Mechanical advance

[tima01864]

I posted in another thread Maybe I should start a new one.
Utilize the timing marks, 0-10 with a compass mark the crank wheel 3.5 times and mark it. I would then need a hand held tachometer.
I have a 2L recently built unbroken in high performance engine, Hi Compression pistons, Ported head large valves professionally built,
It performs, I am happy with it. But I cant push it past 4500rpm maybe I havent tried enough? So I asked the builder,He asked 1. Are the timing marks aligned? Yes I have adjustable cams and believe I payed attention to that. 2. Are you at 10 degrees at idle and 36 degrees mechanical advance? This I need to check. I may put the original distributor back in since i replaced it a few years ago with an off the shelf from a vendor.
Or everything is just fine, leave it

[justrhines]

Hi Tima,

The engine should easily rev to redline. As far as timing, not sure why you would need a tachometer. There is a line on the crank pulley (assuming you have the stock pulley) that is used for timing. Using a timing light off the #4 spark plug, you should be able to advance or retard the timing to align the crank pulley line with the marks on the timing cover.

Justin

[18Fiatsandcounting]

I agree, it should easily rev up past 4500. So, if you put it in neutral or with the clutch in, and you give it gas, the engine peters out once you go past 4500? If so, there's definitely something wrong as these engines love to rev. Make sure your tach is working right, because if the problem is that your tach is wrong, you could definitely do some damage if you over rev. Rough rule of thumb: The tach should read between 3200 and 3500 at 60 mph in 5th gear, depending on model year. If it doesn't, the tach isn't right.

With the ignition timing, note it should be 10 degrees of advance at idle, and then 26 degrees of mechanical or vacuum advance on top of that, to bring you to a total of 36 degrees max once you reach 2500 or 3000 rpm or so. If you max total advance is 46 degrees, that's way too much and could be the cause of the inability to rev.

-Bryan

[RRoller123]

It is most likely the valve timing, Tim. Probably too far advanced, and bringing the power band too far down into the low end of the rev range. Could also be the LSA, or Lobe Separation Angle, also adjustable with the cam wheels.

Pete

[tima01864]

The question is checking the mechanical advance at 3000rpm, I could make my own marks and see if i am getting the advance. The hand held tach would be handy when i am using the timing light.
Bryan yeah that could be the tach is not taching right, I have thought of that, A tachometer to to make calibration.
I will probably do as you say Pete, But first I will check the ignition. Maybe the cams arent set properly need to recheck that.

[RRoller123]

What are the cam specs on your cams? I seem to remember they are different from each other. Knowing that we can calculate the LSA and that will tell a lot. Did the cam cards indicate any built in advance, i.e. valve timing advance ground directly into the cams?

Intake opens at _____ BTDC?

Intake closes at ______ABDC?

Exhaust opens at _____BBDC?

Exhaust closes at _____ATDC?

Could be a leak in your advance hose? It should be pretty easy to see with the timing light if it is advancing somewhere up in the 30's, without being too exact.

[tima01864]

Intake opens at _____63.6 BTDC?

Intake closes at ____102.4__ABDC?

Exhaust opens at ____67.5_BBDC?

Exhaust closes at ____100.8_ATDC?

says 18.5 retaed

duration intake 345.9
duration exhaust 348.3

there is alot here

[RRoller123]

for reference, the 274FI cams that Allison sells have these specs:

INTAKE OPENS AT ------------- 28 BTDC

INTAKE CLOSES AT ------------ 66 ABDC

EXHAUST OPENS AT ----------- 66 BBDC

EXHAUST CLOSES AT --------- 28 ATDC

Does it say anything about whether these measurements are absolute, or measured at some particular lift or whatever? (They shouldn't be, but all the cam mfgs seem to do their own thing.)


Your numbers imply an Overlap of 164.4 degrees, Intake centerline at 60 ATDC, Exhaust CL at 73 BTDC, LSA of 133 degrees. And extremely high duration. Both the Exhaust and Intake are almost never closed, for example.

