Cam Question

[Green67Alpine]

Started by trying to repair a slipping clutch, but decided to look into the engine also, while the cam is still installed we've noticed some wear and discoloration on the lobes, so while it's apart I want to get that taken care of , I've heard about Delta cams , what "grind" do I want? I'm running a 1725 at 40 over , Got some flat top pistons, the head has had the ports cleaned up and slightly polished, and using the CD 150 carbs for now. I also have new tappets, push rods, and will replace other parts as needed.
Thanks for any and all insight into this rebuild,
Tom j

 

[RootesRacer]

Think through carefully what you are going to do as far as the flat top pistons are concerned.
Just installing them without other work will result in too high of compression for a daily driver and turn that engine into a "knock monster".

 

[Tom H]

Just to confirm Rootes reply, if you have a 40 thou overbore and flat top pistons, with no other changes your Compression Ratio would go from stock 9.2 to 10.7 . If the head has been milled by 0.010, CR goes 11.1. If you do a Vizard mod, that adds about 2.2 CC to chamber and CR goes back to about 10.6.

Tom

 

[Green67Alpine]

Ok ,then maybe I'll not use those flat top pistons. Anyone have some information on the cam they'd like to share?
Thanks again, Tom j

 

[RootesRacer]

Ok ,then maybe I'll not use those flat top pistons. Anyone have some information on the cam they'd like to share?
Thanks again, Tom j

First of all, if you have actual flattops they are coveted.
Be sure they have the correct pin diameter and compression height.

Folks in the know take those pistons and perform a holbay or vizard chamber mod (or something like them) to yeild a better compression ratio, but having a better chamber shape which improves power and knock tolerance.
A good net compression is between 9.3 and 9.6/1.

For the cam, the common answer is to send your blank off to Delta cams and specify a "KB" regrind.

This gives a bit more pep without being too lumpy.

 

[Tom H]

Again, I agree with Rootes- on the KB grind from Delta.

But as for using those flat tops - I do not see any way to get to 9.3 or 9.6 CR using those flat top pistons. Even if the head has not been milled at all, you'd need to add 6 cc to the stock 39.2 cc combustion chamber to get the CR down to 9.6.

The Vizard mod adds about 2.2 to 2.5 cc if done correctly. Because of how my machine shop shaped one combustion chamber after some weld-up repair, I ended up grinding all the chambers up to 43.5 cc (that's 4.3 cc larger than stock). But I don't know how I would increase that volume any more than that.

Tom

 

[V6 JOSE]

Hi Tom,

Do you have the set of flat tops already and that is why you want to use them? If so, you might want to consider milling about .030" off of the top to drop the compression. I have never seen a Sunbeam piston,so don´t know if there is enough material here to be able to remove .030". Mose pistons have a pretty thuck deck so removing thatmuch from the top shoulden´t cause any problems for you.

Jose

Ok ,then maybe I'll not use those flat top pistons. Anyone have some information on the cam they'd like to share?
Thanks again, Tom j

 

[RootesRacer]

Again, I agree with Rootes- on the KB grind from Delta.

But as for using those flat tops - I do not see any way to get to 9.3 or 9.6 CR using those flat top pistons. Even if the head has not been milled at all, you'd need to add 6 cc to the stock 39.2 cc combustion chamber to get the CR down to 9.6.

The Vizard mod adds about 2.2 to 2.5 cc if done correctly. Because of how my machine shop shaped one combustion chamber after some weld-up repair, I ended up grinding all the chambers up to 43.5 cc (that's 4.3 cc larger than stock). But I don't know how I would increase that volume any more than that.

Tom

Holbay H120 flat top pistons (same as std 1496 stock pistons) and the factory configured cylinder head had a compression ratio of 9.6/1.

The Holbay reconfiguration is a bit more extensive than the Vizard mod.

On my own engines, I fall in between the two in terms of volume, but only becuase I can reconfigure the distributor timing needed by the higher compression.

 

[mattinoz]

There is a document floating around the net, a copy of which I have that i'm happy to share, that goes into some detail about the cams used in our engines, in particular the 1725 and other English engines, that you might find useful. I'll email it if you want a copy.

 

[Green67Alpine]

Thanks Matt email to green67alpine at yahoo.com
Tom j

 

[midage55]

1725 document

is there any chance i could get a copy of that document also....i to am in the process of adding a bit more power to my 1725....thx....chris
midage43@yahoo.com

 

[hartmandm]

Here is the cam document for download:
http://mhartman.net/files/sunbeam/Camshafts and Understanding the numbers.pdf

Thanks,
Mike

 

[mattinoz]

nice work mike.

