Camshaft Selection

[Mike D'Silva]

While my engine is out (gearbox being rebuilt for the 5th time now) I was thinking to maybe try a different camshaft.

Engine is 3.0 Carrera 930/02

CP 95mm Pistons 10.3:1 compression

42mm itbs from RHD in Aus

Rasant efi/ignition kit with AEM Infnity

1&5/8 inch headers

 

Interesting article on the Supertec website

https://supertecperformance.com/pages/how-to-select-a-porsche-camshaft

Which gives some basics for estimating where peak torque and HP are produced based on intake and exhaust duration. 

This leads me to think that a camshaft helps to determine "WHERE" the torque is produced and not "HOW MUCH" torque is produced. (is this correct?)

I collated some info from the webcamshafts website and the john dougherty website to try to compare and also calculate, using the supertec article, where peaks are theoretically developed.. the duration at 0.050 inch is the only accurate way to compare the cams.

In addition, I keep being told that narrow lobe separation angles makes tuning itbs difficult but yet the older cams for carbs do have narrow lobe separation angles.. and isn't a carburettor and older version of itbs without the electrickery? ie, 1 atmosphere at each intake port.

The cam that is currently in my engine, is a Webcam 464/465. It has quite a bit more duration than stock, and also more than 964 or 993SS etc. To drive, it pulls very well from 3500 all the way to 7k and beyond. It doesn't stop. But this is a street engine and I rarely rev it that high. Also, the 464/465 has a very narrow lobe separation angle of 101 degrees. Driving around town it is still stronger than a stock 3.0, but does feel a little lacklustre below 3000.  Sure, a 'milder' cam will likely pull the torque peak lower and limit my top end hp, but I think that is more about bragging rights perhaps. For interests sake, this one has put down 229hp at rear wheels which I think is approx 260 flywheel hp. 

Considering the Dougherty GT2 cam with a 108 lobe separation. 

I'm open to suggestions and an education.

Camshaft comparisons.xlsx

[Caledonian]

Lobe this post Mike!

I opened it for some time and then closed it for some time..

Now I want to torque about it...... ISO humor sorry🙄

Getting to the question I was going to ask you.... what the go with the gearbox, thought you had that all sorted?

 

[Mike D'Silva]

28 minutes ago, Caledonian said:

Lobe this post Mike!

I opened it for some time and then closed it for some time..

Now I want to torque about it...... ISO humor sorry🙄

Getting to the question I was going to ask you.... what the go with the gearbox, thought you had that all sorted?

 

omg!

I think it will be now.. but don't want to count my chickens before they .. you know....

[P-Kay]

As I no doubt you already know....the tighter the angle, the rougher the idle. Re tight: Bit of a bitch when cold, but if you like the lump, then enjoy

Personally go the biggest lift. Broadly speaking, an engine is an air pump hey, so the more air you can get in and out........

To be honest, it sounds as though what you already have is pretty nice anyway. This would only be an exercise in spending money and cam timing practice. I don't know you personally, but you don't seem to keep your cars too long, so is this one a keeper? If so, and the current cams make it laggy or a pain to drive in traffic, then choose to suit the majority of driving conditions.

Love a strong and angry idle  

[Mike D'Silva]

2 minutes ago, P-Kay said:

As I no doubt you already know....the tighter the angle, the rougher the idle. Re tight: Bit of a bitch when cold, but if you like the lump, then enjoy

Personally go the biggest lift. Broadly speaking, an engine is an air pump hey, so the more air you can get in and out........

To be honest, it sounds as though what you already have is pretty nice anyway. This would only be an exercise in spending money and cam timing practice. I don't know you personally, but you don't seem to keep your cars too long, so is this one a keeper? If so, and the current cams make it laggy or a pain to drive in traffic, then choose to suit the majority of driving conditions.

Love a strong and angry idle  

Not sure how long is considered a long time, but have had this for approx 2 years now. It's a good practice or test bed for experimenting with different exhausts and now cams. But yes, cams are not cheap. 

It is definately not a pain to drive in traffic. But I want to see if it can be perhaps, a little more 'punchy' earlier in the rpm range. 

[P-Kay]

I hope I did not offend, that was not my intent, just cost v reward for potentially someone else.

