Setting Big Block Idle & Total Timing

[savatreatabvr]

I just replaced the timing chain on my 1973 Chevy C20 454 and when I hooked up my timing light and vacuum gauge it was on 14 degrees ATDC and a steady 22 HG but that's pretty much where they were before. Don't get me wrong the truck runs good I just thought I'd see more response. I probably put 5-10 miles on it a week but I start it every couple days anyways. Is setting the Total Timing that important for a non-daily driver and does Total Timing affect stop and go driving?

[donut]

After TDC? Try before tdc with the vacuum advance line unhooked and plugged.

[savatreatabvr]

Originally Posted by donut

After TDC? Try before tdc with the vacuum advance line unhooked and plugged.

I guess I had it wrong, I got "before & after" TDC reversed. I thought after TDC was on top (per drawing) so I assumed it was 14 degrees ATDC but what your saying is it's actually 14 degrees BTDC? What should a high mileage 454 be set at? If it's set anything below 14 degrees BTDC the idle lowers and it doesn't run as good. Excuse my idiocy but shouldn't it run best at like 2 or 4 degrees BTDC?

[donut]

If your retarding the timing, you can keep bumping the idle to keep it running. Just opposite of advancing it. (If you start at about 4* and advance it, idle will go up. Just have to drop it back as you go.)

Beyond what your set at now is trial and error. My dually is currently at 14*, I haven't checked to see if I can use more. My smallblock would start back-lashing the starter at 14*

Total timing (IMO), isn't quite as important as how quick and if it's even functional. Normal driving, I don't run into the issue of higher rpm. My Trailblazer, with the roller engine, on the other hand, will quickly see 5k if I go to pass someone.

[savatreatabvr]

Originally Posted by donut

If your retarding the timing, you can keep bumping the idle to keep it running. Just opposite of advancing it. (If you start at about 4* and advance it, idle will go up. Just have to drop it back as you go.)

Beyond what your set at now is trial and error. My dually is currently at 14*, I haven't checked to see if I can use more. My smallblock would start back-lashing the starter at 14*

Total timing (IMO), isn't quite as important as how quick and if it's even functional. Normal driving, I don't run into the issue of higher rpm. My Trailblazer, with the roller engine, on the other hand, will quickly see 5k if I go to pass someone.

That's what I wanted to know. I've checked all over online but I've never found an actual factory timing setting, everyone has their own opinion on what it should be like 8, 10, 12 degrees. I know every engine has it's own sweet spot, 14 degrees is probably mine I just don't know it yet because these old big blocks run different day to day, lol!.

[vidman]

Mine is at 13 btdc and 33 total..ran great on the Dyno. I,ll see how it runs on the street..

[StarDust]

this was a PAIN in the ass to set i looked at countless videos i understood it but not when it came down to actually do it..what i did is let my motor warm up to normal temp and rose my rpms to around 2500 rpm and set it at 36 BTDC now i can go above 55 all day everyday and my idle sounds good responsive...all the videos ive seen said to set between 34 and 36 BTDC at 3k rpm so thats what i did and worked good

[savatreatabvr]

Originally Posted by StarDust

this was a PAIN in the ass to set i looked at countless videos i understood it but not when it came down to actually do it..what i did is let my motor warm up to normal temp and rose my rpms to around 2500 rpm and set it at 36 BTDC now i can go above 55 all day everyday and my idle sounds good responsive...all the videos ive seen said to set between 34 and 36 BTDC at 3k rpm so thats what i did and worked good

I'll take your advise and try it. I'll post the results.

[StarDust]

This is prob the top 3 of videos that helped me

How to set your ignition timing - YouTube

[savatreatabvr]

Originally Posted by StarDust

this was a PAIN in the ass to set i looked at countless videos i understood it but not when it came down to actually do it..what i did is let my motor warm up to normal temp and rose my rpms to around 2500 rpm and set it at 36 BTDC now i can go above 55 all day everyday and my idle sounds good responsive...all the videos ive seen said to set between 34 and 36 BTDC at 3k rpm so thats what i did and worked good

Just watched a vid on Youtube, the guy had problems setting his timing because he was off one tooth on his dizzy but it showed good vacuum on his gauge and idled fine. He said he re-positioned the dizzy and his problems were solved. I guess my question is, is it possible to be one tooth off on the distributor but still show good vacuum, idle ok, drive fine but lack power?

[savatreatabvr]

I probably should have mentioned I'm running without a thermostat! It takes a while to warm up but does not overheat, could this be a possible factor in having a lack of performance even after reaching operating temperature? It was just a thought.

[donut]

I'd run the thermostat. Just to cut down on sludge build-up in the engine. Living in Apache Jct, my old Fords ran cooler with the thermostat. May not improve performance, but IMO, over time will improve efficiency.

Tooth off? IMO, if your timing is set correctly (with a light) without smashing the vac can on the firewall or the carb, you should be fine. I consider it a tooth off if I don't have enough adjustment to get the correct timing. But that may just be me.

Lack of performance, don't know. Seems like you've checked and adjusted a bunch already.

[vidman]

Never run your engine without a stat....Thats why all autos ever built have them...

[savatreatabvr]

Originally Posted by donut

I'd run the thermostat. Just to cut down on sludge build-up in the engine. Living in Apache Jct, my old Fords ran cooler with the thermostat. May not improve performance, but IMO, over time will improve efficiency.

Tooth off? IMO, if your timing is set correctly (with a light) without smashing the vac can on the firewall or the carb, you should be fine. I consider it a tooth off if I don't have enough adjustment to get the correct timing. But that may just be me.

Lack of performance, don't know. Seems like you've checked and adjusted a bunch already.

For some strange reason I'm thinking my lack of performance is being caused by the T400 tranny! Shot in the dark but hey I've basically tried everything else, lol!

