440 Compression and Cam Choice

[Dano 1]

I was watching a recent Engine Masters show where Steve Dulcich and the gang were testing a super low compression RV 440 with a narrow lobe separation cam. The theory was, as I understand it, the narrow lobe separation angle helped increase cylinder pressure in low compression ratio applications.

I have a bone stock '71 440 in my car which I foolishly put thick felpro head gaskets on so I'm likely in the 8-8.5:1 compression range at best. The engine makes good compression and appears otherwise healthy so at some point I'd like to build a bit more power without going through a full rebuild. Would a tight LSA cam like a Hughes Whiplash be a viable choice? I certainly don't hate the sound at idle but I'd rather have a cam that's properly matched to the engine than build around a choppy idle just for the sake of it.  I have an Edelbrock CH4B intake to go on it as well and it has 1-3/4" primary standard headers with a Holley 750. Rear gear will be a 3.23 with 28" tire, 727 trans with a cheetah manual valve body and stock converter.

Curious to hear some engine experts thoughts on compression ratio and LSA, in general or specifically with my application in mind.

[c00nhunterjoe]

Need more info on the engine. Bone stock, low compression, 8:1 in the 1st breath followed by its healthy and has good compression in the next. Which is it? Not trying to be short, but you havnt given us anything to work with.

[Dano 1]

Sorry, Joe, the engine is bone stock (pistons, heads, stroke, bore etc) with the exception of the headers, intake, and carb. My comment about the 'good compression' was merely in regard to cylinder pressure readings after a normal compression test to indicate the engine is healthy enough to not need a full rebuild.

Standard compression ratio on a '71 440 is 9:1 according to stock literature so given my choice in head gasket I'm assuming I'm looking at 8.0-8.5:1. 

I also realize this topic would probably be better suited for the performance section so mods, feel free to move at will.

[c00nhunterjoe]

What was the cranking compression? What part number pistons did you put in it. What heads and what hewd gaskets?

[firefighter3931]

Dano,

With that combination of parts I would use a Crower HDP 271 grind. It makes really good power and the duration is not excessive which helps build low end power & cylinder pressure. The tight lobed profiles have a narrow power band and dirty idle. Tuning can be difficult when you have lots of overlap. The Crower stick will idle pretty smooth and is compatible with the stock torque converter. 


Ron

[Dano 1]

Joe, the pistons are the stock ones, this engine has never been apart besides my gasket job, it was a takeout from a '71 imperial and was complete carb-oil pan when I got it. Cranking pressure was 125-140 cold and dry across all 8. Heads are stock again, 346 casting I believe and the head gasket is FEL-PRO 8519PT1, installed before I realized it was thicker than stock and would have an adverse effect on compression.

Thanks for the recommendation Firefighter3931, I'll take a closer look at that grind. This is my first big block Mopar so I really want to try different parts to understand the power/drive-ability effects of each. 

[c00nhunterjoe]

Phew, that will be lucky to sit at 8:1. Stick with ron's cam, especially running a 3.23 and 28" tire. It will still have decent torque to get rolling.

[Challenger340]

The 'idea' behind the tighter LSA is to try and pack a higher albeit 'shorter' powerband ..... think of the powerband like a finite length of string ?  that with wider LSA as you can move the ends of the string farther apart you also lower the height of the 'peak' in the middle ?
And Conversely....
if you move the ends of the string closer together.... you can move the PEAK of the string in the middle HIGHER ?

Same-same with Cam choices no matter a 10:1 compression ratio engine..... or 7.5:1 Compression ratio engine.... you wanna bump up the PEAK power just tighten the LSA for any given profile... albeit the "length" of the powerband shortens.

Nonetheless....
and in my opinion only.... "peak" power being a function of engine rpm/breathing power is far LESS important than TORQUE.... and more importantly a broad/wide Torque curve with these big heavy Cars... which related to the CROWER HDP271 makes it an excellent choice for most medium to low Compression 440's.....  mainly because LSA aside, the HDP271 incorporates some valuable Lobe parameters conduscive to the long Rod Ratio(Piston dwell time) found in 6.76"/3.75" Stroke RB Mopars.

No question.... the HDP271 is a hitter camshaft in 440's.   

[Dano 1]

Thanks for the replies, guys. Joe you're exactly right, it's not a great setup but the engine doesn't appear to be in bad shape and a full rebuild isn't really in the budget right now.

That's a great explanation Challenger340 and exactly the type of info I was looking for to better understand the theory. I could just go buy any cam but I really like to understand the theory behind the choice as best I can. I totally agree that peak power is overrated, at least on the street. Just about everything that I've ever driven and really liked for street fun was something that made a ton of torque down low.

[c00nhunterjoe]

In all honesty,  just a cam swap is not going to turn that mill into a race car. 20-30horse behind a 2 ton b body is not going to be super noticeable. Imo, save the money and if it is as healthy as you say, enjoy the torque it currently has until you can build a stout engine.