 

Well in that case....considering the box is out......*cough* LSD and different gears *cough*  

[Mike D'Silva]

1 minute ago, P-Kay said:

I hope I did not offend, that was not my intent, just cost v reward for potentially someone else.

 

Well in that case....considering the box is out......*cough* LSD and different gears *cough*  

factory box has LSD.

Leaving ratios standard

[P-Kay]

Win on the LSD!

Well, then, it sounds as though you have your answer, different cams to change when they operate at their peak!

Good luck   

[Teutonic]

A loose summary of cams is they essentially shift the curve left or right. No point having a “big” cam that makes all its power up top if your engine isn’t built to rev. And I guess intended use plays into it. No point having a big lopey cam in a regular street driven car unless you like that kind of thing. Usual story that an engine will achieve either more or less than the sum of its parts based on how well they are matched. Definitely a lot of science in cams. I ended up using Elgin cams in the US to do a custom set to suit the engine build I did with them having all the info on bore, stroke, port size, valve size, intake, exhaust etc. but for an engine with more off the shelf specs, there should be some good off the shelf cam options. Shouldn’t need to reinvent the wheel. 
 

PS. Time to find a new gearbox guy?? I know a guy   

[Mike D'Silva]

4 hours ago, Teutonic said:

A loose summary of cams is they essentially shift the curve left or right. No point having a “big” cam that makes all its power up top if your engine isn’t built to rev. And I guess intended use plays into it. No point having a big lopey cam in a regular street driven car unless you like that kind of thing. Usual story that an engine will achieve either more or less than the sum of its parts based on how well they are matched. Definitely a lot of science in cams. I ended up using Elgin cams in the US to do a custom set to suit the engine build I did with them having all the info on bore, stroke, port size, valve size, intake, exhaust etc. but for an engine with more off the shelf specs, there should be some good off the shelf cam options. Shouldn’t need to reinvent the wheel. 
 

PS. Time to find a new gearbox guy?? I know a guy   

Yes, but you're in Perth so I think I need to become a gearbox guy myself.. slowly slowly...catchy monkey

As for Elgin, story I heard is they make the cams for Singer motors.. true? Not suggesting they are of any use to me.. just not sure if fact or hearsay.

And that John Dougherty used to work for Elgin...

 

8 hours ago, P-Kay said:

As I no doubt you already know....the tighter the angle, the rougher the idle. Re tight: Bit of a bitch when cold, but if you like the lump, then enjoy

Personally go the biggest lift. Broadly speaking, an engine is an air pump hey, so the more air you can get in and out........

To be honest, it sounds as though what you already have is pretty nice anyway. This would only be an exercise in spending money and cam timing practice. I don't know you personally, but you don't seem to keep your cars too long, so is this one a keeper? If so, and the current cams make it laggy or a pain to drive in traffic, then choose to suit the majority of driving conditions.

Love a strong and angry idle  

I'm slowly learning along the way. Narrow lobe centres equal larger overlap (when both inlet and exh valves are open at same time) which tends to also lower dynamic compression allowing you to run more timing before detonation.

Higher lift cams I think are great if you have an engine with decent ported heads, but perhaps on a stock head, too much extra lift, might be no advantage.. the head can only flow so much air so even if the valve opens further, unless the intake side supports the extra flow, no point in doing it. Also, with higher lift, I think you get to a point where you can use too much energy to compress the valve springs that far.. possibly getting toward coil binding..maybe this is why some people use titanium retainers and stronger/lighter springs?

It's all theory for me so far. I want to be able to say "my car makes X hp at the wheels" like the next guy, but yea, I do want to experiment. My rockers are off in the USA being re-hardended and re-profiled anyway, so, they will be ready for a brand new cam.

 

 

[micknine01]

33 minutes ago, Mike D'Silva said:

Yes, but you're in Perth so I think I need to become a gearbox guy myself.. slowly slowly...

 

 

Mike if you can build an engine you can handle a gearbox. Have a crack 😉

[Mike D'Silva]

16 minutes ago, 901er said:

Mike if you can build an engine you can handle a gearbox. Have a crack 😉

I'm cracking!

 

[Teutonic]

Mike, I’m in Brisbane. But my gearbox guy is in South Australia. Neat Gearboxes.   wasn’t suggesting it’s something I could do.   
 

Yeah, I believe Elgin do Singer cams. I also have the singer heads on my engine