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Old 01-26-2021, 07:15 PM   #1
R32RennSport
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Default Big Bore Do-over

I'm gearing up to do sort of a do over on my B20 big bore (2130cc) engine. In doing so I've been eating up all the information on various engine builds from over the past few years, here and elsewhere. I've put together a list of wants and needs while trying to balance those against a reasonable budget. In a perfect world I send it out to be professionally assembled and would probably throw a stroker crank at it for good measure (I hear those engines are quite the kick in the pants).

Why am I going to put myself through all of this after just assembling this engine and putting approx. 5K miles on it in the last year? Well I discovered that when you do something for the first time you make a few mistakes, sound familiar to anyone? There is enough feedback after the past year to motivate me to do better job the second time around. It runs OK, but just OK, it doesn't feel like anything really special and it's had it's fair share of questionable issues.

The main issue on my first rodeo is I took everything for granted and didn't measure really much of anything. That leads me to not being able to explain why my fresh engine only makes 130ish psi on all cylinders because I never actually measured volume so I really don't know what my actual compression is. I was told it should be around 9.25:1, but the engine feels like a slightly stronger stock fresh B20, (which I recently had the opportunity to drive). Also, the camshaft degree-ing is suspect but again I did no measuring before hand (honestly didn't even know that that was thing until someone asked me). I tried to do it in car with a friend but it was over my head and we were both skeptical of the accuracy of the measurements we had.

I know for a fact the block was not zero decked and from what I gather this an important factor in getting proper squish. IPD big bore head gasket with advertised install height of .045. Pistons were used units with new Hasting .020 rings installed. I do have a new set of complete .030 Mahles on hand for the rebuild if needed. The head is an injected head from a '72/'73 with larger 38mm exhaust valves, stock intakes and mild port work. It looked thick, combustion chambers looked like decent volume, just surfaced but again I did not measure thickness. It has a KG10 camshaft installed and I haven't found anyone having issues with their camshafts. I have a pair of 45DCOEs with long runners and an infinite selection of tuning parts available to me as I'm a Redline Weber retailer at work.

So keeping in mind that I only have blended 91 octane California gasoline available to me what is the highest safe compression I should shoot for and is that compression going to be optimal for the KG10?

Looking for constructive suggestions and or advise.
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Old 01-26-2021, 07:45 PM   #2
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Zero-decking the block isn't really necessary - as long as you accurately measure the piston height at TDC, either in or out of the block, and get a HG of the appropriate thickness to put it at somewhere between .032 and .036. Cometic sells big-bore B20 HG's in a variety of thicknesses. No compression on those, so the thickness it is doesn't change.

I'm not the right person to ask about static/dynamic CR and engine octane, though.
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Old 01-26-2021, 07:56 PM   #3
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Quote:
Originally Posted by JohnMc View Post
Zero-decking the block isn't really necessary - as long as you accurately measure the piston height at TDC, either in or out of the block, and get a HG of the appropriate thickness to put it at somewhere between .032 and .036. Cometic sells big-bore B20 HG's in a variety of thicknesses. No compression on those, so the thickness it is doesn't change.

I'm not the right person to ask about static/dynamic CR and engine octane, though.
Forgot to mention the block is obviously a '74 8 bolt bottom end with B21 rods in conjunction with the B21 pistons.

I do recall the pistons sitting a decent amount below the deck height when I was assembling though. Thanks for your input John.
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Old 01-26-2021, 08:27 PM   #4
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From the original ad when I bought the engine. It was partially assembled when I bought it which was a big part in my laziness.

FOR SALE - Volvo B20 Motor - Bored to 2,127 cc some parts not yet installed but included

Late B20 block (74-75) Short block

All new cam, crank, and rod bearings. Pistons and rods from B21 with new Hastings rings. 8 bolt crankshaft with ARP bolts.

New KG Trimning KG-10 camshaft (Swedish company) 0.437" lift with 280 deg duration and 110 deg LSA

New Al/Steel timing gears from VP Auto (Swedish company) Oil pump with IPD high pressure spring on hand but not installed.

New water pump included along with pan.

Cylinder Head:

72-73 FIX low compression head (8.7:1). With overbore, compression is bumped to 9.24:1

All new bronze guides and stem seals. New larger 38mm exhaust valves with new hardened seats - stock intakes Mild head work on exhaust port, especially short side radius,

casting flash addressed on intake port. New high performance lifters and pushrods from VP Auto. Lifter is lightened to 69 g and pushrods are 4 mm shorter.

