Modifications for the 1500

Because this page is fairly lengthy use the below table to drop to a specific item if you desire.

First lets start with some basic facts about the standard 1500 engine. It has the following specs

• Number of cylinders 4 in line
• Bore of cylinders 2.9 in (73.7 mm)
• Stroke of crankshaft 3.44 in (87.5mm)
• Capacity 91 cubic in (1493 cc)
• Compression ratio 7.5:1 (1976 - 9.0:1)
• Maximum power 53 b.h.p. SAE net @ 5000 rpm USA Version/British 71 b.h.p. Din @ 5500
• Maximum torque 830 lbf/in @ 2500 rpm

Realizing the USA stock 1500 only had 53 b.h.p. post 1977 until the end of production as British Leyand attempted to meet stricter US emission regulations the idea of switching from the stock concave pistons back to the original British flat piston setup immediately jumped out at me as a possible quick upgrade. Just doing this produces 71 b.h.p. Din @ 5500 and is well within the tolerances of the 1500 engine. Something I have in mind to do over the next year or two. However for now I am focusing on what else I can do without pulling the engine out to maximize performance. One useful resource is the following article Spitfire Engine Guide v1.4 which provides greater detail in how one can improve the 1500. It describes the various stages of performance enhancements and how to create them. Based upon this article and others I decided I will be doing the following: Add Exhaust Headers (done), flat pistons (future), improved intake manifold (done), a SU HIF-6 carb setup (done but need proper setup) and a better air filter(this year).

NOTE: When Upgrading the engine the following should be taken into consideration: a Spitfire engine suitable for easy road use can be modified to produce a maximum of about 55>60% more power than standard. There is an established safe mechanical ceiling well known and exceeding it places your engine in peril.

Here is what one can realistically expect to see at the flywheel if you have a well built and carefully assembled engine. For a 1300 & 1500 engines: (the TORQUE will be lower for the 1300 but Bhp will be very similar due to a higher Rpm limit on the 1300s).

The Carburetor

Carburetor Conversion is one that individuals first decide upon. For me it was attempting to adapt the HIF-6 SU carb to the 1500. The choice is personal in my opinion and telling another individual that one carb is better then the another often leads to heated arguments. Whatever direction you go in you will need to learn more about the Carburetors themselves to get the best performance.

My decision to go with the HIF-6 was ass backwards which is not something new to me. I should have read up first before deciding upon the HIF-6 setup but for only $55 I felt I couldn't pass it up and wanted a challenge anyway's.

There are three major players in the USA: The Weber, the Zenith Stromberg and the SU carb. All 3 are of fine quality and perform equally as well however each has its own niche from what I have read. The "DCOE side draft Weber" is more for highly modified engines, while the SU and ZS seem better for all around road use unless modified from what I have read. The choice of which carb you go for as stated is personal however and peoples opinions run strong over which is better. For myself I liked the looks of the SU carb, one can get a used one much cheaper then a Weber DCOE and the SU certainly meets all the needs I will ever have. The SU HIF series is the most modern design with the fuel bowl built under the carb itself along with other improvement features. In the end however when deciding on a carb remember that a bigger size is not always the best practice. The practice of going bigger is all very well, but it can have drastic effects on how well your engine performs over the broad spectrum of its use.

Stock US Carb: The stock carb for the USA 1500 is a single 1.5 inch Zenith Stromberg. Why British Motors switched over to the ZS verses using a 1.5 inch SU carb I don't know but they did. In regards to selection of what size? With engine modifications anywhere from a 1 1/2 to 1 3/4 inch carb is a good choice. The HIF-6 is a 1 3/4 size and with correct needle size and springs I would be able to effect my engine performance over the broad spectrum during its various stages of upgrading. The below table shows possible selection choices for 4 cylinder single carb engines. This is taken from the "How to Build & Power Tune SU Carburetors by Des Hammill" which I highly recommend.

Also allowing better breathing is critical. The use of improved air filters such as the K&N model number = 222-985 is suggested.

