Did a search and didn't see this posted:

http://www.hotrod.com/articles/surpr...der-head-test/

I did notice that the 706s were carrying the power well past peak, likely due to the lighter valves.

 

Yep I saw that. Good info

 

Most likely due to increased compression with the 706

 

Yep I agree stock the combustion chamber volume is 61.15 tighter then most LS heads.

 

If you head flows enough for your combo, going to a better flowing head will yield marginal results, sometimes even killer torque AND power. You can definitely go with too big of a head and hurt your setup overall.

The 706s are a good example. They flow well enough for most 5.3s so going to a better flowing head with a larger chamber just ends up causing power losses because compression becomes the deciding factor.

 

Yes compression is your friend. Especially in a test like this and especially with bigger cams. Need the compression to make them work. Ask me how I know

 

That is like anything really, if the combination of parts is mismatched the potential for loss is higher. The heads can only flow up to their capabilities if the intake, exhaust, and camshaft suit.

The above test definitely didn't choke out the heads with a crap intake manifold or tiny headers, and the valve events favoured the small exhaust ports with a wider split than traditionally recommended for cathedral port heads.

 

So either the price of the 706 is going up or the 799/243 is going down!

Ok, probably neither.....

Intetesting article for sure.

Ron

 

Yeah; not surprising that a small engine with the wrong cam AND a huge intake
seemed to favor the heads that made it "at least" 9.5:1
Sort of a bullshit test really.......................

 

I don't know about that, it's a pretty valid test for those of us with the 4.8/5.3L builds.

 

Very much so.

Results would have been a little different on a 6.0, and likely much different if you added a 4" crank to said 6.0.

But for the average 4.8/5.3 build, very relevant. CFM demand isn't that high. Even the stock heads are able to keep up with it. Therefore, compression is the deciding factor.

 

I wouldn't have been as surprised in the small difference in power if it had the stock cam and intake, nice to see that they were that close with a decent size cam and a 102. And the compression helps, but the compression isn't that much different, difference is only what .3-.5 or so? iirc it's .5 difference on a 5.7

 

I still think the 243 is a better head if you want to get it CNC ported. Stage 1 243 and Stage 2.5 706 are almost the same cost.

 

Any idea on how they compare?

 

We started offering affordable mls gaskets for them for good reason BUT when you look at the flow numbers that went with that test...then its just a tad off. So it should be taken with a grain of salt really.
Esp on an engine with huge injectors for no real reason and no accy etc etc.

 

Were there not affordable MLS gaskets available for the 5.3 before? I keep seeing people using LS9 gaskets on them and have no idea why.

 

LS9 is used for boost bc it has more layers then a standard MLS. Standard MLS should be available for all engines, or worse case you could use a 5.7 gasket on a 5.3 if need be.

 

Well you're right about plenty of 4.8/5.3 builds but IMO nobody is gonna run an LS3 type (E/I split) cam, a FAST 102 intake, and low compression on a small engine without boost. And whatever flywheel horsepower it did make can be dropped by 50 simply because of the water pump, alternator, power steering, air conditioning (perhaps) and an exhaust system capable of keeping officer Bigfist off your backside.

 

Cant use ls9 gaskets on 706/806/862/853 heads that have notch on the deck or any other mls gasket save for pricey Felpro mls or Cometic mls. They use the ls9 because social media and the internet tells them to. Nevermind the horrible quench and cr drop the ls9 gaskets are BADASS and made for boost! Most of them dont even realize some heads have that notch in them.
We have a thread about em here
Pic on customer engine also

 

You would be VERY surprised then how much people still take magazine builds like this literally as law. It boggles the mind, but 95% of the people out there are happy enough to be led by social media and magazine builds etc.