by Lorne M. Goldman January 1997

Suggestions for More Power


By 1965, The Morgan Company was aware that the power output of its four cylinder engine was too small for the demands of many customers. The Company's waiting list had shrunk to two years.

The problem was to find just the right power plant. Triumph's solution had been to fit a great straight-six into the TR-5 but this engine was too high to fit into a Morgan. Lotus's twin-cam was too fragile and the Ford V-6 was too heavy.

In 1966, as a by-product of an unsuccessful take-over feeler from Rover, Peter Morgan was offered a crack at a new Rover purchase from Buick, a lightweight aluminium V8 called the 215 or  the Jetfire which (in 1961-62) had been standard in the Buick Skylark and Oldsmobile F-85 (though each had different heads, intakes and exhaust arrangements).

Maurice Owen, a race engineer, was engaged to experiment with the engine's possibilities for Morgan and worked with drawings until he found an old Buick engine to fiddle with. The engine was literally jammed into a Plus 4 and was rolling in early 1967. After some Leyland/Rover problems, the Plus 8 went into production in 1968 with 20 cars delivered. As a reference point for power, an unmodified 4/4 of that time created about 75bhp. The first Plus 8's (1968 to 1972) put out an unmodified 160.5bhp or 170hp on the American standard, a significant boost of power.

N.B. BHP is a measurement of the actual usable power (not calculated power) measured at the output shaft (usually the crankshaft) rather than at the drive shaft or the wheels. Thus none of the auxiliaries (gearbox, generator, alternator, differential, water pump, etc.) are attached. It is called the brake horsepower because the shaft power is usually measured by an absorption dynamometer or "brake." This is not the brake on the vehicle's wheels but a testing device applied to the shaft. This instrument is applied to stop or absorb the rotation of the output shaft and returns a value.  This standard is considered a far more reliable indication of effective horsepower than the US HP.

In January of 1974, the compression was reduced in stages to meet the first early European emissions requirements and the power dropped to 143 bhp. At the end of 1976, the successor engine to first the Rover V8 was introduced called the SD1 (Specialist Division 1) and power increased again (12bhp) and reliability increased mightily.

In 1982 Stromberg carburettors replaced the SU's as Rover again struggled to meet European emissions standards (calling for automatic chokes controlled by water temperature) while still maintaining the power. The Strombergs did the trick and horsepower held at 155bhp.

In 1984, Morgan offered a few new fuel-injected version of the high performance "Vitesse" SD1 engine as an option. The Vitesse engine, fitted with a new gearbox,  was designed by Rover to be a competition n motor.  Power jumped dramatically on the first delivered Morgan Vitesse EFI model produced without any compromise to the car saving a cut away of the bonnet hinge to accommodate the plenum chamber of the engine. This Plus 8, smaller and significantly lighter than today's version, with the tubular manifolds and twin exhaust of the day (and Morgan's new and first rack and pinion steering a standard), left the factory unmodified with an amazing 205bhp and an estimated 248lbft. of torque at 4000 rpm.. It was capable of  0 to 60mph in 5.15 seconds. A limited number of these optional Vitesse EFIs were produced in the period from September 1984 to early 1985 before the weight when up, the exhaust system became a single pipe and engines were altered.

All Plus 8's were fuel- injected after January, 1987.

The power of the Plus 8's began to drop again in 1985 (190.4 bhp) and the torque tumbled to 198 lbft. with the introduction of more emission safeguards embodied in the addition of catalytic converters, the return to a single from dual exhaust. Structural changes gradually increased the weight from 1884lbs to 2068lbs. Power fell slowly but continually to 162bhp until the production in June of 1990 of a re-bored version of the V8 increasing capacity from 3538cc to 3946cc. The horsepower climbed back up to near 1985 standards and the torque was even better at lower revolutions such that Autocar (May 1991) observed that the 1991 Plus 8 (0-60 in 6.1 sec.) showed its rump to a Porsche Turbo at any speed up to 80mph.