The Purpose of the Carb is to introduce the proper mixture of fuel and air into the engine so it can turn heat into mechanical energy to propel the midget down the road. To achieve maximum economy or power, or combination of both, the two parts (fuel and oxygen) need adding in a certain ratio. Years of development and tests have resulted in certain well-defined limits as to which is relevant where. The carb is designed to complete this duty with efficiency given its mechanical/cost limitations. Manufacturers have carefully considered the carb chosen for each engine application, of which size plays a big part. For a brief history of the SU carb click here.

General Information & Design of the HIF-6 SU Carb

Benefits of the HIF vs the older H and HS model

The Integral float = the 'IF' in the new type number HIF. The previous H and HS type carbs with their side-mounted remote float bowls worked fine until used in racing where serious cornering speeds generated enough G-forces to lean-out the fuel mixture. The remedy was to fit a spacer between the float lid and float bowl to raise the fuel level held in it. OK when running, but at idle and rest, fuel would bubble out of the jet - causing bore washing, poor pick-up, and horrendously rich CO mixtures at idle! Fitting the float integral with the carb, directly below the jet hole (port/orifice), eliminated this problem.

Jet temperature compensation - This was first aired on HS types, and was known as the 'Wax-stat' type. To keep in line with emission control legislation and the need to improve fuel consumption figures, a device was needed to lean the fuel mixture off as fuel temperatures went up. Unfortunately the Wax-stat wasn't very efficient, and increased the likelihood of bending the already vulnerable jet further. The HIF type uses a bi-metal blade to raise and lower the jet as needed - it's construction and location making it a far superior design. Its technical application label is 'viscosity compensator'. This close control means that once correct fueling is established by needle selection, the mixture is maintained over a very wide operating temperature range. Consequently drivability is enhanced and emissions are kept within tighter limits during cold starting and warm-up period.

Cold-start enrichment - HS types used a cable-operated lever that both lowered the jet (gave a greater hole to needle profile ratio to allow greater fuel flow) and opened the butterfly slightly (necessary to prevent low speed stalling with over-rich mixture). Messy and not very well calibrated. Enrichment in the HIF is supplied by means of a separate fuel-path within the carb body between float chamber and constant depression area close to the jet hole. A rotary valve - effectively a long, plain-shanked screw with a slot in it, controls metering. Earlier example used a 'V' shaped groove, changed on the very latest ones to a rectangular groove to achieve better control through more accurate machining when manufactured - a feature that none of us would notice!

Ball bearing suction chambers - A plastic sleeve containing two rows of six small ball bearings were introduced to reduce friction to the absolute minimum in the piston/suction disc/damper rod assembly. The benefit is simply more rapid response to varying demands caused by opening/closing throttle positions. Again in an effort to provide ever closer fueling control.

CONS Vac pipe take-off: There's always something to spoil the party! On some HIF carbs, the vac take-off sighted just after the butterfly - that's between the butterfly and the carb to manifold mounting flange - has been eliminated. Instead, the engines these carbs are fitted to use a vac take off in the manifold. The reason for this is again wholly idle emissions orientated. The higher vacuum that exists in the manifold area can be used to pull more advance. Theoretically this will reduce emissions at idle. Unfortunately it's exposed to induction pulsing. In the A-series, this is UGLY. The pulsing and high manifold vacuum causes rough idling. Particularly where anything 'sportier' (ANYTHING) than a bog-stock-standard cam profile is used.

1. Port Descriptions
2. FUEL INLET PORT
3. FLOAT CHAMBER OVERFLOW/BREATHER
4. CRANKCASE BREATHER PIPE CONNECTION
5. FUEL MIXTURE ADJUSTMENT

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SU Carb Needle Selection: Part of the solution to a well performing engine is getting the proper SU needle installed or if unable to find one carefully making one. It's best to assemble some of the following items to assist you in making the correct selection. There are several software packages that makes comparison of needles very nice, a CO2 exhaust analyzer will be very helpful for fine tuning and the books listed will allow you to assemble a good knowledge of what it will take to make this successful. I will add more as I find them.

