Driveline Angle Analysis and Results

[RRoller123]

That is awesome, and is somewhat as expected. I will explain. I have been watching dozens of Youtube videos on the subject, but to piece together the whole picture is difficult because the videos are all so fractured. They run all over the place, like a rabbit with ADHD, from timing single cam big block US engines, to twin cam Harley bike engines. Not a lot on classical twin cams like ours, which is surprising.

But there are some general rules I have learned so far:

1.) Advance the Intake to raise manifold vacuum, increase cylinder pressure and increase low end torque.

2.) Widen the LSA to settle down the idle and smooth out the range, at the slight expense of overall power.

3.) The ICA is somewhat of a mystery to me, as there hasn't been a very good explanation I have found yet of how to set it and what changing it does.

4.) I have seen references to advancing both Intake and Exhaust by 4 degrees to increase low end power and torque, i.e. shift the power band to the lower RPMs. This is what I seek to do: Increase the low end performance, and smooth out the idle. I couldn't care less about going above red line, so moving the power band down makes sense to me.

I probably have these rules wrong, so I will re-watch the videos I pulled this info from and post them her for review, under a new Topic Title.

[RRoller123]

Hi Steiny:

I had a chance to get in under the car yesterday to check on this idea. I.e. that normal movement of the engine and transmission negates the adjustments I made. I have new engine mounts that allow almost no movement, and more importantly, have the top and bottom studs co-linear. And when we removed the transmission as part of this project, it was apparent that the rear transmission mount rubber had gone completely soft and pliable, presumably from exposure to oil, etc. I put a new one in, which is very rigid.

With the engine and transmission back in, and the transmission support bracket, and the support bar to the exhaust system installed, I grabbed the back of the transmission near the support and tried to move it. I cant move it at all, it is held completely tight, regardless of how much force I apply. This is how it is supposed to be. If one can easily push the system around, say 3/4 of an inch or so, there is something very wrong, and the rubber parts are probably perished. I couldn't get any more than maybe a 1/16" at most of movement with a lot of force applied either side to side or up and down. It doesn't move with new mounting parts installed.

I think this rubber wear and softening is a common cause of a lot of driveline vibration that people experience. It throws the intended design angles way off. The engine mounts get soft and distort. We saw at least an inch (!!) of non-colinearity between the top and bottom individual engine mount studs when we removed them, they were soft and fairly pliable, and the rear transmission support mount rubber was as soft as butter, basically completely useless, doing nothing.

Yeah, this is a lot to take in.

I would think that a ton of your adjustments are negated by the absolutely pillowy soft transmission mount. Even with a brand new mount from AR, I can move the transmission 1/2"in any direction with three fingers. Factor in the car actually moving and going over bumps and this thing is all over the place.

I wonder if there are stiffer transmission mounts available.

[msrichmond]

This is a super-interesting thread, thank you!

I can add something to the camshaft discussion. A change of one tooth is 9 degrees of crank rotation. There is no way that moving that is going to work better than the factory setting on factory cams.

You can however, match the stock cams we have to the cam timing often used in the European models with adjustable cam wheels. Doing this is a labor of fussiness, don't believe anyone who says you can just do it with the vernier markings that come on these wheels. Most of us have heads that have been surfaced, or maybe even the block or have a non-stock thickness in the head gasket, all of these affect cam timing which is why these mods want adjustable cam wheels to begin with, even with stock cams.

The project I did was to set the cam timing for both intake and exhaust to hit peak lift at 110 degrees. This is a change from the 114 degrees of the USA spec. When you do this, the cam timing matches the mythical "European cams".

The whole discussion is here: https://www.mirafiori.com/forum/viewtop ... 15&t=99779

[Nut124]

Agree with MSRichmond here.

Adjusting cam timing by jumping teeth on the cam gears is not acceptable and could actually result in damage.

Anytime a Fiat twincam engine is built, the cam timing should be checked and adjusted as needed. Adjustable cam pulleys are nice but there are things that can be done with the dowel pins if you have the patience and skills.