They must be used together. New springs, retainers, and locks larger from VP Auto. This is a single,
diameter spring with requisite retainer and locks.

Rocker arm assembly disassembled and reconditioned.

IPD 2,127 cc head gasket. Clutch, pressure plate, and 8 bolt flywheel with ARP bolts sold separately.
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Old 01-26-2021, 08:46 PM   #5
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I am rather interested in the compression aspect of this discussion. Especially that I am trying to figure out what the edge of ping is for California 91 octane. I'm still getting the feel for OHV redblocks.

I think your 130psi compression is due to the relatively long duration of the KG10 which should hold the valves open more into the compression stroke. My B20F with a D cam with the same advertised duration does the same thing with about 15k miles on it (according to the person who pulled it out of an 1800). Yet it runs and pulls fine so I don't worry about it.

The lower compression motor, longer duration cam, and larger overlap will result in a relatively low dynamic compression ratio. I've read about people running 9.5:1 B20B's with the more conservative (shorter duration, less overlap, higher dynamic compression) running fine on California gas. Based on that I would guess you could push your motor higher and still have a healthy margin to deal with the occasional crappy tank of gas.

Again as John said and as I have learned from these forums, it is all about getting the piston to head clearance right.
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Old 01-26-2021, 09:23 PM   #6
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A friend just did the same thing with a b18. Bought an engine that needed assembly, but the pistons were 1mm below the deck of the block. Is has a very shaved head, and only has slight dieseling when shutting it off on a hot day. I think his CR was around 10:1 when he did the math, and he's using a Isky cam.

If you get the squish correct, I would not hesitate to run 10:1 or higher on the engine. Something that gets you into the 160+ cranking PSI
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Old 01-26-2021, 09:31 PM   #7
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First off, drop that head gasket thickness down. I found a BIG improvement in knock reduction on mine, going from a stock elring at around .048" crushed to a .035" Cometic. Allowed me another 6* of timing while also eliminating the detonation, with no other changes than the gasket. Mine is also a 2130 with flat tops in it, should be around 9.1:1 I've been told, but I didn't measure the head volume when I built it either.
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Old 01-26-2021, 09:44 PM   #8
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Quote:
Originally Posted by gsellstr View Post
First off, drop that head gasket thickness down. I found a BIG improvement in knock reduction on mine, going from a stock elring at around .048" crushed to a .035" Cometic. Allowed me another 6* of timing while also eliminating the detonation, with no other changes than the gasket. Mine is also a 2130 with flat tops in it, should be around 9.1:1 I've been told, but I didn't measure the head volume when I built it either.
I don't get any detonation with 40+ degrees total advance ( I know that it's excessive with no returns but I'm just stating that it does't) though I have it set at 36 total at the moment on the 123 distributor. Like I stated it runs OK but it just doesn't feel like anything special. I don't have a built B20 to compare to. Unfortunately, in my head I still remember the feel of my 1956 VW beetle with a built 2275cc engine with roughly 10:1 with a short gear box and dual 44 IDFs which I realize is a completely different animal.

Dyno chart for reference from last year with about a thousand miles on the engine.


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Old 01-26-2021, 10:43 PM   #9
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Don't zero in on a HG thickness until you have the head off and actually measure.

If they're too far down in the deck then a thinner HG won't really help much. Squish/quench only works when that piston *almost* touches the head. If it just sort of gets close, doesn't do much. But when they almost touch, ad TDC it *SNAPS* that burning fuel air out of the sides and swirls it into the little bathtub combustion chamber.
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Old 01-26-2021, 11:14 PM   #10
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Forgot to mention the block is obviously a '74 8 bolt bottom end with B21 rods in conjunction with the B21 pistons.