1. How To Build & Power Tune SU Carburetors by Des Hammill
2. Haynes Teckbook Weber Carburetor Manual by A K Legg, Don Peers, Robert Maddox & John Hayes
3. Web Based Comparison SU Needle Guide - FREE
4. WINSU Software - cost
5. Harbor Freight: Co2 Exhaust Analyzer #91978-0CZA for $160.00

In examining the SU needle I had gotten with the carb I found it labeled as "BAL". The needles have letters/numbers stamped along the base of the needle assembly. The "BAL" needle was cross reference to being used in a dual HIF-6 setup for a Volvo. This needle actually seemed to provide fairly good response except I found I had a significant problem with spark plugs foul during idle and the motor died above 65mph. The reason for the plugs fouling became apparent when I looked at a graph comparison of several different needles, including the "BAL". Almost all needles have the same diameter at points #1 and #2 on the needle. The reason for this is simple. It allows most engines to start without major fine tuning occurring first. Once ignition is obtained fine tuning could then occur.

NOTE: Rarely can an engine be started if the needle is flush with the main jet. It is almost always necessary to lower. See tuning section]. On the "BAL" the thinner diameter allows it to run richer then the typical diameters and therefore caused fouling of the plugs during idle:

How Does the Needle Work? You can think of the needle as a tampered piece of soft metal running thickest at the top points and tapering to ever thinner diameters to the very end of the needle. The needle is held in place in a piston that moves up and down into an orificus called a jet. The jet is in a semi fixed position while the needle moves up and down as the piston is raised or lowered based upon the amount of vacuum created by the engine. As the engine revs higher it produces greater suction and in turn raises the piston still higher thus pulling out the needle. As the needle is pulled out, the needle becomes thinner and more fuel can be drawn up between the needle and jet into the carb. This is a basic explanation but greater details can be found else where if desired.

Needles Information: There are two SU carb needle types. Fixed and spring loaded. Fixed are for earlier models = H and HD. The spring loaded are found on the newer model SU carbs= HS and HIF. The fitted needle position for all SUs is basically the same: the shoulder of the needle should be flush the bottom edge edge of the piston surface. working range of SU needles in each type of SU Carb is as follows:

1. 1 1/4in SU up to 9th measuring point
2. 1 1/2in SU up to 11th measuring point
3. 1 3/4in SU up to 12tho measuring point
4. 1 7/8in SU up to 14th measuring point
5. 2in SU up to 15th measuring point

SU Piston Springs: A piston spring combined with the weight of the aluminum piston provides the necessary downward force to maintain essentially a constant pressure loss(depression) at the throat of the carburetor. The springs are initially color coded with paint for identification. The paint disappears with time. Common piston springs are as follows.

Carb Tuning Sequence: The top of the main jet is the effective point from which the fuel is metered, not the bridge of the carburettor.

As mentioned most needles have the same point diameters at #1 & #2 and for all practical purposes #2 is where idle occurs. Needles are typically 0.001in smaller than the main jet diameter. For one to get the car started so further refinements can be made. But how does one determine where to begin. For me exploring the listing in the Haynes Teckbook Weber Carburetor Manual for similar sized engines running a HIF-6 or HS-6 was helpful. There weren't many listed so I had to add the HS-6 as well, which is simple an older model but is the same size. I also spoke with Joe Curto who recommended the "BEL" to start with. The realization may come that a pre-fabricated needle just won't meet the needs of a modified engine. If that is the case one will have to modify the needle by carefully filing it. I recommended reading "How To Build & Power Tune SU Carburetors by Des Hammill" The power tuning book is actually an easy read. Take the time to read it prior to making the change to see if you are up to making the change. It will guide you through that process. One interesting finding has been that as I have asked for what size needle 1500cc midget users who have converted to a HIF-6 setup on Forums I have yet to get a reply to my inquiries. This makes me think few have had success in this conversion.

Below is a selection list I found in the Hayes Appendix for SU Carbs:

Bottom line is its a matter of doing a lot of hunting around trying to select the best needle combo. The above gives you an approximate idea of which needles to start with and one comes to a conclusion that you end up in a ballpark area and will then have to perhaps do some customizing to get maxim performance.

