I'm looking for some help or feedback with getting my specs sorted out for a head-swap on my truck. I thought I had this figured out, but I don't. (Some of you SSS guys have probably run across this info -- just looking to get a thread going on this site)

Current/stock specs: LQ9 6.0L block. Rated at 10:1 by GM. Flat-top pistons, 4" bore, 3.622" stroke, 6.098" rods. 71.06cc chambers. .054" x 4.04" (compressed) gaskets. Deck height - Guessing at -0.008, out of the hole - haven't cracked my motor open yet.

Cam: 210/218 (272/280) on a 110ICL 112LSA.

Throwing these numbers in a SCR/DCR calculator, I'm getting 10.23 static, 8.07 dynamic... stock. Not too shabby. This is showing an alleged quench of .046.

Vehicle useage: The truck weighs in around 5,400lbs - maybe a little more, maybe a little less. I always run 93 octane. The truck is used to tow a 5,000lb trailer about 500 miles a year, otherwise it's a daily 50-mile commuter that visits the track every now and then.

Vehicle mods are listed below. Your usual (minimal) bolt-ons.

I'm looking to install AFR 205's to help out the "torque theme" I have going with the cam. I AM willing to go to just about any size on the cam, so long as I don't lose any of the excellent throttle responce and torque I have right off the bottom of the RPM range. I do NOT want to be "required" to run a stall with my final powerband, and I have little-to-no interest in revving much over 6,000-6,200. I don't mind moving the ICL around on this cam.

My options...

66cc's on stock .054 x 4.04 gaskets - 10.85 SCR - 8.55 DCR. Quench still at an alleged .046".

- Is this too high for all this bulk I'm lugging around? How about towing on those hot summer days?

- If I understand DCR correctly, the "rule of thumb" is to keep it under 8.5:1... but I heard some opinions out there saying GenIII motors are good up to 9.0 DCR. Is that only for the, light GenIII cars?

- Would you go tighter on the gaskets for a little better quench? If "Yes" - where is the line drawn with going too high with the CR for better quench? Is it "not drawn" if you're under, say, 11:1 static?

Just to put the "extreme" end of the spectrum up here... 66cc's on .041 gaskets, assuming 4.04" bore... 11.22 SCR - 8.83 DCR with a flirtatious (alleged) .033 squish.

- Suggestions on gasket sizes to use?

- Suggestions on doing the head swap in general? What you YOU do?

A final side question - I can't... or shouldn't buy head gaskets until I have the motor torn down with the deck height speced out, correct? Kind of a dumb question - but it seems like a lot of head-swaps I read about are a "bolt on in one day and go WOT" type thing. I'm seeing it as much more involved...

Thanks, I really appreciate any help...

-marc

 

I'm sure you will get some good response here in the Truck forums, but don't forget to also post in the LS1-LS6 Internal Engine section as well...that's where a lot of really good knowledge of motor specifics on LS1Tech resides.

 

Thanks NA - I actually posted this up there yesterday, and got like 14 reads and no responces!

 

He will find good info using the search function in the internal section, but good luck getting quality answers from car guys once they read its for a truck motor. When I had question in the past, I started leaving out the part about it being in a truck.

Now Marc, I've already answered most of those questions for you a couple of weeks back, so I won't dwell on them much more. Glad you took the time to calculate out all the ratios. Its better to question everything up front (like GMs alleged 10:1 CR) than to have problems later and try to figure out what happened.

Added thoughts to the things I've already said in your other threads -

You know that adding better flowing heads like the AFRs will increase the powerband / rpm range for a given camshaft. That means a certain cam won't run out of breath as quickly since its flowing more air than a stock head. If your current cam is fine to 6000, I'd venture to say that it will run 6200 with the heads.

I'd be very tempted to just swap heads only and get true results from a head only swap first. Then make the decision on going bigger with the cam.

You know that in general adding duration adds more upper rpm HP while eating away at your very low rpm torque numbers. I honestly think you whould install your converter. It will really desensitize the lowest rpm torque loss from a cam. Then you could go a little larger in the cam dept and not notice the change.

You probably don't need such a large split duration cam with the headers and catback.

I said it before - stick with the stock head gasket.

Now on the heads - On that small of a cam and your weight, I think 10.8+:1 CR is a just little high. Of course I was the one that pointed out the high CR to you in the first place. But the effeciency of the AFR heads will really help out though. Its not going to blow up or anything, it just may be prone to a bit more pinging under heavy loads in overdrive at sub 2000 rpm spots.

So there is the question - would backing off to 10.5:1 really be any different? Honestly, probably not anything you'd notice.


My final opinion - Just install the 66cc AFR heads using stock MLS GM gaskets and keep your current cam for the time being.

 

Thanks a lot, Tex. I was kind of trying to let you off the hook there in the first paragraph.

I C&P'd this from the post on in the car setion - I have every little detail that I could think of up on here, so that they knew were they could and couldn't go with things. I'm not necessarily considering everything.

I'm pretty much dead set on a head only swap. I'd only change cams at the same time if someone had some oddball one-off custom grind that would magically meet all of my needs and somehow make these heads work perfectly.

I guess one thing I may have going for me is that I don't put any heavy loads on the motor at low RPM's... unless I'm towing. All of my kickdowns are at light throttle, and my RPM's bump up to 2,000 or more at anything but the smallest throttle. My TCC lockup is over 45mph to avoid a sub 1,500rpm flat area... the unlock is also very light.

I'm not worried about blowing anything up (much), just worried about having to really neuter the timing, put a lower t-stat in, get my e-fans running constantly in the warm weather -- things like that.

 

Yo Marc -

I searched for your post and found your problem with nobody responding in the other section...

You have 'truck application' in your title (a no-no), and then almost fall over yourself apologizing for posting in the Internals section. If guys don't move on or skip the post immediately because of your title, they will certainly stop reading after you apologize for posting there....

I suggest posting again without putting 'truck'-related in the title. Then just post your questions. Tell them you have a 6.0L block. Lots of guys with F-Bodies lust after the LQ4 block because of the torque down low. Some have gone down the 6 liter path. You will impress them with your willingness to do calculations, and I bet you will get some help.

Toward the bottom tell them you have a truck and as a result you have special considerations (then tell them those considerations).

Good luck!

 

So.... trick them?

I was just trying to be a nice guy, that's all.

 

Naw dude, don't trick them, just give them a chance to help you. You're asking for help, but I think the way you're doing it is hurting your cause.

Your question is essentially a motor question. For that reason, it is really irrelevant that you drive a truck. By saying 'truck' in the post title, I bet people who possess the knowledge to help you are skipping the topic.

Just M.O.

 

Doing the same math using my bottom end specs I come up with 10.088 SCR and 8.886 DCR with almost the same cam and stock 66.67cc LS1 heads.....what exactly am I not seeing here ???

 

But it's in the "car" section..........? I'm breaking the rules!