Spitfire & GT6 Forum

1500 engine performance mods

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geithner Avatar
Hi Jeff-

Here are a few specifics that I hope help. I have a 1500 with the following mods, and I commute with it (~8000 miles a year--drive it when it's dry out) and occasionally autocross with it:

balanced internals
0.020" overbore (1514cc displacement) and flat-top pistons
9.6:1 compression
218139 "big inlet valve" head, shaved, 3-angle grind valves and seats, stainless steel valves
"B" cam (280 degree duration, 0.409" max valve lift)
V.549 dual valve springs
dual HS4 carbs w/ #7 needles
4-2-1 header and GT6 intermediate pipe w/ resonator and small straight-flow muffler
MegaJolt crank-fired Ford/Motorcraft-based ignition
ARP fasteners

I'm very happy with this. Spins freely up to 6500 (highly recommend balancing) and fells comfortable up there, but that's for the few times a year I autocross or when I feel like having fun on an on-ramp; I spend most of my time below 5500. An overdrive tranny is nice to have for a commuter.

I think the "B" profile cam is a good choice for the 1500 because it's a good mid-range profile and fits with the 1500's longer stroke characteristics (I had a stock 1500 cam reground with the "B" profile). I like the twin HS4s personally--easy to set-up and I like the elegant constant-depression design and I agree, they look "right" on a British lump. I've tried many needle combos, and with my compression, inlet valves, cam, ignition and exhaust, believe it or not, the #7's give the best response and don't run too rich; i.e., the engine spins right up to high rpm quickly without feeling starved or choked. From experience, I highly recommend a heat shield--anything to block the view of the carbs to the hot exhaust parts and reduce radiant heat transfer (and won't melt or burn) will help.

I have NOT tried a lighter flywheel on the 1500, but am curious about that. As you note, the 1500 crank is rather massive, but less rotating mass on a long lever arm would be nice to try.

I have a modified small-journal 1300 w/HS2s in a mk3 Spit, and I'm starting a modified 2-liter 6 project w/triple 40 DCOEs, but those are all different from the 1500 of course.

Hope this helps. I'll check out the MG board as you suggest.

Paul Geithner

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oldag98 Avatar
oldag98 Jeff and Brittany Brackenridge
Choctaw, Choctaw, Oklahoma, USA   USA
1969 MG Midget MkIII
1975 MG Midget Conversion
1976 MG Midget 1500 "Yellow One"
1977 MG Midget 1500 "Dunkirk"    & more
That is a nice website you have, Paul. I will be spending some time there in the coming days. Could you perhaps list from whence the above listed parts came? That would help me greatly in sourcing them for my 1500's.

90632D Avatar
90632D Fox Trapper
Various, USA   USA
I'll say I find your question far to vague to answer with specific recommendations. Do you want an engine producing 150 hp or one that idles? Does it matter if it's got torque to pull away from street lights nicely, or do you want racing power that only comes on at 5,000 rpm? Etc.

That said, there are some things I've done tried experienced and can comment on with regards to warming over a 1500. As well things I've seen others do.

Balance it. The whole reciprocating mass it very poorly balanced. Get it balanced and it will last longer and produce a bit more power (it's not wasted tossing around unbalanced parts). This is a good idea even for a street engine, as it will zip up past 4-5000 rpm in use.

Lighten it. From the flywheel to the excessive mass of the crank. The less mass you have to spin up the faster the engine will spin it up. The difference is appreciable. I've never had any trouble with idling or pulling away from stops because of lack of rotating mass.

Squish it. Higher compression means more power. True, you need to burn a higher octane gas. So you decide if you want to spend the money on the fuel. It's worth it to me, but not to all.

Shrink it. Turn the crank to fit the smaller diameter 1300 rods. Vizard, Kipping and others have done studies on this, as well run it. Reduces friction, reduces drag, reduces wear. All good things.

Stroke it. When you turn the crank down do it asymetrically and you can stroke the engine out to about 1700cc, as I recall. Kipping has done this. As I recall, the GT6 pistons work well with this modification.

Cam it. Fit the right one to your application. There is no one best cam. What cam has made me happiest of all the ones I've played with so far? The Isky ZM-66 I've got in one engine. That cam comes on nice! But there is no gentle idling either.

