Cam advance / retard

[fiatfreak]

Cam someone tell me the basic attributes of advancing or retarding the intake cam? Advancing or retarding the exhaust cam? Wanting to know what yields more low end power verses high end power. What about more or less overlap?

Thanks, Mark

[divace73]

I've heard different things on cam timing, but I am guesing nobody is willing to put themselves on the line, cause if it wrong or advance is confused for retard, you WILL damage your engine.
I need to do some reasearch myself, I know as a minimum I'll need a timing wheel and lots or theoritical reading......no real magic answer I'm sorry

[Daniel]

advancing the intake and exhaust cams have limitations when seeking better performance if you advance or
retard to far you lose power across the power band with no gains at all !

To answer your question
If you want to achieve a lower usable RPM power band via cam timing you would want less over lap on the cam
shafts . To reach a higher useable RPM power band through cam timing you want to time them with more over
lap . If you Advance the intake and retard the exhaust cams you'll have less over lap . Retarding the intake
and advance the exhaust cams will produce move over lap .

Hope this helps

Daniel

[coise]

Daniel,
Which dial in wheel do you take to adjust the cams on the Fiat spider 1977? I know that Jeg´s has a lot of them, but which one to choose? Also is there a topic somewhere in this forum, about the whole process?
Thanks.

[fiatfreak]

Thanks, that's the first useful bit of info I've gotten so far. Been posting on several sites.

advancing the intake and exhaust cams have limitations when seeking better performance if you advance or
retard to far you lose power across the power band with no gains at all !

To answer your question
If you want to achieve a lower usable RPM power band via cam timing you would want less over lap on the cam
shafts . To reach a higher useable RPM power band through cam timing you want to time them with more over
lap . If you Advance the intake and retard the exhaust cams you'll have less over lap . Retarding the intake
and advance the exhaust cams will produce move over lap .

Hope this helps

Daniel

[v6spider]

Daniel,
Which dial in wheel do you take to adjust the cams on the Fiat spider 1977? I know that Jeg´s has a lot of them, but which one to choose? Also is there a topic somewhere in this forum, about the whole process?
Thanks.

The 'dial in wheel' you are referring to is called a degree wheel... most if not all shown on jegs are designed for dialing in cams on a Pushrod style valvetrain v8 or v6 made by Chevy, Ford or Chrysler... Although they may have something design for Honda's dual overhead cam setup.. Pushrod driven valvetrains on v8's and v6's have a cam that has both the intake and exhaust lobes on the same cam. Different situation with dual overhead cams... you will also need a dial indicator as well.. it is a long and exacting process and i am not familiar with how it applies to a FIAT twin cam but on a V8 or V6 it helps to properly degree the cam especially if it is an aftermarket performance cam.

Rob

[baltobernie]

There's nothing special about the degree wheel required for the Fiat TC; any one will do. What is unique is the modification of the cam pulleys themselves. The Fiat cams are fixed with a key slot in the pulley. Several of our vendors sell OE pulleys that have been modified, or new adjustable pulleys. Essentially, these allow the tuner to rotate each cam pulley independently of the hub, with circular slots cut in the pulley and secured with cap screws. The only "adjustment" otherwise possible would be to intentionally skip a tooth on belt alignment. This would be a rather coarse jump, and not recommended.

Adjustable pulleys are recommended to Fiat engine rebuilders seeking to achieve optimum performance with stock or aftermarket cams. As I've repeated ad nauseum, most of us don't know the provenance of our engines, and each time a cylinder head or cam box is machined, the distance (and therefore the timing) between the crank and each bank changes. Valve and tappet clearances affect timing too, and cam suppliers specify the clearances vs. degree duration of their products. Ventura Ace has posted some interesting threads and photos of his adjustment experiments. Of course, you'll need the services of a dyno to determine if your adjustments are producing or subtracting power. Oh yeah, as you change cam timing, you are also changing effective compression ratio and other stuff, so each change to ignition timing and carburetion should be documented as well as measured. Cam timing should also theoretically change your intake and exhaust manifold dimensions, so as you can see this is not a matter of turning the mixture screw on your chainsaw to the point where it runs best!

[sptcoupe]

And be sure to make each change one at a time or you will be totally unable to optimze either the ignition or cam timing. And doing it without a dyno is really pretty difficult, too, as a move a little too far either way can substantially reduce performance, even though it may seem to be running just fine. On the other hand, optimizing these two parameters can really get some great results. On some of the 188 + dyno runs we did on the coupe in the past year or so, we saw as much as a 10 RWHP gain through tuning the cams and ignition. We also saw some equally dramatic drops when we went the wrong way or too far, and we would not have known it either way if we weren't on the dyno. The dyno doesn't lie, while the "seat of our pants" does.

