Hello all. I would like an opinion on which heads to run on my build, I have a set of 243's and a set of 317's. I'm building a mild 6.0 for a 1978 Chevy 2wd truck that will never be raced. It will be more for show and cruising around than for performance but I do want to hear the cam at idle. It will be .030 over bored with sealed power flat top pistons (I believe that's factory LQ9). I'm leaning towards a BTR stage 2 Truck cam BTR31218110. The reason for my head decision is that I don't want too much compression for pump gas, which is all I'm ever going to run. I have no idea what my piston to deck, either in the hole or out will be until I get this thing together but I'm figuring to achieve around .035-.038 quench. I don't want to have to rely on high octane pump gas, especially not knowing what the future holds. I played around with compression calculators and it seems like I can get away with the 243's but I want some expert opinions, thanks much to all.

 

I would do the 317’s with flat tops. That’s just me.

 

put all your info into a compression calculator and go from there

but if you only ever wanna run 87 octane i would just stick with the 317's

 

A stock LS2 is 11-1 compression! That's a 6.0 with flat tops and 243s from the factory! They made a zillion of them. You all need to stop giving bad advice! Does anybody ever come on here with a thread and say I'm going to put an LS2 in my truck? Should I put some 317s on it first!!!? Just use a standard fel pro head gasket. Don't overthink it if it's just a street truck. You don't need to be trying to get the Pistons in the valves to make out

 

I had a 408 at 11.5 to 1 static compression running on 91 octane without issues daily driving it for years. The cam comes into play as well as dynamic compression is a factor to consider when pushing the limits of pump gas.

 

The BTR is a 62* IVC @ .006" which is earlier than a stock LS2 cam. Once you have the engine assembled and measured to accurately calculate with each head volume, then decide. <8:1 DCR, 87 octane is possible. >8:1 you'd want 91+ to be on the safe side.. If it's just a cruiser, there's no need to push the limit of a low octane fuel by trying to run high DCR, so just use whichever head matches which octane you plan to run.

 

Most folks here are for higher performance builds, so 243s I think make sense for that.

Based on your needs 317s will be just be fine, especially since you seem to be concerned about fuel grade. Just get a good tune and off you go.
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As has been said here, the 317's might be best for your purposes, but if you have them off, a few things could be done to optimize them, like doing a bowl blen d (AKA pocket port), plus do a good precision multiangle valve job,
These two things will accomplish 70% of a traditional port job.

 

Thanks 68. I've been using the online compression calculators and I'm getting around 10.64 static and 9.4 dynamic, which I think is prob something I'm doing wrong. I'm figuring 4.03 bore, 4.06 gasket, 3.622 stroke, 6.098 rod, 70 cc head. .050 thick gasket. -.01 deck (guess, since it's not together yet). Using the BTR 31218110 card. IVC @ .050 =37*
Am I figuring this wrong? This combination is a factory ls2 isn't it?

 

You cannot use .050" figures to calculate dynamic compression. The IVC will be too early, and if the valve is .050 off the seat, you aren't building compression anyway. 68Formula's .006 figure is correct in terms of being able to get really close on DCR.

 

For a mild build show cruiser it is an absolute no-brainer to use the 317 heads. Save the higher compression heads for a build that needs it, or sell them for likely more than the 317 heads would bring in. Not every build needs to make the most power possible.

 

Thanks, I did finally decide to go with the 317's.

 

Thanks for the reply. I did see where someone mentioned 62* at .006. I'm not seeing that on the card (attached). I don't have the cam yet, I found this on the internet. What am I missing?

 

Ok, I entered info into the Pat Kelly calculator and I now see the 62* adv intake closing angle. I come up with dynamic 8.65 and static 10.64. Can someone verify if this sounds correct? Thanks,

 

A lot of companies don't release their "advertised" numbers because they can vary wildly amongst different companies ( a 280* duration cam from one may be nothing like a 280* duration cam from another ) and since cylinder head flow below .050" is generally a moot point, they choose to show @.050" numbers so enthusiasts have an easier time choosing a cam. If you were to call BTR and tell them you were trying to compute DCR, I'm certain they will give you the info you need to do so.

 

The piston volume of 0cc just means it's a flat top vs. dome, valve reliefs, dish, etc. Doesn't mean it'll end up in the same relative position to the deck as would an LQ9 or LS2. I would wait until the short block is assembled so the piston height versus block deck height can be confirmed, before finalizing any calculations. Then order the gaskets and decide on the head. Probably end up resulting in the 317s being the better choice for what you want. But when it comes to final engine assembly, it's smart to know both your piston position and compression ratio, even if it's just a driver.

 

I agree with the 317's if you are going to run strictly 87. But if you have access to 88 octane E15 fuel, then you could do the 243's and enjoy the free power/throttle response increase. You would be surprised how much more knock resistant that extra 5-6% ethanol is and it's cheaper than 87. The mild built 5.3 in my Yukon will run 22 degrees on 87, but with that 88 E15 I can run 26-27 degrees no problem. I have even seen the same results with my prior GMC Acadia LGX 3.6 and now my Cadillac XT6. On 87 the knock sensors pull the timing back to around 20-21 degrees, but with that E88 they both run full commanded timing as if I was running 93 E10, but for 1.60 less a gallon. It's still low enough E content that you can slide by on a standard pump gas tune without a flex sensor and it will run just fine.