I've asked before, not sure if here though, about dialing in the timing on my SBC 350. In case anyone asks, the engine basics are .60 over flat top pistons, ISKY 270/280 Cam, Balanced, stock heads (1974) that have been machined, and an Eddy 1405 Carb on Performer Mani. Machinist said it should be about a 330HP Engine. The car is a 1960 Chevy Suburban (weight of about 3500lbs), 3.90 Posi Rear Diff(stock diff from this truck) and a T350 ******. When I built the motor, I set the timing at the cam to 4* advance. Some have asked about using a dial, but I honestly don't recall doing this or not. I initially built the motor 20yrs ago for a different project that never came to be, so it sat. Before going into the 'Burb, I stripped it down, replaced the gaskets, relubed everything and put her back together. I didn't have a timing dial and things I read seemed to point to being mainly important on racing engines.....good or bad, that's where I am. My reading also seemed to say Isky Cams are normally spot on, though I realize anyone can mess up. I sort of remember possibly going into this years ago, but too long to say for certain, I just went back through it and put everything back where it was this time. The torque converter is a stock converter because the ****** guy said try it first and he didn't seem to think I needed to spend the extra on one with a higher stall...even though Cam's power band is 2200-6500 rpm. I swapped to HEI Distributor with vacuum advance. It was about $60 on Amazon, because I had several people say great distributor for the price and my needs. I can provide link if anyone wants them. Fast forward to now. The truck has about 500miles on it since getting her back on the road, so time to start going back and double checking everything. She's running well, but I think she's a bit rich and I still question if the timing is perfect. I have been trying to follow the instructions per Bad *** Engines and I've also looked at a few YouTube sights that seem to use the same instructions, BUT I'm still a bit unsure. My understanding is best is about 24-26* advance at the crank and about 10* mechanical advance from Distributor for a total timing of 36* BTC. If I run the RPM's up to about 3500 and set the dial on gun to 36* and get the pointer to O* at the balancer then I should be at my 36*, correct.....I get that, but how do I know if I'm 24-26* at the crank and how do I know what the mechanical advance of distributor is? Is that checked at idle? I think the reason I'm a bit confused on this is because it seems these are all over the place and even reading the instructions from Bad *** Engines, it seems to say some stock style distributors don't fully advance until 4500rpm, it seems even the MSD ones are like that UNTIL they loosen up. I guess I wonder if I should just dial it to 36* at 3500 RPM and call it good? I'm fairly close to that right now, maybe a bit under because I had one or two people say it sounded better turned down a little. I have idle set at about 700rpms and she sounds very nice, but I do have some exhaust issues I'm working on fixing. There is a nice lope to the cam, but that bothers me because I know a guy with a much much larger cam and his sounds no-where near as 'lopey' as mine. I have run this with and without the vacuum advance hooked up, because I want to get the rest dialed in before I spend time figuring that out. I've taken it to one shop to have it tuned (carb still at stock specs from Eddy) and they said it ran great, don't worry about it. They are a shop that is very much into Chevy and they have built very successful drag cars, so I have no doubts they could handle it, just not sure they wanted to mess with it. My concerns are, I think I'm getting very bad gas mileage (best guess when I checked was about 6mpg) she smells like she's running rich. Haven't pulled plug to check it yet, but it's on the short to do list when I go back to mess with the engine. I also think that it should brake the tires loose easier, but it doesn't....very torque when punching around a corner around 2000rpm and if I hold the brake and let off. I've been running 91 Octane Gas, not sure if that's necessary or not with this engine. I've heard no knocks or pings, etc... She does run nice and smooth, but most of my driving is 40mph or slower around the neighborhood, etc. The truck needs more work before I take it up on HWY's.
So, you degreed the cam in at 4* advanced, or just used a timing set that let you take it form "0", to 4 degrees advance? You should verify with the cam card, it's possible the cam was ground with 4* advance in it. You may be pulling the cover again. I would start by advancing the base timing until you like the low end, if it pings, back off. Then check your "all in" advance (w/vac advance unplugged and source capped off) at that point it you may have to change weights and springs and/or advance stops to dial it in for what you want.
When setting the timing, I do disconnect the advance and I plug the port. I've been using the port of the driver side of carb, which is NOT a timed port, but a manifold port on the carb. As for the cam specs for timing, I am not sure I've seen anything other than the ones talking about advancing, standard and retarded timing at the sprocket. I have spoke with Isky tech on this and they verified there is no advance built into the cam. If there should be other specs for the Cam itself, I'll look and see what I can find. I still have everything that came with it. Budget36, that helps regarding advancing until I like low end. I'll see if that gets me anywhere. Am I also correct that if I set Total Timing at 36* at 3500rpm and then check again at idle, I'd have my timing at the crank?
