So we're getting close. Not quite order parts close, but like the very last step before that. I've been planning out my new 400 rebuild all year, and basically, it checks out with everything I know/have been able to find, so this final step is where I fish for criticism instead of blowing up a motor in 2 months.....

The planned build is as follows:

Take my current engine; a 71 400 block, .030" over, flat top pistons with 3 cc valve reliefs, stock open M heads, with moderately heavier springs, and new retainers and locks, a stock cam advanced 4*, double roller timing, Weiand Performer dual plane intake (fairly long runners, about stock size, but pretty streamlined too), a Holley 670 Street Avenger carb on top, and a stock (but new) Duraspark ignition,

AND

replace the stock heads with Aussie 302C 2V's, replace the stock cam with a much more aggressive one, swap the valve springs off the current stock heads, onto the Aussie's (these springs and this cam were originally a matched, planned set), and keep the rest the same.

I built my current engine with a stock cam purposely, in order to get my dynamic compression ratio as close to 8:1 as possible (ended up 8.1:1), with the low compression open chambered heads. The static CR is about 9.2:1. You may be running the numbers yourself, thinking I'm way off somewhere with flat tops, and a tiny advanced cam, even with the open heads, BUT, as with many 400's, my pistons top out at .077" down in the hole. I run this engine on good old dirty 87 octane, and after a little break in, it never pings.

The new build starts off with what some may think is an insane STATIC CR, 10.75:1 or so. But, I'm using a MUCH longer duration cam. It's a regular hydro flat, but with a 218/228 .050" duration, 276/286 full duration, and a .509/.509" lift. It also has a 114* lobe separation, meaning that the intake valve closes at 72* ABDC, giving me a DCR, when installed straight up, of 8.08:1.

The Aussie heads actually flow significantly worse than the open ones, because of the closed chambers shrouding the valves, so with all else the same (intake, carb, headers, exh), and the bigger longer cam keeping the ON PAPER DCR virtually the same (8.1 and 8.08) I may even end up advancing the new cam, to get it to 68* ABDC, giving me a DCR, ON PAPER, of about 8.35.

That would be a mod though, I'm going to start at 72*, first of all in order to air on the side of caution, and second, because I have a huuunch that the long thin ports of the intake, the somewhat flow limiting chambers of the Aussie's, and the relatively long gradual duration, but not especially large lift of this cam, might all work together very favorably, raising the actual REAL WORLD DCR (as opposed to the on paper one, which does not take a specific engine's volumetric efficiency into account).

Whew, that went on longer than I thought, but now get at me! Anything making anybody reeeally nervous? Anything I don't know about Aussie's, different spring seats or anything?

Hope you guys like it, AleX.

 

Sounds good. What ever heads you use I'd blend the bowls and do some porting in the exhaust. Degree your cam in to the mfgr's specs.

 

I can see the wheels are turning in your head. whatever happens you will be a little wiser in the end. learning your situation, nothing like real world application. good luck and I was wondering about the shrouding of the valves with aussie heads. never flowed those heads yet!

 

Eh, I actually don't think I'm planning to do much porting, especially the bowls, I just don't have the tools. I may try to blend the bottoms of the valve guides a little with like a dremel at least I guess. I also don't have the heads in hand yet though, and I know they were just rebuilt and fully worked over by Jasper, so they might already have some port work done to them, we'll see. Also though, I looked into exhaust/intake flow ratios alot last night after posting this, and unported, a Cleveland 2V actually already has a pretty high ratio, especially for a street engine like this. The Aussie's seem to only flow about 70-75% as much volume as the open chambers (though figures on both are EXTREMELY scarce), but the exhaust to intake ratio's are actually really close, both right around 82%. 90% is like the hiiiighest I heard of, and that was on an all out drag engine. What a high ratio means, is that the exhaust valve/port flows almost as well as the intake, AT THE SAME PRESSURE, but the exhaust of course flows at many times the pressure of the intake (exploded mixture pressure, as opposed to atmospheric), so, if they flow at close to equal rates on a bench, the exhaust will scavenge way too MUCH gas from the chambers, yielding a low real world DCR.

All in all though, to both of you, there is not enough info out there, and I don't know nearly enough about engines to plan it out on paper too much better than this, so Mark A. you could be totally right, and Wyo, right, that's the idea, I may not get it perfect irst try, but I *think* I've done enough thunking to put myself within a tuneable ballpark.

 

what tranny? c-6, what stall converter or any mods to c-6 and what gear. Might need a little gear to back up your engine. your getting into tranny mods with the cam your running. something to consider. Atleast a 1800 stall if I'm guessing ballpark. ran a hyd 280 magnum once with a 2200 stall and a 3000 stall. It had a .530 lift if I remember correctly. This was a play/mudtruck on 38" and 4.10's I now run a 4.56 gear and 38" and a 1800 stall and this is border line at 450+ hrspwr. you will be getting into stator issue in converter was told more gear or less hrspwr. In this case your hrspwr will be fine compared to my bigblock application. things to consider and remembering stuff.