The needle I was going to try was the "BAS" with a Red Spring. This is one of the needles listed above and is considerable more rich then the "BEL", that Joe Curto had suggested trying. The "BEL" I had problems with from the very start. I had to jet it to the max to get it to even idle. I did recently get a message from a user who told me he is running the "BCE" and that he gets pretty good performance. In fact by order of lean to richer it goes: The "BEL", then "BAS", then BAL and finally the "BCE". I really have had little to compare a well running midget to since I went from a stromberg with problems to the HIF-6 setup until just recently when I decided to purchase a dual HS4 setup and converted the HIF-6 to that. What I can tell you is that there was a significant difference in performance. The HIF-6 running a BEL is a really old dog that looks nice when sitting around but don't expect it to go very far or fast, with a BAL it was able to go but not very fast so I am quickly drawing an educated guess here that perhaps the even richer needle setup of the BCE might be the direction to go in. At this point I have decided to stick with the dual HS4 setup. It's fun and it's summer and time to just get out and drive.

I replaced the "BAL" needle with the "BEL" one. At idle I couldn't get the motor to run without choke or I had to have the idle screw turned down (faster rpm"rpm's) so it won't stall. The CO2 analyzer showed a CO of <.6%. NOT GOOD. I screwed the mixture screw as far as I could and managed to get the CO2 up go 1.5%. Way, way to lean. Switching back to the "BAL" I was running around 1.6% at base line and adjusted the mixture screw to between 2 and 2.5%. Idles better, etc.

Distributor Information: Careful review and assurance that your distributor is in peak condition is another important part of the process that can make or break this experience. Spend a little time making sure you've tuned the distributor, etc. This is a nice article which should assist you in understanding how distributors function. Tuning the Lucas Distributor

More in depth coverage can be obtained from going to Ignition System on the 1500

Dual HS-4 Carb Setup:

If you go to add the dual setup to your midget there will be some minor structure modifications. Unlike the British midget the USA midget had an extra cross member added in the engine bay that makes it necessary to cut a small triangle shaped section in the passenger foot well to accommodate the setup. Otherwise you will have the SU's filters sticking the frame of the car.

FOR GREATER DETAILS ON CARB SELECTION - CLICK HERE

Fuel Injection

The Intake Manifold:

There are a variety of manifolds on the market, generally cast in aluminium-alloy. Few understand why this is, generally believing it’s mainly down to ease of production and is certainly one of the major considerations. Aluminium conducts heat faster than iron, the benefits of this being two-fold. As far as maximum power is concerned, the cooler the inlet charge, the better. Aluminium’s ability to dissipate heat faster keeps the intake charge down in comparison to an iron one. For economy, quicker warm up is essential, again aluminium's rapid conduction of heat gets it up to running temperature quicker - hence Rover’s introduction of an aluminium-alloy manifold on the MG Metro engine to utilise these principles. The mistake they made was making it slightly too big in the ports.

The engine's power potential can not be fully realized if the internal size of the intake manifold is like the old one. The Inlet intake manifolds must be thought of as extensions of the cylinder head inlet port. As a general rule, the way to check to see whether the size of the inlet manifold runners is reasonable for the particular engine is to measure the diameters of the cylinder head inlet ports and make the inlet manifold runners at least at least 0.040-0.080inches larger in diameter. Take this measurement do so by measuring 1.5in into the port.

The easiest way to check a round manifold runner's individual diameter is to take an old engine value and turn it into a gauge. The diameter of the head of he value is machined to he required diameter and he stem of the value into the runner.

The only measurements I could find are for the mini. I can't tell you how they compare to the mg midget but perhaps there may be some relationship. Things to look for are: It should fit easily, take a standard air-cleaner box and hold the carb high enough to avoid bulkhead/speedo cable fouling. The ports should taper nicely from manifold to carb mounting face and have a reasonable cast finish. There should be provision for water heating. As for port sizing, for road use on practically all engines 1.35” at the manifold face is good for the mini. For big engines, i.e. 1400cc plus or 1380cc where maximum top end power is wanted, 1.4” at the manifold face is needed.

Exhaust:

A good exhaust header you will want to look at a 4 to 2 to 1 build. The standard mg midget has an exhaust size of 1 1/2" diameter. Going larger allows less back pressure so the engine will breath more efficiently.

