• Hello Guest, welcome to the initial stages of our new platform!
    You can find some additional information about where we are in the process of migrating the board and setting up our new software here

    Thank you for being a part of our community!

Big Bore Do-over

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.
 
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.
 
JohnMc said:
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.
Click to expand...

One could also run a draw through setup instead of a blow through.

Although I have been tempted to run a blow through supercharger setup with a weber 38 just because I wouldn't have to worry about making new manifolds. Or I could just do fuel injection with a supercharger.
 
Last edited:
Yeah, but a draw through involves a much heavier redo of the intake system. Otherwise, just blow air on the plenum if you have one. And rejet. And... probably don't use the chokes if you have them (those are vented on the back side of the carb when in use).
 
Thank you all for your input, just getting back in front of a computer after a few days away.

Turbocharging/supercharging never has and never will be a consideration for my build though I do know it's quite possible with DCOEs as I've seen it done quite often when I was in the aircooled drag racing scene but it left much to be desired in terms of reliability. This will strictly stay NA. With that said, I'm interested in efficiency to my current constraints in regards to cam changes and head/block machine work. From what I know about the head previous to me assembling the engine in addition to knowing that an IPD head gasket was used that installs at .045 and what seemed to me a stock B20 block and unmodified B21 rods and pistons:

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
 
Last edited:
Deck the head, deck the block, thinner head gasket, and adjust the rockers so they have a good contact pattern on the stems.

Were the rocker arms refaced at all? I did a few pairs for a local, and they were WAY off from the factory. Lots of side-loading on the valve tip.
I ended up using some 0.080" thick lash caps to get the tip/stem contact where it needed to be.
 
culberro said:
Deck the head, deck the block, thinner head gasket, and adjust the rockers so they have a good contact pattern on the stems.

Were the rocker arms refaced at all? I did a few pairs for a local, and they were WAY off from the factory. Lots of side-loading on the valve tip.
I ended up using some 0.080" thick lash caps to get the tip/stem contact where it needed to be.
Click to expand...

Sounds like the common theme that I'm getting.

I was told the rocker arm assemblies were reconditioned, but I wouldn't know any different myself just looking at them. As I originally stated this was my first time not only assembling an engine but my experience with Volvo's and B18/B20s is fairly limited even though I've owned this car going on a decade now. 6 years with a tired B18 that I limped along with a blown head gasket (not realizing how easy that would have been to repair), 3 years down for restoration, and now just over a year with this B20.
 
I was able to dig through my picture archives and find a picture of the combustion side of the head. I have lots of pictures of the port side from 4 feet away which doesn't do any good so those will have to wait until I take the induction/exhaust off. I'm also seriously considering ditching the cheap Patriot header from IPD and sourcing a stock exhaust manifold.

 
Last edited:
Since you're running larger bores, another thing you can do to improve flow is to widen the sides of the chambers to match the new bore. Lay a BB headgasket on, mark it up, carve it out. Of course, without shaving the head down, that will just lower the compression ratio. But it will give the valves more room to 'breathe' on the 1/3 of the diameter with a chamber wall sitting right in front of the valve opening.
 
JohnMc said:
Since you're running larger bores, another thing you can do to improve flow is to widen the sides of the chambers to match the new bore. Lay a BB headgasket on, mark it up, carve it out. Of course, without shaving the head down, that will just lower the compression ratio. But it will give the valves more room to 'breathe' on the 1/3 of the diameter with a chamber wall sitting right in front of the valve opening.
Click to expand...

That's a great suggestion and I do see the logic in it. I don't know if I trust anyone enough locally to start messing around with my cylinder head beyond basic shaving. I sure don't feel comfortable with tackling it myself even though I do own a Dremel ;-)
 
Heh, I used a hand held router and some carbide bits. You'd spend a year doing it with a Dremel. The router actually worked pretty well for that specific duty. Nice and steady, and the head carved very smoothly (better than aluminum). I got the valves out, set the depth, chose a burr with the correct curve for the chamber edge, and just proceeded to carve away the 'sharpied' metal.

Then I CC'ed it with some grease, a sheet of glass, and a syringe, got them all to match.
 
I rebuild B30E with little hotter cam. Pistons are .015" oversized and I choose B30E head gasket. Measurement showed that pistons were from 0,5 to 0,6 mm below deck, due small variation in rod length. Pistons were dead on and also deck height was same on both ends.

Deck was cut down 0,5 mm and compression ratio was around 10,5:1.

At dyno it started to knock at 36-38 deg at steady speed. Advance is set at 34 now. It made like 185 hp at 6200, little disappointing, also mid range torque is missing. Cam timing and exhaust pipe lengt and diameter need some attention.

Q: Any ideas for off-set keys?
 
Volvo's advertised hp for a B30E was 175 hp @ 5800 RPM. That would be 'advertised / exaggerated' and measured at the crankshaft. If you measured a 'true' 185 hp at the rear wheels that strikes me as probably a very good increase for just a camshaft change and bumping the compression ratio for 10 to 10.5:1. Your missing mid range torque may be a direct result of the hotter cam. Which cam did you use?

36 - 38 deg of total advance seems like an awful lot and detonation would not be a surprise. 32 - 34 degrees of total advance seems to be the consensus advance on a B20 running around 10.5:1 with 91 or 92 (R+M)/2 octane.
 
I used crank dyno.

Cam is 762 from Timos Motors, old profile and I would certainly had another cam, but things are bit complicated with B30. 762 is like K but little more lift. I might go back to C or K cam or Timo 717

I made simulation with cam timing and Y-pipe length/diameter. Advancing cam 5 degrees and longer and smaller exhaust pipes before Y-branch might do the trick.

https://photos.app.goo.gl/i9aFeXsxUZUCVXCU6
 
Bump the compression ratio to 10.1 at minimum

The pushrod heads have horrible flow, pretty typical for the time. I’ll get some pictures of heads that are being totally redone.

Local guy ;)
 
Last edited:
not long to find my picture on facebook, i ask for join the Historic Volvo society so i get you some more pictures of the head.
Head is mounted on 8 bolts B20 block with B21A flat pistons.
I am currently finishing wiring of the ITB on standalone Ecu. Need to find a good solution for throttle cable.
 
You must log in or register to reply here.
Back
Top