Port it. Generally not worthwhile, though it is the first thing most folks try wit ha grinder. The ports themselves aren't bad in stock form. Port matching generally gains one nothing. If you're building a real screamer, there is a good bit of meat in the heads for overall enlarging the ports quite appreciably. I sliced up a 1500 head just to see how meaty it is.

Bowl it. Now in the bowls, there's flow work that can make gains. Some very odd lumps and bumps and sharp edges that screw up flow. Work there instead of on the ports. But do it right, or you'll make things worse.

Valve it. As in a good valve job. 3 angle at least.

Rocker it. People love roller rockers. One of my engines came to me with them on it. Overkill for anything but the most extreme racing engine. But fun and not terribly expensive. Better, plug your stock rockers and redrill, giving more lift.

Zinc it. Ah, the terror of oils and EPA specs. It is a real problem, particularly with sharp ramped cams. So run good oil, like Gibbs, or even consider fabricating a roller lifter setup. It can be done. The more extreme your cam, the more you need to consider it.

Suck it. As in getting the air in. The Euro stock setup with a pair of HS4 SU carburetors is darn hard to beat for power, performance and economy. As in almost impossible. It will do it all with the right needles. Figuring out the needles can be an interesting experience. Folk love to genuflect to the side draft webber. Nifty, but expensive, and rarely setup right. But they look really cool. A dual set of DCOE will work better than the single, at the extreme. The single has problems with gasoline droplet seperation to the #1 and #4 cylinders. The ZS can be made to work well, but not as well as the SU. Interesting setup with a single 1-3/4" SU on certain ZS manifolds can yield very good results, as per John Kipping and a few others. I've built one, never run it. Fuel injection is also possible, as are motorcycle carburetors. Megasquirt has quite a following.

Blow it. The US spec 1500 exhaust manifold is terrible. Anything is an improvement, even a pacesetter header (which is a terrible header). Stahl is fantastic. Watch your collector shape more than pipe length, and quit worrying about equal lengths. Read some of Vizards studies on that. Don't neglect the rest of the system. The stock exhaust (sans cat) flows quite well for a stock or mild engine. Don't get lost in the mistaken thinking that noisy is stronger. Many do.

Spark it. The emissions distributor curve is lousy. Run an earlier distributor. Run a programable distributor (the 123 is pretty cheap), megajolt it.

Scrape it. Is your engine going to be screaming around the tracks at 6000 rpm and above quite regularly? A crankshaft scraper is possibly worthwhile. Oil ropes up remarkably. This sucks power from the wheels and doesn't help lubrication.

Undersize it. That stock alternator is big. So is the GM Delco many folk like to run. So is the stock 1500 crankshaft pulley. Go smaller. Less mass to spin, less mass to drag around.

Underdrive it. This works best with a screaming engine, not a street driven engine. But, no need to waste the power spining a water pump faster than it needs to go.

Disconnect it. No reason to spin things that don't need to be spun. From the air pump for emissions to the alternator. A clutch from an a/c compressor can make disconnecting things easy. But, almost no one does this, so it's pretty doubtful that it would really gain you much.

Lubricate it. Read the competition manual. Read Kas's first book. Then address the lubrication problems correctly. If you still go out and by an external oil line for the rockers you didn't read it correctly.

Cool it. More power is more heat. You'll need to deal with it.

MG it. As in bearings.

Pin it. Pin the thrust bearing. Consider the full circle unit from someone on the web (forgot who). The thrust bearing is a weak link. Treat it with care.

Clutch it. As in don't overclutch it. The American mindset is for massive clamping forces from the pressure plate. Those forces go right to the thrust bearing, wearing it out. Don't run a heavier pressure plate than is absolutely necessary. And almost always, the stock one is perfectly adequate to the job. Play with the disc instead.

Pan it. If you throw the car around on the track, you'll find yourself out of oil eventually. So widen the pan, install flappers, etc. All to keep the oil available to the pump, and therefore the engine.

Accept and understand it. When it's all said and done, you've got a punny little hunk of iron from England, built decades ago with then ancient thinking. After spending thousands of dollars to modify your Spitfire to an undriveable power house, you still don't have the power a stock Miata has. And the Miata idles and has air conditioning. So accept it. Accept the Spitfire for what it is.