Checking cam timing is basic engine building 101 and a required part of any build. Need a properly set degree wheel and a way to measure valve travel, i.e. suitable dial indicator.

This is not difficult but can be time consuming. I find it an interesting exercise. I have tens of pages of notebook and excel data on cam timing tests on my engine.

Typically, the IVC event affects low/mid torque the most. Long duration cams tend to make the IVC happen later. This causes intake flow reversal at low, medium engine speed killing torque. This can be seen sometimes as a standing gas vapor column on top of dual IDF barrels at idle. Harder to observe in a common manifold setup. Also, a prominent, cool intake noise is present when this reversal happens.

For this reason, often, when a longer duration cam is used, it has a different lobe CL in order to keep the IVC about the same. In this case, longer duration cams increase the overlap and LATDC w/o delaying IVC much.

An example would be the Alq 40/80-80/40 cams. Recommended intake CL is 108-110 ATDC. For the 42/82-82/42 cam, which nominally has 4 deg more duration, the recommended intake CL is 106-108. This is to keep the IVC from being delayed too much at all.

Also, setting the valve lash should be based in the cam ramp profile. Setting the lash too tight, increases effective cam duration, delaying IVC and hurting low end torque. Too much lash makes the valve train noisy, valves hit the seats too hard upon closing increasing the likelyhood of a disastrous valve failure.

[RRoller123]

Very helpful! Can you share some more general insights on the effects of advancing or retarding Intake and Exhaust? Which is the engine more sensitive to? I would expect Intake, as it is the source of energy supply?

[Nut124]

Roller, I would highly recommend the Guy Croft book on these engines. Also, there is plenty of info available on the internet although most of it seems to be for the US V8 pushrod crowd where advancing the cam affects both the intake and the ex the same amount. This is not typical of what would be done with DOCH like the fiat. The V8 LSA concept is part of this.

It is important to understand and visualize the terminology or the numbers make no sense at all.

In general, most Fiat factory engines have 110-111 lobe centers on both intake and ex. Performance cams increase both lift and duration. Typically, hot street cams have 108 recommended lobe centers, both in and ex. All out race cams can be 102-106 lobe centers. I have never seen cams for Fiat where the recommended lobe centers are not symmetric i.e. IN and EX use the same center. Most if not all cams have symmetric lobes where the opening side has the same profile as the closing side i.e the lobe center is half way between valve open and valve close.

Many experts suggest that the max torque of a given Fiat twincam is a function of the (intake) cam lift or total lift integral. I.e the size and duration of the intake opening for air to enter the cylinder. There are three ways to increase this: More duration, more lift, or more aggressive profile (fatter lobes). Advancing or retarding the cam(s) lis unikely to increase peak torque, but could make the torque peak earlier or later. Typically, advancing the IN would improve low end torq but hurt HP. Retarding the IN would hurt low end torq and could improve HP but only if the carbs, ports and the rest of the package are up to the task. The idea is that at high rpm, long duration cam, the momentum of the intake air keeps pushing air into the cylinder even though the piston is moving up trying to compress the air, here the IVC is at 80 ABDC where the piston is almost half way up on the compression cycle. This is why many engines have long intake runners, to create a long column or air with mass and inertia.

Effects of EX timing are harder for me to understand.

In case studies in the Guy Croft book, any adjustments to cam timing were in the +/-2-6 deg range. Way less than the effect of jumping a tooth on the timing belt. Jumping a tooth is likely be detrimental unless the initial timing is way off and the jump moves timing into the right direction.

I would recommend sticking to and verifying the cam makers timing suggestions. Typically 110 stock, 108 street, 104-106 race.

Below are some images that may be helpful, or not.

[RRoller123]

Excellent info! Thank you very much, that is really helpful. A lot better than just stabbing around blindly in the dark to see what seems to work best. I am mostly interested in low end torque, and good acceleration, don't really care about top end. I very rarely go over 5000 rpms, usually by accident, and the car almost never goes over 70 mph. I have Mark's 274FI cams and adjustable wheels, but I think I am going to put the original cams back in and see if I can solve this vibration problem that is so persistent.

