Head upgrade from O44 to Superflow

[AlexB]

Currently in the process of upgrading the engine from my drag car ( The Jagerbug)

I’m changing the 2276 (82x94) engine from Cb 044 heads to some secondhand superflo heads I picked up a while back

The Superflos have been flycut somewhat so have a chamber volume of 30cc which is pretty small, I want a final cr of about 12:1

Current deck height is 0.90 mm

My calculations so far take me to using a 1.5mm copper head gasket (gives another 11cc according to my maths) which gives a top end volume of 41cc
Using a 0.5mm cylinder spacer drops the deck to 1.4mm

According to the Jmr calculator this gives a CR of 12.2

Does this sound correct ?

Engine runs FK89 , 48 Ida’s and is not street driven - just want to up the breathing with the bigger valve better flowing heads

Cheers Alex

[richie]

I make that 12.4/1

Forget all the calcs for 1.5mm copper to cc, its just deck height in real world so

deck height is 0.9+1.5+0.5mm= 2.9mm[ which to me is way to much for a N/A race engine]

head cc 30
with 94x 82 on jmr calc shows 12.4/1

cheers Richie

[AlexB]

I make that 12.4/1

Forget all the calcs for 1.5mm copper to cc, its just deck height in real world so

deck height is 0.9+1.5+0.5mm= 2.9mm[ which to me is way to much for a N/A race engine]

head cc 30
with 94x 82 on jmr calc shows 12.4/1

cheers Richie

So with a deck of 1.4 and 30cc chamber I get a comp ratio of 15.3 /1

To drop that further would I be better off machining pockets /dishing the pistons ?

Cheers Alex

[Erlend / bug66]

If the superflos has been running a lot with 30cc chambers, they could be pretty tired.. Depending on the year of production, the aluminium is pretty "light"..

Hold a SF in one hand and a new competition eliminator in the other. The difference in mass is pretty obvious..

[leec]

Would you need valve notches as well? Do you include the cc for them as well in CR calculation?

[AlexB]

Hadn’t considered valve notch capacity - although thought they might be necessary, I suppose a decent pocket machined
In the piston crown would solve the need for valve notches and decrease CR

[AlexB]

Ok - so rather than increasing the deck, if I machine a 70mm dish 1.5mm deep in the piston crowns then it will gain 5.6cc into the combustion chamber, then keeping the deck at 1.4mm that gives 13.4 compression - sounds more reasonable ?

[DaveN]

If it was my engine, I would increase the deck height, notch the pistons accordingly  and the compression ratio is what it is. It’s a race motor so you’re going to be running race fuel so high compression ratios won’t be a problem.

[Martin S.]

For mine it was unshrouding the valve. Then, dishing the pistons to match.