Presently, the Morgan website still lists its 3.9 litre engine as producing 185bhp though this figure is dated and 190.3 bhp is  a more accurate figure. (The U.S 4.0 Plus 8 produces about 186.7bhp.) The site also shows the 4.6 litre version but does not indicate performance specifications or details but the Morgan dealers list the 4.6's power at 194.4bhp with 260ft/lb of torque. This too is probably inaccurate and an appeal to Land Rover directly gives more plausible figures of 218bhp and 300 ft/lb.s of torque.
N.B. I have written a supplement to this article including a power-to-weight analysis in response to questions on this article.

N.B. Please note this article does not apply to Plus 8's made for the U.S. market during the
period from 1976 to 1996. Please refer to an analysis entitled  Made in the U.S.A (1971 to 1996).

J.E. Engineering, an advance British group specializing in the Rover V8 performance engine has recently produced a 4.5 litre based on the same engine block that reputably produces the better part of 300 horsepower and Rpi sells a 5.2 litre model that can be camshaft adjusted to produce greater torque or horsepower according to your needs. The dyno claims that the engine produces 334 bhp at 5500 rpm.

N.B. As a side note here, there has been much said about the frightening mysteries of fuel injection. It is bunk. Fuel injection systems were clouded with rumours by the manufacturers wishing you to service at their dealers. The Plus 8 standard ECU (Electronic Control Unit) has an inbuilt adjustment factor of 25%.

The Rover Vitesse / Buick Jetfire are amazing lumps. With mild attention, they easily produce the magic one-for-one solution or one horsepower per pound weight. For this  reason, they are a popular engine swap choice among hot rodders and kitcar builders. They collect myths and fancy like few others. I will try to distinguish some from fact from fiction.


There is no argument that an improved exhaust system is good for the car. The engine will breathe better and engine temperatures will drop. As the factory system installed is very restrictive, a free flowing change is a fine adjunct to other major alterations to the engine. A stainless or treated system is also   prettier and maintenance free.

However, exhaust is exhaust. It is not a prime ingredient to combustion and happens after rather than before that fact. Aside from mild adjustments to back pressure, the horsepower claims of exhaust system sellers are simply ridiculous. You will be lucky to obtain an extra 2-3% power from any exhaust system only but it will allow you to effect other changes that will produce much more power than that. A twin big bore system (2 diameter) is a start and will go well with flow-thru silencers (1976 style). The sound is simply incredible.

N.B. Remove your resonators. They are too far away from the heat to properly clean themselves so they rust quickly, block the airflow, reduce power and sound lousy. Please beware of the local emission requirements if you choose to throw away your catalytic converters and CHANGE THE RESISTOR (check out the Plus 8 page on "Cats").

Considering the price of a good full exhaust system from manifolds to tailpipe, assume you will pay about $800.00 per horsepower with the aesthetics unconsidered.

There is one codicil to this section that is the difference between a single and dual exhaust system. For those of you unfortunate to have a Morgan with a single exhaust system. Cars tested before and after a switch from a small bore single system with manifolds to a dual large bore system with tubular heddars have shown remarkable power increases far beyond the minor percentages indicated above.


This is the best bargain for your horsepower dollar. The standard paper filters, or even worse, foam filters restrict airflow and thusly the engine. Both dirty up over time causing further prejudice to your power. K&Ns will clog over time as well, but that merely makes them filter better until you clean and re-treat them with their oil again. I do mine once a year.

Off hand, I cannot think of a stock Plus 8 air filter, for carb or EFI,  that does much for these engines. 

