bigger cam vs tranny: teach me about this

[onurB]

Hi folks,

First, I would like to mention that I made my homework, I've read almost all threads up to page 7 that the search button gave me as results for the keyword «cam» in scirocco/technical vw/carbs-itb's and 8v engine forums.

I learned a lot, thanks.

So I made my mind on a cam swap, I'll probably go with the tt 268* for the drivability, along with a tri-y header.
However, I read that a bigger cam move the powerband upward in the rpm's, depending on how big the cam is…
My question is : what is the interraction (if any) the cam will have on performance on an engine coupled to a short ratio tranny?
I don't know if it's clear (I'm no mechanics as you can understand): In other words, I have a AEN (8v short ratio) tranny on my carb'd 1987 Scirocco 1.8 8v, and it rev's up relatively fast. As an example I'm doing around 3350 rpm at 70 mph (205-50r15 tires 3.67 final and 0.89 5th; do your math, fun on sinuous country roads but pretty boring on the highway) and I wonder how it will do with a bigger cam.
I know I can move the powerband down in the rpm's with an adjustable cam gear (that I will get too), but will this turn a little power gain into a loss of time and money?

Another point is about the carb (a single down draft Pierburg 2e2). At full throttle, the second body opens up around 4000-4200 rpm IIRC, which gives an appreciated little humph. I understand that I should try to match the peak in the powerband with that sweet spot, right? But again, is this too low in rpm to give a noticeable gain (I’ve read about big cams that kicks off at 6-7k) ?

Am I right in my questions or totally wrong and cams just don’t give s*ht about trannys?
Any inputs appreciated.

Regards

[ny_fam]

Good points.

What most fail to point out is that yes peak power moves up the power band, however low end power also increases unless the cam selection is radical.
I don't believe that a cam with a little more lift(+ .02 or less) and little more duration( 15 deg or less) than stock will lose low end power, if anything you'll gain low end power, if you do loose then its due to other problems. I consider low end power 2.5k rpms to 3.5k rpms.

[ziddey]

268 is nice and mild and what most would say is what stock should have been.

If you do go to a higher cam and lose that immediate off the load power due to lower dynamic compression ratio, it can make clutching a bit more difficult on inclines. Of course, these cars are generally cake compared to some other ones out there. If anything, a lighter flywheel would have way more impact on this.

Otherwise, no problems running a nice cam with a short ratio tranny. If you're likely to be running out the gear anyway, perhaps you could benefit from going bigger than a 268.

[onurB]

Thanks for the hints.

If you're likely to be running out the gear anyway, perhaps you could benefit from going bigger than a 268.

What do you mean by "running out the gear"? And how much bigger?

Ok, I missed that part on low end power increase. Good to know.
About lift, I read that the max lift without HD springs on these heads is .450", correct? Combined with duration, which one does what?
I mean, for what I've read, cams are often refered to by sole duration, rarely specifying the lift. Tell me if I'm wrong, but lift is acting on valve opening, and the more lift, the better the flow, no? This might be important to mention?
Anyway, I asked about max lift because maybe I'll give a look to find the best match between lift and duration...

[ny_fam]

Duration has to do with vale timing events - when the intake valve opens, when it closed and same for the exhaust valve. Timing effects the power the engine makes, Also effects at what rpm the power is made, how well it will idle.
Most advertised duration numbers aren't enough information to make cam choices from, be cause it leaves out how long the intake is open after BDC, and when the intake opens before TDC, and the same for exhaust.

List is more straight forward, as you said, its how far open will the valve be opened at max lift.
As you'd seen depending on the head in use there are spring requirements for higher lifts. Also same for injection system, some don't behave very well with some of the after market cams available.

Best things to do is speak with other who have the same setup you do with the cam your looking at, and speak to the cam maker they tend to know what cams will help meet your goals and not cause other problems based on previous customer experience.

[WaterWheels]

Some things said and asked need comments or questions in my opinion. The first is the vehicle itself as I see no mention of year and engine which can have a big impact on the questions and responses. You state it has a 2E2 carburetor so that begs asking if it is a mechanical or hydraulic cylinder head? This will make a real big difference in what type and “size” camshaft you search out. So that question really needs to be answered.

Your big question in the original post, about the interaction (if any), no, there is none. Just like the transmission cares less what engine or its state of tune/modification it is bolted to, the engine could care less what transmission you are using also regardless of engine modifications. Yes they interact in gaining the most from the total package but one really has no direct effect to the other. Your example of what you are asking is a good way to explain my response. If the engine speed was 3350rpm with the current transmission/tire combination at 70mph, the vehicle speed will be the exact 70mph at the same engine speed it you change camshafts, or pistons, or cylinder heads or . . . You can in more extreme cases cause driving issues because you don't have enough bottom end torque to get the vehicle moving with street car engine speeds, but this is fixed by using higher engine speeds to take off or re-gearing the car. But this is really more in the race car circles and not street cars.

As you said, using an adjustable camshaft gear will allow you to “move” the power band (not as much as some would like to think). It will not affect the engines power at all (yeah a pony or two in some cases), you do not gain or lose any, just shift it a little up and down.

