I have an engine builder currently building me a sbc. He knows his stuff and I really trust him because he has been building and racing for most of his life. He has a "nickelblock" (if the termination is wrong it may be my fault not his) that is going to be bored .030 over. The heads are world sportsman II cast iron with 64cc chambers with a little bowl polishing. He also says that we can run 11:1 static compression with a comp 260 (if that doesn't sound right its my fault) cam on premium gas without pinging. The heads are mine and I want to use them if at all possible.

I have read here that aluminums are better for 11:1 but he says that we can run the iron. Would this be a problem on a weekend warrior?

 

in louisiana? yep. I think 11:1 on iron heads, with a small cam like the 260 (or just about any remotely streetable cam) would be trouble-a-brewin'.

64cc heads, and flat top pistons shouldn't get you 11:1 though. I have that, with a somewhat decked block, and it's a hair over 10:1. Use an internet static compression calculator, and do the math. Phone him up to get the actual #'s, and do the math.

I'd stay around 10:1, or slightly lower if you can.

 

Thats what I thought too, but he says otherwise. I guess we could just try and if it causes a problem I'll just swap for some aluminums with one of his pals. He just insists we can do it. I know that he is not lacking in building or racing experience.

Once again, I'm confused.

 

Sometimes, what works on the strip, ¼ mile and 11 seconds or whatever at a time, doesn't work on the street for a hundred thosuand miles in all kinds of conditions.

You're not building a race car motor (I don't think, anyway... correct me if I'm wrong). You'll want a motor that will run on the watered-down cat pee you can buy down at the corner store, on a 105° day, sitting in a traffic jam with the A/C running, and then gagging it to get back up to speed on the expressway.

Don't go past about 10:1 with iron heads, and that, ONLY IF everything else supporting such a compression ratio is PERFECT. Consider the implications of that word carefully: PERFECT. That means the quench is right, with the block zero-decked to the pistons; the combustion chambers worked PERFECTLY, so that there are no sharp edges to create "hot spots"; the tune (timing, jetting, gearing, converter, etc.) is PERFECT; etc. etc. etc. Any of those things that isn't right, will cause trouble even at 10:1. The kind of trouble that causes internal motor parts to be scattered all over the highway.

A zero-decked 350 with 6cc-valve-relief flat tops, 64cc heads with minor polishing, and a .041" head gasket, is pretty close to perfect. I'd shoot for that combo, right there.

I'd also put more cam in it than a 260. Go with the XE262 instead.

 

he builds more street engines than strip ones. I don't know, if I trade for aluminum heads I should be able to go 11:1 right? Its just a weekend warrior not a daily driver. I want it to be really stout. How much hp would I loose going to 10:1?

 

OK....called my guy back. I was wrong. He says 11:1 pistons with .040 head gasket and the bowls are going to be opened and polished to maybe 68cc will give me about 10.2 - 10.4 which is still a little high, but he says he has "secrets" that will get me on pump gas with no problems.

Does this sound better?

And the cam is a comp cam 280, but he is not set on that. I'm open to suggestions!!!

 

A lot better especially with the comp 280 cam. It will depend on what the dynamic compression ratio is. I would not go over 8:1 dcr with iron heads and all the secrets.

 

that cam should suite that combo and compression ratio.

I have a buddy with an 11:1 sbc running a roller cam on 93 octane and iron heads. Sure you gotta have it timed perfectly, and if u get a bad batch of fuel your pretty much ****ed, but basically its doable. Static compression isn't as important as dynamic compression, with the right cam you can run high static compression and have a streetable dynamic compression ratio that will run on pump gas..

 

Thanks guys...I knew he wasn't crazy.....but for a second, I thought he was!

anyone have a suggestion on a cam that might be better?

 

i've just posted the question on your other thread about your plans to run 11.1 on cast heads. but now i see you've got it sorted

 

on the cam note. i'm no expert but having spent months checking out different combo's the XE274 comp cam seems to be a cracking streetable cam with the right stall

 

hey i dont mean to hijack the thread (but i guess i am, sorry) but my brother is having some problems with his motor, we just put together a 355. its got flat top pistons, a crane cam w/ 518 intake lift and 536 exhaust lift, and he put a set of stock 305 heads on. dont know the compression exactally but we're thinking its something outragous. and he runs it on premium but gets an accasional ping at moderate throttle position, he has a vaccum flutter at idle, it holds about 20lbs of vaccum but it flutters and it still pings even after putting a tank of 94 octane sunoco gas w/ octane booster. it has an edelbrock carb, not sure what cfm rating it is but we dont think its that much could the carb be causing a problem?
Thanks
Joe

 

Install cooler champion RV8C spark plugs. (gap @.035")
set ignition timing to 32-34deg total mechanical advance.
A motor with this cam will want a lot of initial advance, you may want to lock out the advance curve (34 initial, 34 total)
Limit vacuum advance to add 15deg at high(est) vacuum cruise. (typical 20 deg too much)
Find the model number of your carb and verify jetting. May be too lean.

This motor would be much better if the 305 heads were ported with larger 1.94" x 1.60" valves. This would result in a slightly larger combustion chamber size (deshrouding) which would tame the compression ratio just enough.