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Old 07-17-2020, 08:27 AM   #1
mitch1971
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Default B20A Improvements

I’ve got my B20A in my 142 running lovely but she feels like she could handle more zip and acceleration. This is not a quest for max HP numbers or trying to one up but I want to improve acceleration in the 1000 to 3500 rpm and 3500 to 5000rpm ranges. Now there is a reasonable size BUT as well, my car is lovely and original and I want to keep it looking like that so I’m keeping the single 175CDSE stromberg carb. I will be converting to an adjustable jet so I will be able to play with mixtures to a limited extent with the carb but I don’t think there’s a huge range of needles available so might have to do it the old fashioned way of removing thickness from the needle at certain areas. Will have to see. Currently running a all new ignition with a 123 dizzy and like I said the car engine runs spot on.

I’ve contacted Ben at Tinus Tuning and the TT3 cam seems like a very decent upgrade from the A cam. Other changes nailed down in my head are a 7kg flywheel and 2” exhaust. Now what I’m not sure of is what head changes if any to do considering my remit of improved HP at low to mid range rpm. Ben suggested his stage 1 head which I’ve replied asking him will this improve HP in the 1000 to 3500 rpm and 3500 to 5000rpm ranges. My initial thoughts for the head were to increase CR up to 10 : 1 and add 44mm intake valves. CR increase is a no brainier I think but what I’m not sure of is there any point doing anything else to the head as I might not get any gains in my rev range or maybe even make it worse?

The B20a single carb and B20B dual SUs are pretty much identical to 3500rpm but the B engine gets about 16hp more at 4500rpm and 23hp at 5000rpm. The B20E injection engine seems to be consistently higher at all revs which is probably a mixture of Cam, CR and FI. So I know doing all of the above with twin SUs will be better than a B engine so if I have to put a number on it what I’d like to achieve is for my single carb engine to get 110hp at 4500rpm. Possible?
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Old 07-17-2020, 09:45 AM   #2
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Your single carb will be the power killer overall.

I know you said you wanted to retain the single CD175 but you will wake that engine up immensley with a pair of SU's or Strombergs. You're on the right track with swapping camshafts, however the area which will benefit most from the improved cam (in the top end of the rev range) is going to be restricted by the single carb.

I wouldn't push static compression past 9.5:1. Not because the bottom end can't handle it, but because of the trash fuel we have today (though ya'll across the pond may have far better fuel than us 'muricans).
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Old 07-17-2020, 10:10 AM   #3
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Yeah, the A motor power was kept down largely by that carb, along with the cam. Keeping the carb will really limit what the motor does. That said, low in the RPM range, you don't need much carb to make torque.

A stock cheap 'D' cam is a nice perk up for any of the lwoer-specced motors. But again, bear in mind that the peppier cams are moving peak power up higher in the RPM range (torque is nice, torque at higher RPM is more HP), and if the single carb can't flow enough air there to work, it's jsut going to make less power overall, tading off lower RPM power for higher RPM power it can't make.

If you are super dedicated to keeping the single Streomberg - is there a larger version you could put on? Like the dual HS6/HIF6's Volvo used - there were HS8/HIF8 carbs used on larger motors.

If you keep the single carb, I also wouldn't bother with larger valves - at least not the intake valves. The exhaust valves are the biggest restrictions in a B20 head.
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Old 07-17-2020, 10:10 AM   #4
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Yeah the stromberg is staying. I'm not so sure the single stromberg is such a power killer compared to twin SUs in the rpm range I'm talking about. The B20B with a C cam and 9.5 : 1 compression v the B20A with a A cam and 8.7 : 1 compression produced no additional power under 3500rpm. Between 3500rpm and 5000rpm maybe the single stromberg will lose out but how much in real terms?

What I'm really wanting to know is are there any real HP gains with 44mm inlets valves and 37mm exhaust valves and a little porting which is the stage 1 head under 5000rpm or are the gains pushed up the rev range with more top end power?
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Old 07-17-2020, 10:15 AM   #5
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Yeah, the A motor power was kept down largely by that carb, along with the cam. Keeping the carb will really limit what the motor does. That said, low in the RPM range, you don't need much carb to make torque.

A stock cheap 'D' cam is a nice perk up for any of the lwoer-specced motors. But again, bear in mind that the peppier cams are moving peak power up higher in the RPM range (torque is nice, torque at higher RPM is more HP), and if the single carb can't flow enough air there to work, it's jsut going to make less power overall, tading off lower RPM power for higher RPM power it can't make.

If you are super dedicated to keeping the single Streomberg - is there a larger version you could put on? Like the dual HS6/HIF6's Volvo used - there were HS8/HIF8 carbs used on larger motors.

