Camshaft: Trying to identify and check

[GDCobra]

Hi all

I've frequently been bothered that I don't know what cam is in my engine but short of stripping it out to look for markings have never really known what to do. Since I've been bothered recently with some issues regarding setting idle speed and the timing which I'm having to run I thought it time to do some testing to:
A) Identify the cam
B) Check if there are any issues with the timing or lobe issues.

I don't want to take the engine apart any more than necessary (if there is no issue) so I've decided to check in situ'

Firstly I've made up a crank pulley with degree markings on it.

Then I made up a spark plug holder for a DTI to check that TDC on my timing pointer is at true TDC

[GDCobra]

This verified that TDC is correct on the pointer.

I've than created a setup to hold a DTI against a pushrod which is bearing against the lifter.

I've setup an endoscope to make it easy to see the engine position and the lifter position at the same time.

[GDCobra]

So now I simply rotate the engine and read off the lift values


Please bear in mind I've never performed any cam checks before so this may not be and 'established' method but I believe it is sound.

I've initially started taking lift reading as soon as a movement appears on the DTI and plotted these based on 0.01mm movements at first then with increasing lift up to about 1mm then taking readings at 5° increments up to around the peak where I've dropped back to taking readings based on the lift values.

I've plotted these in a spreadsheet which gives the following result.

First of all the positives:
The peak lift on the inlet cam is at 110.5° ATDC with a value of 7.56mm translating to 12.1mm/0.476" valve lift assuming 1.6:1 rocker ratio.
The peak lift on the exhaust cam is at 110.25° BTDC with a value of 7.54mm translating to 12.064mm/0.475" valve lift assuming 1.6:1 rocker ratio.

The peak angle appears to be in the ballpark for other cams I've seen values for and the lift is a couple of mm above standard if I've understood correctly (this is a 3.9L engine BTW)

Now the bit I could do with some help on.
The inlet cam starts lifting at 43°BTDC and continues to 268° ATDC, a duration of 311°
The exhaust cam starts lifting at 268° BTDC (92° ATDC) and continues to 322.5° BTDC (37.5°ATDC), a duration of 30535°
Both of these seem a bit long as most of the cams I've found values for show around 285° or less.


I'm getting the feeling that the duration should be measured from a specific lift from the base circle rather than as soon as the cam starts to move, is that correct? If so is there a standard for this starting point?

I'm quite happy to share the full data if anyone is interested and if anyone can identify the cam from this I'd be interested to know any likely candidates.

As always thanks in advance for any advice.

[stevieturbo]

It is common for durations etc to be quoted on a 50 thou basis, or 1mm ( not the same oddly ), so that can vary by cam manufacturer. Generally they don't go by from actual lift from zero to actual close....but sometimes that can be given too.

I presume some of that is because all cams will have a softish open/close ramp to appease the lifter/valvetrain so that initial lift you might see, may not be considered the real starting point.

eg

https://www.tildentechnologies.com/Cams ... of%200.025.

So read your duration from those two lift values at the cam, which I would guess not just means lifting your baseline on each graph up a little.

I'd like a setup with linear transducers to measure lift whilst cranking, but yet to find any that would work fast enough ( and cheap enough ) for use during actual cranking to measure valve or lobe lift whilst logging crank position, cylinder pressure and in/ex lift.

Although in some cases you can get an idea of opening/closing points when logging cylinder pressure during cranking, although as cams get bigger with more overlap, that picture gets more muddled.
Obviously it won't tell you lift or anything, but would give a quick picture if something was miles off.

Doing the manual test as you are, is probably the easiest DIY, even if a little slow and tedious.

[stevieturbo]

A quick google for some cams,

Given some numbers here are quite high, I would think they are trying to quote seat to seat.

http://www.wolfitt.com/kentcamdata.htm


A chart of different cams, again it doesn't specify

https://sideways-technologies.co.uk/for ... son-chart/

Here is a seller quoting at 1.0mm, this seems to be a more British thing ( or not at all ), whereas the US generally uses 50 thou. Small difference really.

https://www.shopbhp.com/products/rover- ... th9PoWYnw1

[GDCobra]

It is common for durations etc to be quoted on a 50 thou basis, or 1mm ( not the same oddly ), so that can vary by cam manufacturer. Generally they don't go by from actual lift from zero to actual close....but sometimes that can be given too.

I presume some of that is because all cams will have a softish open/close ramp to appease the lifter/valvetrain so that initial lift you might see, may not be considered the real starting point.

Thanks Steve, all good information and I find that when applying the methodology you outline that the figures give a bit more confidence.
I did expect that to be the case as the initial figures are very small hence difficult to get an accurate reading of angle, this is why my initial, final and peak readings were performed by tracking the lift and noting the angle whereas on the main rise and fall I took the readings at 5 degree increments.
One benefit of my method (completely by accident) is that I have readings at 1mm (valve lift not lifter lift) which give the following result:
Inlet Open @ 10 BTDC Close @ 230 ATDC, duration of 240 peak at 110 ATDC.
Exhaust Open @ 230 BTDC Close @ 10 ATDC, duration of 240 peak at 110 BTDC.
So doesn't change the peak angle but does reduce the duration. Based on the values I've looked at for various cams the duration seems on the low side (seems like I'm never happy!) which makes me wonder if those values are to a different lift.

I'm going to run the same test on all lobes just to check that they are all in good shape.
Although this seems like a performance item given the lift I do wonder if I'd be better with something more like standard for smoother running.

