Valves are identical, ports are almost identical. Go with 243 or if your wanting more compression go with a 706

 

The 243/799 will raise compression to about 10:1 with no other changes

 

Thank you. I thought the 706's along with some 862's are the Castechs that crack. I'm surprised to see a 706 recommendation. I don't have a set of those so they're kind of out of consideration.

IF Summit is right, there is a smidge of difference on the exhaust valve

 

I don't have pistons yet. Heads will dictate which piston is ordered, flat tops vs. dished. CR has to be regular fuel friendly, not running high test all the time, so somewhere in the 10's I suppose. Perhaps in this application it doesn't matter which head I use as they all flow roughly equivalent in the daily driver rpm range. Just didn't know if there were any other extenuating factors why to use a 317 head vs. a 243 head vs. also a 706 head. Thx.

 

Pump gas 91 or 93? I might have missed it
either way a stock lq9 is 10-1 and they suggest 91-93 but can easily be ran on 87

Since this is a daily, I’d be wanting to run 87, so I would stick around that 10-1 number and use the 317s with flat tops.

if you would rather spend more in fuel then do something closer to 11-1 like the flat tops and 243

The casteck head cracking must be rare these days because I haven’t ran into any from the junkyard, nor do I hear about it anymore from anyone else.

 

He mentioned wanting to use regular (87). Most Gen IV truck engines are 10:1 and use 87 so he should be fine that way.
I think you're right about the Castech heads. I think the ones that would crack have mostly done so.

 

High octane usually costs about 35-50 cents more per gallon, and most of us put around 20-23 gallons in on a fill up. That's about 9-10 dollars per tank. HOWEVER with higher octane you get a lot more throttle response, power and MPG so the additional cost washes out with the additional MPG and makes for a lot more fun and powerful build.

OP how much more is high octane (91/93?) where you live? How many tanks do you go through a week?

When I did a 93 tune on my bone stock 2004 5.3 truck, I gained 2 mpg, and generally used a tank a week, but I would get another day out of the fuel. 93 was usually about 40 cents more per gallon for me and I always put in 20 gallons to fill that truck from E to F. Doing the math it came up to somewhere around $4 a week extra. And was a hell of a lot more fun to drive and faster.

 

There is 87, 89 & 91 gas here in CA. The plan is to build something that can be run on 87 if need be and under light load, but also wouldn't mind flirting with a CR that does better on high test 91. I just don't want to married to running high test 91 at all times. If I find myself where it's prohibitively expensive or unavailable, I would like the ability to run 87 or 89 as necessary. I can adjust driving style and load accordingly. I see the factory lq9 was a 10.1:1 factory set up with 317's. Is 10.5:1 too much with my fuel requirements??? I think the flat top piston and 243 at 11:1 is out for my application. I just have to see the light of which head to run so I can purchase the pistons to go in this thing. Right now, I am leaning towards the 317's and possibly have them surfaced just a tad more than ensuring flat/straight to bump the CR.....or is that more effectively accomplished by going to a thinner head gasket to tighten up the quench at the same time?


In regards to the 706's, I thought all of them eventually crack and not "if" they crack??? I guess I learned something new. If anyone knows, what CR would I be at with lq4 dished pistons and 706's? I know lq9 pistons and 706 heads would be way too high.

 

I haven't had a 706 head crack..... not saying they still dont, but I haven't.. My 5.3 in my suburban has 706 heads with over 300k miles on them??? I have seen cracked ones before but never had it happen.

If using stock Lq4 dish pistons the compression ratio is as follows give or take 0.1
706/862 heads 10.6:1 with 62ish cc combustion chambers
243/799 heads 10.4:1 with 64ish cc combustion chambers
317 heads 9.5:1 with 72ish cc combustion chambers

If using stock flat top Lq9, Ls2, or L76 style pistons give or take 0.1
706/862 heads 11.4:1 with 62ish cc combustion chambers
243/799 heads 11.1:1 with 64ish cc combustion chambers
317 heads 10.1:1 with 72ish cc combustion chambers

 

Thanks for all the info above. I'm coming around to finding a set of newer 706 heads that are not the Castech Crack Head Special. I've not replaced a cracked Castech head myself, but there are enough reports of them to make your eyes bleed if you read all of them and most of the results mention the 706 casting # specifically with a few 862 mentions in there too.

I suspect if I found a set of 706 heads from an 05-06 Silverado/Tahoe/Suburban that I'd be safe with those later year heads, but is that not necessarily the case? Seems like the most common cases of Castech Crack Heads are earlier gen's 00-03-ish? Would it be worth the effort on the 706's to upsize the intake valve to the 2.00" valve of the other LS heads when I have them rebuilt, valve job, etc?

