400 HP open chamber head cleveland

[Omie01]

Does anybody have experience building a 400 HP cleveland with 73 open chamber heads? I got a pair of 4 bbl open chamber heads for almost nothing, and they are freshly rebuilt. I would like to build a 375-400 hp motor using these heads. My questions are, do I need pop up pistons? If so, can I expect detonation issues? Any good cam suggestions? The heads have the .205 intakes. (small valves). I have been thinking about the kieth black pop ups that everyone seems to recommend. I am using a 2 bolt bottom end block so I dont want to get to crazy. I'm thinking a roller hydraulic cam, and going to have rocker studs and girdles installed. I just want to hear from someone that has experience with these heads. Any input would be helpful. Thanks........

 

[InjectedMach]

comp cams roller cam(mid to aggressive grins), roller rockers and 750 cfm carb or efi, mid length or short headders ,hot ignition not a cd box. I think you will see 430 flywheel hp easily.

 

[Jeff73Mach1]

yes to pop ups-though they aren't 100% necessary, they improve detonation resistance in my experience. Will need more total advance than closed chamber heads. I think it all depends on getting your tuning right and when isn't that true?

The price is the cost of rebuilding heads these days with all clevelands needing aftermarket 1 piece intake valves as the factory ones occasionally fail spectacularly

Verify they are one piece valves and I say go for it!

 

[MotoArts]

And don't fret about the "2 bolt" bottom end... It's no weak-kneed small block Chevy!

 

[Omie01]

Thank you for the input guys. My goal is to build my 72 FB into a Boss clone, and I would like to see at least 375 HP so it feels like a real boss. I know they were 330, but hey, a little more never hurts. Could you elaborate a little more about pop ups NOT being necessary? I can use regular flat tops? I'm not looking for 11:1 or anything, I think 9:5.1 will do it. Is this right? I know I have to replace all the valves. and get better rockers. I just dont want detonation issues. Should I use the multi set timing chain then for advancement? Thanks again.

 

[MotoArts]

Here's some stuff to make yer head spin... but don't get too caught up in it! LOL

http://www.network54.com/Forum/119419/thread/1315299641/351C+cylinder+heads+-+squish+and+other+issues




http://www.network54.com/Forum/119419/thread/1278202223/open+vs+closed+chamber+heads

These look interesting, too:

http://forums.corral.net/forums/351c-bbf-parts/1299980-new-domed-pistons-open-chamber-351c-heads.html

Find everything, and I mean everything, on 351C stuff - here:

http://www.351c.net/

At the end of the day, it's how fast do you wanna go, and how much do you want to spend?

In a nutshell, more compression gets you to 375 easier.

But, do you want... or need... the components to get you the compression?

Remember, you'll need to feed the engine what it wants.

Expecting 375 on 87 octane probably won't happen.

The ultimate timing set need will vary depending on cam, head and compression choice.

As you see, there is NO one simple answer to your questions, unfortunately. The variables are endless...

 

[Jeff73Mach1]

a Boss 351 was rated at 330, but I've seen some dyno testing of matching builds and they seem to be more like 385 hp. It is relatively easy to do better.

the pop ups aren't exactly for compression they are to "mirror" the shape of the combustion chamber to allow the flame front to spread evenly which is part of what helps the ignition system work without detonation or pinging or preignition. As I said, you can not use them and at 9.5:1 compression on 91 octane gas, you should be just fine with proper tuning. I'd call a cam maker and have a custom ground cam to reach your goals with your major components selected.

as to the 2 bolt block . . . all Clevelands have bosses for 4 bolt mains-the problem comes in finding a set of caps. ( I have a spare set I'd sell if someone wanted them. After installation the machine shop will have to line bore the block so figure a few hundred for the extra machining.

What I chose to do was invest my money in a fully internally balanced engine and an ATI dampner and a neutral balanced Centerforce flywheel. The improved harmonics will, hopefully, allow the two bolt block to live at my 600 hp level.

 

[c9zx]

Go to this site, Mahle catalog, page 19, -3cc valve relief.

http://www.us.mahle.com/media/motorsports/mms2014appguide-compressed.pdf

Then, go to this site, Diamond Piston CR calculator to play with the variables to see the range of CR possible with the Mahle flat top piston.

http://www.diamondracing.net/tools/

Some of the variables are deck height (9.206 stock), piston height (.000-.010 ex.) relative to the deck height, distance to first ring land (.275 ex.), Gasket compressed thickness (.035-.041 ex.), gasket bore diameter (4.060-4.100 ex.), piston dome or dish (-3 for the piston cited above), head chamber volume (72cc-78cc ex.). Rod length is 5.778. With readily available parts, and a VERY COMPETENT machine shop, Static CR of 8.9 to 9.4 are achievable. You will need to match the cam characteristics with the SCR to end up with a Dynamic CR that indicates it will be compatible with the Octane number of the fuel you plan to use. Do not seek cam advice from people who are not VERY familiar with Clevelands. "If some is good, more must be better" turns out to be wrong a large percentage of the time. There are many other variables to consider as well. Good luck with the build. Chuck

 

[Omie01]

So the pop ups are for better ignition characteristics. Well thats a bonus in my book. As I said, going for a mild build. I will call and go over my plan with a cam maker. Thanks everybody for the info!! Such a big help!!!

 

[droptop73]

The domed pistons may be a little less prone to detonation but any dome hurts flame travel across the piston. Keep it sane, it's good to have a goal but dont make it undriveable.