MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Need Replacement Cam Suggestions

Hey Folks -

I am going to replace the cam in my 1971 GK series 1800 MGB engine. The tappets and cam were worn.

I am not interested in a "hot" cam, but wondered what replacement suggestions the group might have. Should I buy the Moss cam that covers 1965 - 1980 MGBs - this is $219.00.

I could go for a slightly modified cam - but welcoem your input and advice.

Thanks.


I am not making any modifications to the engine - other than the cam and a lightened flywheel.

Jeff

Jeff,

I would suggest using the standard grind cam, either from Moss or someone else, so long as it is made from a new blank and not a regrind. When I rebuilt the engine in my 71 BGT, that was Peter Burgess' recommendation. He supplied a stock grind cam from Piper.

You might want to go to 18V style tappets and pushrods while you're at it. Much lighter than the older style tappets. If you do that, spend the money for the uprated ones that are hardness and dimension tested. Too soft a tappet will ruin the cam lobe quickly.

Paul K

Jeff,

I've always been a novice in working on my 69B, which I've owned for 27 years. But last year, I rebuilt the engine, and it runs again.
During the rebuild, I found my camshaft and tappets scarred. Figured I would replace tappets and not worry about the cam until a machine shop owner said he had one he could sell for $90. Maybe it was refurbished, but it was in great shape.
Another friend has a smorgasbord of MG parts, and I would have gotten the cam from him. But the machine shop turned my crankshaft, so I bought the cam from there.
If you'd like contact numbers, let me know.
Mike Kaylor

Jeff-
I'd suggest a Piper BP270 camshaft if you want to perk up the engine by about 10 HP. It's a mild street camshaft for those who prefer tractability and reliability. Unlike some camshafts that have long duration timing, it does not require large amounts of compression to compensate for poor volumetric efficiency at low engine speeds; thus it is less apt to produce detonation and is less sensitive to small variations in ignition timing. Its high volumetric efficiency at low engine speeds will give a smooth idle with excellent throttle response and power right up to 6,000 RPM with a stock configuration cylinder head and up to 6,400 RPM and yet more power across the entire powerband when used with fully ported heads. Best of all, you can retain the option of using your standard ignition curve and avoid the worst of the excessive side thrust loads on the valve stems that are produced by more radical camshaft lobe profiles on the tappets and lobes of the camshaft as it uses only 12% more lift than a stock camshaft. You will, however, need to either use stronger valve springs to handle the greater inertia loads resulting from the more rapid openings of the valves or, preferably, lighten the reciprocating mass of the valvetrain to reduce the inertia loads. In the interests of long-term durability, decreasing the reciprocating mass of the valvetrain is the preferred approach to the problem.
Peter Burgess offers the Piper BP270 camshaft with additional lubricating passages in its helically cut drive gears for providing supplemental lubrication in order to reduce wear. These specially modified camshafts are not regrinds. They are made from new billets, thus providing a larger heel diameter than that of a regrind. While this feature allows the use of gentler ramps which will reduce stress at the interface of the domed end of the tappet and that of the lobe of the camshaft, the rotational speed of the tappet is increased, making an oiling hole in the sidewall of the tappet a wise precaution against accelerated wear. They also have provision for the mechanical drive mechanism of the early MGB engines and those of the MGA.
Steve S.

I have to disagree with Steve S and instead suggest that you go with the stock early style camshaft. The Piper is definitely a high quality cam and probably does everything that Steve S and Piper says it will, but for a stock unmodified engine I don't feel it is ideal.

My reasoning is based on the flow capabilities of the stock engine and also on where that "10 HP" happens in the RPM band. Additionally, while Steve's comments are probably correct in regards to compression ratio "sensitivity", for the Piper cam to be used to it's fullest an increase in compression ratio WILL be in order.

In short, I'd agree with Paul K's post to the fullest. The stock cam Moss is currently selling is a quality early style piece and other parts suppliers are also selling the same cam.

Sean
Sean Brown

I am with Sean - Piper actually claim 12 bhp increase with the BPP270 but I would take that with a heavy pinch of salt.

The standard 88G303 cam is still an excellent cam for a standard engine.

The Indian camshafts made to that spec are very good value for money.
Chris at Octarine Services

Hey Guys -

Thank you all so much for the excellent information. I have been on the road for work and am just now reading the responses. I appreciate the time you all have devoted to the question.

I am somewhat conflicted. I have never been overly interested in modifying my MGs...due primarily to my lack of funds and my feeling that I have been happy with standard performance. As I reach middle age - with thinning hair - at 44... I have started thinking about jazzing up the B and A just a little.

Midlife crisis I guess!

A modified cam is very tempting.. but should I have the head ported and balanced and so forth...larger exhaust and the new cam and lightened flywheel.... one thing leads to another .......

I'll run through all of this as I am cleaning all the oily goop off my engine as I get it ready to paint.

Thanks again guys!

