camshaft troubles on a 308i

I know this is time consuming but have thought about degreeing the cam?

 

The good news is stock US 308i cams aren't in high demand

Do you have lift and duration values for your "aftermarket" cams?

 

The cheapest thing to do is to send them to web to be re-ground back to stock.

I'm sure the various salvage yards could hook you up with a fresh stock set then you could sell the aftermarkets cams on ebay.

Be aware though, if those are decent cams you're engine probably makes 20+hp more than stock and will will lose that when you go back to the "only good for a smooth idle" stock cams.

 

Thanks, but can you please clarify at what lift the duration applies - 0, 0.5mm, 0.05", etc.

And for the lift values are those both 0.32"?

 

*looking for cam chart*

What do we have here, guys???

 

That's pretty normal and a pretty simple process and nothing to worry about.

 

I agree, I'd focus on degreeing them in and see how it runs, that might have been the trouble all along.

Take the time with the sprockets and pins, to get within 1 degree.

You might end up with a fire breather!

 

Degree them within 1 degree of what? these are not stock cams so the stock timing numbers are almost certainly not where the cams want to be.

The rough idle is due to the longer duration and it's not going away with timing changes. CIS hates longer duration which is why ferrari didn't do it even though it make way more hp.

 

Ah, of course you are right.

Order Webers!

 

"Be aware though, if those are decent cams you're engine probably makes 20+hp more than stock "

Maybe, but at the expense of power in the mid range. There is no magic involved. You can move the power band to wherever you want it but unless you increase the engine displacement, or go to forced induction or nitrous you can't increase power throughout the rev range. Do you want max HP or driveability? That's the decision you have to make with cam changes; You cannot have both on a "traditional" engine. It is NOT the case with modern engines that have variable cam timing, variable intake volume, variable ign timing etc. and that's why they can do both - have top end and bottom/mid power.

 

This is true on newer engines. But on older engines sometimes you can have your cake and eat it to. The really good cam designers can update old profiles giving better idle, mid range and top end. They didn't have cam design software back in the days of the Duntov 30/30.

 

CIS is a mechanical injection system and is pretty sensative. Electronic injection will tolerate almost anything and make way more hp in the process.

The cams you have are pretty mild so carbs would be fine with them.

 

Just so I understand, rewelding profiles moves the lobes, and makes the reference marks worthless?

I dunno why I assumed the lobe peak stayed in the same in location...they were adding shoulders and lift.

 

The 2vi engines are a little different case from normal. The cams in these engines have so little lift and duration that they are a problem at pretty much all rpms. The stock early Us or euro carb engines with their bigger cams and better breathing make more power across the board. The 2vi engines leave a lot to be desired performance wise.

 

I may misunderstand the post but without variable cam timing capability, like many modern engines, a cam cannot alter itself to enhance both low and top end power. The cam profile that gives you great top end power is not the same as the profile that gives you good low/mid. If you look at cam specs, a high performance street cam made today for, say a 426 Mopar hemi street motor (did a ton of work on these), has essentially the same profile as a cam for that purpose did in 1970. In fact, one of the most popular cams for the hemi is what was originally Mopar's "Purple Shaft" that came out in the mid 70's as part of Mopar's "Direct Connection" program. The same cam is now produced by a number of aftermarket suppliers...exactly the same profile as the original and still considered one of the best street/strip cams.

I do not mean to be argumentative and perhaps I misunderstood the post but I did professional competition and high performance engine building from the mid 70's until 2006 and I am not aware of any way to increase both low/mid and top on an engine by just changing a cam. However, I must admit that I have not kept up with the most current info - post Nov 2006 so perhaps there have been developments since then. But I still can't see how anything could be done differently - the laws of physics are the laws of physics and Hi RPM breathing is different than low/mid RPM breathing; what makes for great High RPM power kills low/mid.

 

The lobes centers would almost certainly have been put in the stock locations.....but they aren't stock lobes so the correct timing is almost certainly different form stock making the stock marks and triming info useless. The cams would have come with a cam card that had the cam grinders recomendation for a baseline timing, but the only way to KNOW where to set them is trial and error on the dyno. Once you start messing with stuff you open a can or worms which is way so many prefer to just leave it stock.

 

What you're saying is normally competely right but 2vi cams are not normal, they are really really bad for the application. The only mission these cams had in life was to get the engine to through emissions testing. They work great up to about 1000 rpm and above that there is not enough lift or duration to work well.

 

OK...I totally agree that if the cam was designed for - say purely emission or whatever - than you are absolutely right, and a far better cam could be installed that WOULD improve power through the entire rev band. I didn't realize that the stock cam was that bad. So I totally withdraw my statement that a cam change couldn't benefit every aspect of the engine's operation. It certainly can based on the fact that the stock cam was that intentionally "conservative" by the factory.

I ASSUMED (Yeah, I know what they say about assumptions) that Ferrari - it is a FERRARI, after all - would have put the best cam they could in the car for overall driving capability.

 

Remember the late 70s-early 80s nobody really understood how to make engines run clean. A 2v engine guess won't make power with ZERO degrees of overlap but that is what was required to make the CIS system work. This is what finally pushed ferrari to the 4v heads where they uses the exact same cam grind that they used in the 2v engines. 0 .305 lift is not bad with a 29mm valve, but for a 42mm valve you don't even have enough lift to get out of the curtain flow region so you never get the valve open far enough to get near peak flow. The 2vi cams are Horrible.

I just the cams back from the grinder for my engine. Here’s a pick of what I’m putting in a 4v TR head compared to the stock 2vi grind....notice a slight difference?
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Jimmy, a more extreme cam is going to show its ugly side most obviously at idle...that's were a lot of overlap affects smooth running in a very noticeable way. When the engine is at WOT at 5,000rpm the more aggressive cams are right at home and engine will be putting out more hp (and perhaps tq) without being noticeably rougher running than stock. If you've heard the phrase "lumpy cam" that means a cam that has more overlap than stock and really shows it at idle. Some of the lumpiest sounding old skool V8s (chev/ford) on the race track (Can Am cars) sound horrible at idle, but sound smooth and powerful at full tilt down the front straight....

Your mechanic probably has the right idea. If you can't get a smooth idle and you've done all the obvious things (new injectors, plugs/wires/cap, ignition check, fuel pressure, etc.) then going back to stock CIS cams should make an improvement.

Frankly, the 2vi 308s aren't down significantly on power over say a US QV - maybe 15-20hp at the wheels. I doubt many folks here can feel that under the pedal of a 3,300lb car. So don't fret about some perceived "performance loss" - it just isn't there. These engines are too small, and all have relatively solid head and cam design so big differences in hp/tq through different cams isn't possible. That's in stark contrast to say a big block Ford or Chev engine where the stock heads and cams are absolutely horrible and it's easy to get another 100-150hp/tq out of it just by bolting on some aftermarket heads and cam.