[donut]

Could be if your shift points are way off. When I rebuilt my trans, upon first run, I was in 3rd by less than 2k rpm. Shifted way to quick, so much that 3rd you could feel it lugging.

[savatreatabvr]

Originally Posted by donut

Could be if your shift points are way off. When I rebuilt my trans, upon first run, I was in 3rd by less than 2k rpm. Shifted way to quick, so much that 3rd you could feel it lugging.

Exactly what mine does! If I let it shift normally it's lugging and it shifts to 3rd soft, if I let it build up RPMs and then manually shift in to 3rd it shifts harder! Always shifts in to 2nd just fine!

[donut]

Ok, hate to ask, but is the vacuum line to the trans modulator in good shape?

On some the modulator is adjustable (allen wrench in the nipple.) If your not sure, a new, adjustable one is about 15-20 bucks. Should be available at any auto parts store. Just a replacement modulator, I believe it's a red stripe. (may be wrong, but maybe one of the experts can help). I drove for a few short trips with the allen wrench on the front seat and adjusted until I liked it. I also believe instructions were included.
Seems like it took quite a bit of turning until I noticed a change, then it was 1/2 turn increments. This may vary, but that's how it worked for me.

I started with 1/2 turn at a time, after 3 times crawling under the truck I got sick of it. Cranked it all the way and backed off like 2 turns, then went from there.

[StarDust]

i am really not sure about all that @savatreatabvr, i just barely learned whats involved with timing and troubleshooting so i just gave my 2 cents on what solved my timing issue . and hmm transmission can make a engine sluggish? not wanting to highjack thread but after timing my truck it feels much quicker in response and overall performance so i tested raced my friend (stock v6 on 22s) and got my ass handed to and i have a v8 with just headers? what gives lol my transmissions shift points are at 2nd at 25mph 3rd at 35mph 4th at 45mph and overdrive at 55mph, should i invest in a tach?

[cool68]

video link above good but, did not mention about disconnecting/blocking distributor vacuum line to carburetor. plus, did not give beginning RPM to set carb at for initial timing before going up the 2500 they talked about. need to make sure carb is set properly too. most engines do not have the timing tape shown, or run a MSD distributor.

[StarDust]

Well that's why you don't go by one source gotta watch multiple videos, thanks for putting that out though from what ive heard. If stock or close. Rpms should be at 650-700ish and to adjust carb just pull out a VAC gauge and keep adjusting until you get maximum vac reading...dont go by my words though as i already stated lol

[savatreatabvr]

Originally Posted by donut

Ok, hate to ask, but is the vacuum line to the trans modulator in good shape?

On some the modulator is adjustable (allen wrench in the nipple.) If your not sure, a new, adjustable one is about 15-20 bucks. Should be available at any auto parts store. Just a replacement modulator, I believe it's a red stripe. (may be wrong, but maybe one of the experts can help). I drove for a few short trips with the allen wrench on the front seat and adjusted until I liked it. I also believe instructions were included.
Seems like it took quite a bit of turning until I noticed a change, then it was 1/2 turn increments. This may vary, but that's how it worked for me.

I started with 1/2 turn at a time, after 3 times crawling under the truck I got sick of it. Cranked it all the way and backed off like 2 turns, then went from there.

Yeah, my vacuum line is good and hooked up to straight manifold vacuum but I have no idea how old the tranny modulator is. Oh and it's not adjustable. I'm confused on what the factory idle RPMs are supposed to be because everyone has their own opinions, I think my idle is set to low at 600 RPMs but when I raise it it sounds too high, lol! Could missing some emissions equipment hurt performance, I don't have an EGR valve, air pump, vacuum canister or catalytic converter but I don't believe that equipment was factory installed on a 1973? All I have is the PCV valve, the vacuum modulator vacuum line and the distributor vacuum advance line. I also don't know how many miles are on the 454, it could be pushing 200,000 miles, that's a guess but I have no idea.

Sorry about the sh-ty video, it was taken with my phone.

[donut]

For a '73, you wouldn't have all that smog equipment. I believe my old K-20 just had a PCV valve. Some folks, the first thing they do is ax all the smog equipment. Whether needed or not.

Idle, if the rpm works for you, then it'll work. I'll set my idle to whatever sounds about right, then try it in gear. Simple, may not be 100% correct, but my idle in gear has to work without stalling. When I put it in park, don't want it screaming either.

Link for a modulator-

http://www.oreillyauto.com/site/c/de...0073&ppt=C0338

[savatreatabvr]

Originally Posted by donut

For a '73, you wouldn't have all that smog equipment. I believe my old K-20 just had a PCV valve. Some folks, the first thing they do is ax all the smog equipment. Whether needed or not.

Idle, if the rpm works for you, then it'll work. I'll set my idle to whatever sounds about right, then try it in gear. Simple, may not be 100% correct, but my idle in gear has to work without stalling. When I put it in park, don't want it screaming either.

Link for a modulator-

http://www.oreillyauto.com/site/c/de...0073&ppt=C0338

Hey thanks Donut, I'll pick up a modulator as soon as I can! It still may be a dog but at least it will shift correctly, lol!

[donut]

Cool. I think just about every parts house has a modulator, wasn't like half a billion vehicles didn't have them in the day.

Yes, it may be a dog, but a proper running dog. That in itself says something for a 40+ year old vehicle.

[savatreatabvr]

Originally Posted by donut

Cool. I think just about every parts house has a modulator, wasn't like half a billion vehicles didn't have them in the day.

Yes, it may be a dog, but a proper running dog. That in itself says something for a 40+ year old vehicle.

Absolutely! Still runs better than I do after 40 years old, lol! I think I'm just expecting to much out of an old truck that weights over 2 tons!