std block

[bob dunn]

i have a spare spit mk iv 1300 engine . what con it be bored out to ( also herald block) . just a thought  may be non std con rods and flywheel.

[bob dunn]

sorry lads is my question to broad or to complicated for those with a tecnical bent . what i am hoping for is an answer like . for an engine with more power and less response . put on a herald flywheel , bore out to two mill plus and put in dished pistons to increase the volume to 2L . gas flow the head and fit the next size up carbs. ( i just make this stuff up and it is not to be taken internally or to heart .) hello is there any one there , or should i just phone jigsaw.

[Deleted User]

it depends what you want from the engine really....do you want top end speed .. acceleration of the line .. a nice fast cruiser ..there are lots of mods ,boring oversize [up to +60]  ,lightening flywheel, and a raft of different cams that give power at different rev ranges
The list of mods is endless [only governed by the size of your wallet]  easier if you tell everyone what you want the engine to do then people can tell you how best and possibly cheapest to achieve it

[ghr630]

Standard GT6 2 litre pistons for 1340cc (I think). Cheap as chips s/h, light and strong just re-ring 'em.

[JohnD]

OK, you asked for it.
I think you're talking nonsense.
1300s get their performance by revving, not by increased capacity.  Fit bigger pistons and you will inhibit that.
And "dished pistons to increase the volume to 2L"   Dished pistons have no effect on capacity, and will reduce CR.

Oh!  You "just make this stuff up"?  
Sure!  Don't forget to have the bearing surfaces ceramic bonded and to fit water injection into the inlets.  You will definitely benefit from a large coloured strip down the side of the car, and blacked out windows, too.

John

[bodders1]

Bob

Leaving aside John's slightly grumpy reply, improving Spitfire performance is best taken in stages of increasing cost.  Going straight for the engine internals first will not give you a good result because it will be hampered by the Spitfire's inherent tendency towards asthma.

Step 1:  fix the breathing.  A good after-market tubular exhaust manifold and performance exhaust + K&N filters + richer needles

Once you have done this, you can then start to think about squeezing more go out of the engine.
The block does not respond well to radical over-boring, so you are basically stuck with standard bore sizes, going up to around +60.   A few years ago there were some "1700cc super sports" engines being marketed by an engine builder but I understand that they had one or two  reliability problems.

Step 2: Make sure that the bottom end is in good nick - get a regrind if necessary - and fit new bearing shells.  Then consider getting the crank, flywheel and clutch balanced.  As John rightly says, performance involves revving, so you need to get the rotating mass well balanced to stop it trying to shake itself apart.
You may want to get the flywheel lightened as part of this - it doesn't give you any more power, but lets the engine respond to throttle changes faster by reducing the inertia.  The downside is a poor idle and tendency to stall when trying to pull away gently.

Step 3: head modifications and different camshaft profiles.  Head mods begin with smoothing and polishing the ports with a die-grinder, skimming to raise compression (if necessary).   More radical head mods include large inlet valves, "triple grid" valve seats, re-shaped combustion chambers, etc..  Various tuning companies package up these mods as "stage 1", "stage 2", etc..  Not all suppliers agree on what constitutes a particular stage of tuning, so it is best to check what mods are included in a particular package.  Off the shelf camshafts come in increasing flavours of potency from standard through "fast road" to "full race".  it depends on how deep your pockets are.

step 4:  if you have gone for a wilder cam and head mods in step 3, then you will need to change your distributor for one with an advance curve matched to the camshaft.  This is something you can do yourself, using different advance springs, but you ideally need a rolling road to quantify the effects of your changes.  Also you will have to alter the carburation to match the increased demands of your engine.  If sticking with SUs, then richer needles and different weight springs will be needed, together with other mods such as removing the poppet valve from the throttle butterfly. plus you should make sure that the inlet manifold is matched to the ports on the cylinder head.  Eventually, the SUs will become the limiting factor and you should then look at side-draught carbs such as Weber or Dellorto.




I hope some of this is useful to you.

cheers
bodders

[bob dunn]

sorry to pull your legs men , but at least this has made me think about what i want . in the west of ireland most driving is 60 mph A road N17 Galway to Sligo and motorway Galway to dublin ( 2hrs) . acceleration is not the main worry  fast cruiseing is  so overdrive and does a herald flywheel sound silly . at the moment people on bikes can go quicker.

[JohnD]

Grumpy? No, tit-for-tat.
Well done Bob, you fooled them all.
'cept me, of course.
Who fooled them as well.

Pity it's not April yet.

John

[bob dunn]

they used to call my dad , devious dunn , they are still trying to find an adjective for me , i wish them luck .

[JohnD]

Dunn Down?

OutDunn?

John (not Donne)

[bob dunn]

there is a man in galway who will port polish and gas flow the head for a few hundred . i imagine i will need a new exhaust manifold and an o/d box . is there still a cow on the line?

[bob dunn]

once again sorry for pulling legs a little , the man in galway worked at jensen years ago mike wirakone   from cylon . i think i spelt his surname wrong. he is not cheap but when he is finished it is right . he set up the carbs and timing for me . the car now does 32mpg runs smoothly to ninety ticks over at 700rpm, its like a gold watch . this cost 50.00 euro. i will save that in petrol. my other car is a bmw 523 its good but its like moving house to go to the shops in a suit.

[ghr630]

Why nonsense John?  Std GT6 pistons are 2.94" which represents a .040" rebore on a 1300 (not excessive) and with the corresponding 2.99" stroke makes for a pretty much square engine. I fail to see how that would impede the engine's ability to rev? My point (not well explained and it's certainly not my original idea - old as the hill's I believe) is that the original Brico GT6 pistons can be found in good condition, are light and strong and much better than new County if you need a rebore. So with a set of good piston rings you have a much cheaper and better option than some of the stuff that is available on the market today. Nonsense? I don't think so!