Opinions on 1950cc engines?

[MGBGT_noob]

I have my engine (1974 vintage 18V) over at a local rebuild shop, getting stripped down and cleaned. I need to decide on what I want done to it.

I know I want to:
<ul style="list-style-type: disc">[*]install a "fast road" cam, like the Piper 270 [*]install HS4 carbs and a tubular header [*]port and polish the head [*]install valve seats [/list]
Now, I need to decide if I want them to bore out the block to 83.5 mm, so that I can get the extra torque of a 1950cc motor.

Some sources say that a good machine shop will have no problems boring an 18V block to 1950cc. Others say two out of three blocks will fail, when you try to do this. Still others say that you can expect high oil consumption from such a motor, because the cylinder walls will flex, allowing blow-by.

Does anyone have any experience building a 1950cc engine?

I'd like to know, before I commit to a mod that could prove a nightmare.

 

[tony barnhill]

Here's an article Gerry Masterman wrote for my web site on just that subject:

https://www.theautoist.com/1950ccengine.htm

 

[MGBGT_noob]

Thanks Tony

It looks like "British Automotive" has left the business. Do you know of another source for the pistons Gerry mentioned in the second note?

 

[tony barnhill]

No, did you contact Doug to see if he has any left?

And talk with Hap - he's got other thoughts about the Lotus pistons.

 

[billspohn]

Using the Lotus pistons is ....dumb. But so many people have to 'save money'. Biggest mistake with these large overbore engines.

Get proper forged pistons (they ain't gonna be cheap, but how much are you spending on the engine?) from one of the usual manufacturers - I used Ross Racing when I needed a fancy raised crown on a big bore Twin Cam MG motor, but I believe Venolia also does them.

Or don't bother, just do what they would have done 'in the day' and fit .080" over flat tops. The difference isn't going to be earth-shattering and the risk you take that the block you start with on an 83.5 mm project will turn out to be one of the 'bad' ones isn't a factor.

BTW, I've seen these blocks take the bore just fine to 83.5....and then perforate the cylinder wall in a very small area when the final honing was done because of a small casting inclusion that probably wouldn't have turned up on a sonic test!

 

[DrEntropy]

THANK YOU BILL!!!


The block castings on these lumps (18V's) was done by English Union employees.

Q.C. was: "It started!! SHIP IT!!"

If you want to build a Go-Fast MGB, do a V8 conversion. Don't waste a good set of Lotus pistons!!! :smirk:

 

[vping]

What is the most you should bore an MGB block?

 

[DrEntropy]

My "personal best" with any success has been 0.040" (with any measure of reliability), and that on an 18GB block. Not real keen to go THAT far on a later 18V. Mebbe others have had better luck but that's been my experience. Short of sleeving one, I'd be lookin' at 0.030" as a max.

 

[ronzet]

I must agree with Doc... All of the engines that I have rebuilt were bored a max of .040 with a preference of .030...

IMHO

The law of diminishing returns can kick in here pretty quickly.. The money that you spend on the MAXed oversized bore and special pistons could be better used elsewhere..

As you have stated, ported heads, cam, et al, will provide a very nice performance boost. With these performance additions you will be putting a bit more strain on the engine anyway and with the cylinders bored out to the MAX, you are reducing its reliability component...

As I said IMHO... starting with a nice solid foundation with a block that has some bore thinkness left and adding performance enhancement to that will be a better all around approach....

 

[AlanT]

I offset bore the block .025 and use Ford flat-top pistons ala Cortina. The effective bore is .088 over. I built a few this way and all but one went into vintage racing MGB's. This was before my machinist had a cylinder wall density checking device.
We noticed no changes in coolant temps .
Alan T