Edit
I was just looking at some of the information on the Realsteel site regarding their RV8 cams which are measured at 50 thou' and the lift and duration of my cam seems to be similar to their Thphoon cam which may give good performance but doesn't seem to have much in the bottom end which I'd prefer given that this is a street car and when I'm trickling through villages I like to keep the volume down.
May think about changing this.

I'd like a setup with linear transducers to measure lift whilst cranking, but yet to find any that would work fast enough ( and cheap enough ) for use during actual cranking to measure valve or lobe lift whilst logging crank position, cylinder pressure and in/ex lift.

Although in some cases you can get an idea of opening/closing points when logging cylinder pressure during cranking, although as cams get bigger with more overlap, that picture gets more muddled.
Obviously it won't tell you lift or anything, but would give a quick picture if something was miles off.

Doing the manual test as you are, is probably the easiest DIY, even if a little slow and tedious.

I must admit I did think of something similar as I was working through it, not so much for when the engine is running but if I had an encoder on the crank, as feed from my digital DTI and a motor to rotate the engine it could certainly automate the process I'm using.



One other thing I did wonder about is whether there is any lost motion with a hydraulic lifter. I've never had one of these apart but I'm guessing they have some sort of port in them to let oil in which will close off as the lifter rises (similar to a brake/clutch master cylinder) this could result in the base of the lifter rising somewhat before motion is transferred to the pushrod. Perhaps during early motion when valve spring is not applying too much force the oil pressure is enough to prevent relative motion - Any body know more?

[FBW]

Hello,

I'm guessing it's a DW270 Viper Typhoon.





Regards, Frank

[GDCobra]

Hello,

I'm guessing it's a DW270 Viper Typhoon.

Regards, Frank

Hi Frank
Thanks for the feedback. I agree, those charts look virtually identical to mine, the peak measurement at the lifter is 7.56/7.54 on mine and the angle values for lift at 0.5 lift is also very close.
By coincidence this is the cam I was looking at earlier o Real Steel, it is really a bit more 'wild' than I need/want I'd rather have something which works from at least 800 or 1000RPM, I may look at swapping that out.

From the description on the RS site it would appear that my heads must have had some work done to allow that cam to work which makes me question whether swapping to a standard or mild cam would give me some issues with mis-matching components.

[FBW]

The modification usually involves the height of the valve guides. To allow for the increased lift, the guides need to be shortened at the top. Different valve springs are probably also installed.

A camshaft with slightly less lift isn't affected at all.

I've had good experiences with the Viper Stump Puller, and when you really need low-end torque, with the Kent H180.

But all of that was on large engines. The 3.9 reacts differently. Displacement tames camshafts.

[GDCobra]

The 3.9 reacts differently. Displacement tames camshafts.

Cheers Frank.
By that I'm taking it to mean what may be wild on a smaller engine will be less so for larger capacity?

Just looking at the notes on the Stump Puller it looks like this has an narrower RPM range than the Typhoon at 1500-5800 vs 1200-6200. Difficult to see why as all the figures seem to point to a more tame cam. I can understand power dropping off higher up but I'd have expected it to be improved at lower RPM.
I think if I were to swap the current cam out I'd probably go for something like the Hurricane or possibly even a standard item.

[FBW]

That's exactly right. A camshaft that makes a 3.5L engine aggressive will, at best, make a 4.6L engine sound sporty.

The stock camshafts are already quite tame. Unfortunately, I don't have a curve for the 3.9L.

Here are the curves for the 3.5L, the Typhoon, and the Viper Hurricane.






The engine is in a Cobra, right? The Hurricane should be a good compromise.

Regards, Frank

[GDCobra]

Thank you very much Frank.
Your charts make the characteristics of each cam very clear, including the slightly greater lobe separation on the Hurricane.
I'm really going to have to think about this, balancing the benefit of a milder cam against the work and cost involved.

The engine is in a Cobra which is quite lightweight, my driving these days 1ncludes more slower speeds than fast where I could live with a bit less power and would prefer better slow speed manners.

My next move is to check out each lobe and make sure the cam is at least doing what it should across all cylinders.

[FBW]

A key factor in determining whether a camshaft performs well at low RPMs or whether the engine reacts roughly is the overlap.

The lower the point at which the intake and exhaust curves overlap, the smoother the engine will run.

As is often the case, more isn't always better. Sacrificing a few horsepower for better drivability is often a wise decision.

Regards

[GDCobra]

As is often the case, more isn't always better. Sacrificing a few horsepower for better drivability is often a wise decision.

Yep, totally agree, a few years ago I may have been interested in the top line numbers but these days I'd rather have smoothness and drivability plus the ability to drive at lower RPM in built up places keeping the noise down although it is fun sometimes driving past parked cars settings alarms off!

[stevieturbo]

One other thing I did wonder about is whether there is any lost motion with a hydraulic lifter. I've never had one of these apart but I'm guessing they have some sort of port in them to let oil in which will close off as the lifter rises (similar to a brake/clutch master cylinder) this could result in the base of the lifter rising somewhat before motion is transferred to the pushrod. Perhaps during early motion when valve spring is not applying too much force the oil pressure is enough to prevent relative motion - Any body know more?

Sort of, depends...

Rhoads lifters are designed to bleed down. And this would be more so at lower rpm, when there is force over a longer time to eject oil and effectively reduce lift/duration seen at the valve.

Normal lifters would bleed down far less and should appear solid, although by design there has to be some ability to leak.

I have used some of the Real steel cams years ago, and certainly don't recall them being crap low down, but it's sooooo long ago not really sure. And my RV8 in various guises was always twin turbo, never n/a
I think I always used the Rhoads lifters too, tickety tick.