 

[Tom H]

Mike, and others

Be careful in interpreting cam specs. I am trying to understand the document and cam specs. I see the document notes the SV cam inlet is Open at 29 BTDC and closes 63 ABDC. Duration is then 272 ( 29+63+180). These are the same specs noted in the WSM for the 1725 But it is unclear to me what is considered "Open" or "Closed". (Also lift is not specified).

I have installed a KB grind cam in my 1725. The specs I have from Delta for this cam shows Open at 5.4 BTDC and Closed at 37 ABDC, with duration then 222.2. This would imply that the KB grind has less duration and is a milder cam than stock. (lift is specified as 0.408", which i assume is same as stock)

BUT, if I look at the details of the Delta cam specs, I can see that "Open" and "Closed" are considered as the point where the lift is 0.050". In fact, there is a statement "events rated at 0.050" tappet lift". Furthermore, if I look at the table included in the Delta specs I can see that if I assume the lift point is considered as 0.006", then the Open and Closed points would be 46.3 BTDC and 71.1 ABDC, for a duration of 297.4. More duration than the stock cam. Without stating the definition of the lift point, I don't see how to compare profiles.

In reading a wiki article on Camshafts I see that it is common to rate open and closed at several different lift point, with 0.002", 0.006", 0.020" 0,050" and 0.200" being common. Depending on which lift point is used will give you different insight into low end torque, high end, peak power, etc.

So without lift point definitions in these comparisons I suspect this article has little value.

I am very happy with the performance of the KB grind in my 1725, bored, stroked, and Vizarded to about 1820, with CR close to stock 9.2:1

Tom

 

[Bill Blue]

Also with the advent of variable valve timing, guys are finally finding that cam advance/retard is not the key to magic hp gains. Mostly shifts the power range a little.

Notice the author never mentions cam lobe separation, which defines the character of a camshaft as much as lift and duration. Choosing the proper cam is incredibly complex and difficult. Unless you foresee something unusual in your Alpine, get what makes the most Alpine owners happy.

I can't believe I just said that.

Bill

 

[Asm109]

Author focuses on valve overlap. Overlap is the measurement that most directly correlates to the character of the cam. You can change overlap by decreasing lobe separation OR increasing duration by starting lift earlier.

The numbers quoted by the author are factory number and most likely are quoted at 0.005 inches lift, maybe .002. Either way the numbers are far larger than you get when quoting duration at 0.050 in lift. Aftermarket use 0.050 because it is much simpler to measure duration at 0.050 on an assembled engine than 0.005.

 

[Tom H]

Asm, indeed, as I said, the numbers quoted in the article for the 1725 engine are from the factory specs. But how can they publish specs without defining them? I would assume that if not defined in the spec there is/was some general industry standard implied. How confident are you that the numbers are quoted at .005 lift (or .002 lift) ?

If we assume .006 then the KB grind would have the Open and Closed points at 46.3 BTDC and 71.1 ABDC, for a duration of 297.4, from the chart I have. More duration than the stock cam.

If we assume .004, the the KB grind would have 54.5 and 79.4 for 314 duration.

And, of course, also the overlap depends on the lift spec of Open and Closed.

Anyone out there have a high confidence in some standard lift for defining Opened and Closed valve in these Alpines? It appears that Asm's thoughts on 0.050" lift as the defining point for aftermarket cams makes sense. But it sure makes any comparison to the stock cam difficult.

By the way, the article also makes a reference to longer duration cams in "late Series 4" Alpines. But according to WSM124, all S4 (from B94100000 on) had the longer duration cam. Maybe he meant "late 1592's". Although he also states that he has an "early 4" with the older cam.

 

[Tom H]

I may have the answer to the question on lift point. The WSM describes how to check the valve timing. on #1 Intake. It says adjust the valve lash to 0.019 - 0.020 instead of the normal 0.012. Then turn the engine and cam until the valve just opens,and then defines that as when a dial gauge moves 0.001 or when the valve can be turned by finger pressure, indicating it is no longer in contact with the valve seat. This point then is where the valve is defined as Open. Note that this achieves accuracy sufficient to tell if the chain is off by one tooth, not a real precise cam angle measurement. But, if we then (theoretically) readjusted the valve lash to the standard 0.012 while the cam was still at that position, the valve would open by .007 to .008 more. So maybe .006 (or .008?) is the standard lift point definition.

Tom

 

[Bill Blue]

Years ago, the cam grinders said they selected .050" as the reference lift point as very little air is flowing before that point and the valve is the lift ramp. Some say there is real value in comparing the .050" value with a lower standard, say .005" as that gives you an idea of lifter acceleration rates. I'm not sure, but I think some grinders use valve lift while others use lifter data and some use the cam lobe data.

The problem is the cam is the sum of ALL parameters mentioned (and probably some not mentioned) working in concert with head, intake manifold, carb, header, exhaust and gearing.

Get a KB.

Bill