This seems pretty radical, especially the Exhaust closing at 100.8 ATDC.

I need to take a look at those videos I posted again to see if they give any insight into what the general effects of this setup may be.

I am no cam expert, but am learning. But these seem like pretty radical numbers.

[18Fiatsandcounting]

Tim, I agree with Pete that your cam numbers imply a very wild cam, wilder than any I've ever seen. 26/66 66/26 was stock in the early engines, and fairly aggressive cams are 40/80 80/40, but you're well beyond that. Can these numbers be right?

Pete, I l believe that there was an attempt at one time to standardize cam numbers using the crank angles when the lift was 0.050" and above. No guarantee how successful this attempt was, so unless the cam card says what was used, it's anyone's guess.

If it were me, I'd get the ignition timing working correctly and then move on to the cams. The advance at idle should be around 10 degrees BTDC, and it should advance smoothly from there as you increase the rpms, reaching a maximum advance of around 36 degrees at around 3000 rpm. If your engine differs significantly, there's something wrong.

-Bryan

[RRoller123]

Is that advance "curve" linear for a stock distributor? I am having trouble getting my car to idle low enough to use the timing marks correctly. It just won't idle smoothly at a low enough rev to do the timing the normal way with a light, so I have to guess what the advance would be at say, 1500 rpms, and set it there. I am thinking like 15 degrees? But I don't really know. Does anyone have a drawing of the stock advance curve for the '80 distributor?

Tim: Maybe double check those cam card numbers? If those cam numbers are taken at a particular lift, ( a lift of 0.050" is the "standard" starting point now, having been established by Harvey Crane, who passed away in 2013), and not pure, i.e from zero lift, then it would make those numbers even wilder. Something ain't right there.

Pete

[tima01864]

That what I got cam lift .003 these are the numbers. The cam itself is 35/75,
This cam profile came back to me from Delta camshaft. All greek to me

At .05 lift
11
48.9
duration 240.00
13.1
49.5
duration 242.7

I asked the guy who had them profiled if he can explain the report to me. Will see

At .015 lift

29.8
68.7
duration 278.4
33.9
66.7
duration 348.3

One more int/exh specs
intake duration @ 0.05 239.97

If I interpolate those numbers they equal 35/75?
Opening 11.03 Closing 48.94

Exhaust duration 242.67
opening 13.3 closing 49.55

If any one can help

[RRoller123]

That seems more normal.

[18Fiatsandcounting]

At .05 lift
11
48.9
duration 240.00
13.1
49.5
duration 242.7

I would interpret this to mean that at 11 degrees BTDC, the cam lobe has risen to 0.050" over its base.
At 48.9 degree ABDC, the cam lobe has dropped back to 0.050" over its base.
The duration is simply 11+180+48.9, or 240 degrees give or take a bit.
Based on your other data below, I think this is for the intake cam, and the second half is just the exhaust cam.

At .015 lift

29.8
68.7
duration 278.4
33.9
66.7
duration 348.3

This is the same as above, except using 0.015" of lift instead of 0.050".

One more int/exh specs
intake duration @ 0.05 239.97
Opening 11.03 Closing 48.94

Exhaust duration 242.67
opening 13.3 closing 49.55

Essentially the same data as above, but perhaps a different measurement technique (or standard) was used.

So, to summarize for your intake cam: At 11 degrees BTDC, it is open by 0.050", and this continues all the way to BDC (another 180 degrees), and then your intake cam lift drops below 0.050" again when it passes 48.9 degrees ABDC, or a total of 240 degrees where the cam lift is at least 0.050". This sounds reasonable. Same analysis for the exhaust cam.

-Bryan

[tima01864]

I kept editing my comments Pete, Maybe you missed something too

[tima01864]

The exhaust cam is Standard for the engine, The manual states Open 53 deg BTDC Closes 5 deg ATDC. The gut who did the work recommends keeping the standard camshaft