[18Fiatsandcounting]

...I think I am going to put the original cams back in and see if I can solve this vibration problem that is so persistent.

It seems I've forgotten, but what is the vibration problem that you've got?

-Bryan

[RRoller123]

It is somewhere in the engine, persists even after short block rebuild. All rpms. Have large valves, 4mm domed pistons, adj wheels, 274FI cams, lightened flywheel. Rebuilt AFM, mostly new FI sensors. Plugs, wires, disty, hoses, are all fine. Have a couple of ideas; I think it is in the cams, they may not have worn properly, or are not spinning properly in their "bearings". Oil screen was nearly 60% blocked, found at rebuild of short block. Exhaust cam seems harder to turn when adjusting the cam wheels. Gets fed oil through a really tiny oil hole at ~#4. When it warms up a little, I am going to measure the lobe peaks with them in the car, see what I get. Then put in the old cams. I have a spare regular valve head too that I can swap out to try and isolate the problem. Leakdown test was fine, but there may have a sticking or bad valve guide or a slightly bent valve stem. Had a few bad backfires over the years, due to FI issues at the time. Lately a small smell of oil on decelleration at highway speed.

[Nut124]

Roller, what are the symptoms of the problem you are trying to fix?

Cam oiling is adequate unless the belt is way too tight, or oil too light. What oil are you using?

Many adjustable cam pulleys are not quite concentric. Can result in a situation where the belt tension varies as the pulleys run non-concentric. I have seen this and it resulted in a pulsating variable pitch belt whine, not good.

Was the crank, rotating assy balanced? Crank, FW, clutch?

[RRoller123]

Oil is Rotella 15-40. Good idea about the concentric adj wheels, I hadn't thought of that. I will measure it first thing. I may swap in the original wheels, as that is pretty easy to do, and I can do that right off the bat. Change just one thing at at time. But there is no belt whine nor pulsating, more like a minor but noticeable engine vibration, the tiniest of all possible shakes (don't even want to use that S word) at all speeds, including idle. Engine runs very strong, all speeds, goes easily to redline, really flies now.

Yep, the entire system was balanced, Danny did our short blocks and transmissions. Not concerned there. Quite sure that it is somewhere in the top end. I have a noid light set and will first check all the injectors for signal. They are also new. Also a possible ECU issue, I suppose.

[Nut124]

Roller, I find it unlikely that the vibration you describe could be caused by the cams.

I asked my balancer about balancing the cams, pulleys for my build. He said not worth it. He said some builders star trying to balance cams for race engines that run in excess of 10000rpm. Even then, he said, it is questionable whether it is worth it.

Cams run half the speed of the crank and are so much lighter than the main rotating assy. Was the clutch pressure plate balanced as well and indexed to the flywheel?

[18Fiatsandcounting]

I have no experience with lightened flywheels, but my understanding is that they do show a bit more vibration due to less rotational mass to dampen any pulses. I'm kinda thinking the same as Nut124, that is, in the flywheel or clutch pressure plate area.

I assume you've changed the motor mounts?

On the other hand, 4 cylinder engines inherently have more vibration than the silky smooth feel of a 6 or 8 cylinder engine. Could it just be normal behavior for your engine?

-Bryan

[RRoller123]

Brand new motor mounts, that was all part of the driveline analysis that started this thread. The mounts can easily be off by an inch (!) colinear! The vibration was there before the lightened flywheel went in. The only thing I notice with the lightened flywheel is some surging at very low speeds, makes heavy traffic a pain. The entire system was balanced by Danny, I trust that it was done correctly, and an alignment jig was used. Flywheel is Allison's. But I never am in heavy traffic, so I don't really care. The car is much faster accelerating with the lighter flywheel too.

[tima01864]

clutch and flywheel balanced