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-   -   Mac Shorty Header Comparison (http://www.focusfanatics.com/forum/showthread.php?t=310560)

79mgb 03-01-2013 09:56 AM

Mac Shorty Header Comparison
 
I decided to use a Mac shorty header on my build because it's very simple for my application and I should be able to see some gains when it's paired with a 2.25" exhaust (and no catalytic converter). I couldn't find any decent photos of it online so I decided to take some myself. This post isn't a rave review to over-glorify the Mac header but to simply compare an aftermarket shorty to the stock header. You can probably find similar specifications and quality on many other aftermarket headers and that's why I think this comparison is worthwhile for those who are interested in upgrading.

I was able to find a Mac header for an affordable price on eBay (Slightly more expensive than Pacesetter or OBX). It included a copper gasket and was finished with a polished ceramic coating. When I first pulled it out of the box, the ceramic coating looked a little hazy (probably due to some left over residue from the coating process) but some mothers aluminum polish was able to quickly clean it up to a better shine.

As you can see from the photos, the Mac header is a bit larger than the stock manifold. The Mac header's primaries have a 1.65" inner diameter while the stock is about 1.4" (It's been a while since I've measured the stock manifold so correct me if I'm wrong). The Mac header's welds appear to be good on the flanges, as well as the slip fits on the primaries.
http://25.media.tumblr.com/eb275e6b4...53to1_1280.jpg
http://25.media.tumblr.com/a4543bfe9...53to3_1280.jpg

The collector size on the Mac header has an inner diameter of 2.5", which is larger than the stock header by .25". The inner weld on the Mac is also not as profound as the stock header which may help with exhaust flow.
http://24.media.tumblr.com/658e39460...53to4_1280.jpg

The difference in the collector probably helps with flow the most. Ditching the clam shell style of the stock header is probably the biggest improvement for flow.
http://25.media.tumblr.com/d8c8ea342...53to6_1280.jpg
http://24.media.tumblr.com/50229fe39...53to5_1280.jpg

Overall, It looks like it will be a good performer. I hope this helps people who are interested in upgrading.

TerryB 03-01-2013 01:39 PM

Did you do the install yet ? I have an OBX shorty and I had a heck of a time trying to get to all the header bolts. I gave up. I do have a large assortment of tools. I tried evrything I had. I think it was some of the top bolts I had a problem with.

79mgb 03-01-2013 02:00 PM

I mocked it up to my cylinder head when I got it and didn't seem to run into any problems. Did you just have issues getting around the primary tubes?

My build is different than others on this forum since I'm building my engine and installing it in my MGB. I'll have pretty easy access to everything in the engine compartment. http://www.focusfanatics.com/forum/showthread.php?t=302371

TerryB 03-01-2013 02:12 PM

I think it was behind one of the primaries. I couldn't get any leverage to get one of the bolts started, and couldn't get a wrench near it either. The previous owner definitely got it done. I can see the marks on the flange from the bolts he used. Nice MGB ! My friend had a black on black back in the early '80's. And my brother had a MG Midget in the '70's. I've always liked them.

79mgb 03-01-2013 02:54 PM

Thanks! [cool] I really like the car so far.

As far as getting your OBX installed, I've read that getting the bolts started on focus headers can be a bit difficult but not impossible. I'd start a thread, ask for some pointers and reattempt installing them.

I'd highly recommend installing a high flow cat or ORP.

TerryB 03-01-2013 03:25 PM

Quote:

Originally Posted by 79mgb (Post 4615422)
Thanks! [cool] I really like the car so far.

As far as getting your OBX installed, I've read that getting the bolts started on focus headers can be a bit difficult but not impossible. I'd start a thread, ask for some pointers and reattempt installing them.

I'd highly recommend installing a high flow cat or ORP.

I already have the ORP. That's what I wanted. The shorty was part of the purchase. I just went outside and looked at the header. I can't picture which bolts were the problem. I know leaning over and trying to do it myself was frustrating. I tried the stock studs, bolts, and ARP header bolts. The weather has been crappy around here with no garage. I'll take another crack at it in the spring and have my son give me a hand. It's not essential, but I might as well use it now that I have it.
http://i89.photobucket.com/albums/k2...esCAT9XZG0.jpg

zetecDon 03-01-2013 06:06 PM

Installing these types of headers is always easier when the motor is out of the vehicle. TerryB did you take out the fans when you tried to get to the bolts on the stock manifold? I found I had a lot more room to work when the fan was removed. I had plenty of room to work once I removed the whole front end also lol. The one that is on the farthest right side underneath the power steering pump was the one I had the most trouble with.

TerryB 03-01-2013 06:16 PM

Yeah, fans were the first thing I did. I learned that with my 4-2-1 install. The usual trouble bolt is the far left ( from the front ). I think on my OBX, it was a top middle one. I put the stock one back on in no time at all. Like I posted above, I'll have my son help. I always forget to take pics, that would explain my troubles.


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