MGB & GT Forum

Just listed at ebay.co/uk is a brand new Brown & Gammons HRG Derrington cylinder head with SU and Weber manifolds, item #126456837166. I tried to buy it but the seller will only post within the UK. These aren't perfectly bolt on, but close. If you aren't capable of doing your own head work I recommend taking it to Peter Burgess who did the development work on these heads. One thing I found on mine is the valve spring recesses needed to be milled .1" lower to avoid valve spring binding with .435" valve lift.

This sold to someone in the UK, May 1st.

Silas



Edited 1 time(s). Last edit at 2024-05-01 08:20 AM by SilasW.

Good find Silas!

I should think that for those in the know, purchase it and have the vendor post it to Peter B shop. Peter will do his magic and when completed he will post to US or Canada. I have sent him two cylinder heads over my long BMC cars stewardship (s) and always a pleasure to deal with him

B

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Life's most persistent and urgent question is, "What are you doing for others?"

Any MGB head, cross flow or factory will experience coil bind around the above number, at that lift level, one needs to get a better valve spring, the uprated valve spring will handle valve lifts above .500". Alot of folks will make the mistake of using stock dual spring with vavle lift numbers over .400" and that is where one gets into trouble. Most of the popular street performance cam will net around .400" valve lift with stock roocke, but put a high lift set of roacke on it and now if the same valve springs are used, you are in the danger zone. Coil bind is some you won't to avoid, and destroy your valvetrain.

Also, people need to realize valve lift numbers are established by simple but flawed math, rocker ratio x the camshaft lobe lift, this is a theoretical number that does not exist in reality. See as cam lobe lift increases rocker ratio drops, it is just simple physics. Here an example on the race car I have a cam that has .340" lobe lift and Harland Sharp 1:625 ratio rocker arms. With a lot of work making the exact thickness of pedestal shims, and using adjustable test push rods, and establishing the push rod length that net the high est lift, I ended up with a rocker ratio of 1:59,and trust me when I say that was as good as it gets, which needed me .525" valve lift with lash set, lots of time numbers are quote with no valve lash includiuen because it higher number, AKA, marketing. The average MGB with street performance cam and stock rocker net about .400" which equates to about 1:35 rocker ratio which is a drop from stock of the factory rocker ratio quoted at 1:45, which they don't always meet. However, at the end of the day you are still netting valve lift gains vs stock cams.

A D9 cam has cam lobe lift quoted at .295" cam lift, if you the flawed math that nets .427 lift with stick rocker arms, but trust me when I say you can't get there. First off valve lash will reduce that number by whatever it is, most are around .015"-.016", then once you factor in the rocker ratio for gross valve lift, the rocker arm ratio loss from a higher lift cam, the stock rocker ratio drops to more like 1:35, which is .398" then once you reduce the valve lash more like around .375" valve lift. This is still a nice gain over stock, which is somewhere around .350" valve lift. A few like Adrian have modded stock rocker arm to get more lift, and found success, but I doubt most of you if you did do this would notice much difference in how the car drives, but for the person trying to maximize everything than add up all the small gains and you have a larger gain. Many time people will minimize these mods or that mod, but if one gets caught up in that then you can leave a good 10-15% on the table, if such a thing is important to you. I see it all the time, person X want X number of HP, but is not willing to do the work it takes to get there. I mean how many of you building engine, even checked your assembled valve lift, I am sure that is very small percentage of people.

You hear a lot of "hogwash" here on the forum. "Higher lift will only net you more power at higher rpms", LOL. Anyone who ever spent any time on a flow bench knows one thing for sure most gains happen well before max valve lift and as one reachs max lift then gains are way smaller. So think about what a better cam does, two thing over stock, lift the valve opens more, and stays open longer, and yes indeed most of that happens well before max lift, in fact the greatest gains are in the mid lift areas, not at the max lift.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com



Edited 1 time(s). Last edit at 2024-04-30 02:37 PM by Speedracer.

Bruce,

Excellent idea. I hadn't thought of that. I may just try that.

Hap,

You don't know how truly anal I am. First I checked 2 sets of rockers (16 in all) in the same position and recorded the lift each gave and stamped numbers on them (they fell between .435 and .420). I used the four with the highest lift on the inlet valves and the next four highest on the exhaust valves. After the engine was fully assembled and lash set, I recorded opening degree, full lift degree and closing degree on all 8 valves. This was on a factory AEH770 cam and you know how much variance the factory cams have (sloppy is being kind). Luckily, I'd used a vernier cam sprocket so I could easily split the difference among all 8 valves. If you time the cam just on the #1 valve you're just guessing on the other 7. Recently produced cams should be better than original factory cams but you never know until you check. It took me more than half a day to accomplish all this.

Silas

OH I can imagine how anal you are, I raced to win, I know that disease very well.

Cam grinding on a typical cam grinder, which in many ways is like a key cutting machine will always vary a slight amount, but not a significant amount, I would say .001-.003" on cam lobe lift is more than acceptable, same for lobe center line, so not enough to make a difference you would ever be able to notice. Our engines are old school, for sure, but no engine, even F1 race engine is perfect. One of the most innovative things that ever happen in computer controlled engines was the computer being able to feed each cylinder independently the amount of fuel and ignition timing it needs, as none of them with be the same. I actually met the guy who developed and worked on that for Ford, I want to see his dyno, and got a lesson on that as a bonus. Something I learned in machine tool and die school is every job has a tolerance range, and you try your best to live in that range. You can't make something imperfect perfect, but you try your best to get in a tolerable range. So I commend you for checking all 8, and all we are really doing is looking for something out of the range. Another thing worth noting and I had to deal with with some really smart folks, many of them engineers, is when you get down to precision measuring, part of inaccuracy lies in the person measuring. There is the crnakshaft only machine shop in my area, that is really the tightest measuring we do, tenths of thousands of inch, and two seasoned veterans who run the place can consistently read a tenth or so off form each other, that is what I call the human tolerance range. One might own mic, can read mic, but they need to be able to read the same number repeatably, say 7 out of 10 times and even then the difference may only be a single tenth. Long story short, even smartest man has to develop "feel" and feel can't be taught by others, it has to be self developed through experience. So you really just looking for something out of ange, not slightly off, slightly off is the norm, but we are still talking tight tolerances.

With SCCA limited prep and all the required stock parts, finding 8 rocker arms that were exactly alike, was impossible, can't be done, but you look for the 8 that were as close to the same as you can get. Very few national racers were ever willing to go the distance on that, while others were seeking perfection, when what was really happening was a tolerence range.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com



Edited 2 time(s). Last edit at 2024-04-30 02:35 PM by Speedracer.

What is with all the negative votes? This sounds like a very informative post.

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I would never join any club, that would have me as a member. - G. Marx

Some forum lurkers have personal vendettas against certain people. It's childish and stupid behavior. I expect to see some neg votes for this post.




Edited 1 time(s). Last edit at 2024-04-30 04:32 PM by filospinato.

What is with all the negative votes? This sounds like a very informative post.
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Thanks, I try to give information based on actual experience. It's probably these guys, haters gonna hate.

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Hap Waldrop
Acme Speed Shop
864-370-3000
Website: www.acmespeedshop.com
hapwaldrop@acmespeedshop.com



Edited 2 time(s). Last edit at 2024-04-30 07:01 PM by Speedracer.

This listing sold to someone in the UK before I could arrange for the seller to send it to Peter Burgess as Bruce suggested. Hopefully the buyer will let Peter do his magic and get good use from it.

Silas

Hap-
Some people lack the technical knowledge to understand the significance of your postings, so for them your posts are "unhelpful". So they down-vote them. Pity.