018, 04:02 PM

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.

grubsster · 04-14-2018, 11:43 PM

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.

grubsster · 04-14-2018, 11:51 PM

Updated with pictures...

**mattfranklin** · 04-25-2018, 07:22 PM

Quote:

Originally Posted by grubsster

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.

04-02-2018, 07:02 PM	#1
grubsster Registered User Join Date: Sep 2011 Location: N.C. Posts: 133	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.

04-02-2018, 07:12 PM	#2
YoungPup1977 Account Suspended Join Date: Jun 2015 Location: No longer here Posts: 1,000	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.

04-02-2018, 07:52 PM	#3
grubsster Registered User Join Date: Sep 2011 Location: N.C. Posts: 133	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

04-02-2018, 08:09 PM	#4
geezer#99 Registered User Join Date: Aug 2009 Location: Bowser Posts: 13,512	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.

04-02-2018, 09:11 PM	#5
Wrenchbender Ret Registered User Join Date: Oct 2005 Location: Overland Park, Ks. Posts: 5,190	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.

04-03-2018, 08:17 AM	#6
PGSigns Senior Member Join Date: Jan 2011 Location: Hayes Va Posts: 4,569	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. Jimmy __________________ 60 to 66 Chevy and GMC window decals http://67-72chevytrucks.com/vboard/s...d.php?t=661131 Good friends, good food and a hotrod what else do you need? 1966 BBW long fleet Daily driver 1965 BBW short fleet Sold and going to a good home 1965 Suburban 2003 3500 Duramax 2005 Ultra Classic

04-04-2018, 11:55 AM	#7
toolboxchev Registered User Join Date: Jul 2015 Location: 2nd left past the stump on a dirt road. Posts: 2,629	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.

04-04-2018, 04:02 PM	#8
Dead Parrot Registered User Join Date: Aug 2012 Location: Oklahoma City, OK Posts: 2,474	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.

04-14-2018, 11:43 PM	#9
grubsster Registered User Join Date: Sep 2011 Location: N.C. Posts: 133	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.

04-14-2018, 11:51 PM	#10
grubsster Registered User Join Date: Sep 2011 Location: N.C. Posts: 133	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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