home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > performance & modifications

Reply
 
Thread Tools Display Modes
Old 11-24-2020, 09:39 PM   #1
fatcatbestcat
Professional Hack
 
fatcatbestcat's Avatar
 
Join Date: Oct 2019
Location: Toronto, ON (Canada)
Default B20F Head - how far should I shave?

Pending my hoist's delivery and assuming the weather holds, I'm going to be yanking the carb-converted B20F out of my 144 for a partial rebuild. While the head's off, I'm going to be taking it to my machine shop to have the spring seats enlarged for Iske double springs.

I figure while I'm there, I might have the bottom surface of the head milled for a bit more compression, but I'm not really sure how much I should have taken off.

I'm doubtful at this point that the car's going to be daily driven, so it would probably be fine running on 93 or 94, but that's not always available at any pump, anywhere. The flexibility of 91 would be nice, in case I ever take this further than around the block.

Any advice would be helpful.

EDIT: For reference, this is a B20F with probably 8.7:1 compression, and I'm looking anywhere between 9.5:1 and 10.5:1
__________________
Doing the wrong thing the right way.

If you happen to have a metric '67-'72 140/160 gauge cluster, please do PM me.

Quote:
Originally Posted by redblockpowered View Post
Will you do $14.99 shipped?
Quote:
Originally Posted by IansPlatinum View Post
please no more prying things with screwdrivers and bashing things with hammers!
fatcatbestcat is offline   Reply With Quote
Old 11-24-2020, 10:08 PM   #2
culberro
Ronald Culberbone III
 
culberro's Avatar
 
Join Date: Feb 2010
Location: Portland, OR
Default

I have no clue what the limit is, but I do know that a friend had a 11:1 head done and it was machined over 0.125... maybe 0.150". It was a lot.
The chambers were drastically different, and it was a full port head. It was done Rob Gordon at Vol-tech in Portland. I just did the valve job and blending, and final assembly of the head.

Edit: This was a b18 head with conversion valve guides to run oversized b20 valves.
__________________
Cult Person. Pissing in your Kool-Aid.
culberro is offline   Reply With Quote
Old 11-24-2020, 10:37 PM   #3
hiperfauto
The Librarian
 
hiperfauto's Avatar
 
Join Date: Nov 2011
Location: So Cal
Default

The E head gasket is thinner than the F gasket despite what this catalog page says. The E gasket is ~.8mm compressed which, when combined with .080" milled off a stock F head will yield approximately a 10.5:1 compression ratio.

hiperfauto is offline   Reply With Quote
Old 11-24-2020, 10:41 PM   #4
JohnMc
PV Abuser
 
JohnMc's Avatar
 
Join Date: May 2004
Location: St. Louis
Default

You could also measure the chamber volume and then use a CR calculator.
__________________
'63 PV Rat Rod
'93 245 16VT Classic #1141
JohnMc is offline   Reply With Quote
Old 11-24-2020, 10:54 PM   #5
hiperfauto
The Librarian
 
hiperfauto's Avatar
 
Join Date: Nov 2011
Location: So Cal
Default

That'll get him in the ballpark. Use a burette to measure the chamber volume if you want to be accurate.

hiperfauto is offline   Reply With Quote
Old 11-25-2020, 11:15 AM   #6
FrankBooth
Board Member
 
FrankBooth's Avatar
 
Join Date: Jul 2018
Location: SoCal
Default

Quote:
Originally Posted by hiperfauto View Post
The E head gasket is thinner than the F gasket despite what this catalog page says. The E gasket is ~.8mm compressed which, when combined with .080" milled off a stock F head will yield approximately a 10.5:1 compression ratio.

What's been your experience with running an engine like this on pump gas?
FrankBooth is offline   Reply With Quote
Old 11-25-2020, 12:11 PM   #7
fatcatbestcat
Professional Hack
 
fatcatbestcat's Avatar
 
Join Date: Oct 2019
Location: Toronto, ON (Canada)
Default

Quote:
Originally Posted by FrankBooth View Post
What's been your experience with running an engine like this on pump gas?
This is an important question.

Also, if I go with compression this high (10.0:1 - 10.5:1), would it be worth the extra few bucks to get a distributor with an electronically controllable curve so I can retard timing if I can't get 93 or 94 at the local pump?
fatcatbestcat is offline   Reply With Quote
Old 11-25-2020, 03:23 PM   #8
hiperfauto
The Librarian
 
hiperfauto's Avatar
 
Join Date: Nov 2011
Location: So Cal
Default

I wouldn't raise the compression over 9.5:1 unless you're going to use a D cam or larger or it'll ping. Use 91 octane minimum.

An electronically controlled advance is worth the money mostly because any 50+ year old mechanical advance distributor is likely worn out by now.
hiperfauto is offline   Reply With Quote
Old 11-25-2020, 03:41 PM   #9
fatcatbestcat
Professional Hack
 
fatcatbestcat's Avatar
 
Join Date: Oct 2019
Location: Toronto, ON (Canada)
Default

Quote:
Originally Posted by hiperfauto View Post
I wouldn't raise the compression over 9.5:1 unless you're going to use a D cam or larger or it'll ping. Use 91 octane minimum.
I have a few cams lying around right now, a D cam, the K cam that came out of the motor, some kind of R cam and a VV91 now. I'll make my decision at some point in the rebuild.

Quote:
Originally Posted by hiperfauto View Post
An electronically controlled advance is worth the money mostly because any 50+ year old mechanical advance distributor is likely worn out by now.
Well, I'm comparing that to a new production Bosch 009 or something like that. My current cast dizzy is probably toast.
fatcatbestcat is offline   Reply With Quote
Old 11-25-2020, 04:32 PM   #10
JohnMc
PV Abuser
 
JohnMc's Avatar
 
Join Date: May 2004
Location: St. Louis
Default

Measure piston height at TDC very carefully, then use an MLS head gasket to get a very precise distance for best squish. Something like .032 - .036". Getting a good tight squish will make it less prone to pinging. But you'll still probably need to run 93 octane.
JohnMc is offline   Reply With Quote
Old 11-26-2020, 12:04 AM   #11
fatcatbestcat
Professional Hack
 
fatcatbestcat's Avatar
 
Join Date: Oct 2019
Location: Toronto, ON (Canada)
Default

Alright, thanks for the replies, everyone!

It looks to me like I should be aiming to have .050" shaved, to bring it closer in line to what you get with a B20B head.

I'm not exactly sure what gasket I have, since the Elring kit just says 'fuel injection gasket set'. I'm going to guess it has the somewhat thicker gasket, as opposed to the E gasket.

Or maybe I'm just an idiot.
fatcatbestcat is offline   Reply With Quote
Old 11-26-2020, 12:12 PM   #12
OttoB
Board Member
 
Join Date: Aug 2006
Location: E(Seattle!Vancouver! San Francisco!LA!) Helsinski
Default

I measused a couple B30, all pistons were about 0,5 mm below the deck at TDC.
Slight variation on that measure, rods were +- O,1 mm in length.
OttoB is offline   Reply With Quote
Old 11-28-2020, 04:23 PM   #13
Jussi Alanko
Board Member
 
Join Date: Jun 2020
Location: Finland
Default

You could shave it even 3mm, but pushrods and rocker arms must be set to this also.
Jussi Alanko is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 05:03 PM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2021, vBulletin Solutions Inc.