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MG TD TF 1500 - For my education. Increase in bore size

How much increase in Cubic inches (or liters) does each progressive boring of a motor add to it?

MyTD is at 20 over and my MGB at 30 over.
Bruce Cunha

A 30 over 1798 MGB engine = 1836cc
A 20 over 1250 MGTD engine = 1270cc
William Revit

Not for XPAGs but other mg engines see m chart here - https://octarine-services.uk/bore_capacity_CR.htm
Chris at Octarine Services

Here you go Bruce. The chart is from a publication "Tuning the Head of a T Type Engine" By Hal Kramer.

Tim

Timothy Burchfield

Remember that volume is pi x R^2 x stroke so, if you don't change the stroke, the increase in volume is proportional to the square of the increase in bore. The second 0.0020 increase in bore increases the volume considerably more that did the first 0.0020 bore increase. At least I think that's right.

Jud
J. K. Chapin

Sorry Bruce, I misunderstood your question. This is probably more helpful (from the WSM).

Tim

Timothy Burchfield

Tim - I believe your second chart comes from Woody Wood's manual, not the WSM.

I don't have a copy of Hal Kramer's head info - how can I get a copy?

Tom Lange
MGT Repair
t lange

Get a copy of Hal Kramer's Article "Tuning the Head of a T Type Engine" in the June 2001 issue of TSO. It can be found on the TSO CDROM. Bud
Bud Krueger

Tom, check your mail. Bud
Bud Krueger

Tom, you are correct. Thanks for catching that. I also sent you an email.

Tim
Timothy Burchfield

Tim, Tom & Bud For many years I took Hal's Tuning the head of a T type and Wolseley 4/44
Engine Re-build and Tuning as 100% correct. The calculations for C/R are incorrect for both. Using their calculations for bore size & chamber volume an XPAG .060" overbore with a head thickness of 2.925" and Chamber volume of 38 CC would result in a C/R of almost 9.6 : 1, using math instead of these 2 published articles it results in a C/R of almost 8.7 : !
Pi R squared H and gasket volume of 4.5 CC with 38 CC chambers.Both however do have other very good information!
Len Fanelli

Len, I'm having trouble understanding where the error is in Hal's computations. My engine fits his sample right on the nose: .100" removed from head for a thickness of 2.922", .060 in. overbore. His calculation for Vcc (Combustion Camber Volume) would be 40cc, not 38cc. Plugging these numbers into his work would give a compression ratio of about 9.17:1, not 9.6:1. What am I missing? Bud
Bud Krueger

The gasket volume I Imagine. I think its included in Hal Kramer's numbers.
Dave H
Dave Hill

Mine is .80 over,I have seen one that is .100 really thin between 2 and 3 my engine runs strong and was overhauled in 2007l and no trouble If I had to go hundred, think I would re sleeve.
TRM Maine

TRM, I've been running my .120 over 51 TD for two years now without problems. The machine shop did sonic test the cylinder walls before boring.

Tim
Timothy Burchfield

Bud & group, Oops!@ .060" over bore, about 9.6 was predicated on my old head that measured 2.900", sorry. My new head ( my original head was destroyed by Storm Crankshaft & Welding) measures 2.920" with 38 CC chambers due to my larger 37 & 35 MM valves proud of the roof of the chamber. So Hal's numbers were closer to what I got Sorry. @ .060" over bore & 38 cc chambers I get 8.69 : 1 C/R. Therefor Bud if you use the formula and not his calculations you should end with a C/R of slightly lower than 8.7 : 1. Please correct me if I have missed anything! PI X R squared X H then add the 4.5 CC for the gasket + the chamber CC, then divide this total number by the 4.5 CC + the chamber CC.In my case it was 369.38 divided by 42.5.
Len
Len Fanelli

Len, I think that Hal's Table 1 (Combustion Chamber Volume vs. Head Thickness) includes the head gasket. A 2.920" head would have a Vcc of about 39.8. Your 369.38 divided by 39.8 would then give a CR of ~9.28:1.
Bud
Bud Krueger

Bud sorry that I was not clear, (not firing on all cylinders today) 369.38 CC is the total cylinder+ combustion chamber + gasket volume. Divide this by the gasket volume 4.5 CC + chamber volume 38 CC = 42.5 CC.
369.38 CC divided by 42.5 = 8.691 : 1
Again if you use the formula PI x r squared x H for the cylinder volume, 38 CC for the chamber volume & 4.5 CC for the gasket volume, then use 42.5 to divide into 368.38 = 8.691 : 1
Again Please correct me or comment as needed!
Sorry to hijack this thread.
RIP Hal Kramer
Len
Len Fanelli

Len, our arithmetic works the same way, Pi is still 3.14159.... The difference is in Hal's computation of Vcc. On Page 18 of TSO (June, 2001), Hal's definition is "(Vcc) is the combustion chamber volume in the head and the head gasket thickness. Using Hal's Table 1 for determining Vcc for a head of 2.290" would give a Vcc of about 39.8cc. Duplicating the gasket volume results in your 42.5cc Vcc, hence the lower compression ratio. Using the 39.8cc value gives about 9.21:1. Bud
Bud Krueger

NEMGTR link to Hal Kramer presentation:

https://www.nemgtr.org/images/stories/Research_Lib_Files/Tuning_The_T_Type_Head_V3.pdf

Lonnie
TF7211
LM Cook

This thread was discussed between 11/01/2020 and 16/01/2020

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