B20 Stroker Buildup

[volvoracer]

I'm putting a B20 together for my '67 1800S, got a stroker crank done by Paeco in '90 and never used. Anyone know about these cranks? I'm wondering about reliability etc...

Tempted to just build the motor the same way I had prior; 2130cc pistons, balanced, Stage 3 VCS head, VCS intake manifolds, 44mm Mikuni carbs, Stahl header...

On paper the 2.5 Stroker should make approx 220hp...

[Phil Singher]

I'm not clear on whether that's a new billet crank or one that was offset ground. For 2.5L w/ 92mm pistons, stroke would also have to be around 92mm. I don't think you can grind a stock crank to anywhere near that. ???

How well the exhaust ports flow will determine the max power potential. I don't think you'll get 220, but you can get near 200 and have a very fat torque curve.

[volvoracer]

Looks like a re-grind to me, not a new crank.

Likely a 2.3 set up...as you say 2.5 would involve serious geometry changes to the crank.
I'll give my Shop a stovker and this stroker for side-by-side evaluation.

Stage 3 VCS head flows very well, so I err on the high side of calculations.

Machine Shop has to pronounce this crank as usable before I decide to try it.

[Phil Singher]

I had a crank offset ground last year, and my super-experienced machinist sent it to a specialist on the east coast somewhere to have that done. It was welded, index ground and then nitrided. That one I trusted...

I don't have any direct experience with VCS or R-Sport heads, but I understand they were different castings from any of the stock heads. Of those, the F ports out the best, but it's still always the exhaust ports that ultimately set the HP limit. I'm using an Enem K19 cam -- 246 degrees @ .050 lifter rise / 296 seat-to-seat and .472" valve lift @ .016" lash in my 93 x 80mm (2174cc) street performance engine, and it makes a very tractable 200 HP. Maybe you can get 220 from a stroker with more cam than that with one of those heads. ???

[VBigDog]

Adam,
My block is currently being sonic'ed to check casting thickness - as I'm also in the early stages of building a stroker (not yet sure if 2.3L or biting the bullet / billet of 2.5L.

I too, am north of Boston (Marblehead) - and also pulling a '70 P1800E together.

Where are you located? Conversation at Maddies, perhaps?
Tom

[volvoracer]

Hi Tom,

sorry so long in replying...

I'm still on course to build a stroker b20. I'm adding an Isky "R" cam and a VCS/R-Sport Stage 3 head I bought new in 1985.

Who is your machinist?

I've used Precision Motorwerks (Kent Jones) in the past...

Hope to build up the mill over the winter as I'm getting my car back in April/May.

Best,
Adam

[volvoracer]

I just spoke to Dave at Granite State Balancing.

I'm dropping off my B20 stroker crank and '75 block there in the next few weeks.

I offered use of my bore plate for any other B20 jobs going on there.

[volvoracer]

Dropped off my '75 b20 block and stroker crank at Granite State Balancing in Marblehead for evaluation.

If the Stroker crank passes inspection, I may sell it off and stick to my old recipe; a 2130cc motor with my tried & true Lindskog-balanced stock crank...

[VBigDog]

Let me know how that works out -

I'm sorting the top end at the moment. Planning to send the cylinder head out for a 5 axis port job.

[volvoracer]

check yer IM (instant message)

I'm selling my Stroker Crank and a set of Steel T-Gears also.

[gdill2]

Bump.

George Dill

[volvoracer]

Update:

All parts back from Granite State Balancing, went with my old trusty B20 w/ new Mahle 92mm pistons, and a new ipd "R" cam...


BTW, does anyone one know if the Isky "Hardenable" 202-H lifters are the same as the ipd lifters? I got a set form Isky, but the lifter faces look polished, rather than hard-faced...

[Phil Singher]

Yes, they are the same lifters.

[gdill2]

Just bumping to get the spammers off the...

George Dill

[volvoracer]

Update: Stock (balanced) Crank, ipd "R" cam & Steel Timing Gears installed in Block.
I sized the rings, next have to fit rods and pistons to block.

[volvoracer]

Painted block & head.
Pistons & rods going in shortly...

[volvoracer]

Waiting on Mahle to send me correct Piston Circlips...
Crank is installed.

Ordered ARP head bolts & studs.

[volvoracer]

Got Mahle piston circlips, fitted to #1 Piston, fit piston to crank with Plasti-Gage, mistakenly spun engine 1/2 turn w/ Plasti-Gage in the bearing...now engine won't turn...backed off rod nuts, engine turns again...odd.
Plasti-Gage told me I was at .0005 or .0007...alarming as it should be .001...seems too tight.