I see flat top pistons paired with 706 heads would be out of the question for my daily driver, but would the dished piston of an lq4 paired with 706's be unfriendly for daily driver duty on low octane regular fuel? Anyone done this? As I mentioned before, I don't want to be married to having to run high test 91 fuel. I will consider running it but there are times and places that I want to be able to pump the cheap **** in to get me home. If the 706's will make it a little more finicky about fuel requirements, then I suppose I'm leaning to lq9 pistons and 317 heads to keep it in the 10:1 range which I know is 87 capable. Thanks again everyone.

 

I wouldn’t be scared to do the 706 heads and lq4 pistons but I would get the tune right and watch for knock when it’s up to temp at low rpm on hills and accelerating with 87. I have no doubt that you could tune it just fine on 87.
If I was going to be towing I would just throw a tank of 91 in there during that time due to the extra load.

I think having the heads worked and installing a 2” intake valve would be pretty much useless unless your going to be revving to 7k With a huge cam lol.
I would do the 706 heads and a 08+ 4.8/5.3 intake
longtube headers and let it eat.
The increase in compression would get better fuel mileage also.

 

I appreciate all the info you guys are giving on here!!! I’m in a similar boat, debating on working the 317’s that came on my LQ9 or going to grab a set of 706’s and having them done, so this helps with some questions I was thinking about 👌🏼. Mine is not going to be daily driven and will be in an old K10.

 

I would defiantly get the 706s especially if staying NA

 

Old thread resurrection.

This build has been slow going with the last year slipped away. I'm finally at the assembly point with it. All machine work is completed, other than cylinder heads. I did decide on lq9 flat top pistons, which I got as part of the $700 WS6 store kit. The pistons that arrived were Enginetech pistons, not Silvolite pistons as advertised. Both Silvolites and Enginetechs are a Made in Mexico product, so they 'could' be the same piston, but there are noticeable differences when comparing the two in pics.

The last piece of the puzzle is cylinder heads and the plan at this point is to use the 317 heads since I now have flat top pistons, and to keep the CR in friendly territory for daily driver and tow rig duty. Cam will either be factory, Summit 8719, or TSP Stg 2 low lift as I want no lope so it's more of a sleeper.

Need to get the heads gone thru and checked, but have a question on them. I've been happy with the results from the machine shop that did the block, and rotating assy, and recently found they do cylinder heads too. It sounds like reconditioning LS cylinder heads is their "bread and butter," their words. However, they do not do bowl blend or any sort of port work from what I understand. It sounds like they do more of a stock rebuild valve job, surfacing, etc.

Gotta get the heads done to keep the build moving. Would I be leaving much on the table in not having these heads massaged with a little bowl blend work, back cutting intake valves, or other mild port work and just going with a run of the mill multi angle valve job?
Thanks.

 

The best thing for the heads would be a bowl blend and a top notch multiangle valve job.
80% of a decent port job are in those two things alone.

 

I agree with the above...... but with the RPM range you will be in and a low lift cam I honestly doubt any gains from porting or bowl blending would be noticeable.

 

Thank you both for the suggestion and info. I was wondering if my RPM range(500-5000RPM) would factor in on whether the bowl blend, head mods even would be noticeable. Multi-angle valve job is what this machine shop offers but I think the bowl blend is something they do not offer. I should probably clarify that with them to be sure. I also asked about cutting a bit more when they surface the heads in order to bump the comp up above 10:1 of the lq9 and stock 317's. My thought was around 10.5:1 CR to shoot for, since the huge chambers of 317's have a downside, and a compression bump never hurt anyone. The machine shop advised against this because it will likely contribute to valve train geometry being off spec with the heads being cut more, which theoretically makes sense.

 

The bowl blend (or pocket port) is to smooth the flow more than increase it. It gets rid of the ridge right below the valve seat.

 

You would just need shorter pushrods to correct the geometry, they should know this.
I am not sure how much would need to come off to get the compression to 10.5:1, but I do know that using 706/862 heads will get you very close to that.

 

So it sounds like the bowl blend/pocket port is something I should not leave undone before re-assembly. Any other opinions or suggestions on necessary head work for a 500-5000rpm daily driver lq9?

I do believe they know that shorter pushrods will correct everything, I think the point is once you go down that hole, the ability to use all factory parts is out the window.

Have to check but I think using the 706/862 heads with flat top lq9 pistons would yield over 11:1, which is out for this vehicle.
Thanks all.