The Compression, mild cams, idle vacuum, and DCR boogie.,

hoffbug · June 30, 2014, 12:20:26 PM

So I was able to find a set of 534 castings for my Olds 215... These are 38CC's and apparently gave a static compression ratio of 10.75 to 1 in the stock application... The 195 horse 63 4BBL automatic engine.

I want to run FAST EZ EFI on this engine so Ill need a minimum of 10" of vaccum at idle and above... I know aluminum dissapates heat faster than cast Iron and can tolerate about .5 to 1 point higher in compression than Iron ( see epic web threads debating this). Ive also read many conflicting storied about DCR and what is maxiumum for pump gas... some say 8 others say up to 9 for alumium heads... Cranking PSI seems to fall around 195 PSI or lower in most of what Ive read. THe DCR of my intended combination falls around 8.67

So. what I would like to do is run the 38cc heads and a Crower 50230 cam on pump gas (91 to 93 octane with 10% ethanol here in MN) with the FAST EZ EFI... In reading some of the tech articles Curtis has saved I noticed a car owned by Robert Edgeworth who is/ was running an Olds 215 with a Rover hotwire setup...apparently using this same cam profile. So Im hopeful that this combination will work.. What do you think?

Crower 50230.jpg

hoffbug · June 30, 2014, 12:40:00 PM

OH and I forgot to add.. Most of the Dynamic compression ratio calculators fail to take into account the Volumetric efficiency of the engine.. I cant imagine stock Olds head being any better than 80-85% with my intended combination... Wouldnt that also effectively lower the DRC number?

mgb260 · June 30, 2014, 06:50:52 PM

Tony, In my opinion with say 10.5 ( factory was inflated)compression you need a hotter cam like Crower 50232 to lower Dynamic compression down to around 8 for pump gas.

hoffbug · June 30, 2014, 07:15:08 PM

My fear with anything hotter than the 50230 is that the idle vacuum would be too low for the EFI....I do have the option of going with the 43cc heads....

RobertE · June 30, 2014, 11:51:42 PM

Tony, just saw your PM. The idle characteristics on the 230 are nice, nothing crazy. I'm running that on both MGs (3.5 and the 4.9). Not sure on the exact vacuum numbers.

At the same time I'd like something a bit more aggressive and agree with Jim with respect to the higher 10.5:1 compression.

hoffbug · June 30, 2014, 11:59:37 PM

Thanks Robert..... I just want something to cruise around in for now...So your Hot wire system in the 3.5 is working good? What compression are you running in that engine? What octane gas are you using....

RobertE · July 02, 2014, 11:15:41 PM

No problem. My father built the 3.5, it's running 10.5:1 comp and I've always used 93 octane. Idle is fine. It makes a great street car, the cam dies on the top end, but that's to the expected.

My 4.9 is the same compression ratio as well. Only reason I want a more aggressive cam is to match the ported heads. But as of now it's got way more than enough umph.

The 3.5 is actually 14cu/flapper system. Good manners and can get 30mpg on the high way. The 4.9 has the hot wire system from a 3.9 with a chipped ecu. I haven't put a lot of miles on the 4.9 setup, but I'd say the only difference is hot wire feels slightly more responsive.

hoffbug · July 03, 2014, 12:48:32 AM

OK.. Ill have to see where the shortblock comes out and see if I can stack enough clearances with valve relifes deck height and gasket and see If I cant open up the 38cc heads a bit.. The 43cc heads need some welding.. Previous owner bought the engine and it had a bolt dropped into the cylider..

roverman · July 11, 2014, 11:00:28 AM

Tony, You "might" want to mag that crank and rods/big bang theory ?

hoffbug · July 12, 2014, 12:39:53 PM

I bought a soda blaster attachement for my blasting cabinet and cleaned up the heads.. The 834 castings were worse than I thought .. It appears they have been froze and repaired once and then froze and cracked in another spot.. Just too much to repair.,

Art. those heads were off a different engine... My crank will be sent out and resized and checked.. Got ARP bolts fo the rods... Pistons are still up in the air.. I guess Ill have to see how clearances stack up with the small chamber heads.. Im not real fond of using cast pistons but the 4BBL Olds pistons do have 4 valve reliefs.. If I had my way and money I would order forged pistons with a reverese dome to mirror the chamber..

BlownMGB-V8 · July 12, 2014, 05:32:28 PM

Doubt you'll need valve reliefs. I have 10.6 compression and 1/2 of lift and still have about 1/4" of piston clearance. Buick 300 heads though. Zreo deck, 13cc dish.

Jim

hoffbug · July 12, 2014, 07:47:40 PM

Yeah.. The 2BBl pistons are flat tops.. I only mentioned to 4BBL heads had valve reliefs cause it would help lower the compression, not because of valve clearance.. . There are many more options for the Buick/Rover Head chamber design.. Only two real Olds piston designs that I can find. Ill just have to wait and see how the deck and heads true up after machining.