K&N produce high-capacity, low restriction washable filters that fit without any modification. (Buy the full K&N kit with cleaner and oil will need them) However, their Part No E-2350, wrongly recommended by dealers for ALL EFI Plus 8s, is a disaster for the 3.9s and GEMS though adequate for the fappers (1984-1990) The cost is about $65.00 and they can be ordered through any auto supply specialist. You can assume a 4-6% power increase for three minutes of work on the Flapper +8s.  But they create a bad blockage for the Hotwires and GEMS. If you DO get it right, (read on) the power imporvements can be substantial..but this fiddling is more complicated than it looks.  I highly recommend..if it is merely a filter swap you want to do with stock 3.9s/4.0s/4.6s, that you stick with the original paper filters..or do what I did below.  Please remember, I dyno test everything.
WATCHPOINT I FOR HOTWIRE PLUS 8s: Please note that the Hotwire engine is very sensitive to greater airflow. The stock fuel map was made too "lean" as is and more air can make that worse. For that reason, any improvement with a Hotwire must begin with better fueling. (new chip  hopefully an Optimax or Tornado)

WATCHPOINT 2 FOR HOTWIRE PLUS 8s: The K&N commonly sold to fit the Hotwire trumpet air filter holder is a disaster.  It works barely well enough for the earlier American-football black helmet used for the Flappers (pictured on the left) but is insane for the Hotwires (to the left). The same filter creates an air block/dam and gratly reduces bhp. I discovered this when I swapped out MY ugly football helmet for a pretty chromed trumpet from the Factory. The Flapper air filter holder has its inflow access from its side and, aside from cleaning or merely turning the filter so that the air enters a still clean part of the filter, it is a partial improvement over stock. But using the same filter in the Hotwire trumpet is nutty, but most owners and dealers do it without a thought. Pictures tell the story.

The internal holding plate of the trumpet blocks the airflow, forcing it to try to find a path in the tiny space between the circumference of the filter and the filter holder. In the main, the air comes rushing down the horn of the trumpet and slams into the filter holding plate...and the E-2350 K&N makes this worse. It also comes from the Factory improperly angled, as can be seen from the picture. 
and influences the resultant idle's steadiness aside from thinning the mixture which is sad as the stock air/fuel mixture already produces high heat. Even on my Flapper system, I noted a significant dyno difference (I tune my Plus 8 on a dyno). On the other hand, the football helmet is super ugly! Lastly, Hotwire air/fuel mixtures cannot be easily adjusted to compensate as can Flappers (with an adjustable fuel pressure gauge and/or the flapper tension spring inside its AFM.

WATCHPOINT 3: When I got very into experimenting with my Plus 8s, I called the UK and struck up a friendship with their technical design team for this area. I also spoke with other air induction experts. They all told me that a differenty sysdtem was not always a blessing. Seems the  quantity of air must be properly complimented by shaping the air correctly or that power and more importantly, torque, can be prejudiced unless the conduit can be "shaped" to enhance same and its steadiness. I confirmed their advice a number of times on a dyno. For example, attaching a large free flowing K&N type filter directly to the MAS/AFM can increase power while making its delivery unsteady and, in the case, of the 3.9 (which arrives with a too lean mixture) WAY TOO LEAN. (Plus 8s have been saved from the ravages of these over lean mixtures and other problems by the fact that their load is so light.) Additionally, suspended cone filters produce an unsteady flow as well.

I like them. But they do not shape the air flow as well as the right air filter holder and conduit. And, on an enhanced Plus 8, after a certain point of tuning and capacity, they make (at least for me) an unacceptable induction howl. Admittedly, this occured on my Canadian Plus 8, a lightened Factory one-off designed by yours truly with the Works and many Morgan celebrati and powered by a tuned 4.8 LR V8 (increased capacity from Omega pistons) and increased air flow due to Super Flares trumpets and a larger Bosch L-Jetronic AFM from Jaguar. I found the induction noise embarrassing..though the power & torque did go up while both became unsteady. I do like engine rumble and exhaust tone..but those, on my car, are controllable by my throttle foot.