Just a few more tuning observations from our hours of dyno experience on the 2.0L TC in the coupe, although not directly related to cams and ignition.

Cold air and straigthening the air intake as much as possible makes a big difference - as much as 5 RWHP! In this case, I am talking about getting the air through an inlet that is completely outside the engine bay, and where the intake plumbing is kept completely on the intake side of the motor - unlike the normal K&N set ups we use on our spiders (me included). This is why we are building another custom air box to use with the IDFs, similar to what we used on the FI system. A pain, but it gets you the optimal performance from those expensive TB's or carbs, and in my mind is well worth it. BTW, I would not have thought it so important before seeing the results in living color on the dyno.

Also, although we didn't specifically measure it, the Allison "snakes" header made about an additonal 4+ RWHP over a popular aftermarket, "traditional" header. In this instance, we were trying to isolate the cause of the power band stopping at 6000 rpms, so we replaced the Allison with the popular aftermarket unit I had run on the coupe for years on an 1800cc "full house" motor, and did some runs. The new header did not change the 6000 rpm wall at all (which was what we were looking at), so we put the Allison header back on, and on subsequent runs saw a 4+ RWHP gain over the runs done just previoulsy with the other header. It may be that the difference is greater now that the engine makes power through the full rpm range. But that is a really nice gain for a header on a 4 cylinder. And this gain is over an aftermarket header, not a stock unit, so presumably the gain will be larger going from a stock header to the "snakes" - but there is no way to determine that for sure without a dyno. One note about the Allison header. The design creates really long runners (part of why it works!) that are relatively high up in the engine bay. On a normal header, the runners come off the engine and generally head downward fairly quickly. On the Allison unit, the bulk of the runner are comparatively high up in the engine bay, which means they don't cool down as much or as quickly as other headers, so the heat under the hood is noticeably higher. NOT the engine operating temp, just the heat under the hood. For us, that meant moving the ignition spark towers forward of the headers to keep them from frying (which happened), and using 4mm insulators under the IDFs to deal with some fuel percolating we had when we first put the IDFs on. It also underscores the importance of that cold air intake taking air from outside the engine bay. All worth it to get the extra kick.

Csaba - any other general observations/lessons learned?

[baltobernie]

Before Csaba jumps in here, I'd like to concur with your observations regarding intake air and cam timing.

I simply could not get my new 1800 engine to idle, or produce any power at low RPM. Jetting, ignition timing ... tried everything. Turns out one of my cams was out by 8°, which we fixed with Miller's Mule wheels. We picked up something like 8 RWHP as measured on the dyno, and the bottom end was cured. No other changes except properly timing the 40/80 cams to IAP specifications.

We lost 9 RWHP affixing the lid to the air cleaner housing! That's with a K&N element, to boot. I was going to go with a cold air setup; even had a "funnel" tacked onto the rad support bracket where there's an OE hole. My intention was to run flex aluminum hose to the OE air filter housing. Dyno guy said, "Nah ... you're trying to keep the OE look, right? Just drill as many 3/8" holes in the underside of the OE housing on the outboard side of the element as you can. I did, and all the power came back. Looks stock (but doesn't sound stock ). I'm not saying you guys with stock engines will see this kind of gain, but if there's anything I've learned with this project, it's that when you change one thing from OE, you've got to probably change a lot of other things as well.

[sptcoupe]

AMEN! Even the simplest changes/mods seem to bite back in ways you can't imagine. So it you have the time, do one thing at a time, evaluate the results, then do one more thing.

I have seen and heard of drilling holes in the OE air cleaner box (or any box) as a way of getting it to breath, but we want to try to quiet down the coupe, as we really do like to drive it. So we want to seal up the carbs in a box that dampens the sounds of the carbs, and bring in pure cold air front the wheel well. The resaon we are getting the air from the wheel well is that whenwe dyno'd the air box setup, we found that the bends and twists we needed in the plumbing to get the air from in front of the radiator also caused about an 8 RWHP loss. Once we straightened it out, we only lose about 1 + RWHP from running it with no top on the box at all. That's acceptable to me.

[coise]

Thanks guys for all the good exponations. I can tell now, that it´s not for me. I don´t have access to a Dyno.
Thanks again for all thoses great advices.

Coise

[Daniel]

Daniel,
Which dial in wheel do you take to adjust the cams on the Fiat spider 1977? I know that Jeg´s has a lot of them, but which one to choose? Also is there a topic somewhere in this forum, about the whole process?
Thanks.

Sorry i didnt read this sooner but Rob gave you a good lead already to find a timing wheel or you can
just make one like i did .


Daniel