I do recall the pistons sitting a decent amount below the deck height when I was assembling though. Thanks for your input John.
A decent way down is normal for stock. When I assembled my B20E the pistons were on average 0.02" below the deck. Even with a 0.028 gasket from the B20B that piston height gives a quench depth of 0.048" which is far from ideal (probably ineffective). I have heard of people pushing 0.028" for quench; but, that seems to be pushing it - probably not so good for a high revving engine. Around 0.032 - 0.035 seems to be a consensus number for good /safe quench.
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Old 01-27-2021, 01:04 AM   #11
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I cant remember what you are running for intake and exhaust. I have been putting together a similar engine and running it all through my cheezy desktop dyno program. The results on the several engines that I have built and dynoed have actually been within a few percent,so at least it is a good method for comparing cams etc. So in messing about with your build compression made a little difference but not much. Exhaust flow made a huge difference. Of course everything has to work as a package and certainly reducing your squish clearance should be a good thing all around for detonation resistance,volumetric efficiency,and not that we are terribly concerned, emissions. It would be helpful to know what your head actually flows to try to figure out more specifically what your engine wants to make some more powah
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Old 01-27-2021, 10:49 AM   #12
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A decent way down is normal for stock. When I assembled my B20E the pistons were on average 0.02" below the deck. Even with a 0.028 gasket from the B20B that piston height gives a quench depth of 0.048" which is far from ideal (probably ineffective). I have heard of people pushing 0.028" for quench; but, that seems to be pushing it - probably not so good for a high revving engine. Around 0.032 - 0.035 seems to be a consensus number for good /safe quench.
I targeted .035".

The b230 elring is 1.2mm or .047" compressed thickness as per the engineering department at Elring.
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Old 01-27-2021, 11:10 AM   #13
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And the F heads need work in the exhaust area. If you take the exhaust valve out and look at the port, it has a bit of a constriction past the valve seat. Seems to be intentional, not sure what the idea was. But the HP/flow through the head seems to be somewhat intentionally gimped at that point.

Of course, work in the exhaust port on an OHV head is touchy, from what I hear. I really have no experience myself. But apparently it's not easy to get that exhaust flow to do the *tight* 90 degree bend it needs to make because the exhaust ports on the outside of the head are so low (because the intake and exhaust are on the same side, the exhaust manifold needs to sit low).

AFAIK the short side radius shouldn't be enlarged at all, other than smoothing. Making it bigger on that side just makes the bend even more acute. And the angle on the long side of the bowl needs to be treated carefully - the exhaust shooting up from the open valve needs to be gracefully deflected there and off to the side down the port. Enlarging the bowl there might make a swirl/reversion/confused flow situation.

All hearsay on my part (and what I've seen looking at my R-Sport stage 3(?) head) aside - you'll be limited on HP with a stock head until someone does a fair amount of educated, knowledgeable work on the exhaust ports.
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Old 01-27-2021, 01:27 PM   #14
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Here's a good starting point for pushrod porting. Translate the page, and it'll make more sense than not.
Pay attention to the last section with the PipeMax calculations. Erland has PipeMax dialed to give him very repeatable and accurate results with simulation vs dyno testing.

http://www.topplocksverkstan.se/b20historiskracing.html
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Old 01-27-2021, 02:09 PM   #15
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Nice link! /\ /\ /\

And a good graph in there showing where 99% of the money spent porting a B20 head/installing larger valves should go. On the exhaust side.

I have half a hunch that Volvo wanted to keep the HP levels down on the motors so they'd last longer. Building that 'reliability' reputation. So they gimped the HP in a hard to find/hard to fix way. Not with carbs that were too small (too easy to fix), not with a tractor cam (although thy did that on some 'lower spec' pushrod motors, keeping the cheaper cars from being faster than the $$$$1800).
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Old 01-27-2021, 03:31 PM   #16
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There was also the emissions aspect of things, that got progressively worse. Detune the engine so it flows less, and you'll get less from the tailpipe.
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Old 01-27-2021, 04:08 PM   #17
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Presumably the reference
Quote:
72-73 FIX low compression head (8.7:1)
means a B20F head? If so that probably has the best exhaust ports of any factory B20 and provide a better starting point for future porting work than other heads.

You mentioned the stroker crank option. That is a decision that you should make early on. The stroker affects everything. It obviously increases air flow and if the intake / head / exhaust cannot accommodate that increased airflow then you may not move the peak horsepower much, although it would increase the torque and horsepower at lower RPM reenforcing the tractor motor origins of the B20. If you want to target more peak horsepower you are going to have to figure out what intake / head / exhaust modifications are required to support that stuff. Significant head modifications to improve flow are outside my range of experience.

The stroker increases the cylinders swept volume so alters the static and dynamic compression ratios. If you deck the block and alter the head to hit a target compression ratio with the stock crankshaft you are going to have to repeat the head work to increase the clearance volumes to get you back to your target compression ratio with a stroker crank. That is okay if you don't mind repeating that work.

