That's really something but not surprising. That said, the old 2v motors are not particularly picky when it comes to cam timing as long as you're within a few degrees. The 4v motors on the other hand are far more picky as you've pointed out in the past.
Quite so. I have seen 2v injected motors out a tooth and run just fine. It is not so much a matter of # valves though. A 275 4cam really wakes up when cams are spot on. The more conservative a tune the less little stuff matters.
Makes me glad that I decided to go with the larger degree wheel, I had not known the dwell was that short at TDC, that sounds like a pretty small window to measure with any accuracy using a timing wheel. If I have any fear of my Ferrari, it's replacing the belts and somehow getting it wrong (unlikely and irrational perhaps) but potential to have 40 bent valves does not warm the heart. M
My ex-Ferrari trained dealer mechanic has successfully set my 575 cams at SA spec. I presume he would have used Ferrari's procedure.
Yes it would a very small amount and the crank turns twice when a cam turns once making that effect even smaller. It is not clear to me what RD is trying to say. He seems to be saying TDC is not what most people think. What is “TDC is defined as the time the piston arrives at top?” Did Ferrari mean when your dial gauge says you have reached to max reading in the driven direction? Or did Ferrari mean the “top” as the top of all possible piston travel when the engine is running? If it is the latter then that would jive with 99% of the rest of the world that sees TDC as that place interpolated between 2 points either by dial gauge or piston stop method. We are making too much of this process. Use common sense and look at the big picture and we won’t get confused by all the noise. If the result of your cam timing exercise, regardless of your method, leaves you close on the assembly marks you are probably correct. Certainly you will bend no valves and every car despite its variance in cam timing will run "consumer acceptable" on assembly marks. Cam timing is a precise process. Even the “scribe marks” on some engines can look dead nuts on and still need +/- 2 cog holes to be per the WSM and marks appear to not move at all! Anyone who comes to my garage I’ll prove to you that the rear scribe marks are no better than the assembly marks. Optimum cam timing does not exist. There are reasons for why timing specs can change within a small window in the same motor to achieve different results for things like emissions or torque or horsepower. Racers guard their data on how their motors are set-up for different race tracks and track conditions. That data is expensive to obtain and gained by trial and error and many long hours of blood sweat and tears. There is no one perfect setting. The specs in the WSM are a good start and the end point for 99% of drivers. For racers it is just the beginning.
The subject of dwell at TDC, can be longer on an engine with longer connecting rods. That is why US. engine builders use true TDC. and .050 cam lift. So they can compare apples to apples. As explained Ferrari uses the procedure as soon as the indicator shows max movement, that is how they determine TDC. The US. procedure normally uses a piston stop, and the degree wheel is split equal between the two. Listen to the Ferrari experts on here and do it as the explain how Ferrari does it.
Im dense. I don't get it. You are saying ferrari tdc is defined differently than everyone elses tdc which is determined by piston stop or symetrical use of a dial gauge?
I believe Brian is saying Ferrari's TDC occurs at the beginning of the dwell, not at the center of the dwell.
OEMs do not use degree wheels and the techniques we use to set timing. They have a completely different system with precision tooling to set the timing. Many of the engineers I have worked with would have no idea what you mean when you talk about dwell. For them it would be a tolerance stack up that would cause measurement errors. You can not assume that the way they set the timing results in a tbc reading slightly before the actual tdc. They will analyse that kind of thing to death. In the end the results will be the actual tdc with an allowable tolerance band. Cheers Jim
The part I did understand is wrong. Sorry but it just is. Have you ever seen a Ferrari degree wheel? Stop by, I'll show you a few.
Interesting discussion but somewhat confusing for someone like myself who is learning and wants to do things right. How many degrees out of time can you be before pistons and valves come into contact ? Seems like using the beginning of the dwell leaves less room for error ( piston/valve contact) than using the center. Also using the center method compensates for lost motion due to wear. Just speculating, as I said this discussion is confusing. Thanks, Brewman
A lot of variables there. On a Ferrari 4 or 5 valve motor they need to be a very long way off to hit and as a practical matter the most common reason that happens is the cam drive breaks in some way while the motor is running or someone makes the mistake of installing the cams with the motor at TDC and rams a valve into a piston during the assembly process. I see that one a lot. On a 4 or 5 valve, the valves are so small and the lift low enough the pistons and valves don't come very close unless something is way off.
