Amazon: Changing cam on single carb B20

[TomTom]

I'll have the chance to get some work done on my '70 Amazon next month.

1) I'll be having the gearbox reconditioned. Is there anything small that I should be looking at doing or checking while the box is out? I seem to remember that the rear crank seal can usefully be replaced.

2) Although I'm happy with the single stromberg set-up, my only issue is a slight lack of gumption in the mid range. Is there any point in putting another cam (at the moment A) on the car, without making changes to the carb set-up and exhaust? I don't want to go to a lot of expense, and if this won't really make a difference I won't bother.

3) I'll also be getting a 123 distributor fitted and will post about any improvements this makes to starting, petrol consumption etc

Thanks

Tom

[tom-madbiker]

unless you set a cam up properly you will not get any real improvement its the same with any tuning you will probably at the very least have to adjust the carbs and the idle and the ignition

[asneddon]

I was under the impression that some Volvo cams wear pretty flat over time. If your cam is worn, then a new one might be a good idea. If replacing, then there is no point going for an 'A' grind, may as well use a 'C'. I don't think you would gain anything out of a 'D' without twin carbs etc.

I'm interested to see how the 123 goes for you. I'm right on the edge of ordering one myself (while the GBP is so low against the NZD). Saves me about NZD200 buying from the UK vs Australia!

[swedishandgerman]

I reckon you'll find you'll get a good improvement just by putting in a new A cam for the reasons given in the above post. It's just a personal thing, but I like the way a standard B20A drives

Don't know about this for sure, just my understanding about camshafts and stuff.

In an ideal situation to get the most power, the valves would be instantly opened and closed to get as much air into the chamber and exhaust gases out. To replicate this ideal, race cams have a very steep ramp with strong valve seat so that they close properly when following the cam profile. However, these cams make far too revvy and peaky engines for normal road use.

On the opposite, a cam with flatter ramps (A-profile cam) gives a smoother running engine at low rpm plus quieter valves. As these cams rotate it allows the valves to lift off of the valve seats slowly and slowly as they return. Consequently you don't get as much sealing on the compression stroke nor as much time with the valve open to get the exhaust gases out.

On a tall cam, a way of getting the more instantly open and closed style is to increase the valve clearance thus increasing the power a bit. The downside is a bit more valve noise. You'll notice there are different valve clearances for A-cam engines compared to all the others

It's just me - I drive my Amazon farily steadily. Putting in a taller cam allows you to rev the tits off it which, frankly, I never do

If you put in another A-profile cam, you won't have to re-needle your carb. If you put in anything steeper, you will have to. I don't know what needle you'll need, but it might mean a session on a rolling road otherwise it'll run lean at high rpm

With reference to your gearbox, what are your getting rebuilt? Do you have an overdrive? If not, I have a reconditioned 4-speed box that the previous owner of my car bought, but never fitted. Let me know if you want it. I went down the route of an overdrive which I rate as the best improvement on my Amazon.

I can't speak from experience about the 123 distributor, but I can say with absolute confidence that the standard distrbutors are extremely good, provided they are in good nick. If worn out, then I'd consider a 123 distributor. Again, just personal opinion, but I think they're VERY expensive if what you already have is in good nick; a good replacement for a knackered distributor if you're unable to source a good (no longer available new) standard one

[TomTom]

Thanks for all this advnce on cams. I think if mine is worn I'll go for another A, since valve noise can be an issue. Nice to hear about the relative issues regarding revving, noise, exhaust rate etc.

The main reason I wanted the 123 was for easier starting. On cold wet days I sometimes spend 30 seconds getting the car to fire up. Other benefits hoped for are smoother running and slightly better economy.

The gear-box is 4+OD. Very rattly in third and quite rattly in second. Normal of course in 4th.

Thanks
Tom

[swedishandgerman]

How many miles has your motor covered?

[asneddon]

Originally Posted by TomTom

On cold wet days I sometimes spend 30 seconds getting the car to fire up.

That doesnt sound right. With my slightly dodgy distributor (timing variation of +-5degrees at idle) I start up with just an instant twist and release of the key. Ie, I dont even listen to see if its started, just twist for half a second and release the key. The only time it doesnt start is when its been sitting for a week or so, then the fuel pump has to refill the float chambers.

I would look at replacing your plugs/leads/rotor/cap/points/condensor first. Should cost something like GBP50ish from brookhouse for the whole lot. Then you will know whats going on. Its the best thing I did for mine!

It could also be your carb being incorrectly set. I tend to fiddle with mine a lot, so I know how much choke I need for the air temperature of the day.

[loon]

all i know is
the more bhp you get from the engine the oposite happens to the torque

now i like bhp and i like torque but what is the best?


fight

(HARRY HILL)

[asneddon]

um... No.

You can get both. You can even get more BHP, more Torque, and more economy. Its just harder.

A cam that suits you driving style will give more power where you use it, and since you will be 'on cam' more often, you economy will go up.

Also, efficiency increases will give you HP and torque. Ie, a freer flowing exhaust will (with some gotchas) always improve both.

What you might notice is the ratio between HP and torque. That can be balanced, but not normally on the type of budgets that end users have.