The Pierburg 2E2 uses vacuum operated secondaries. So any changes in camshafts which effect the engines vacuum, and almost all camshaft changes do this, will cause a change in the opening time or speed of the secondary throttle blade. Also id you have a vacuum problem, leak or what not, it too will have an effect. But the big thing about the Pierburg 2E2 is that when it works it works well, but when it is bad, going bad or set wrong it is a real monster. I suggest replacing that expensive and hated carburetor as soon as you can.

“Combined with duration, which one does what?” This and some of the other questions or suggested questions really opens a can of worms that can’t be covered correctly in just a few responses. It would take a small book or large booklet to address all the different camshaft grind/fitment terms and requirements, and some have been written. Even after reading and understanding all that has been written you still can not pick the perfect camshaft for every engine. But to your basic question above, duration is the number of crankshaft degrees a valve is off its seat. Lift is the distance a valve moves away from its closed position before returning to the closed position (seat). These are the two (2) most important terms when choosing a camshaft. It is kind of like bore and stroke of an engine, it does not tell you all about the engine but enough to get you started. There are lots of other terms which relate to data about the camshafts grind, like lift at TDC, overlap, lobe centerline angle, etc. which narrow down the camshaft for a better fit and function. The basic bottom line is area under the curve. If you plot a camshaft grind, the one which has the most area under the curve will produce the most power. But you have to take in other factors also like drivability if it is a street engine or if it is going into a race engine. This area under the curve is one reason not all popular mild street sport camshafts have the highest lift or duration. A lower lift with more duration will produce more area under the curve then a high lift short duration one will in some cases, and vice versa.

The best thing really said so far is to contact camshaft grinders and ask them for their suggestion. Contact more than one and when they ask for information be truthful. Tell them exactly what you have or exactly what you plan to do. If you fudge on the information their suggestion will work but maybe not as well as if you had told them correct information. The camshaft is one of the most important parts in the engine and just guessing or buying in the old school “bigger is better” mind set might bite you in the a&$ later.

[Glegor]

Hi folks,

First, I would like to mention that I made my homework, I've read almost all threads up to page 7 that the search button gave me as results for the keyword «cam» in scirocco/technical vw/carbs-itb's and 8v engine forums.

I learned a lot, thanks.

So I made my mind on a cam swap, I'll probably go with the tt 268* for the drivability, along with a tri-y header.
However, I read that a bigger cam move the powerband upward in the rpm's, depending on how big the cam is…
My question is : what is the interraction (if any) the cam will have on performance on an engine coupled to a short ratio tranny?
I don't know if it's clear (I'm no mechanics as you can understand): In other words, I have a AEN (8v short ratio) tranny on my carb'd 1987 Scirocco 1.8 8v, and it rev's up relatively fast. As an example I'm doing around 3350 rpm at 70 mph (205-50r15 tires 3.67 final and 0.89 5th; do your math, fun on sinuous country roads but pretty boring on the highway) and I wonder how it will do with a bigger cam.
I know I can move the powerband down in the rpm's with an adjustable cam gear (that I will get too), but will this turn a little power gain into a loss of time and money?

Another point is about the carb (a single down draft Pierburg 2e2). At full throttle, the second body opens up around 4000-4200 rpm IIRC, which gives an appreciated little humph. I understand that I should try to match the peak in the powerband with that sweet spot, right? But again, is this too low in rpm to give a noticeable gain (I’ve read about big cams that kicks off at 6-7k) ?

Am I right in my questions or totally wrong and cams just don’t give s*ht about trannys?
Any inputs appreciated.

Regards

personally, i think the close ratio trannies are only good for stock engines, or engines that can safely turn 9k rpms..

if you are neither of those, then a nice long ratio trans is where its at.. (thats just my opinion, im sure others will have something to say about my comment)

you cant get a REAL LONG 020 VW trans.. they are all pretty close geared, even the LONG ratio trannies are still pretty close geared for my tastes.

ive got a Neuspeed 268* cam, and its not a whole lot different from a TT cam.. its a BIG UPGRADE over the stock cam, even a G grind..

really tho, 3500 revs @ 60mph? thats HORRIBLE..

my car turns 2450 revs @ 60mph w/ and ACN code transmixer..

still gets out of its way very easily tho.. it pulls to 6000 revs easy.

you can hold your gears longer, when they ARE longer..

if i were you, i would look into a different trans as well, it will get your cruising RPMs down a BUNCH..

myself personally, since long ratio VW trannies arent all that long, i like the way they feel, more than the close ratio boxes..

[Mtl-Marc]

Keep your close ratio tranny. Better acceleration with it.

Tried and true recipe: get a free flowing 2" exhaust (Techtonics Tuning). A free flowing tri-y or a 4-2 manifold and dual downpipe, which you might already have, and get a G-Grind, which I can sell you one for cheap.

If you want more, just get a 2 liter bottom end.

There is no need to worry too much about tranny ratio and RPMs and what not.