Doc_speeder

iTrader: (1)

So there's practically a thread a day about guys wanting more low end for their 6.0 for towing etc.

Back in the day, I built a SBC for my '81 fleetside. The book I read to prep for the build said that heads with smaller runners and valves generally improve throttle response, low speed torque and fuel economy (yes of course at the expense of ultimate high rpm max HP). I built it like that, and it worked VERY well for my intended purpose of towing and generally acceptable fuel economy. Remembering this got me to thinking...

I'm planning on swapping my iron heads on my 2000 LQ4 for some aluminum castings. I was thinking 243's to take advantage of the higher compression ratio. Then I noticed through some searching that the 706's have even slightly smaller chambers, as well as slightly smaller runners and intake valves.

***Please keep in mind, this motor's target power range is 1800 to 4500 rpm, NEVER more than 5200 rpm as that's my shift point at WOT.

Do the same rules still apply to the smaller runners/valves? Better velocity at smaller cruising throttle openings and lower revs should equal better low-speed torque/throttle response/economy?

The lower total flow #'s compared to the 317/243's really won't affect me, as that mainly comes into play at WOT/5000+ rpm right? Is it worth the $150 or so that I can get a pair of these heads for just to try it out? I'm really curious and want to get experience first hand rather than all the inter-web theories...

GMCtrk

iTrader: (27)

Zippy did this years ago with an LQ4 in his Tahoe. Low end was excellent.

silver-mod-o

iTrader: (15)

I'd say some 706's very lightly cleaned up by hand (properly) to improve velocity without opening up the runner or port would be great for what you have in mind and I'd be willing to bet that it would still make power to 6K if you wanted to. The right cam will be a must, I'd say something in the low 2-teens with .55x-.57x lift would work well with a tight (107-111) LSA would also bring the power on a hair sooner.

Your head choice is right on track IMO, but don't forget the camshaft that will complete your theory and your build

AKlowriderZ71

iTrader: (22)

I think you've got the right idea on the heads, with the goals that you've outlined for yourself. I also agree that the cam choice will be critical to making your combo work how you expect. I'd recommend you to take a look at the Vinci Hi Performance "Ultra Torque" cam (#80). Specs are DUR @ .050" 210*/218* LIFT .551/.551 LSA 116*, and description is "POWER RANGE 1500 TO 5800, PROVIDES VERY HIGH TORQUE GAINS, GREAT FUEL ECONOMY & POWER, LIGHT THUMPY IDLE."

Doc_speeder

iTrader: (1)

Actually I've been emailing Roger at Vinci about that very cam. Sounds like a good choice to me too! He says the wide lobe center really flattens out the torque curve.

Thanks for all the input so far. I'm pretty much set on trying this out.

grey matter 04

iTrader: (9)

you should swap the 1.89 intake valve out to a 2.00 from a set of ls1/2/6 or 317 heads
This will help flow also
the small valve hurts these heads!

jmj85

iTrader: (2)

Doc, Any update?