396 bbc heads ??

[grumpyvette]

Wanting to build up my big block - I got talked into what I now think are the wrong heads, I think the CR will be too low.

Here's what I've got already

Edelbrock E-street 110cc chamber
KB-Silvolite 4.125" 17cc dome

looking at a mild hydraulic roller Comp Cams Xtreme energy XR258HR
Duration .050 in 206.0 ex 212
Lift .510 .510
Timing (seat) In Open 23 In Close 55 Ex Open 66 Ex close 18
Lobe centreline 110
Intake centreline 106

With a .040" gasket & zero deck height I come up with:
static CR of 9.0
Dynamic CR 7.7

Fuel here is 95 RON

So will this work? these heads have hard seats & heavy valves, so will only take the mildest of hydraulic rollers - I DIDN'T KNOW THIS-.

ok,first issue!
I build mostly big block chevy engines, and those particular cylinder heads are MORE than adequate if your going to use a mild cam similar to the one you listed, better flowing heads will be wasted as youll never be able to reach near the potential with that mild of duration and lift.

http://www.jegs.com/i/Edelbrock/350/504 ... 1800263821

Id surely select a dual plane intake and a bit more lift and duration, on the cam but without knowing the car weight, rear gear ratio,transmission used tire diameter and several other factors I can,t really guess at the best match
now I would not be thinking your working at a huge dis-advantage due to the use of those heads, those heads are rated to flow over 309 cfm at .600 lift and with a bit of port and bowl clean up flow more, most SBC engine in the 383-406 displacement range WISH they had heads that could equal those flow rates.


you might want to stop and think thru the cost of rebuilding and modifying the current engine Vs upgrading some or even most of the components, in some cases youll find you can buy new components or even a crate engine or short or long block assembly, at a cost level similar to what all the parts and machine work might cost to refurbish the current engine.
http://paceperformance.com/search.html? ... &go=Search

http://www.cnc-motorsports.com/short-bl ... -deck.html

http://www.edelbrock.com/automotive_new ... /50459.pdf

http://edelbrock.com/automotive_new/mc/ ... reet.shtml

you might find the links useful

viewtopic.php?f=69&t=2165

viewtopic.php?f=69&t=7722

viewtopic.php?f=69&t=9930

 

[grumpyvette]

if it was my car Id sure advise a change too, a 3.35:1-3.54:1 ratio rear gear ratio, be used and a edelbrock intake with a 650-700cfm vacuum secondary carb
http://www.summitracing.com/parts/edl-7561/overview/
and a cam like this, one linked below,
but remember if you order a cam the rear main journal must be grooved for oil flow on a 1966 396 engine

the 1965 and 1966 big block 396 had unique rear cam bearings and required a grooved rear cam journal, most cams you buy currently are not grooved

 

[Crusty]

Thanks Grumpy,

I have an Edelbrock Performer - not the airgap due to hood clearance. I'm running a late q-jet M4ME off of a 454 RV & have plenty of spares, jets, rods, hangers. Should be capable of 750 cfm, maybe 850.

Will I have enough compression with that combo? The UEM piston calculator gives me a dynamic ratio of 6.89.

 

[grumpyvette]

its not ideal, to have the dynamic compression that low, but if you go too use of a lower in duration cam,that in theory keeps the dynamic compression higher, you significantly restrict the breathing potential of the heads,once the engine starts to spin up into the 3000rpm and above rpm band, and by about 4500rpm a milder cams restricting power. but I can,t help point out that it will run far better if you change that rear gear to a mid 3 series ratio, and changing the converter stall to a 2500rpm,would also help as both changes allow the engine to quickly reach and operate in the 3000rpm and higher power band those heads and that cam will allow the heads to breath.
you do realize that there are 4" AND 4.25" STROKE INTERNALLY BALANCED CRANKS THAT WOULD SIGNIFICANTLY INCREASE BOTH YOUR DISPLACEMENT AND DYNAMIC COMPRESSION???
JUST FOR GRINS REDO THE CALCS WITH A 4.25" STROKE AND 6.385" CONNECTING RODS in that 396 bbc
as always why not call a couple cam manufacturers and get their thoughts?

I'D ALSO POINT OUT THAT FINDING A GOOD USEABLE 454 BLOCK IS GENERALLY NOT TOO DIFFICULT

http://www.summitracing.com/parts/esp-445442526385

READ THRU THESE LINKS and SUB LINKS CAREFULLY
viewtopic.php?f=52&t=82

viewtopic.php?f=69&t=2165

http://www.carcraft.com/techarticles/cc ... ewall.html

 

[Crusty]

Well I have a 454 in the car now that is tired. Looks like I should forget the nostalgic feelings of using the original 396. Would be easier to get that DCR up with the 454.

I'll start looking at the rear end. And read more of your excellent links!