Porting Single Carb Manifold

[Derek UK]

Mitch, you can mirror polish the exhaust side if you have the time. There is often some lumpy welding on the downpipe flange and blending the 2 together at that junction not a bad idea.
Having said all that, some people, P Singher I think, likes a mismatch at the head to manifold junction as it causes a back pulse that aids chamber filling and extraction. This is partly down to the bad exhaust port design and shape. Black Arts indeed.

[mike gilbert]

Interesting thread. I have a B20A engine that I was goiing to install in my 1800S (which has a tired B18). I was going to upgrade it to B spec first but I'm also more interested in low end torque below 4000rpm and I notice that the torque figures are not much different between the B20A and B. In fact according to this chart on Wikipedia the DIN torque figure is actually higher for the B20A. Is that really true and if so what advantage in the real world is there for someone like myself in changing the cam and compression ratio (or even retaining the twin carbs, though obviously I will)?
https://en.wikipedia.org/wiki/Volvo_B18_engine#B20

[DWeed144]

Originally Posted by Army

Having access to Solidworks is a luxury - how did you determine the air flow requirements?

Way way back in the day when I was learning about (now really old) FE software the main thing that was taught was to not always believe the number that gets produced. This kind of makes it interesting to learn how you set the flow requirements? Can you also fiddle around with wall roughness in the model or is it not that advanced?

I can imagine that is the case - however it shows graphics of the flow so it's very easy to get a basic understanding of the turbulence and pressure differences using the different colour overlays and squiggly lines! In terms of air flow I seem to remember just looking at it at a variety of pressure differentials from idle to a boost type scenario. It seemed relatively consistent across those changes so I didn't bother going to deep into that. You can factor in roughness, certainly something pretty significant if I were to sand cast it myself!
I am certain I was not using it either to its full potential, or even correctly, but it was still easy to see what changes had what effects and through that optimise the basic design.

[Army]

Originally Posted by DWeed144

I can imagine that is the case - however it shows graphics of the flow so it's very easy to get a basic understanding of the turbulence and pressure differences using the different colour overlays and squiggly lines! In terms of air flow I seem to remember just looking at it at a variety of pressure differentials from idle to a boost type scenario. It seemed relatively consistent across those changes so I didn't bother going to deep into that. You can factor in roughness, certainly something pretty significant if I were to sand cast it myself!
I am certain I was not using it either to its full potential, or even correctly, but it was still easy to see what changes had what effects and through that optimise the basic design.

Thanks - that looks interesting

[Army]

Originally Posted by mike gilbert

Interesting thread. I have a B20A engine that I was goiing to install in my 1800S (which has a tired B18). I was going to upgrade it to B spec first but I'm also more interested in low end torque below 4000rpm and I notice that the torque figures are not much different between the B20A and B. In fact according to this chart on Wikipedia the DIN torque figure is actually higher for the B20A. Is that really true and if so what advantage in the real world is there for someone like myself in changing the cam and compression ratio (or even retaining the twin carbs, though obviously I will)?
https://en.wikipedia.org/wiki/Volvo_B18_engine#B20

My immediate impression of what's going on with the B20 data in that table is that the compression ratio is probably playing the bigger part in produced power. The torque number is kind of staying about the same but the position of peak torque happens at very different rpms.

The bore and stroke of the B20 engine remains the same 88.9 mm bore and 80mm stroke making it a slightly oversquare engine. If you really wanted more torque from an engine design perspective you'd start (probably) with an under square engine design.

https://en.wikipedia.org/wiki/Stroke_ratio

I can only assume that the position of the peak power (which on that table varies from 4800 rpm to 6000 rpm) and peak torque (which on that table varies from 2300 to 3500 rpm) is mainly due to a combination of compression ratio and cam profile. There's a lot of chat about B18/B20 cam profiles on the interweb but from what I can make out there seems to be very little difference between the factory fitted versions.

More information can be found here =>

http://www.1800philes.com/ianr/_superlist_grinds.html

In the pre-blurb on that site it is stated that the longer the duration (when the valve is open) "the peak torque is not raised, merely moved higher in the rpm range"

I conclude if you wanted the peak torque to be lower in the rev range then you'll be best off sticking with a smaller duration on the camshaft as you're gonna have trouble trying to make the engine an "undersquare" engine...

...thing is most people want to get the drop off in torque as the rpms increase to coincide with the rising power curve so you don't get the feeling of a flat spot (I'm not sure how that works for the B20 - need to speak to someone with a bigger pay grade!)