The crank timing doesn't really matter too much, so long as it starts OK. Let it fall where it may, to get the 36° or whatever total you want. You should check it, so you know where it's at. At a slow idle, for accuracy. Timing advance does affect fuel economy, a lot. Vacuum advance helps economy further, adding maybe 15% or so. So your issue now is tuning the carburetor, yet another minefield of misinformation and old wives tales out there. Get the manuals and study them. Get yourself a wideband O2 sensor kit. It will pay for itself the first roadtrip in fuel savings alone.
Whole lot of info being p***ed back and forth here, but I agree with truck 64, get your 36* at full advance with vacuum disconnected. And if that cranks OK , chances are that you'll be in the ballpark. BUT, the one thing mot mentioned, or at least I didn't see it: Are you sure your pointer and balancer marks are accurate? Only way to be sure is with he positive stop method. If you need that explained to you, then speak up now,
Time it with a vacuum gauge, run it up to roughly 2500 rpm and turn your distributor until you reach your highest vacuum reading then lock it down. That should put you in the 8-10 degree range (no vacuum advance) for initial. This is of course ***uming everything is set up as it should be. What's the compression ratio on the motor, the LSA or valve overlap on your cam need to jive with compression ratio. With more overlap you need more compression than say 8:1. I will also ***ume your stock converter will not play nice with your cam. You should have a 2200/2500+/- range converter. I always have my distributors dialed in on a distributor machine at a local speed shop....well worth the money. Isky should be able to provide you with basic info/specs on their cams as to what will work and what won't.
I'll look this over more when I an at my pc, but for now. I bought this distributor from a seller on Amazon and asked what the mechanical advance is and was just told 8°. IF that is true then I'm in line with what Bad *** Motors says is preferred. I know you guys say put total at 36°, so I'll do that. For my own benefit though, Am I correct that when I set it to 36° total at 3500rpm, then when I drop it back to idle and lets say it now reads 28°, then my I do in fact have 8° mechanical advance in distributor? As for compression, machinist said it will be about 9:1. I could have swore he said 10:1 when the motor was originally machined 20yrs ago, but he went into a full explanation as to why with these heads and based on the receipts I showed him off original work he had done as to why they are NOT 10:1. We didn't re cc them to find out because he was confident. I'm pretty confident the timing marks are all accurate. I checked piston coming up on compression stroke for #1 cylinder and all seemed good. I have a homemade tool for stopping piston, but it didn't seem right for these heads so I just went with trying to figure out when piston stopped coming up. I think my tool was for my boat motor where the plug is perpendicular to piston.
8° of advance inside the distributor equals 16° at the crank, since the distributor turns at half the RPM of the crank. A modern V8, depending on compression, al***ude, fuel quality etc, wants somewhere around 34°-36°-38° total mechanical advance. Meaning whatever the initial crankshaft timing is at idle + the internal distributor advance. How fast and at what RPM it comes in is governed by the distributor weight springs. For performance lighter weight springs are used, and as the RPM comes up they will advance earlier than heavier springs. When you rev up the motor to check with the timing light be sure it's done advancing all the way. A stock OEM distributor will sometimes still be advancing even as much as 4000 RPM. They usually have too much advance built in. Be careful, and stay out of the plane of the fan when checking. If the fan is old and rusty, replace it. OK for example a stock OEM curve might have been 4 or 6 degrees at the crankshaft, and 15 degrees internal to the distributor (30 at the crank remember) and with heavy springs. Sluggish, maybe though perfect for hauling gravel up the mountain. So Johnny Outlaw is a hot rodder and wants a little more zip, and a little rumble on deceleration, and better mileage. He swaps in lightweight springs for heavy ones, bringing all of the advance in before 3000 RPM or even earlier. He limits the the internal distributor advance to say 10 degrees (20 at the crank) and then sets the initial timing to 17 degrees. The total amount of mechanical timing doesn't really change, just when. Then re-connect the vacuum advance, and tune that. Don't re-connect the vacuum advance till you've got it tuned right without it. The vac advance adds another 10 or 15 degrees at most, primarily when cruising in high gear on level ground. It does add better all around driveability. If you drive on the street you want vacuum advance. At just a part throttle, steady cruise situation on level ground the fuel mixture leans out quite a lot, the RPM is relatively low, so additional vacuum advance is based on engine manifold vacuum as the signal. If you could somehow check with a timing light at highway cruise you might see 50 degrees BTDC. You're doing what you need to do, this is how we learn. You will even understand it when you're done.