Is there more that can be done? Sure there is. Carrillo rods, Honda pistons, custom heads, blowers, etc. As always, speed costs money, how fast can you afford to go?

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SpitfireBGT Avatar
SpitfireBGT Mike Soltez
Irwin, PA, USA   USA
If you want to go faster and improve handeling you could take the Colin Chapman approach. ADD LIGHTNESS. If it dosen't make the car faster take it off.

geithner Avatar
Thanks Jeff. My thing is putting together fun, reliable, useable street vehicles at reasonable cost that don't require constant and expensive attention. I'm not into racecars or garage queens, nor do I want to spend an inordinate amount of my time on cars--not that there's anything wrong with all that ;^) You asked about specifics and "a good engine building recipe I could replicate for my 1500's...Not for racing, just to bring them into the 21st Century and to get my little Midget screaming down the road." My point example of a system solution is one specific answer.

I've gotten most of my new parts from the following:

British Parts Northwest
Spit Bits
Mountjoy's Auto Shop (nearby British car shop)
APT in Riverside, CA
TS Imported Automotive (Ted Schumacher)

...and most of my used stuff from:

Crazy Rays-Hawkins Point (local salvage yard)
Team Triumph (a big "breaker" located in Ohio)

I've used others (like John Esposito's Quantumechanics for recon'd trannys) and I have a partial list of suppliers on one of my pages ( Don't forget the suspension (including wheels and tires) and brakes so you can make the most of more oomph and have fun tossing it around while enhancing safety too. Good luck and enjoy!

Paul Geithner

prisoner2019 Avatar
prisoner2019 John Petroviak
Milwaukee, WI, USA   USA
I haven't done too much for mine yet. I installed a dual carburetor setup, headers, and performance exhaust. Next Spring is my engine rebuild, looking to lighten the flywheel with that.

tktrain Avatar
tktrain Tom Kohlmeyer
Evansville, IN, USA   USA
OK, now I'm very intrigued, Fox Trapper mentions the small journal 1300 rods and offset grinding the crank to get a stroker with GT6 pistons. Would anyone have any specifics on this? I am desperately looking for a good source of info on journal diameters, deck heights,rod lengths, interchangeability of parts. Basically, internal engine dimensions and clearances. I'll buy a book if someone can point me in the right direction.

Thanks again for any assistance.

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geithner Avatar
Hey Tom-

Buy a good manual or two. The Haynes manual for the Spitfire has some of the info you are looking for (e.g., journal diameters, stroke), but not all (e.g., rod lengths, wrist pin to piston top distances). I don't have a Bentley or a factory manual, but maybe they have even more of the specs you are looking for. Other references include John Thomason's "Triumph Spitfire and GT6: A Guide to Originality" and Graham Robson's "Triumph Spitfire and GT6." I have some of Kastner's books and I don't recall what specs they have in them exactly, but there's some good info in them. You might consider picking up manuals for the GT6 and TR6 as well, since you may want to use parts from them, like GT6 or TR6 pistons. Also, check out the 1500 competition prep manual. It's brief, but has some stuff in it you may want to throw into the mix as you consider the various trade-offs and decide what to do. Have fun-

Paul Geithner

tktrain Avatar
tktrain Tom Kohlmeyer
Evansville, IN, USA   USA
I've gotten a Haynes Restoration manual, but I'm ordering the Haynes workshop manual as you suggest. I'm going to look into the factory books and order them as well. I guess I'm going to have to piece the information together for now. I'm so used to all the info being readily available on the domestic stuff that I guess I kind of took it for granted that the Brits would be the same way.

I really am interested in the stroker concept for the 1500. Especially since these aren't your typical high rev engines and stroke instantly means torque. Torque is king on the street.

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90632D Avatar
90632D Fox Trapper
Various, USA   USA
You can dig up some hearsay things about the stroker concept on the web by googling it. I talked to John Kipping himself about it, as he's the one who first told me of it. But that was some years ago.