[Burdekin]

Originally Posted by mike gilbert

Interesting thread. I have a B20A engine that I was goiing to install in my 1800S (which has a tired B18). I was going to upgrade it to B spec first but I'm also more interested in low end torque below 4000rpm and I notice that the torque figures are not much different between the B20A and B. In fact according to this chart on Wikipedia the DIN torque figure is actually higher for the B20A. Is that really true and if so what advantage in the real world is there for someone like myself in changing the cam and compression ratio (or even retaining the twin carbs, though obviously I will)?
https://en.wikipedia.org/wiki/Volvo_B18_engine#B20

If you could have a drive in my 142 I think you'd be pleasantly surprised at how well it goes but it also isn't a standard B20A but does still retain the single stromberg. It is the later stromberg with a adjustable jet fitted. I have a Tinus Tuning TT3 Cam, 0.8mm head gasket, lightened flywheel, lightly skimmed head with new valves and hardened seats. It performs not too bad, it starts instantly from cold or hot and idles lovely and probably gets about 30mpg. It's feels like a very civilized setup for a car of it's age now.

Tough decision for you with regard to the original engine. The P1800 has the looks but more performance wouldn't be a bad thing either.

If you're going to rebuild your engine best to speak to the guys who build the engines and parts. Ben from Tinus Tuning is where I got my latest parts from and gave me good sensible advice. It does get expensive though.

[morwenna240]

This is true, it does get expensive, yet, you can't take it with you, an time is trotting on; spend a few k an feel that surge of power. . .

[Clan]

Originally Posted by Army

My immediate impression of what's going on with the B20 data in that table is that the compression ratio is probably playing the bigger part in produced power. The torque number is kind of staying about the same but the position of peak torque happens at very different rpms.

The bore and stroke of the B20 engine remains the same 88.9 mm bore and 80mm stroke making it a slightly oversquare engine. If you really wanted more torque from an engine design perspective you'd start (probably) with an under square engine design.

https://en.wikipedia.org/wiki/Stroke_ratio

I can only assume that the position of the peak power (which on that table varies from 4800 rpm to 6000 rpm) and peak torque (which on that table varies from 2300 to 3500 rpm) is mainly due to a combination of compression ratio and cam profile. There's a lot of chat about B18/B20 cam profiles on the interweb but from what I can make out there seems to be very little difference between the factory fitted versions.

More information can be found here =>

http://www.1800philes.com/ianr/_superlist_grinds.html

In the pre-blurb on that site it is stated that the longer the duration (when the valve is open) "the peak torque is not raised, merely moved higher in the rpm range"

I conclude if you wanted the peak torque to be lower in the rev range then you'll be best off sticking with a smaller duration on the camshaft as you're gonna have trouble trying to make the engine an "undersquare" engine...

...thing is most people want to get the drop off in torque as the rpms increase to coincide with the rising power curve so you don't get the feeling of a flat spot (I'm not sure how that works for the B20 - need to speak to someone with a bigger pay grade!)

That might have been the case 90 years ago .. Back when the 998cc mini came out , the new 875cc Hillman imp engine was a revolution having a big bore( 68 mm) and very short stroke ( 60 mm ) it produced more torque than the 998cc mini at a lower rpm ... then when 4 valve heads arrived that stamped on the old theory even more .

[Burdekin]

This was Ben from Tinus Tuning's reply when I was asking him about compression ratio for my build, thought it worth sharing:

"The TT3 has very good filling capacities which translates to good torque. Since the filling of the cylinders is good, you should not have a too high compression ratio. If you do, you’ll risc pinging or engine knock. So my advise is to stick with the B20A head and just use the thin head gasket that will be in the shipment. The stock B20A head gasket is 2,0mm while this one is 0,85mm. Imho this will raise you compression ratio a bit but not far enough to get engine knock. If you do want to seek the limits in regards to compression ratio, you should aim for a 9 : 1 compression ratio or 9,5 : 1 max."

[Army]

Originally Posted by Clan

That might have been the case 90 years ago .. Back when the 998cc mini came out , the new 875cc Hillman imp engine was a revolution having a big bore( 68 mm) and very short stroke ( 60 mm ) it produced more torque than the 998cc mini at a lower rpm ... then when 4 valve heads arrived that stamped on the old theory even more .

Ha ha - 90 years ago eh?

I did put a probably in brackets!

In my opinion more modern 4 valve per cylinder heads make for a nasty panicky driving experience as they are also often geared to be used in the higher rev power range. It is like having to wrestle with two disobedient Huskies on one lead - a tedious tiring driving experience.

Can't wait until I can afford electirc motor conversions for my old cars then I'll have lots of low down torque and a lot less fuss (with these stinky silly fossile fuel powered things)