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What are the Super Six Gains
https://slantsix.org/forum/viewtopic.php?t=54568		 Page 3 of 3
Author:  wjajr [ Wed Feb 12, 2014 6:31 am ]
Post subject: 
Just my two cents:

One has to picture this in their mind’s eye, an engine is an air pump, and what would restrict its performance, and what would enhance its performance.

Stock air pump (engine): small single barrel carburetor (restriction); low lift cam (restriction); stock valve and low compression head (restriction); stock exhaust manifold (restriction); stock 1 7/8th inch exhaust system (restriction) as compared to a race engine.

Ask yourself what can one do to improve flow through this air pump. If one were to increase the flow through any one of the above restrictions, would that one change increase the pumps ability to move more air, or any two, or… You get what I driving at here; any one restriction remaining in pump’s flow, relative to any modifications made to increase flow, will govern how much air can be moved, thus limiting potential power increase.

How much you decrease all of these restrictions will result in how much more power output is developed. Some of the changes won’t cost a dime more over stock rebuild parts that one would be purchasing for a full engine rebuild. I think to get the most out of your engine, additional money would be spent on two barrel intake and carburetor, possibly oversized valves (if stock were reusable in stock rebuild), modified stock exhaust manifold (hogged out and addapted to accept 2 ¼â€￾ pipe), and new larger exhaust system. Aside from a two barrel the engine will look like a stocker, but perform well enough to keep up with modern day traffic increasing the car’s pleasure factor.

Some grist for consideration, [url=http://slantsix.org/articles/Josh_Carb_Article.htm]here,[/url] [url=http://slantsix.org/articles/combustion-chamber/sl6-combustion-chamber.htm]here,[/url] and [url=http://slantsix.org/articles/supersix/article.htm]here[/url] which I suspect you have already read.
Author:  1930 [ Wed Feb 12, 2014 6:53 am ]
Post subject: 
Author:  Wvbuzzmaster [ Wed Feb 12, 2014 7:20 am ]
Post subject: 
Wjajr,

I appreciate the recap on basic principle, and the links. I had actually seen and read two already, but the one about cylinder heads was the one I missed and now understand enough to belive that I should look for a 1968-up head to have rebuilt for my engine rebuild. Not that there is anything wrong with the original 1966 head. But with the newer head that is not original to the car I could get a bigger chunk sliced off to boost compression and not feel so bad lol. Not to say I wont take some off the block too, but I will favor the head for added slicing.
Author:  Wvbuzzmaster [ Thu Feb 13, 2014 1:31 pm ]
Post subject: 
Now for technical questions regarding the 1968-74 cylinder heads. When did they switch from flat top pistons to the dished pistons? I plan to use the flat top pistons in my 1966 block with the 68-74 head and the 72-up stock cam. The engine only has around 110-120k miles and if the bottom end looks good I may only hone with new pistons and rods. I want to have the head rebuilt with stock valves, hardened seats, clean off the flashing, and chop it down (.050 or .060). I don't want to chop the block down if I dont have to, espesially if it doesn't need to go to the machine shop at all. The most I would chop it if need be would be to make up for thicker head gasket (.020). I probably wont hit the magic 8:1 DCR, but it will at least come up a little. If anyone wants to do the math to see where it could be, that's fine. But I am more interested in the logistics of the valves and pistons, as I don't want to find I have interference later.

I want to have a rebuilt head ready to bolt on before I even tear it down next winter.
Author:  DusterIdiot [ Thu Feb 13, 2014 3:03 pm ]
Post subject:  What are you smokin?
Quote:
When did they switch from flat top pistons to the dished pistons?
Flat top pistons were OEM all years 1960-1987, only in the exports and the 1980's/cast crank engines could get the dished piston option(in those it;'s listed as the low compression part, typically for trucks)...all replacement pistons are flat tops.
Quote:
But I am more interested in the logistics of the valves and pistons, as I don't want to find I have interference later.
You must only believe what V-8 guys tell you, with the piston in the hole .175 and a .050 cut on a 1974 head (54cc-aout 7cc=47 cc...leaves about 5 cc left before the head is almost not useable of warped)...with a stockish lift (.420-.440 lift), the valve at max lift is still 3/8-1/2" from the piston at the worst timing chain degree/dot matching goof up...if it's all degreed, you will have almost 1/2-3/4" of clearance between the intake valve and the piston face as they chase each other during the intake event...this engine is so "loose" that you can almost drop a 3/8" nut into the intake and have it spit out the exhaust if it's stock compression... :lol:

You only worry about valve collisions if you are building an 11:1 or better engine or a long rod with a high lift cam....

-D.Idiot
Author:  Wvbuzzmaster [ Thu Feb 13, 2014 3:39 pm ]
Post subject: 
Thanks for the confirmation. I only ask to double check my work before I have a problem. So is .050 all I want to take off the head to keep room for it to be trued up once more in the year 2060? Lol

I guess the next question I would begin to have is would it be better to get the head myself and attempt to find someone I can trust to rebuild it? Or, since I don't have a head, try to buy one already rebuilt and ready to go?

Would anyone here have a 1968-74 head they want to sell that is rebuilt and ready to go?
Author:  Reed [ Thu Feb 13, 2014 3:47 pm ]
Post subject:  Re: What are you smokin?
Quote:
this engine is so "loose" that you can almost drop a 3/8" nut into the intake and have it spit out the exhaust if it's stock compression... :lol:
It is funny you mention that. Years ago, back when i first started working on slant sixes, I was running a stock 68 225 with a mid 70s head in a 1976 Volare. The car ran beautifully and then all of a sudden ran like crap and was missing on one cylinder. I chased ignition, timing, and carb diagnoses for a few weeks and then finally pulled the valve cover. Lo and behold the intake valve on the #3 cylinder was stuck open. It wouldn't move with the engine running.

I pulled the head and discovered that somehow a nut, about a 3/8 size, had made its way down the intake tract and had gotten lodged between the head and the back of the intake valve. I removed the nut, bolted it back together, and all was well again. No damage to the piston, head, or valve.

The surprising things were (a) how the nut got in there since I hadn't had the carb off for months; (b) how the valve didn't hit the piston; and © how nothing was damaged.

True story.

My point is that like DI said there is a lot of room between the valves and the piston on a stock motor.
Author:  slantvaliant [ Fri Feb 14, 2014 7:20 am ]
Post subject:  Late to the party ...
Back to the original question, the main gain I'm looking forward to in my long-delayed Super Six swap is ... retiring that worn-out Carter BBS. :wink:

It's really showing its age. Just a "new" BBS would help, I'm sure, but another barrel shouldn't hurt.
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