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Methods for increasing compression

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the big valve heads are certainly still sought after. However, I was reading about a project on https://www.flowspeed.com where they documented the tuning of 3 heads for people from another message board. Of the 3 heads, I believe 2 were "Big valve" heads and one of them was cracked beyond repair.

Optionally, one can obtain one of those "alloy" heads and have the big valves fitted to it. Of course, that route is probably more costly, and well, an obvious non-stock item. Though, I personally wouldn't think that should matter if your performance mod'ing a head.
 
The '72-74 heads (2923 with a big L cast on the back face) are known to crack. If that's the head you really have to have, I'd consider an alloy one. I seem to remember Sean Brown recommending the same.
 
Just curious: How ya gonna get THAT past the emissions nazis?
 
Racers most of the time look for the early pre smog heads, you can put the big intakes in them as well. On the subject of cutting a MGB head for compression, sure you can do it. David Anton says all uncut MGB heads can be decked .040" without any real problems for street use, I normally cut atleast .020" on even stockish rebuilds, it's cheap performance.
 
DrEntropy said:
Just curious: How ya gonna get THAT past the emissions nazis?
Click to expand...

Eh, increased air flow doesn't necessarily mean increased emissions. If I'm not mistaken, part of the emissions equation is whether or not you are achieving 'complete combustion', and I'm working from the assumption that if I increase the compression it'll be easier to make a more complete burn. My thoughts are along the lines of making the engine a more 'efficient' air pump, and with better efficiency you'll get more power, and better economy. Of course, if I wanna tune for minimum emissions on the road, I'll more than likely need some time on a rolling dyno; like wise for optimum power /bcforum/images/%%GRAEMLIN_URL%%/wink.gif

The emissions nazi's don't look ~inside~ the engine; what they can't see won't hurt /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif. Every time I've been to visit them, they've only compared what I had under the hood to the drawing in their book. Also, if'n I do an alloy head, I just need to make sure I have the air rail ports put in and I'll be golden from the inspectors POV.

I seriously doubt I'd be able to pull the wool over the inspectors eyes if I have a huge honking supercharge hanging off the side of the engine. If'n I were to get one, I do believe that I'd have to implement other plans of a devious nature to pass my bi-annual nazi inspection.
 
LISTEN TO HAP!!
 
They got all amped up here 'cause the cat converter on my Alfa didn't "look" like a converter. Told me to go to the local "dealer" and get a letter to the effect that indeed it was fitted. Told 'em there WERE no dealers in the US. "Go to a muffler shop then!"

sheesh.

I wrote it on letterhead from the shop. /bcforum/images/%%GRAEMLIN_URL%%/devilgrin.gif

Maroons. They didn't seem to notice the signature onna letter matched the one on my paperwork.

feh.
 
heh... the emissions place I took mine to didn't even look for the cat... /bcforum/images/%%GRAEMLIN_URL%%/smirk.gif

Hap - would you happen to know the ratio between shaving the head and increase in compression? Or would a good head shop know how much to deck if I tell them the 'stock' compression and what I want to go up to?
 
Bit more involved, Rob. Chambers should be shaped and CC'd, piston shape taken into account... more factors than just trimming a given amount from the head.

Waitaminnit! You KNOW that! /bcforum/images/%%GRAEMLIN_URL%%/shocked.gif
 
d'oh! momentary lapse in thinking! that's my defense and I'm sticking to it!
 
TROLL!
 
There are NO emissions tests here in the boondocks, where I live in Utah. Some Counties here do have emission testing. In those Counties they hook your Exaust pipe up to the "Sniffer" {Exaust Gas Anayliser} If the "Sniffer" says go, you get a certificate. If Not you get a rejection slip and 14 days to comply. Most of the people running the "SNIFFER" wouldn`t know a turbo from a beer can. As far as H.C. engines go ..... been there done that, in fact I have a facsimily there of in my M.H.. A Mild 400+ H.P. 460 Cu In. Ford. Not better economy but much more power for luging that monster M.H. up a grade. A lot of $ later, from Just over 200 H.P to 400 H.P. tho. How much power do you want and how much money do you have .... anything is possible. I can tell you this .... the expected economy will go right out your tailpipe unless you can resist the temptation to "Feel the surge" and "Hear those Pipes sing"
Take a better man than me! /bcforum/images/%%GRAEMLIN_URL%%/lol.gif
 
erm... yeah... not so much ~expecting~ better economy, because i ~know~ if it's there I'll try to use it every chance i get. Heck, I already trying to use it all the time and there's nearly nothing to use!
 
A supercharger is cheap horsepower. No mechanical issues to worry about like you have from high-lift cams, noisy soild skirt pistons, rough idle, etc.

The only problem to contend with is heat if your boost levels are too high. Other than that it's an EZ add-on.
 
eh, for the cam, I'm thinking maybe a Piper 270. This is a daily driver that likes going up the mountain roads. Not a daily driver that doubles as a track car.
 
Why not get another engine & slowly build it the way you want while you continue driving...you could then look for an OE "X" head, etc.
 
that would be included in the 'long term' goal. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif
 
Sorry to hi-jack Nunyas...

I checked today. YES! I have the big valve head! It has the "18" 7 "L" cast into the back, and is not drilled for a water choke.
 
I just saw the thread and I do have some thoughts. I have a SC on a motor built for a SC and it is awesome. If you want to go there, do it!! I'd suggest to find another motor, preferably by scrapping a rust bucket or 2 and get the best parts of the lot, because they are expensive if you go buying them. Second, if you want to simply up the compression, you can have the head decked, but you need to have shorter push rods. My sons TR6 had this done to it. they are very low compression and it did make a world of difference. Really though, horsepower is money and a willingness to modify. Decking the motor will probably give you the most HP for the money. Good luck.
 
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