• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

powertune techniques

Share this page

NutmegCT

NutmegCT

Great Pumpkin
Bronze
Offline
In his "How to Power Tune MGB 4 Cylinder Engines", Peter Burgess gives many recipes for increasing bhp. Some are simple (use K&N filters over WalMart varieties), others way complex and expensive (a crossflow cylinder head - a cool $800). Hey - you can even add the Moss supercharger for only $3000! Burgess also gives seven areas which can be tweaked (or sledge hammered ...) to gain power.

1. cylinder head modification
2. air filters
3. camshaft mods
4. exhaust mods
5. ignnition system
6. carburetion
7. dyno tuning
and I would add #8 - weight reduction

I'm looking to add a bit of road bhp - not for racing or sprints, just for keeping pace with those semi's on the Interstates.

Which areas do forum members actually implement?

Was this discussed in an earlier forum thread?

Newbie Tom
(rated 99.44% free of avatars and gremlins)
 
I have few modifications to my own engine, but the only mods I have personally witnessed and can vouch for are air filters, camshaft and exhaust. The cylinder head is a major improvement once reworked but it will be expensive. Personally I plan to do #1 - #4 on that list in addition to what little I've already done (skimmed block, Peco lower exhaust). May add a supercharger later on but still undecided.
 
[ QUOTE ]
In his "How to Power Tune MGB 4 Cylinder Engines", Peter Burgess gives many recipes for increasing bhp. Some are simple (use K&N filters over WalMart varieties), others way complex and expensive (a crossflow cylinder head - a cool $800). Hey - you can even add the Moss supercharger for only $3000! Burgess also gives seven areas which can be tweaked (or sledge hammered ...) to gain power.

1. cylinder head modification
2. air filters
3. camshaft mods
4. exhaust mods
5. ignition system
6. carburetion
7. dyno tuning
and I would add #8 - weight reduction

I'm looking to add a bit of road bhp - not for racing or sprints, just for keeping pace with those semi's on the Interstates.
Which areas do forum members actually implement?
Was this discussed in an earlier forum thread?
Newbie Tom
(rated 99.44% free of avatars and gremlins)

[/ QUOTE ]
Hi Tom,
I'm sure that Burgess must have stressed that the engine is a system of parts which must all be coordinated together when modified. To get maximum benefit, they must all be implemented.

Not a whole lot can be gained without modifying the cylinder head first. Larger ports are not necessarily better. The shape of the ports & areas on both sides of the valve seats are most important. This needs to be determined by someone with experience on your particular engine. I haven't seen the Burgess book. Maybe he gives port shape & size information. Port velocity in the right places is far more important than sheer port size. In fact over porting can turn an engine into a real dog.

Air filters can help a little. Better exhaust can help a little. Cams can help a little or hurt a lot. Carburetion can help a little. Better ignition will help if the other modifications cause a need for it. Dyno tuning will only help a little if fuel mixtures & ignition timing are quite a bit off. It is a good way to find out where you're at after a series of modifications.

With a coordinated set of modifications, the whole combination will help a lot. These benefits can only be realized if the engine is in top mechanical condition to start with. In fact, the engine will not stay together long if it isn't mechanically up to the added stresses imposed by the power increases.

All of these modifications, with the exception of higher compression, or supercharging, will move the power band higher in the rev range & reduce low rpm torque somewhat.

Sometimes, simply a good overhaul of a worn engine, can increase power to a very noticeable extent. This would be the time to increase compression ratio by using higher compression pistons instead of milling the head which can create it's own set of problems.

I'll leave it up to those with "real experience" on your particular engine to give further advice on specific details. I'm sure you will get some good responses. However you can't violate the above principals very much & have real success.
D
 
Tom,

I see you have a '76 MGB. If you still have the stock ZS carburettor that will need to go. Your engine stock is probably producing 65-70 hp at the flywheel. Peter's book which I have states the 75-80 MGBs produce 64hp at the wheels, but that would be with the SUs which the Home Market(UK) still had.

Boring the engine to the next allowable size is recommended. If the cylinder walls are in good shape 20 thousands would be a good overbore size. Remember that the difference between 20 and 40 thousands is 2 sheets of paper.

While not knowing your experience with SU's or Weber's I'd say the Weber is much easier to set up for someone with little Mechanical know-how. The twin SUs are by far the best all around carburetor for the MGB engine.

Porting the cylinder head is the first place to start when rebuilding the engine for a significance increase in horsepower. It is very crucial that you find a shop that knows MGB cylinder heads. Some shops to think about are Mike & Sean Brown at Seven Shop British (Oregon), Tom Bedenbaugh at Import and Sports (Memphis,TN). These shops will be able to get the most out of your cylinder head. With standard valves an increase at the flywheel will be 20 hp. Using Rim-Flo valves will get you up to 30 hp.

I'd recommend a new camshaft and specifically the Crane Cams 342-0010. An almost "Fast Road" cam it is made from a block of steel, refered to as a Billet cam. This is how the original cams for our engines were made and will last 100,000 miles. Regrind cams, which most of the aftermarket companies sell can last a few minutes to 50-75,000 miles. Make sure to get their Chilled iron lifters to go with the cam or it will wear out the stock lifters.

Exhaust systems will only give you 5 hp max so you can choose which one soots your taste (Loudness). Peco and ANSA systems are great.

K&N filters do work and you will see an increase of 3-5 hp at the wheels when using them. If you end up running SUs they will need a richer needle (AAA).

I'd highly recommend an electronic ignition system from Pertronix. They can be bought on the net for as low as $60.

Other parts that you might want to look into but are not neccesary are a Double Row timing chain and an adjustable cam sprocket.

The last option would be OVERDRIVE if you don't already have one. They really let the car cruise easier on the interstate.

Tonight I had my '74 MGB out for a evening ride. On one deserted stretch of road I had the car up to 6300 rpm in 3rd gear. I was going about 85 mph. I shifted gears when i felt the valves starting to float ! This in the first time I've pushed the car that far past redline. My engine is built like the the one in Peter's book that puts out 87-90 hp at the wheels. /ubbthreads/images/graemlins/hammer.gif /ubbthreads/images/graemlins/driving.gif /ubbthreads/images/graemlins/patriot.gif
 
David, just a question. Are you saying that the switch to K&N filters, alone, mandates the use of AAA needles with SU's? I removed the stock air cleaners and housings and installed the K&N's recently on my '71 B and have experienced backfiring through the filters. I was searching for other sources of trouble, never thought about new needles.

Frazier
 
Thanks, David. I'm in touch with Joe. No mention of AAA needles in Moss, etc.

Frazier
 
Back
Top