B20A With 8 Bolt Crank

[mike gilbert]

I've just bought a B20A engine for an upgrade to my '68 1800S. Anyway on removing the gearbox and clutch I see it has an 8 bolt crank. So I know this makes it a late 140 engine and the rods are compatible with B21 pistons but also did these last B20's come with larger inlet valves as per the B20E/F heads? I'm sure I remember reading that all B20's got larger inlets at some point but the exhausts remained the same throughout. Excuse my ignorance but despite owning umpteen P1800's I have have always previously rebuilt and restored to original spec - unimaginative I know - and so never got involved in engine upgrades.

[Burdekin]

Yes and you can tell as they have the casting in the top of the head where the fuel injector hole would go. The casting is a P shape, see attached pic. It’s not the best pic but hopefully you can see what I mean.

[Derek UK]

The parts book for late B20 in the 140 lists 7 different heads coving carbs and F.I. Interestingly they all list the same part for the inlet valves. Exhaust valves are listed for the carb models B20A/B and another part number for injection models. Pick the bones out of this. That took a while!
B20 Early 140
In #419639 B20 A/B/D
In #419760 B20E/F
Ex #419640 B20 A/B/D
Ex #419735 B20 E/F
B20 Late 140
In #419639 B20B
In #419766 B20 E/F
Ex #419640 B20B
Ex #419735 B20 E/F

All Carb heads after the introduction of F.I. had the blank pad for the Injectors. Numbers above indicate that both early and late carb heads used the same small valves in both positions. Later F.I. engines got the larger inlet valves.

[Burdekin]

Originally Posted by Derek UK

The parts book for late B20 in the 140 lists 7 different heads coving carbs and F.I. Interestingly they all list the same part for the inlet valves. Exhaust valves are listed for the carb models B20A/B and another part number for injection models. Pick the bones out of this. That took a while!
B20 Early 140
In #419639 B20 A/B/D
In #419760 B20E/F
Ex #419640 B20 A/B/D
Ex #419735 B20 E/F
B20 Late 140
In #419639 B20B
In #419766 B20 E/F
Ex #419640 B20B
Ex #419735 B20 E/F

All Carb heads after the introduction of F.I. had the blank pad for the Injectors. Numbers above indicate that both early and late carb heads used the same small valves in both positions. Later F.I. engines got the larger inlet valves.

That’s interesting Derek as Rob from Amazon cars says in one of his videos if a carb head has the P casting it will have the 44mm intake valves.

Towards the end: https://youtu.be/eZJF2x8ybKw

[mike gilbert]

Well that is interesting and theres only one way to be sure. I have been offered a head labelled 'B20A from bigger valve era' and asked the owner to measure the valves for me. Mine definitely has the P shaped castings on the head but I dont want to take the head off yet just to measure the valves. We shall see.

[Derek UK]

As said, my numbers from the 140 parts books. Amazons and pre F.I. 140's with B20 heads I'm sure don't have the pads. 7 different heads listed which would have different specs of valves along with other fittings for both types of F.I.
As Rob said smaller ports keep the gas flow up, larger valves would slow it down and those heads may have had no extra port work. Some say keep the inlets small and make the exhausts bigger as the exhaust ports are so bad. No mention of raising the exhaust port floor but that takes us out of simple and cheap.
He said that they keep their engines simple. Fair enough, that also keeps the costs down too. £1k for a stage 2 (?) head for little practical gain. Rallying at less than works level and a little less power won't keep your engine from performing well. Lots of tuning things not mentioned. Decking the block to match the lowest piston for instance and that is basic blue printing and not "tuning". This maximises squish to get the maximum amount of fuel into the combustion chamber. Relieving around the inlet valve on the b18 if you fit a larger valve is effective on B20 too but it lowers the CR.