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Spitfire & GT6 Forum

High Compression spitfire pistons

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69Mk3Spit Avatar
69Mk3Spit Silver Member Dino Finelli
Oakville, ontario, Canada   CAN
Not really looking for advice or approval just sharing....

The engine is going through lots of great modifications to take my spit to the next level at Active Race engines.

I've owned her for 25years and finished my second restoration 3years ago, this winter my project is engine and transmission.

Even after 25yrs still enjoying her like day one!

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20170207_111357.jpg

Born Loser Avatar
Born Loser Silver Member Matthew Taylor
Land O Lake, Florida, USA   USA
Very pretty!



Matthew
1960 Triumph TR3a
1970 Triumph Spitfire MK 3
2012 Mini Cooper SS Convertible

FrankD Avatar
FrankD Frank D
Doylestown, PA, USA   USA
Cool, what compression ratio are you going for?

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69Mk3Spit Avatar
69Mk3Spit Silver Member Dino Finelli
Oakville, ontario, Canada   CAN
I'm looking for a true 10 to 1 by not taking the head down.

clshore Carter Shore
Beverly Hills, Florida, USA   USA
Interesting dome configuration, I've not seen that before.
Where did you source the pistons, are they custom?

I assume from your iD that this is for a 1296 small journal motor?

Is this approach the result of issues you've encountered from milling the head?

SpitMan Avatar
SpitMan Doug Walls
Brandywine, Maryland, USA   USA
1970 Triumph Spitfire MkIII "70 Spit"
1998 Chevrolet Corvette "Silver Fox"
2007 Chevrolet Silverado
2013 Chevrolet Malibu "Pearl Baby"
thumbs up Good question..........informed minds would like to know!

Tonyfixit Avatar
Tonyfixit Tony M
Duncan, British Columbia, Canada   CAN
Interesting. I wonder how the pop up area in the combustion chamber will effect squish? (But I assume the pop up area is not a tight fit) But then, the surface area of the combustion chamber will me increased reducing thermal efficiency?

I am not nay saying here, I am honestly interested!

What other engine mods have been made?

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tapkaJohnD Avatar
tapkaJohnD John Davies
Lancaster, Lancashire, UK   GBR
Gosh! That must have cost a bomb!
Please tell why you are reluctant to use the cheap, time honoured method of reducing head height?

John

tmpass Avatar
tmpass Tim P
Medway, MA, USA   USA
1970 Triumph GT6+ (MkII) "Capo"
1970 Triumph GT6+ (MkII) "Blue Oxide"
In reply to # 1433676 by tapkaJohnD Gosh! That must have cost a bomb!
Please tell why you are reluctant to use the cheap, time honoured method of reducing head height?

John

I was always under the assumption that a zero deck, then milling the head for final compression was the way to go.. but I guess using pistons to accomplish would be the same result... curious about valve clearances too and the rest of the build specs.. and where the pistons came from??

My GT6 motor needs some ideas

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69Mk3Spit Avatar
69Mk3Spit Silver Member Dino Finelli
Oakville, ontario, Canada   CAN
My spit is a 1296 small journal.

This are custom pistons that were made to hit the 10 to 1 that the engine builder was looking for, I believe JE is the source. Active was not a fan of milling the head to get the desired compression ratio. Active Race Engines is a very meticulous engine shop that prides themselves on attention to detail.

There was work done to the head as well bigger SS intake valves (back cut), stronger springs with hardened cups, using WBC518v2 Camshaft from Wishbone classics.
We've lightened the flywheel, uprated the oil pump, and will be running the 1/2 su's, kevlar clutch and....... roller rockers from WBC(I thought what the hell as a Canadian I wanted to help my friends south of the border with this purchase) The guys at WBC have been great and offered lots of knowledge and support. I will get it Dyno tested when done and share my results.

As for the "squish and thermal efficiency" I will talk to my engine builder this week and get back to you!

69Mk3Spit Avatar
69Mk3Spit Silver Member Dino Finelli
Oakville, ontario, Canada   CAN
I believe the new pistons are around 500US, so i guess it translates to a bomb in Canadian!

clshore Carter Shore
Beverly Hills, Florida, USA   USA
I've seen Spitfire pistons with a popup, but it's been many years since they were available.
They featured a popup section that was more 'D' shaped, to match the shape of the combustion chamber.
ISTR that they were cast rather than forged, and cannot recall the manufacturer, maybe Venolia?.
They used to be the go-to custom piston vendor.
But could also be Egge, they do specialty and custom pistons.
Nowdays lots of places do them, and prices have become reasonably competitive.

I would question only the sharp right angles where the 'domes' transition to the piston.
Sharp external angles (as at the top) tend to become localized hotspots, ie the first thing to melt.
Sharp internal angles (as at the base) tend to run cooler, trap endgas and can lead to preignition.
Most pistons with valve reliefs will feature a 1/8" radius at corners.

Too late now the (forging) die is cast! winking smiley

Anyway, the dyno and the track will tell the tale, and pistons are pretty easy to replace.

SpitMan Avatar
SpitMan Doug Walls
Brandywine, Maryland, USA   USA
1970 Triumph Spitfire MkIII "70 Spit"
1998 Chevrolet Corvette "Silver Fox"
2007 Chevrolet Silverado
2013 Chevrolet Malibu "Pearl Baby"
thumbs up I too was wondering why the edges of the raised portion were so sharp looking instead of rounded. Look like hot spots to me.........but what do I know anyway!

69Mk3Spit Avatar
69Mk3Spit Silver Member Dino Finelli
Oakville, ontario, Canada   CAN
I will be contacting the engine shop tomorrow to discuss this issue and get back to you.

carChips Avatar
carChips Victor Harnish
Kelowna, BC, Canada   CAN
1933 MG Magnette
1973 Triumph Spitfire 1500 "Chip"
1989 GMC Sierra 1500 "Bush Truck"
Milling off the head costs about 100 bucks and those funky pistons cost 500, hmmm....



'S all for now
Vic

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