Yes Dave...what RD is saying sounds clear enough. It must have shocked him too if he asked "with a good interpreter to be sure I was correctly understanding them and it is how they do it." It is news to me over 30 years never heard what RD is saying. I learned to time motors from Lyle Tanner's head mechanic doing race prep for rich Ferrari guys and lessons reinforced by two different FNA mechanics I hired to teach me how to work on these cars. TDC was found by Piston stop or either side of the dial gauge is what they taught just like timing a chevy. One day I will have to clock the dwell and see how much there is. It is a nice little tidbit of knowledge as we diy'er's try to up our game. For now, I will stick to what has worked for me which is the chevy way. Heck I'm still "doing it wrong" setting timing belt tension by feel.
Yep, technically it's 12' that's 12 minutes of a degree. Mathematically that's the avg for Ferrari V8's. Simple two bar trig calcs. Dwell for each, F360 = 0*12'0" 328 & F355 = 0*13'12" 308 = 0*42'0" 348 = 0*43'12"
Incidentally this is what makes dialing in these motors a bit of a PITA. With stock parts sticking to the factory setup is best. Now once you start altering the cam lobes, cranks, pistons etc.. the fun begins. I've had to make custom degree wheels that include minutes as with such short strokes as you can see measuring less then a degree is a touchy PITA. looooooong handles and smooth turning. By comparison American Iron has upwards of 20* of dwell, hence why stop to stop works.
On my F119 I found it to be 2º of dwell time (via the degree wheel on the crank). That is from the time the dial gage stopped movement on the piston up stroke, until it started moving again on the down stroke. Keep in mind the stroke on a F119 is 75mm. So the dwell time will be different for the various engines because of different rod to stroke ratios vs that of a F119 block.
I should clarify that the mathematical dwell is based on the piston movement raising to it's max position and not changing while the crank rotates. It's would be near exceedingly difficult to measure the true dwell as you'd need a gauge reading into the microns and a degree wheel measuring seconds. Best would be optical measurement. I'd have to go back and run the numbers again but most dial gauges and degree wheels would measure a couple degrees of dwell, even though none of them engines actually have that much. Here's the F355 AKA F119 Engine 180=75.5 180.12=75.4999 180.2=75.4998 180.26=75.4997 180.3=75.4996 180.34=75.4995 180.38=75.4994
I get mathematical dwell. But I think of dwell as all the slop in the system too like bearing clearance. It is kind of like 4 points on a chair really can't measure a plane of 3 points. All that slop needs to be in the equation and why Ernie can measure 2 degrees while math dwell says minutes of a degree. To me just another reason to use the piston stop/dial gauge split for TDC.
exactly! Technically there's no piston dwell, nada, nil! just 1 singular point of TDC. The dwell is real to us because of the kind of measurement accuracy isn't easily obtained!
Thank you all for such an informative discussion. I am currently doing the major again on my 550 and this time around have used the actual "Ferrari" method for determining TDC. It seems like on my F133 that the amount of "dwell" time is relatively small anyway, maybe no more than a degree or so. I can't say that with certainty because of the fact that I haven't specifically measured it. The biggest issues I have with all the timing components in place are: 1. The timing system wants to "spring back" a degree or two when I get to TDC, making it difficult to adjust cams precisely while keeping the degree wheel exactly at TDC. 2. Getting that damn camshaft to STAY PUT exactly on 0.7mm when retorquing the cam bolt. That's driving me up the fooking wall.
Why are you even trying? Read it Adjust it Read it again. What you are doing is not possible. It will never stay still.
Well Brian, probably because I find myself saying "how precise would Brian Crall or Dave Helms be at trying to get this cam exactly to WSM spec?" However, as it stands the best that imperfect me can get this cam to read with a fully torqued cam bolt is this (Photo 1) 0.015mm beyond spec. It probably needs to stay here; I don't think I will ever be able to get it any better. Image Unavailable, Please Login
