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MG TD TF 1500 - cc calculation

The engine shop that rebuilt my TF's 1250 engine, did a slight increase in the bore size by .040 in, increasing from 2.618 in to 2.568 in. Although it was just a small increase I decided to calculate the new cc displacement.
I used the following formula:

displacement = bore (squared) X .7854 X stroke X # of cylinders

the .7854 comes from pi/4

displacement = 7.06 X .7854 X 3.543 X 4 = 78.52 ci

Converting cid to cc, cc = ci/.061024 = 1287 cc for the TF's new displacement

I'm thinking of having a couple of rectangular badges made for the engine side panels, like the 1500s have, and the value on the badges would be 1287. Should keep the judges wondering, eh? I could say, "What, you didn't know that in '53 ( the actual year my TF was built) they came out with an experimental model that had a displacement of 1287?" Ha!

Anyone know of where I could get such a rectangular badge made?

Having fun -- John



John Brickell

I'm sure the same place thats making our badges could do it. I'll send you the contact if you like. I don't see in your calculations where you included the head volume.

Just saying.
MG LaVerne

I would round up to 1300 CC.

Jim B.

From Wikipedia

"Engine displacement is the volume swept by all the pistons inside the cylinders of a reciprocating engine in a single movement from top dead centre (TDC) to bottom dead centre (BDC). It is commonly specified in cubic centimetres (cc or cm3), litres (l), or (mainly in North America) cubic inches (CID). Engine displacement does not include the total volume of the combustion chamber."

JA Benjamin

Both LaVerne and Jim have raised question that I'm not sure of or aware of. Maybe this is more complex than I initially figured. I just went to a web-sight that had the formulas for calculating engine displacement and used those in my calculations.

LaVerne, appreciate the contact info you mentioned.

Jim, I like the idea of using the value "1300".

Thanks to both -- John
John Brickell

If the diameter after the boring was 2.658" (2.618+0.040) then the formula is pi (3.141589) X (2.658/2)^2 X stroke (3.543") X 4cyl. = 78.638 cid = 1,288.65 cm^2. Maybe you shoulg go with 1,290 just to confuse them.

Jud
J K Chapin

Jud and Jim, I wonder which would get more attention, 1290 or 1300? The 1300 might have more of an authenticity look to it for the uninitiated. One of the members of what I call the "big MG club" in the state, hung an oil cooler off the back of his MGB just to see what folks would say at gatherings like ABFMs. More than once at such gatherings he would get comments like, "My dad had that after market thing for his MG too." Or, "did you add that to get better gas milage, or is it a power boost?"

Fun stuff, especially when there's not much to do during these winter months -- John
John Brickell

John, I almost got into responding to your post, but thought better of it. As Jim B. pointed out, displacement is defined as the swept volume. If you want to include the combustion chamber volume (Vcc) our basic engines would be referred to as 1450cc. The Vcc is 50cc/cylinder. Add that to the swept volume of 1250 and you have a 1450cc engine. Your Vcc is 44cc, so your combined volume would be your 1288 + 4*44=1464cc. A 1500TF would then be 1500 +4*50=1700cc. BTW, if you still have a stock head, your compression ratio is now 8.37:1. Got enough numbers? Bud
Bud Krueger

Bud, I appreciate all of the information I can get. Although I don't have and engineering or mechanic background and got into this late in my life, I enjoy improving my knowledge whenever possible. Your explanation adds to that knowledge. Thanks.

I don't have a stock head as the shop had the "Cylinder head cut to 2.908" to achieve 9.2:1 CR"

The following is a summary of what was done in the rebuild of my engine:


1. The engine & cylinder head were thermally cleaned & shot blasted then magnafluxed
2. Connecting rods & crankshaft were cleaned & magnafluxed as well.
3. Cylinder bores were resized to 2.658 (+ .040"), diamond honed
4. Cylinder block deck was notched to allow clearance for the valves & resurfaced (-.008")
5. Custom brass core plugs in block
6. The rear main seal carrier was align bored to match the main housing bore (.005" clearance)
7. The crankshaft was reground, radiused &; micropolished (-.020 rod &; main journals both)
8. Connecting rods were modified to accept ARP MGB rod bolts (11/32")
9. Connecting rods resized & aligned
10. High strength socket head cap screw gudgeon pin bolts were installed
11. The rod beams were polished & shot peened
12. The block interior & rocker galley surfaces were treated with Glyptal for sealing & to promote oil drain back
13. The flywheel was resurfaced and a new ring gear installed
14. The rotating assembly was balanced to within 1 gram
15. The cylinder head has been ported & polished - intake ports "knife edged"
16. Oversized stainless steel valves
17. Cylinder head has hardened seats conversion for unleaded fuel
18. 3 angle competition valve work
19. Cylinder head cut to 2.908" to achieve 9.2:1 C.R. approximately
20. Cylinder head is machined to accept positive viton valve seals
21. Bronze valve guides installed
22. R&L performance valve springs
23. Crane Camshaft street performance grind
24. The lifters were refaced, polished and have had the oil holes elongated for improved oiling
25. Crankshaft & lifters were treated with TX-1 a proprietary anti wear/friction treatment (  http://www.rlengines.com/tech/TX1.pdf )
26. Custom ARP cylinder head studs were installed
27. Rocker arms were refaced & the rocker assembly completely rebuilt
28. Custom JE Pistons with rings approx. 9.2:1
29. Carburetors rebuilt
30. Distributor has been blueprinted with an electronic conversion on an Allen Syncrograph

May be more than most would want to know, but decided some might find this list of changes/improvements of interest.

Regards, John
John Brickell

Can't say about the effect with your JE pistons. With stock pistons the cut to 2.908" and the .040" overbore would compute to a compression ratio of about 9.35:1 with a Vcc of about 39cc. You might want to get your hands on a copy of the June/2001 TSO and read Hal Kramer's article "Tuning The Head Of A T Type Engine". Bud
Bud Krueger

The head volume comes into play when you want to work out the compression ratio.
With the head off and the valve gear in place pour water into the inverted head and measure the volume of water in one chamber(assuming the valves seal nicely). Allow for the thickness of the head gasket and the distance down to the piston if it is not flush with the head at the top of stroke. Then divide the combustion chamber volume into the piston stroke volume to get the compression ratio. Someone will probably explain where I am wrong on this!!!

Max Irvine

For compression ratio you add the swept volume and the head and gasket volume and divide by the head and gasket volume.
Dave Braun

John: I am beginning the restoration of my TF 9867 (finally)and I was wondering who you had do the engine work. Found my car in No. Cal. circa 1987. Thanks, Keith

K. G. Meyer

This thread was discussed between 01/02/2014 and 08/02/2014

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