Interestingly, I tried the cone filter on my UK Plus 8..which is set up a bit differently. It is a lower (8.5) comptression 4.6, also with greater airflow and on a fast road cam and Jag AFM that puts out significantly more power than stock but 42 bhp less than the CDN car. The
induction noise disappeared. Image to the right. For the holding bracket, I merely had on made in polished stainless steel. The image was posted to eMog in 2005 and there have been many who copied the idea since.

I finally found a filter for CDN car that touched all the right bases and that the dynometer saluted at. :)  I have to thank the Factory Parts department in Malvern, who tempted me with a chromed trumpet they had!!!! With the right inverted K&N cone filter, my problems with Canadian car were resolved and

1. It produces as much power as the cone filter
2. It has a shaped flow and a much steadier power/torque
3. It fits into the original 3.9 Trumpet filter holder and looks like it belongs on a Morgan.
4. It allows for both indirect AND direct airflow and elimionates the air dam, not creating the problems that a huge filter directly on the conduit (without a filter box).

Avoid forced air systems that pick up debris and force feed it to your engine. This might make sense for racers who retrict their Morgan usage to carefully prepared and cleaned race tracks, but make NO sense for a road-going Morgan. I have seen or opened up a fair number of Morgan engines and you would be appalled at their innards after a some time with a low intake. A racer's priority is to win. However, a mogger's priority is to have a car capable of meeting all conditions WITHOUT A RACER'S SUPPORT INFRASTRUCTURE A COUPLE OF HUNDRED METERS AWAY and surviving these conditions with aplomb. 


Another goodie! But you have to be careful. Dyno tests have shown a 12-16 bhp boost is possible by advancing the engine timing up to 4/5 degrees from the stock 6 BTC. 

The care comes in for three reasons.

A) You might have trouble with this timing with consistently hot weather ie. 95F+. So time will tell you the best advance.

B) You have to use premium gas (octane 93+ [aka 97/8 in Europe]) or better still octane boosted premium petrol;

C) Your emissions may increase which may cause a problem in annual testing jurisdictions.

The best way to try this is to increase the timing one point at a time and test drive the machine up a familar mild long slope in a higher gear (i.e.4th) after each adjustment. When the car starts to "ping" reduce one point and there you are!

Costs per horsepower are 0...only time and optionally the ongoing factor of premium gas and/or octane boosters.


Your ECU can be reprogrammed with a performance chip, a new fluel map. We have had great success with Mark Adams Optimax and Tornado chips for the 3.9 and his chips for the GEMS plus 8s are a life saver. These specialist chips deal with the mid-range power slump of the hotwire Plus 8s and improve gas mileage. For the GEMs, they solve a slew of issues. Power gains here are from 20-30  horsepower and costs of the performance chip are approximately $600.00 or $20-$30 per horsepower.


There are scores of other improvements to performance that are possible with this marvellous engine. There is, however, a Law of Diminishing Returns. Each extra horsepower costs more and presupposes other modifications or compromises. One should assume the maximum hp one can coax from and injected 3.5 or 3.9, while still being able to smoothly drive it to the pharmacy, is in the neighbourhood of 265 hp. A carburetted version can go as high 215 hp without sacrifice of a smooth idle.

There are three facts to consider. Firstly, full performance engines run well at mid and high revolutions and poorly at low. That type of power will not help you unless you are a racer. Secondly, most power adjustments are concurrent applications not cumulative. In other words, many power increasing modifications presume others will also be done so that you can assume a power gain from each but only in concert. Lastly, each improvement puts a strain on the whole system and a previously unnoticed weak area can "pop" up to give you headaches.

A quick overview of other changes;

Options here include a Mallory Unilite (NOT a Mallory Dual Point) with Vacuum Advance. See other parts of this Manual for full instructions. ALL Rover distributors deliver a degraded, inferior spark. A Mallory cures that.