The earlier 1300 engines had smaller diameter bores on the big end of the rods. And, correspondingly smaller sections on the crankshaft. The late 1300 and 1500 engines were made much larger. I've heard various stories about why this happened, I do not know which stories are true.

In any case, the techique is to get some early 1300 rods and bearings. Take them in hand with the crankshaft and go to a good machine shop and have the crankshaft turned down to the appropriate size for those bearings. Have it done offset, so you increase the stroke.

The piston recommendation, as I recall, was GT6. Again, as I recall this works nicely because it is a lower piston and just so happens to work well with the stroked 1500 crank, not popping out of the block, smashing against the valves. Again, no experience, and this is just recollection.

I have never run one of those engines. John told me his worked great. I don't dispute his words. I would have concern about stroking out a 3 bearing crank myself. But, if one were to behave with it, it should be just fine.

SpitfireBGT Avatar
SpitfireBGT Mike Soltez
Irwin, PA, USA   USA
You could ask Mr. Kastner and his followers here I think Kas goes by "Hicompression". I read it from time to time but I'm nowhere near intelligent enough to contribute to it.

tktrain Avatar
tktrain Tom Kohlmeyer
Evansville, IN, USA   USA
I just found the following post on the club triumph forums by a poster that goes by "slimboyfat" that was made back in July of this year. He says:

"Bore to standard TR6 piston size (and use standard TR6 pistons!). Offset grind crank to TR6 stroke (using small bearing rods), and you end up with 1660cc.

You have to compensate for large increase in compression by using one of the low compression California market heads. We were using the air injection type with the holes blocked off because they used to be cheap, and plentiful.

The 1660 in our Courier was probably the first ever of the breed as it was the engine we (John Kipping back then) developed the theory with back in the 80's. It's still going strong nearly 25 years later although it has had a few lay-ups over the years. We gave it a precautionary strip down a couple of years ago and the bearings (Vandervell) still had plenty of meat on them.

As an aside when the 1660 first went onto the road it had a Catalytic converter fitted, that used to confuse the MOT man!

At this point I would like to mention that we had nothing to do with the disastrous 'Sports' 1700's that were sold to unsuspecting Spitfire 1500 owners in the late 90's, early naughties. By that stage we had come to the conclusion that the 1660 is a fine old slogger that deserves to be in something that needs torque (that's why they powered out Couriers!). No way could it be described as 'sporting'. Treat it as such and expect a ventilated block. This was the experience of a goodly number of those poor unsuspecting Spitfire owners."

I think perhaps I need to go back to the Spit6 approach since the 1972 GT6 I have would make a great 2500! Hmmm, a 2500 would make a 1700 look slow even if it could stay together.

spitfire50 Avatar
spitfire50 Paul Mugford
Rochester, N.H., USA   USA
The 2500 has the advantage of a stock Triumph crank, but I don't think those who have used both would say it is as "lively" as a 2000. Then again it does have torque.
An issue with the 2500 is the crank doesn't fit in the 2000 oil pan (I think), and the 2500 pan hits the Spitfire steering rack. I seem to recall that judicious use of a hammer gets the 2500 pan in though.
Good luck,

cokerart Avatar
cokerart Bob Coker
Atlanta, Georgia, USA   USA
1973 Triumph GT6 MkIII "Spit-6 Or Dr. Frankenstein"
If I recall it correctly, the 2.5, with the same block as a GT6, will work in a Spitfire, but requires the shallower GT6 oil pan to fit. The oil pan, in turn, requires some judicious "persuasion" on the shallow end to accommodate the swing of the counterweights from the 2.5 crank.
The TR6 pistons are the same diameter as the GT6, but the wrist pin (Gudgeon) is higher up in the body of the piston, to allow for the longer throw within the same block.
The TR6 transmission may require (Someone confirm this) alteration to the frame in the area where the wishbone spine comes together. I think the GT6 diff will handle the torque of the TR6 if it is not wrung out, but who would have such a beast without pushing the envelope, just a little. I'm told Nissan and Subaru diffs (Very probably many others, as well) work well with a little fabrication.

tktrain Avatar
tktrain Tom Kohlmeyer
Evansville, IN, USA   USA
Thanks Bob and Paul. How about the GT6 transmission. I have one of those and the Spit transmission as well.

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