Ajusting CR on 2.5 conversion

[Anglocanadian]

Seems like the "spacer" solutions been around for a while and i thought I had come up with something new !
The deck height must have been borderline with those heads if you had to use a spacer ?

[faapgar]

Henry,I like the head treatment on the 2.5.Very slick.Keeps the charge in the center for better flow.

[Henry Schmidt]

Originally Posted by faapgar

Henry,I like the head treatment on the 2.5.Very slick.Keeps the charge in the center for better flow.

Our big concern was flow around the valves (valve shrouding). Our thinking was smaller valves or high lift cams. Next time around I believe we will polish the chamber to improve flow....if there is a next time.
In this instance we went with high lift cams. @ 490 intake lift the heads flowed better than expected. Bill @ Extreme was surprised at the flow with all things considered.

[jm993rs]

Very very interesant .....

[r lane]

I suppose at some point you can have too small of a chamber that will not accommodate the air and fuel charge available. Don't know what issues would materialize from that condition, cavitation, scrambled fuel mixture? Anyone have a base formula for calculating optimum cylinder head volume based on overall displacement. Obviously other factors have to be considered, but a base number.

[r lane]

I wrote prior to thinking. Your desired compression ratio will determine that relationship.

[911pcars]

Originally Posted by r lane

I suppose at some point you can have too small of a chamber that will not accommodate the air and fuel charge available. Don't know what issues would materialize from that condition, cavitation, scrambled fuel mixture? Anyone have a base formula for calculating optimum cylinder head volume based on overall displacement. Obviously other factors have to be considered, but a base number.

High compression ratios as a result of piston or combustion chamber shape is beneficial for both power and fuel mileage - up to a point, as long as moving parts don't collide and/or detonation isn't the result. Fuel octane, ignition advance settings, altitude, ambient air temperatures and operating conditions are variables that will greatly affect engine longevity. Pay attention to those conditions.

As a rough estimate, depending on the above plus the physical engine specs, compression ratios approaching/in the range of/exceeding 10:1 may/will require twin plug ignition or other strategies to mitigate destructive detonation.

Some ATF, 1/4" sheet plastic, a graduated burette, an assembled cylinder head and a calculator can be used to calculate the physical CR.


https://www.google.com/search?q=measure+compression+ratio&client=firefox-b-1-ab&sxsrf=ACYBGNTZVuVcyy39xKIr6Kc99WS2UzWoBA:157540548 5933&source=lnms&sa=X&ved=0ahUKEwimxPbiqprmAhVDrZ4KHb7yDh4Q_AUIDCgA&biw=1076&bih=674&dpr=2.22

Sherwood

[Walt Fricke]

I have just mocked up one piston/cylinder/head, run the piston to TDC, measured what the VTDC is directly by filling the chamber through the spark plug hole (engine on stand appropriately tilted, and a modified spark plug with a clear plastic tube with an X extra CC mark on it, as a filler funnel). It is a quick and dirty, and probably not the way to CC every hole to get that super exact match. But seems to work - the MMO didn't leak by the rings. I've not compared the result to that achieved in the usual way, but I can't see why it would be off.

[Anglocanadian]

I did mine in the same way through the plug hole, the C/R is in the low 8's and the deck height 1mm . I figure that's about as good as it gets without going "super modified" as Henry has done.
I am using the QSC iron barrels and pistons as the engine is a low budget Sunday afternoon cruiser not a track day car.