The configuration of the Morgan front  end and the placement of the distributor make for water access into the distributor. Inevitably, this leads to rust within the distributor, a poorer spark, poorer combustion and trouble during damp conditions. All this leads people to believe that the Lucas distributor is the culprit. The solution is quite simple. Clean your distributor thoroughly and regularly. Be careful, as more than one RR owner has found the rotor arm stuck fast to the distributor shaft when trying to replace it during routine maintenance. Pulling up too hard on the rotor can break the plastic C-clip that holds the upper and lower parts of the distributor drive shaft together. If it is stuck, try hammering DOWN with a screwdriver or chisel and break it into pieces to get it off the shaft.

The stock leads are not great. Changing them to Magnecor "Blues" or "Blacks" will serve the power goal well.

On all distributors from 1976 to 1982 and from 1986 on,  the ignition amplifier module (on the outside of the distributor) can give trouble. This item converts the magnetic impulses from the distributor into a larger signal to fire the primary circuit in the ignition coil. Often, the heat build-up under the hood will eventually cause this amplifier module to fail intermittently, stalling the engine. The faulty unit can become so sensitive to temperature that even a minute or two of cooler air provided by opening the hood can get it working again.

This cute little item increases your fuel pressure when you are accelerating at a faster curve than stock and is adjustable as well..thereby effectively "reprogramming" the fueling on Flapper engines. With Hot Wire Sytsems , one still gets the acceleration boost and one can trim the pressure to correct parameters. As well, Hotfire systems are only closed loop until 3000 rpm. That means that after this point, the lambdas will not null out increased fueling. Set the pressure to 40-41lbs and see the difference.

For carb'ed models, try the Weber/Edelbrock 4 barrelled 500 CFM. This carb will fit into a Morgan using an Offenhauser "low rider" intake manifold. Some Plus 8s can fit the Edelbrock Performer intake. The Weber is easy to set up and easy to maintain, rejet and rebalance unlike the commonly used 4 barrelled Holly 390 CFM.
(The Holly venturi size is too small for a heavy breathing engine resulting in additional vacuum, which in turn confuses the vac secondary. Its design also forces you to spend too much time assembling and disassembling the thing to get it right. All to no end or a sacrifice in power in comparison to the better designed Weber.)

see the Offenhauser from Edelbrock above. All intake manifolds can also have the ports widened and polished for better airflow. See manual for that.

There are many made for this engine and each have advantages and disadvantages depending what you expect from your motor. Check out the lines of Oselli, Kent, Piper, Crane, J.E. Motors and Crower. (The writer prefers the Piper 270-272). Calculate 0-25 bhp depending on which of the "reasonable" camshafts you choose.

It is wise to be very careful with the choice you make here. It is not simply of decision of how much power you want but "where" you want it. A cam developing large amounts of power at high rev's are good for those of us who specialize in Autobahn  racing in a straight line with hands clutching the wheel and a crazed grin frozen on one's face for hours. On small country roads this same camshaft will perform poorly.

Install a duplex venier timing chain. (This is an eventual must anyway as the standard Rover chain stretches very badly over time.)

This can be done with seasoned 3.5 or the 3.9 all the way up 5.2 litres. However, if  you are going this far.. why not buy a new lower engine block at a much cheaper price? New 4.6 blocks, with their structural improvements and better oilways, can be had for 1500 USD  making stroking a less than ideal solution. The parts of the engines remain  interchangeable. The 4.6 can itself be modified to a capacity of 5.5L

The intake can be modified to take larger trumpets or one can use carbon fiber Super Flares trumpets.

There are many other possibilities. For those of you with a fascination for power or a yen for the "fastest" Morgan, I strongly suggest that you adopt a "buyer beware" attitude.  A good automobile is a well harmonized compromise of many parts. Also, never believe the claims of your "expert". No one knows the true performance of an engine without a proper dyno testing. If you have not done this,  your claims to horsepower are most likely wishful thinking.

Come to think of it though, there is nothing wrong with  wishful thinking.  Costs are nothing, installation time is negligible and horsepower gains are unlimited.

Should you wish further information, I would suggest you join the eMog Pub or email me .