Starting to come together more. Was going to mess with it tonight, but as I went to shuffle cars around I think the flex plate/starter is acting up, so time to put this on hold a few days and crawl under to see what's going on. Lots of grinding when cranking, when she fires she's good. Did this one other time with about 150 miles on her. Starter let loose and took a tooth and several partial teeth from flex plate. Sounds the same again. Not crawling under tonight though. I suppose if it is the flex plate, now's the time to try a higher stall converter.
As alluded to above, SBC engines have three (3) different timing pointer locations:- Pre '69 engines, TDC mark is 2° to the left of the keyway centre line; '69 and later, TDC mark is 10° to the left of the keyway centre line; and 1984 -'95 engines, TDC is at 12 o'clock position on the damper.
I'll double check this, but my engine is '74 Block, so it should be 10* to the left. Unless the balancer was mis-ordered for a different motor, all should be ok there. I don't think I'm off by very far as she starts pretty easily and does have good power. I just want to know it's dialed in perfectly or as close as possible. Once I figure out what is going on with my starter/flex plate, I'll look into this more and get back to the timing issues. Thanks for all of the feedback!
If you are using a normal timing light set your timing so that you are reading about 8 degrees advance at your harmonic balancer. Now start playing with it, you will probably end up running in the 12 degree range before you are done. Unless you have a distributer bench there is not much you can do to change all in so just live with it. If it starts and pulls well you are fine. you guys all think that you are building a pro mod car, just keep it simple its just a car that you are going to drive.
Somewhat good news is that I pulled the shim from the starter and no more grinding. Something tells me this starter will be toast before too much longer. Doesn't make sense why it would be perfect shimmed for several hundred miles then have issues, but that's another topic. For now I truly am a bit curious about the below quote....I do agree with him that it seems a lot of posters get caught up with what needs done for a high HP race type motor and forget the lower HP street motors don't need the same treatment. That said, I've read several things that seem to say around 12 degree for a basically stock SBC, but other things I read seem to say most SBC's like 32-36 degree. What gives? Should my 330hp SBC 350 have the higher advance or not? How does one determine....does the cam dictate this or the complete package? I realize I'm complicating things a bit, but want to learn what I can.
The September issue of Hot Rod had a great article on timing and they were using a 350. Very good educational info. I suggest reading it. Sent from my SM-N910V using The H.A.M.B. mobile app
Don't confuse the initial timing degrees set by turning the distributor at idle with the total timing that is measured at 3000 RPM, say. The complete cam and everything else determines how much ignition advance the engine will tolerate. Keep in mind any gasoline engine you want to tune it so it has as much advance as it can stand at at all times, under all conditions, just short of any engine knock or ping. This is the entire reason for the springs, weights, and vacuum diaphragms. Today it is done with computers, old school stuff is done differently but is the same principle. Has nothing to do with whether it is a high performance engine or not. The intended use will factor how much timing can be used. The manufacturers were conservative in their settings for several reasons, mainly because they had to be a one size fits all. If you own a gravel truck hauling loads up a mountain, lots of ignition advance coming in early isn't what you want. Higher compression motors will not tolerate as much ignition advance. Poor quality fuel will not allow for as much ignition advance. But every engine will benefit with as much timing advance as possible at any speed or rpm, coming up or coming down. The initial timing number set by rotating the distributor doesn't really matter, it's not critical. Somewhere more than 10° and less than 20° is typical. On the high side engines may be hard to turn over because of starter kickback. Let the initial timing fall wherever it needs to be so you can reach 34° to 36° when you spool up the engine in neutral on the far end, this is important and a cl***ic error is not verifying this. There is no technical benefit whatsoever to ever running a retarded ignition advance anywhere in the curve. When you are satisfied with the mechanical advance under different conditions, re-connect the vacuum advance and tune the can to pull in as much as the engine will stand under part throttle conditions. Keep in mind you're done with the distributor timing, don't try to compensate for a vacuum advance issue by retarding the mechanical advance. Cl***ic error #2 It is true that racing engines are tuned differently, because they are designed for one application - wide open throttle.
With your HEI you really can't change your all in advance. 12 degrees is what the books used to say about corvette motors, that would be idle and the vac advace not hooked up. Idle would be around 600-700 RPM. You can change the advance weights and springs on your HEI but that basically changes when the ignition goes to full advance not the full advance. Most of these guys that are giving you this X degrees at full advance and XY degrees initial don't have a clue what they are talking about. They are just parroting something that they have read on the web. Their cars don't do it that way unless the distributer was set up that way, something that most of them don't know how to do. If your initial advance (at idle) with the vac advance disconnected is in the 8-12 degree range, the car starts runs and pulls well you are fine. Don't sweat the little ****.
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