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MG TD TF 1500 - Gasket for super charged engine

What thickness of copper head gasket is recommended with a super charger giving 1.2 - 1.3 bar, assuming neither head or bloc has been machined?

What sealant is recomended?

Can two standard gaskets be used, or will they blow.

YS Strom

First of all, yours is a huge assumption - most heads have been re-surfaced more than once in their 60+-year lifespan.

Are you planning to use a copper-faced compositon gasket, or a solid copper gasket which is available in various different thicknesses? Has the engine been overbored? These variables all contribute to the CR.

With a stock head gasket a standard XPAG engine has about a 7.25:1 compression ratio, and an XPEG has a standard CR of 8.33:1. I recommend staying below 8.5:1 for a street machine with a supercharger, but a racing application can go higher. Of course, the higher the compression ratio the more critical is the need to have the carb and distributor properly tuned (on a rolling road), as there is greater potential for damage to the engine, and liklihood you will blow a head gasket.

The condition of the head studs is also critical. See mgtrepair.net for the head studs I sell, which have cured many engines of blown head gaskets.

Tom Lange
MGT Repair
t lange

I know how much head and block has been machined and will add for that- 0.4 mm. Therefore I wrote assuming it was not.

New bolts might be worth considering thou. I have not installed the SC for increase of power, rather as an technical challenge and there are speed limits of 70 Kph. almost wherever I drive.

So my question is still open, what should the thickness of the gasket be, assuming head and block has not been machined?



YS Strom

I have absolutely no qualification to say this but I am going to say it anyway.
!.2 BAR (17.4 psi.) to 13. BAR (18.85 psi.)seams like a LOT of boost.

My guess is that it would more than double your CR.
Can you throttle it down? Do you have a waste gate?

Jim B.
JA Benjamin

Jim - Hmmm - I didn't notice that detail - the street Mirage Garages supercharger we sell puts out about 6psi; the race one is closer to 10psi.

As for the gasket thickness, I can only say that a compressed stock head gasket on a stock engine running 7.25 CR is .045".

I wonder how long your engine will last long at 16-17 PSI boost...

Tom Lange
MGT Repair
t lange

Could it be that YS is giving absolute and not guage pressures for his boost? That is, the boost raises normal atmospheric (1 Bar = 14.7psi?) to between 1.2 Bar(17.4 psi.) and 1.3 BAR (18.85 psi.)?

Jud
J. K. Chapin

yes Jud;
I did not think of that.
Could be total pressure.

! BAR is 14.5 psi.
One Atmosphere is 14.7 psi (at STP)
Thus the bust would be between 2.7 psi and 4.15 psi.
That's tolerable.

Jim B.
JA Benjamin

It is of course indicated total pressure. I run it now with a total pressure of max1.5 bar which is far too much, so I drive it with a very light foot. Therefore I have now made a reduction gear that can be adjusted to give a total pressure of around 1.25 bar. Will report more on that when installed.

The 0.045 gasket referred to equals 1.143 mm. A standard seal from Moss is about 0.7 mm. when compressed. So is the answer that 1.143 mm. plus what has been ground off will do the job?

And is sealant recommended and if so, what type?
YS Strom

Have now measured two used modern gaskets of standard type. One is approx. 095 mm. and one 1.25 mm.so 0.7 mm. was obviously not correct.

What thickness is recommended for an engine without CS?
YS Strom

With the Mirage Garage SC and using a standard gasket of 1.14 mm. will give a considerable increase of pressure compared to original design. Is it better fuel making that possible? Or is it advisable to reduce pressure by using thicker gaskets? And if so, how much?
YS Strom

Y
There is a simple (safe) formula to follow as far as reducing compression against boost pressure
But
First, is your engine 1250 or 1500
What is the octane rating of the fuel you will be using

willy
William Revit

It is a 1250 and 95 octane.
YS Strom

Good quality, solid copper head gaskets are easily available in material thicknesses of .022,.032,.040,.043,.054,.063,.070, .086, .093, and .125 inches. from The Gasket Works Company, see:- http://www.headgasket.com/gaskets.html.

I bought one for my blown TD and proceeded to put 40,000 miles on it w/o removing the head before I sold the car.

