Stock Chev 350/TH350/12 bolt .308/1. Recurved the distributor with Moroso spring kit.....48 degrees all in at 4800-5000 rpm reduced to 48 degrees all in at 3200-3500 rpm. New curve starts about 1200ish rpm, idle steady and smooth at 750 rpm in drive. I thought $60 for a rear sway bar was the best money ever spent, but by seat of the pants, $15 for springs has them all beat by a long stroke. So, am I crazy? Setting aside the new snappy seat of the pants feeling in the cars driving range of not over 3300 rpm......The tach seems to be telling me that the RPM required at any given highway speed is as much as 300 rpm less than what was previously required. Mileage seems to be up too and I've got to get a tank this week to measure it off, but.... I know a good tach dosn't lie but never having experienced a dizzy recurve to operating rpm range, am i right? For less than a set of points is what i feel on my **** and see with my eyes correct?
I hadn't really thought of comparing ignition advance at a given MPH with engine RPMs. But it would seem to make some sense. By improving the timing and feeling a "seat of the pants" improvement, it would seem that you now don't have to open the throttle quite as far to produce a given amount of torque. At a given speed and throttle position you may have picked up another inch or so of manifold vacuum too. I'd say you'll probably see a little increase in fuel mileage as well, if you can keep your foot out of it . . . You'd probably only see a drop in RPM with an automatic transmission w/out a locking convertor. With a lock up convertor or manual trans the RPM should be the same.
Torque is what most street driving is about, not HP. Sounds like tuning for more advance worked out for you at the rev range you are driving. Claymart mentioned manual VS auto. I agree that a solid (engine, clutch, gears) connection should 'tach' the same at a given speed, so I'd guess you are running an auto. Yes, the engine can develop a bit more power at the same or slightly less RPM when tuned for that RPM/load, especially with a 3.08 rear gear. If you increase the torque 10% at 2000-3000 RPM, it will have a noticeable effect, but not change the advertised numbers.
It's a tci street rodder trans, so no lock up. I'm kinda flabbergasted. It seems to be a $15 performance mod that actually works. My Gosh, all the money I spent as a kid with J.C.Whitney and I could've just swapped springs. All that .99 cents a 6 pack Pearl Light and Lone Star Beer I could a bought instead.....
Does the 48 degrees include your vacuum advance? It seems like a lot if it's just the initial plus the centrifugal advance (I'm running with 38 degrees all in at 3000-3200...plus vacuum advance drawing on manifold vacuum).
Wait until you find out about ADJUSTABLE vacuum advance cans! Stock on Mopars, aftermarket on chevys. https://www.chevelles.com/threads/setting-an-adjustable-vacuum-advance.163584/
Already got one! Its been great. Started with min setting and went up till it ran best. Did the same on the can for the spring swap. Best settings either way we're within 1/2 turn of the other. The engine seems to like a half turn less on the new springs.
Pretty much all my builds....various Mopars, some air cooled VWs, and others, have responded well to a higher initial advance. Some can't tolerate a bunch of total advance, so the key is to limit the total within the distributor. For example, a certain OT drag race motor liked a bunch of initial but could only handle 30° total. Most likely because of 14-1 CR I'd reckon. So, the advance was reduced to 12° in the distributor, and all in by 2000rpm. So we had 18° initial timing, 30° total. This was done with tiny bushings at the limit pins. Bigger bushing = less advance. The advance jumped around a bit before 2K because of the super light springs, but was solid above that since the weights were at full limit. Since this particular ride didn't operate at less than 2K rpm, so it didn't matter. I could have easily locked out the advance, but it started easier with less initial timing. So, just an example of what is do-able. If someone is willing to put in the work, it's an inexpensive way to improve performance. They all be different, so experiment away. They'll tell you what they like and what they don't if you listen to 'em. Just don't argue with 'em. I've never ever won a single one of those arguments!
Them's the wisest words I've seen around here lately! Argue with your friends if you have to. But it never pays to argue with a dumb, stubborn, old engine!
The way fuel keeps getting modified for modern cars, you'll find that engines need more and more initial timing. That's the way its always been. If you look back at your tune-up specs for cars in the 40's and 50's, TDC was your base timing. By the 80's we were up to 10 BTDC. Now we're getting closer to 20 BTDC where most cars idle and start best, once the AFRs are corrected for that setting. Any car will be difficult to start if its lean or rich. Most V8s prefer 16-18 BTDC at idle as the base timing setting. Race engines - our Bonneville setup at 14:1 would hold a 550 rpm idle at 24 BTDC, 28 total all-in at 3100. The days of 10-12 BTDC at idle are long gone if you're looking for the best drivability.
48° - 52° BTDC at steady highway cruise is typical for many overhead valve V8. The only practical mechanism to get all around driveability and that much lead on the highway (before the advent of electronic computerized ignition controls) was springs, centrifugal weights, and especially the clever use of engine vacuum. Two separately independent systems, one RPM based, one engine load based. Ordinarily one is taking out some timing when the other is adding some in. They are both (kinda) additive at steady cruise.
SBC with 48 total seems like a lot . Is the mark on the dampener correct at TDC ? Ring slipped on the dampnener Most SBC run best about 36-38 total . Vortec even less total
Geting the ignition advance right on all rpms, and all throttle openings can make a HUGE difference. But just like carbs, people tend to jsut get the cool ones and slap them on there, they forget about the careful adjustments they need to do to actually get performance out of them. And economy of course, important with the fuel prices of today.
Learning the hard way. Popped a pair of pistons in a 6 cylinder before I learned to sneak up on it. Evidentially I missed something important with that motor.
Nothing out of line/slipped, it's all new. 48 is with the vacuum at hi rpm. Everything I read says 48+ at speed with a stock 8 to 1 sbc. So far it seems right. No ping with quite a hard pulls
Each engine is different, there are 8:1 engines that with detonate with the least advancement of timing, and there are 10.5:1 engines that can handle locked out timing at 38 degrees on pump gas no problem, quench, combustion chamber shape/ efficiancy, piston top shape, sharp edges....... You just have to give the engine what it wants and can handle in small increments of adjustment Look at the plugs for little black specs on the porcilin, that is an indicator for detonation in case you dont hear it.
“Total” timing isn’t. It’s a drag racing term, that has stuck, but is misleading because race engines do not include vacuum advance. Ignition timing advance measurement while engine is in neutral, to include vacuum advance, the numbers will not be very accurate because there is no load on the engine in neutral. Might see 50°+; it doesn’t mean anything bad, it isn’t “too much”. Without any vacuum advance, 34° - 36° BTDC at wide open RPM, under heavy is typical for about every V8 ever made. That is about the limit before stuff starts breaking. Sometimes a little more or less depending on compression ratio and other factors.
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