Will clean off the bearing and try again...

Anyone had this happen to them?

[volvoracer]

OK, I'm a dunce.
Measured the new Rod Bearing shell, it is for a re-ground crank.
Measured another set I had laying around, .007 smaller diameter.

Will fit correct size to Rod #1 and I predict it will fit properly...

[Walrus3]

Better luck this time!

[volvoracer]

Question for your 1800 gurus: Is a .120" thick head gasket OK? Stock is .040.
I'm trying to get my compression ratio to 10.25:1, static as of now is 13:1, too high for Pump Gas.

I previously "dished" my piston tops to fix it.
New pistons are flat-top...

I can have a custom Head Gasket made by Cometic for about $240, dish my pistons or have a thick Copper Gasket made up...

I'm also concerned about rocker arm geometry if I jack up the head with a thik gasket...

[Phil Singher]

The further you move the head away from the pistons, the less squish/quench effect you have. Less squish/quench means a slower burn rate, which means you need more timing advance, which means you lose power due to the lower compression while doing nothing to combat pinging. It actually works against you.

What do your combustion chambers CC at now?

[volvoracer]

R-Sport head cc's at 37cm.
I ordered a .120" thick head-gasket from Cometic, which should give me about 10.3 : 1 C.R.

My block was decked years ago, head surfaced (when it didn't really need it arrgghh!) so I'm actually bringing the geometry back to "normal"

Rods & Pistons are in, all Plasti-gaged around .001".

Oil Pump (with ARP studs) and Pan are next.

[Walrus3]

An extra thick head gasket is anything but "normal". It is MOST desirable to have the piston crown flat and not more than about 0.040" from the flat surface of the head to get plenty of turbulence in the combustion chamber. This enhances mixing and although it may increase the compression ratio, may actually reduce detonation.
I've got a big bore block and the only regular headgasket I could get for it (from Mike at IRoll Motors) is 0.050". I'm not happy about it and may go to Cometic for a thinner one.

[Phil Singher]

This is not going to work at all well, and I will explain why in detail.

When a piston approaches the flat area of the head on two sides of the combustion chamber on the compression stroke, it produces a shock wave that serves two purposes: 1) it mixes fuel droplets that fell out of atomization getting into the chamber back into atomization (fuel will always drop out going around the short radius of the port and around the intake valve), and 2) it helps control the way the flame front propagates after ignition. This effect is called "squish," and it's very important in producing a fast, complete burn. A fast burn is desirable because 1) it completes while the piston is still close to the chamber and in a position to receive the energy transfer efficiently, and 2) it reduces the amount of timing advance needed, thereby reducing the chances of pinging or detonation.

As a piston drops away from the flat area of the head on the power stroke, pressure drops quickly until there's not enough to support combustion, and the burn snuffs out. This is called "quench," which should happen abruptly and at the proper time. This reduces heat transfer to the head and pistons.

The benefits of squish and quench are greatly magnified by moving the head closer to the pistons, the closer the better. With stock pistons and rods, the safe distance is around .032" cold. By using the fat head gasket you are proposing, your piston-to-head clearance will be roughly four times that. This will produce something on the order of 1/6 or 1/8 the squish and quench possible. You will have slow, ragged combustion. You will have to run over 40 degrees total advance to get any sort of performance, and the engine will ping, even at 10.3:1 compression. It will also run hot.

So, don't use the R-Sport head. It was a fine thing in its day, but you'll do far better with a B20F head that has some decent porting done to it and some larger exhaust valves. Deck the block for .032" clearance with a thin head gasket, then shave the head for the desired compression ratio. The engine will not want more than 32-33 degrees total advance, it will not ping, and it will inherently run cooler.

.001" bearing clearance is tighter than I would recommend...

[volvoracer]

Excellent explanation of squish & quench.

As my initial piston-to-deck clearance is .006 (my block was decked in the past) I should have "enough" S & Q.

The R head was something in it's day and still is in my book; the key is in the port floor casting; as you look in you can see the valves. That straight shot equals better flow.

I'd like to see charts on a heads-up comparison between the R head and a modified stock head.

It is easy for folks who have never seen an R head to talk about it as a quaint antiquity, I've run mine for years and it really does work.

No disrespect to Phil, who knows ALOT and shares info. freely...

I did get my rods & mains clearanced properly...turns out the numbers on the rod caps and rods have to be on the same (non-camshaft) side...oops...