Decking the block and selecting a head gasket to get you into a quench zone around 0.032- 0.035" will never be a bad move. Decking will reduce clearance volume bumping the CR slightly. Once you know your combustion chamber volumes you can then figure out whether you can manage your compression ratio with changing the combustion chamber volume slightly. Depending on how far you have to go with changing the combustion chamber volume you may elect to leave the pistons slightly below deck level. It will become a balancing act between maintaining a target quench thickness and a target compression ratio and are you comfortable fiddling with the combustion chamber volume (do you really know what you are doing - I don't when it comes to meddling with combustion chamber shape). Your KG 10 camshaft has a similar duration at 0.020" lift as the Volvo D cam. Total lift is higher and as a result so is the initial opening. Given the similarities in the cam's 0.020" duration to the D and running 91 octane (R+M)/2 I expect that if you target a static compression ratio in the 10:1 - 10.5:1 range you will be safe. All of this will achieve incremental improvements in operation; not big horsepower increases.

You mentioned that you had run with 40 deg of total advance without detonation. More advance does not mean more horsepower. As you crank the advance up the crank angle at which peak cylinder pressure occurs changes. Crank up the advance enough and the increase in pressure prior to TDC will reduce the potential peak horsepower. The 'internet wisdom' is that ignition timing should be set so that peak cylinder pressures occur about 20 deg ATDC. You will find that more modern engines with compact combustion chambers that have a lot of turbulence to promote flame speed run with much less total ignition advance. My recollection was that Phil Singher said that from his dyno testing that total advance on the B20 engines for maximum horsepower was in the 32 - 35 deg range. This would be affected by the RPM at which the total advance was achieved and that higher RPM engines (> 6000 RPM) may need more total advance at higher RPMs in order to achieve peak pressure at the right time. B20s that operate below 6000 RPM usually work with total advance being achieved in the 3200 - 3500 RPM range. Of course, Phil Singher's comments would have been based upon engines with quench / squish optimized as much as possible for the B20 which affects burn rate and the tendency to detonate. Ultimately you will need to do repeat dyno runs to determine the best ignition timing for maximum performance.
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Old 01-27-2021, 06:21 PM   #18
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Dunno on the 74 head being the best exhaust port. Maybe once you remove the restriction right behind the valve perhaps, where it necks from 35mm to what, maybe 20 at best? lol
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Old 01-27-2021, 06:30 PM   #19
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From what I've heard, the E/early F/late F heads all flow pretty much the same through the ports, but the late F head can be ported more where it needs to be - there's some thicker metal in the port area.
*hearsay on my part of course*
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Old 01-27-2021, 06:50 PM   #20
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Dunno on the 74 head being the best exhaust port. Maybe once you remove the restriction right behind the valve perhaps, where it necks from 35mm to what, maybe 20 at best? lol
I probably should have worded that as best in terms of being able to make it better in terms of how much weld was required to fill the floor of the exhaust port to improve the short side radius. My recollection was that the floor of the port was slightly higher than on the E; but, that could have been pure imagination. All of them are constrained.

If you are going to try improving the short side radius problem you are into serious work and presumably know what you are doing. Not a place I am going!
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Old 01-27-2021, 07:43 PM   #21
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Just put a turbo on it
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Old 01-28-2021, 12:59 AM   #22
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Just put a turbo on it
Incorrect.
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Old 01-28-2021, 12:05 PM   #23
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Just put a turbo on it
The more I debate about how to ruin my rotbox, the more I see this as the most logical solution.
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Old 01-28-2021, 01:58 PM   #24
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I have also mulled a low pressure turbo application as an alternative to increasing valve lift and valve duration (and valve train wear) for a modest across the RPM band power increase. The Aerocharger turbos appeal because of the no oil / cooling water requirements and having a variable aperture exhaust turbine which should facilitate a broader torque curve. However, their price doesn't fit with the typical Turbobricks sensibility.

That said, the OP has dual Weber DCOE 45s which isn't really going to work with a turbo application so we can probably shelve that suggestion.
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Old 01-28-2021, 02:51 PM   #25
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DCOE's work fairly well in light pressure turbo situations. The bowl vents are on the front face of the carb - so if there's a plenum, just pressurize that. Might need reinforced bowl lids if you plan on running higher boost.
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