Newbie Bugeye Sprite owner engine advise needed

[tim66ah]

Hi all, I recently purchased a 59 sprite with loads of spares. My car is drivable, but needs exterior painted and a few things sorted. I need to correct transmission problem of having smooth case shift lever in rib case. Will swap shift towers to correct this and look stock.

I have several 948 engines with this car. One is rebuilt with flat top pistons and 12H185 head. Does anyone know what my compression my be? I did compression test cranking it over and came up with 125-130 readings.
This engine has hs2 carbs.

The current engine in car is 90 psi and is 8.3:1 as stock.
I would like to swap engines while I'm at the transmission.

 

[AN5Sprite]

The only head casting numbers I can remember off the top of my head are the 12G202, 12G206 and 12G295.
I wouldn't hesitate to drop in the engine with the higher compression readings. I'm not going to speculate what the CR is, but I doubt it's too high for pump gas. I bet it's just fine and it will sound great!

 

[HealeyRick]

12H185 isn't the head casting #, but the motor # from an Austin Anerica 1300. The America had a 12G 940 casting. Are you saying you've identified the head as coming from an Austin America that's been fitted to a 948 or maybe the whole motor is an Austin America unit?

 

[racingenglishcars]

Unfortunately, contrary to opinion, the compression readings by gauge don't reflect the compression ratio. This had to do with the inlet valve closing angle. The inlet valve closes at somewhere around 100 degrees before tdc. At this angle, the piston has already moved up the bore a bit less than half way. What air is left in the cylinder is then compressed to fill your compression gauge.

By comparison the calculated compression ratio has to do with total displacement (stroke times bore) theoretically fitting into the combustion chamber within the head and the piston dish.

At very low engine speeds (cranking) the difference is large, though with the dynamics of airflow at higher engine speeds this late inlet valve closing allows more air to enter the cylinder.

Camshafts are thereby tuned to specific engine speed ranges.

My compression ratio program is a bit helpful for figuring out what you have and need.

 

[mxp01]

Tim:

I sent you a PM earlier. If you have a stock 948 available, I'm in the market.

Mike Pennell

 

[tim66ah]

Tim:

I sent you a PM earlier. If you have a stock 948 available, I'm in the market.

Mike Pennell

Mike, I sent reply. I do have a stock 948 FS.