Not expensive either. Can't recall what I paid, but I believe it was less than $75 (in 1985).

Gord Clark
Rockburn, Qué.
Gord Clark

1250
95 octane
std-7.25:1 comp.

The following is my own opinion--I'm sure others will have different opinions---

Rough guide for a std engine which works out on the safe side---
10:1--needs100 minimum octane
9.5:1--needs95 min.octane
9.0:1--needs90 min.octane
8.5:1--needs 85------etc
Remember this is a rough guide but safe

Your fuel is 95 octane---

Working out your std comp ratio of 7.25 against 95 octane fuel gives a max safe useable boost pressure of just under 6.25

Which I believe is more or less the same as what Tom's Mirage Garages street supercharger is doing
What octane rating fuel are you using Tom
Bearing in mind of course I am using Ron rating where you will be Mon
95ron=91mon
98/100ron=93mon


The calculations I used for this info were from a chart sourced from an old Phil Irving book-
"Automobile Engine Tuning"
It's an old book but worth it's weight in gold
Hope this helps-
willy
William Revit

Willy, here in Sydney the highest octane rated fuel available is 98. My compression ratio has been calculated at 10:1 to 1 as there has been plenty removed from the head, more than is recommended in fact. How or where do you source 100 octane? Can this be achieved using 98 with an additive of some sort? Cheers
Peter TD 5801
P Hehir

Thank you all for a lot of interesting information, but I am still hoping for information on how thick CU gasket is recommended using a SC giving a total pressure of 1.2 - 1.3 bar. with head and bloc leveled 0.2 mm. each, i. e. a total of 0.4 mm. and using 95 octane.
YS Strom

Peter
I reckon you'll get away with 98, it'll be borderline and maybe need the timing pulled back a little or as you say some octane booster would sort it if you want to keep the timing up to it
100 octane racing fuel is quite expensive with the tax that is on it
If you know someone who has a plane avgas is an option but a pain if you're going somewhere and need it while you're out--
It's a common mistake to go too high with compression ratios, better off back a bit in my opinion so timing etc can be set up for it

Y
If the std. gasket is .045" and gives 7.25:1 you should be safe with that at 1.3bar =4.4lb boost
5lb boost you should be able to run 7.5:1 comp and the only way to acurately tell what gasket thickness would be to cc the head and piston spaces and calculate the gasket thickness to get the comp. ratio you want

personally, I'd go the next gasket up which would be .054" and run with that

The .2mm off the block is real but the .2mm off the head is semi false as it's only .2 off the depth of the combustion chamber which doesn't cover the whole area of the bore so not the full .2---.4=really only .3+
so probably worth around .012" extra to add to the .045" std gasket==.057"

So considering your boost is slightly down on the 6lb (4.4) the.054" gasket is the one

In my opinion---------------

William Revit

Plug all of your numbers in here.

https://www.rbracing-rsr.com/compstaticcalc.html

Change the gasket thickness until you get to the desired compression ratio you seek.

You might also want to use this as a guide to assist you.

http://www.goodvibesracing.com/Compression_Ratio.htm
L E D LaVerne

Williams and LED

Very interesting information!!!
Sounds as it is worth trying with a 1.5 mm cu gasket.
Y Strom

Interesting--that 'goodvibesracing' chart is almost exact to what the formula in my old book (printed in 1962)comes up with--
And saves working it all out-----Thanks LEDL
willy
William Revit

And--your other question on sealants-
My own opinion again--happy to be wrong but
With a solid metal, or any metal gasket it's important to use a metal based sealant-
If you use a sealant that insulates the gasket from the head and block there is no path for the heat to soak out of the gasket and you run the risk of the gasket melting or burning
A good metal based sealer like VHT's Copper Kote works well but only a light spray, it doesn't need to look fully coloured
It comes in a pressure pack (rattle can)
Have everything ready for assembly, a light spray on both sides of the gasket,wait till it's dry but still a little sticky, pop the gasket and head on and bolt it down
There are surely other brands that work as well---------but I know this stuff works
willy
William Revit

Thanks William
I will do so. Will order a can on monday.
YS Strom

This thread was discussed between 15/11/2018 and 24/11/2018

MG TD TF 1500 index

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