I’m all Torque

Just driving the bus on the weekend after the new top end. Really impressed with the low down torque - so low revs has really decent pull e.g. quite tight roundabouts in 3rd gear and pulling away well! Similarly pulling away in 4th from 30mph feels strong.

I have no rev counter but I’d say 1500/2000rpm feels strong. Any faster say from 30 to 45 in 3rd, or 45 to 60mph in 4th there seems to be quite a tail off. This is probably normal for type 4 2 litre?

I found a torque curve on the web, I guess curve B describes this quite well.

I guess this is normal. I’m not too concerned about it. Would be great if it carried on through the Rev range though. I’ve no plan to change any cams etc this is just a comment/ question

 

But it does! Pulls really well here. I have driven the upright engines before and yes I had to thrash these and it felt rewarding and right.

My type 4 feels like the power bands are very different lots of power at low revs and less at higher revs - just as curve B shows

 

30mph in 4th is indeed about 1600rpm.
It is cruel to accelerate in 4th from that speed.
Over its peak power at 4000rpm but still should be going well to 5,000rpm (on rare occasion).
It should be happy to go 55mph in 3rd, 70mph in 4th @ 3,600/3700rpm, round about it's peak power, though perhaps not for hours.

Leaky carb spindles run out of puff. If you have solex carbs and it drives better first thing with the choke on, could be.

 

This is my graph, same cam as yours but more cc. Doing pretty much the same as the 1500 single port you posted?

 

Having a low rev peak torque is nice for a bus - as the revs drop off the torque somewhat compensates so you have relatively more HP at lower revs that an engine with "more" cam. Mine has more hp at 1600rpm than a 1500 flat out.

 

Nice info there! I suppose when I say 30mph in 4th gear I mean, when you’re in 4th doing 30mph/35mph in town and you accelerate up to say 40mph it pulls well and there is no need to change to 3rd.

Yes, when I accelerate through the gears onto a motorway I guess I’d take it to about 45ish in 3rd.

My point is, there seems to be a disproportionate amount of power low down. And this is what the graphs show, a fall of in torque from about 2000rpm onwards. I’ve had quite a few modern cars where the curve is flat from 2000 to 4500 rpm.

It rewards lazy driving, and doesn’t encourage enthusiastic revving

 

Now fit a bigger carburettor and a better flowing exhaust. Your curve will flatten .

I can persuade my bus to pull from an indicated 25mph/1600 rpm in 4th (which because of wheel sizes is nearer 22mph ...
Not kind I will only do it on a flat road. And I have been noticing getting up to 32mph in second recently .. 4500 rpm plus... also not kind.

 

Interesting, I’d didn’t think of a better flow exhaust helping out with torque curve. I already have twin Weber icts, but when I decide on an exhaust I’ll look for any improvements

 

Your exhaust will make a huge difference, well perhaps that's an exaggeration, but certainly noticeable. We were chatting about this with @zedders and at @77 Westy and others not long ago.

 

Not so much with a stock 2l.

 

That performance curve appears to be for a 1500. A 2.0l will be somewhat different and it will certainly make more than the 47bhp that the curve indicates. Modern cars have maximum torque at much higher revs and therefore make much more bhp.

Don’t expect the engine to last too long if you punish it at very low revs, the fan speed and cooling is low but engine power and heat will be high.

 

Ok, noted. Quite happy to make the engine sing