Installing A Oil Feed Kit

One of the weaknesses of the 1500 Triumph motor is that it does not get enough oil to the values. A simple correction process can be had for around $50. It's called an "oil feed kit" and depending upon which one you get it is installed in the basic same way. One end is connected to a oil channel located at the rear corner of engine and the other either attaches to the oil pressure inlet if the kit has a dual channel connection or to one of the lower oil feed channels located along the left side of the motor. There are two bolts located just below the level of the oil filter. One just to the right of the oil filter and one just to the right of the distributor. Just remove the bolt and install. It's that simple.

Adding An Oiler Cooler:

While this will not directly lower the coolant temperature it will address one of the significantly weaknesses of the 1500. Even with moderate hard use the oil temp can be sent soaring past 100 centigrade-excessively thinning the oil and dropping the oil pressure to the point where bearings will suffer. For normal driving a 13 row is adequate. Also consider adding a oil thermostat. This will help prevent the opposite, too cool of an oil temp from developing. One other weak area on the 1500 is inadequate oil supply to the values. Remember these engines were NOT designed for modern day motorway use and the sustained high speeds.

When adding an oil cooler consider adding in addition to the cooler itself an oil thermostat as well. Running too cool of an oil temp can also harm your engine. The oil cooler can be mounted using the mounting location used on the 1275. The holes can be easily found which are just in front of the radiator on the bottom sheet metal. I had some difficulty getting the hoses to sit well and added a 90 degree elbow that swiveled to allow flexibility.

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Oil Filters to use: Pure One filter, the number model is PL10017, if you're interested. Other filters that might be used are

1. AC-Delco PF-53 (will work on all models of Spit.), PF-13 - requires an adapter
2. Carquest 85084 (said to be a Wix product)
3. Castrol PH922A (all Fram numbers should be same on Castrol filters)
4. Champion D102 (though not recommended)
5. Crossland 573, 595
6. Fram PH2825, PH922A, PH966B, PH16 -may be too large for later 1500's w/air pump
7. Fram PH8A (large can) using the oil filter adapter from MkI 1147 engines, (or non airpump 1500's?)
8. Motorcraft FL-2005, FL-1 (large- non-Air pump Spits only)
9. NAPA 551312 , Gold-1521, Gold 1374
10. Purolator #L10017, PER-1
11. UNIPART GFE150, GFE119
12. WIX 51084

Crankshaft Thrust Bearing Washers: A known weakness on the 1500 are the crankshaft thrust bearing washers. This link shows what to look for and what can happen. Click Here

Air Filters:

Some consideration to air filters should be made at this time as well. Increasing the amount of air flowing into the engine will effect the needle selection as well. The air filter housing used in the British dual setup will not fit in the american version. It hits the frame. This leaves you with the option of using the standard air filters without the housing or switching over to an aftermarket brand. Example - K& N air fitlers for instance.

The exact model of K&N Filters is K&N # RU-4410 from what I am being told. These filters come with a large band-type clamp that fits over the neck which fits perfectly over the stock air horn of the carb.

To create the setup as outlined by Hap Waldrop of Acme Speed Shop, you need to get the back plate adaptor for the HS stock carbs. These can be found from an MGB using the HS dual setup or ordered new for about $35 each. See image below to get the exact item you will need.

Hap writes: "Well I finished my new air filters, I had to make one small modification to the stock velocity stack, but other than that it was pretty much bolt on. For what it's worth the filter and velocity stake now is totally unobstructed by bolts, etc...I just counter bored the stock holes to accept a socket head allen bolt so it would be a flush mount, also included is a photo of the velocity stack mounted."

"The filters have a rubber flange on the mounting side, so they slide over the velocity stacks which measures roughly 3.475" and the RU-4410 is 3.5" at the rubber flange, it snugs right over it like it belonged there, and then the suppiled clamps keep them secured, about a easy as you would want it to get".

I have read in a couple of articles that using the larger tapered filters actually caused a decrease in performance when measured on a rolling road. This contradicts what many have written. It has to do with the air turbulence created by the introduction of large amounts of air. These authors suggest using the pancake style verses the tapered cone shape. I really don't know what is best and would think unless you are racing either one would be fine.