Corrected - is the VCH carb same as VH?

[Simon.Gardiner]

Shawn - you may well have found this already (lots of cam discussion, nominally about tuning the 350 but it's all good info, and has Pete C's VCH profile)
viewtopic.php?f=21&t=1428

SG

[Roger Gwynn]

In my experience to get the best out of any sporty cam in an Ariel you will benefit from increased compression ratio. I use an A6/664 with standard single lobe followers and a 9:1 piston. The parts books will tell you which cam and card were fitted to which models, however, as I thought, the 1950 VCH book doesn't list a cam so in theory it is the same as standard. The carb isn't listed and the 1950 VCH catalogue that list the details of the engine at some length does not mention cam shaft nor carb and the accompanying picture shows a distinctly standard type 6 carb. The 1952 parts book lists a 289 carb for the VCH which is the same as VHA and VH, spec on Draganfly. This is the not so special VCH of course.

[SEDoan]

Thank you Roger and Simon. The club spares description indicates a 1953 VCH profile, so how is that different than the 1950 or '52 profile? Probably not different?
The engine already has a 9:1 piston with a 1/16" decompressor plate which, as near as I could measure it gives a little more than 8:1. The HS followers seem to give better mid-range than std, but it got hot quick before I backed off the timing. It was fun though. Thinking the same setup with the VCH cam and std exhaust follower will be fun, but not destructive. (it's already fun!) Need to do some reading now.

[david.anderson]

Shawn
I think that you will find that the 53 VCH cam referred to by the club is actually the 1952 profile posted by Pete Collins. The 1952 VCH profile is profoundly different to the standard single lobe cam. It has a lot more lift, duration and overlap. The VH cam and follower lifts the valve .316 and the VH follower has a lift ratio of .86. That means that the vch profile with VH follower will lift the valve .373”, almost a 1/16” more. I have never run or measured the 53 VCH cam but it appears to have slightly more lift than the mk3 cam but a little less duration. Being a full width cam I would guess that its use would be with the standard VH single lobe follower, as the HS followers were not available until 1954. That said the prior twin lobe follower has a HS profile foot. A HS follower has a lift ratio of .923 so the HS follower will lift the valve .400” with the VCH cam. While the foot of the twin lobe follower is HS, the pushrod cup distance is different so the lift ratio of the twin lobe follower is less than HS.
The 1950 A7/642 cam is a twin lobe cam which is slightly milder than the single lobe VH cam. The single lobe VH cam has 8 degrees more overlap 7 degrees more duration and .004” more lift than its predecessor.
When it comes to carburettor for jetting, the starting point would be standard jetting. In my experience a change in compression ratio will have more effect to the jetting than a cam change will.
David

[SEDoan]

Thank you very much David. Burlen also list the same 289 carb for the VCH so I will start with the settings I'm using now.

A question about the HS cam follower foot. I have followers with 2 different foot profiles and read where the smaller radius, thicker foot is HS. Are there 2 HS follower profiles?

The upper followers I have understood to be HS.

[david.anderson]

Shawn
Yes the top followers appear to be HS. Both HS and VH followers are the same radius (or at least they start out that way but do wear in use to a flatter radius). There is only one HS profile. The difference between HS and VH followers is that the heel of the HS follower is lower so the contact point of the follower with the cam is closer to the pivot point ie the centre point of the radius for the grind is different.. This increases the lift ratio and alters the valve timing by about 13 degrees. The inlet valve opens sooner and exhaust closes later so valve overlap is increased by about 26 degrees.

The 52 vch cam has a very long ramp of 35 degrees which is actually 70 degrees of engine rotation, but the ramps are not of the constant velocity type. The initial ramp velocity increases for several degrees, then reduces somewhat until the point where the ramp ends and lift actually begins. This is not necessarily a bad feature, but rather it is somewhat unusual, and such ramps would not be used today.
The cam form itself is perfectly symmetrical, but owing to the use of lever followers, the valve lift design becomes non symmetrical. While HS cams require .010 tappet clearance, the 52 VCH cam should have 0.15mm (.006” and .008 exhaust due to extra heat) tappet clearance which is where the ideal take up point would be, and from this point on the valve train mechanism would be steadily loaded until lift commences. Apart from being much easier on the valve train mechanism, the actuation is much quieter.
A computer analysis that was provided to me calculates about 2bhp more with this cam.
David

[SEDoan]

Thank you David. Your information clarifies a couple things, I really value your knowledge and experience.

[john.mitchell]

Members interested in the VCH should read the excellent articles by Ralf Arvidsson in Cheval some years ago. Go to the Members Area on line. Click on Library. Click on Knowledgebase. And in the Search box enter VCH. The articles will then appear. You will see that the VCH had many versions. Not mentioned is a Plunger version but I am pretty sure one or two versions were made.

[SEDoan]

Thank you John, I will look that up.