Jeff
Jeff

When I rebuilt my engine I looked at this too. I just went for the standard cam. Mine was a US engine with the low compression pistons. Since I needed new pistons and had to have it bored out +20 anyway I used the high compression UK style pistons (or rather normal compression ones). The only other mods I have done are fit K&N air filters and a pertronix thing to the dizzy. Car still isn't on the road though so I am not sure what it drives like! You are right about one thing leading to another. I did have mine all balanced and was careful to make sure my CC volumes in the head were matched and the head didn't have any burrs but that was about all. Just simple things. Iwant it to run as well as can be done with the existing parts rather than going down the track of having to buy lots of expensive fancy ones!
Simon Jansen

Really, the early stock MGB cam is not a terrible hindrance to the performance of the car, they are really quite good. What most aftermarket cams do for an MGB engine is shift the powerband up the RPM range. You need to look at where you want the RPM range to be, and also where the associated components of the engine will provide their best performance within that same RPM range.

It makes little sense to make an engine which will provide good power above 4,000 RPM if you shift at 3,800, and this is not at all uncommon to see.

Additionally, it makes little sense to put a cam into the engine that increases the theoretical RPM range of the engine, if the head, carbs, manifold and distributor are designed and tuned to the old, lower RPM range.

If you want to increase the performance of the engine, you need to look at the specific components which are the biggest hindrance and then rectify them to compliment the rest of the engine package.

For a '71, I'd start with the head, then do the carbs, then the distributor and finally consider the inlet and exhaust systems. Only after doing ALL these things would I ever consider going to a different camshaft.

That's the way we do it anyway, it's the old "plan your work and work your plan" approach and it's very rewarding vs other, less methodical methods.

For what it's worth, dyno testing has shown the street performance Crane cam (sold also by Moss) will gain about 4 HP above 4,000 RPM and lose about 2-3 HP below it and these results are typical to most cams of this nature.

Sean
Sean Brown

The 270 cam will add power to the otherwise stock B engine. "any" other cam will add power to the 74 and later smog engines.

Changing the ignition vacuum advance and mechanical advance curve to put more advance in early will be helpful with a "hotter" cam, as there is less combustion pressure at lower rpms with a mod cam.

I'm not sure how much additional lift the suggested cam offers. The higher lift cams often need heavier duty valve springs. The stock dual valve springs will probably do up to at least 5500 rpms. A set of different needles in the carbs can richen up the mixture at full throttle and help power as well.

Looking at a good exhaust system will make a difference again at hi rpms although the stock cast iron dual system is pretty good.

road gas mileage will probably increase with a mild modified cam. Around town will probably be worse mileage.

With a Kent 270 cam I noticed a distinct bump in power at around 2500 rpm. Below that the power was less than stock. It's sort of fun to feel the cam "come on"

Barry

Barry Parkinson

Jeff-
You asked for a camshaft that could be used without having to make further extensive modifications to the engine. For that the Piper 270 is ideal, being about as "hot" as you can go within the limits that you've imposed. You should also install the stronger valve springs that Piper offers to go with it. To answer the questions posed in your second posting, yes, having the head reworked is a good idea and will help develop the potential offered by a hotter camshaft. Balancing the engine will smooth it out, that can and should wait until you're ready to rebuild the engine. A Big Bore exhaust system will offer little more with a Piper 270 camshaft. Having approximately a 30% greater cross section than a 1 3/4" diameter system, the Big Bore system is actually intended for use on larger bore engines (1868cc or larger) or smaller-bore engines fitted with flowed heads and hot camshafts such as the Piper BP285. It seems to be particularly beneficial when used on engines that are tuned to produce 125 HP or more. When fitted to smaller bore engines with Original Equipment camshafts it will result in a bit more high-RPM power at the expense of some tractability at low engine speeds. This is due to the approximately a 30% greater cross section of the exhaust system reducing exhaust gas velocity, which in turn reduces scavenging effect in the combustion chambers at low engine speeds and thus increases "Pumping Losses". In addition, radiant heat from the tubular steel of the header is much greater, exposing the air in the engine compartment, the intake manifold and carburetors, and the fuel system to more heat, thus reducing fuel/air charge density and hence reducing power output. Jet-Hot coating of such headers is therefore highly recommended. On a very mildly tuned engine simply removing the front muffler (silencer) and replacing it with a length of tubing often suffices. It will then be noted that the exhaust note becomes deeper. This is because the function of the middle muffler (silencer) is to dampen bass note frequencies, while that of the rear one is to dampen the higher frequencies that give the exhaust a rasping tenor.
Steve S.

Barry-
The Original Equipment camshaft produces a valve lift of a mere .3645" with the Original Equipment rocker arm ratio. A Piper 270 camshaft produces a valve lift of .405” with the Original Equipment rocker arm ratio.
Steve S.

This thread was discussed between 05/07/2006 and 16/07/2006

MG MGB Technical index

This thread is from the archive. The Live MG MGB Technical BBS is active now.