If you keep the single carb, I also wouldn't bother with larger valves - at least not the intake valves. The exhaust valves are the biggest restrictions in a B20 head.
Thanks John. I'm just trying to gauge what is going to pay and what is not with my carb. I don't want to spend cash on a new head if it's not going to give me what I want. If a modern cam grind, larger exhaust and lighter flywheel are where the gains are to be had with the single stromberg then that is fine, I'm okay with that. I also don't want to lose originality of the car as that is a big part of my 142.
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Old 07-17-2020, 11:02 AM   #6
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The cam might not help, though. Although it might if it's some magical modern cam lobe shape that doesn't trade off low-end torque for high-end power. But mostly, cams just move the peak power up or down in the RPM range. Moving it higher creates more peak hp[, because (to simplify) HP is torque times RPM. But if the cam wants to make power higher, but the carb can't flow enough air, you 've made a tradeoff with no benefit, traded low-end torque for no high rpm power (because the carb can't flow).

Very generally speaking, the valves on a stock B20 head flow well enough at low RPM's, I don't think you'd gain anything, but then again I've never tried to make a stump-pulling low revving B20 either. One thing that WOULD add torque - doing an overbore and putting B21 pistons. Almost 10% more displacement. If you do that on an otherwise utterly bone stock motor, you won't increase peak HP much (because it won't flow much more air at higher RPM's), but you will fatten up the torque down low. And if you really feel like hitting it with your purse, stroker crank (and special rods and pistons) - a different way to add displacement, combine both and make a 2.3L (or bigger).

I'm not sure what sort of use the TT3 cam is suited for - but again, you're going to want to stick to 'tractor' cams - cams optimized for lower RPM use. The valve timing and overlap and even lift that makes more power at higher RPM's doesn't also make more power at lower RPM's. To get maximum results, everything needs to be sort of built around a certain RPM range.

It's just that usually, that RPM range gets pushed up higher and higher because that's how you make more HP. Which requires lots of changes to support revving it higher, flowing enough air through the whole system, the ca, etc. Making more torque at low RPM's where there are few bottlenecks, to begin with... is trickier.
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Old 07-17-2020, 11:36 AM   #7
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My very basic understanding is greater lift creates more HP at all rpm, duration changes the max HP rpm and modern grinds create faster lift. The TT3 has in and out specs so not sure how you go about directly comparing but ‘in’ spec has 1.4mm more lift than a A cam and duration sits between the A and D cams. So my thinking is HP should be increased at all RPM ranges and max HP will be pushed up the Rev range a bit but less than a D cam. Is this right or wrong?

Ben has advised me that the TT3 cam will give quite a torque/power upgrade with the Stromberg and will match the carb well.
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Old 07-17-2020, 12:02 PM   #8
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Certainly getting way out of my realm of limited knowledge. Even if they're trying to sell you something, I'm sure they know FAR more about it than I do.

I do have a set of higher ratio roller rockers on my pushrod motor - which result sin a bit more lift, whatever cam your using. And it's pretty easy to swap back and forth with stock rockers - like 15 minutes or so. I haven't done that in a lonog while, but I recall it being a nice sprinkling more more power noticeable over most of the RPM, range, but jsut barely so down low, much more noticeable up high (6000+ rpm). The PV's motor is made to rev, of course. Most of the parts on it are all geared toward making power at high RPM's. Carbs/head/cam/exhaust.
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Old 07-17-2020, 12:45 PM   #9
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I had one Stromburger with D-cam like camshaft.(Timo 717) worked nice with 1 mm shaved head and that thinner head gasket. I sang quite nicely but was clearly limited by carb. Swap to twin SU's widened power band.
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Old 07-17-2020, 05:16 PM   #10
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The limit with the B20A is the manifold rather than the carb.

You are on the right track for the mid range. C cam, 44mm inlet valves, 10-1 CR ( or a touch higher) and good free flowing exhaust with 2.25 inch working best makes for a nice B20A
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Old 07-17-2020, 06:12 PM   #11
mitch1971
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I was wondering if there was anything I could do with the inlet manifold, maybe a bit of porting to smooth any edges. Interesting about the 44mm valves, I have heard there’s no reason why not to have 44mm valves. A nice B20A is the goal.
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Old 07-17-2020, 06:28 PM   #12
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An alternative viewpoint:

Changing a B20A to a B20B won't destroy the car's originality much, especially since the B20B was offered concurrently with the B20A in the 140 series. So, might as well consider upgrading if it turns out that the single Pierburg (also known as a Zenith-Stromberg) carb doesn't provide what's desired. Most people would prefer the B20B anyway.
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Old 07-22-2020, 02:27 AM   #13
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Ordered a TT3 cam, 7kg flywheel, 2”exhaust and all the bits needed plus a new clutch and aluminium/steel timing gear set. Ben didn’t recommend a 44mm inlet with the stromberg and decided against a stage 1 head which would have given about 5 or 10hp so it was all getting more expensive than I wanted to spend. I might get a B20B head and whack that on instead.

If I do the build it won’t be until winter, not many experienced classic car mechanics here but I might get a mechanic to do the build, will see. I will try and get it dyno’d before and after to measure improved performance.

Last edited by mitch1971; 07-22-2020 at 03:00 AM..
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