I hope this is the best place to post this. If not, let me know where it should be moved.

The criteria I'm trying to fulfill is a daily driver passenger car (78 caprice aerocoupe I've had for 21 years now) with low end torque that will be fun. Fuel economy is a big consideration and I would like to have low end torque. I'm less concerned about high rpm power numbers as I don't go to the track and just want something that would "feel" more fun around town.

I have a choice between a 5.3 and a 6.0. I've been told that a 6.0 with 5.3 heads would make much more low end torque and could get equivalent mileage if backed by a (admittedly weaker) 4l60e and decent highway gears. Is it possible for a 6.0 to get equivalent mileage while maintaining more low end torque? I've read until I'm cross eyed and keep going in circles.

Brandon

 

You will have to watch the compression ratio with the 5.3 heads on the 6.0. It could get too high to run regular.

 

A 6.0l with 862 heads could do what you are looking for but it will need a camshaft change for the mpg to match the 5.3's mileage . The smaller port volume and smaller chambers will help with torque but to maximize the combination I would install a cam something like 210*/218* LIFT .550/.550 LSA 116* 2A

 

Are you talking stock 5.3 heads?

 

862 is an early 5.3 heads. 243 are later 5.3 heads.

 

Compression should be around 10:58 to 1 LQ4 with 5.3 heads.

 

I suppose the theory here is that the 6.0 would have much more low end torque, which would allow it to pull the car around (approx 3600 pounds) with less effort and not strain the motor as much as a 5.3, which could allow them to get comparable mileage. Does that sound realistic? What effects would the cam have on things like interstate mileage?

Thanks,
brandon

 

6.0 has more torque. the 5.3 can probably be spun a bit higher with ARP rod bolts

 

I have a 6.0/LQ9/ engine with milled 799 heads and .041" thick head gaskets. I cannot run regular unleaded. I am relegated to 93 octane gas to keep it from pinging itself to death. I have a mild cam 220/224 .575"/.575" 112 LSA cam and get about 10 miles to the gallon. If you think you are going to get good/decent gas mileage with a 6.0.. I can only say it has not been my experience. Even on the freeway, it still averages about 10 MPG. I do have a 4L80E trans with 2800-3200 Circle D stall and that may factor into the poor fuel economy.

 

Depends on which 6.0 you have and which 5.3 heads you want to use. Most 5.3 heads are 61.5 cc chamber and 799 5.3 heads are 64.5 (64.something I think it's .5).

One wonderful thing about the 6.0 with 5.3 heads (either one) is it will have high compression, higher compression is more efficient and will yield higher power, torque and mpg throughout the rpm range.

All things equal (compression, static and dynamic) etc the 5.3 will get a little better mileage at equal cruise speeds only because it's a hair smaller. Can a 6.0 get 5.3 mpg? Depending on the setup it could get better mileage, but the question is so subjective there's not cut and dry yes or no answer.

If I were you I'd go for the 6.0 over the 5.3, 3600 pounds is a lot and if you're going to be cruising mostly you can still get good mpg. Another way to look at it is, a bigger motor that's not struggling to pull a load will get better mpg than a smaller one that is struggling and you're having to throttle it a lot to pull the weight. At 3600 pounds this isn't a concern or actually an issue, but it's just another way to look at it, more of an extreme case.

EDITED I did some calculating wrong: If you do an LQ4 with dished pistons and 799 5.3 heads with stock .052 thick gaskets you'll be at 10.35:1 compression. With 61.15 cc 5.3 heads it'll be 10.75:1

With flat top pistons (LQ9) the 64.45 cc heads will be at 11.1:1 and with 61.15 cc heads 11.6:1


The mpg game is all about efficiency. Big cams, low-ish compression, big converters, big gears are all a waste. A lot of power can be found going the efficiency way too.

A crank scraper would yield some power and mpg, electric radiator fans, electric water pump, low drag ps pump, underdrive pulley etc..

 

Good compression, tall gears, tight converter, mild cam, free-flowing intake and exhaust, and all tuned to within an inch of its life(lol). You will then have efficiency.
Good explanation, 00pooterSS! The above is the Cliff's Notes version lol.

 

Yeah I think a 6.0 LQ4 bottom end with some 799 heads, a truck intake or LS6, long tubes and a stage 1 or 2 drop in truck cam would make a really nice driver with great efficiency and plenty of power. It would also be a low end setup that's real efficient in the lower end (cruising rpm) but still make plenty up top. It would be a fairly low cost build too since you can use stock pushrods and LS6 springs that are like $70 new

 

Yep, the tune is critical

 

If you can go TFS heads.... do so.

 

Absolutely agree.

Thanks for posting that, I knew those heads kicked absolute ***, but I didn't expect them to embarrass the LS3's that bad. I knew the LS3's would likely drop some on the low end but I figured they would at least compete on the big end or be close. Those TFS kill right out of the gate and just keep pulling away. And compared to the 799 head, ho-ly-****.

 

WHOA! Them TFS heads flat ROCK!

 

You welcome guys.

The cam tested really hurt the true potential of those TFS heads as well and helped the LS3 heads.
Cam used in the test was a 231/247 duration. That's too much exhaust for a good proper cathedral head.

I love my LS3 heads on my top of my LS2 motor but if I could do it over again i would do TFS up front.

 

I went and did some reading and saw a lot of what you just mentioned. The LS3 stomped all over the stock cathedral head, and the TFS stomped on that lol. However, the LS3 heads were like $700 vs I believe it said $2500 for the TFS. The as cast would fall nicely in the middle price wise and give a majority of the power increases those fully finished ones did.

Would be nice to see the TFS truly shine with the proper cam, but damn it still did really good with the wrong one.

 

The LS3 heads are the BEST BUDGET heads period but not the BEST PEEFORMING heads. Pooter, I have also seen TFS heads do well on a single pattern duration cam that no one used no more. Something to think about on that vs the wrong cam for those tfs heads used in the comparison.

 

Yeah, I think a lot of guys forget that while LS3 heads need more duration "spread", cathedrals do NOT. LS3 intake ports are so big that the I/E ratio is more lopsided than with cathedrals. So Yeah Tusky, the TFS heads should have had a more cathedral-friendly cam to fully exploit its potential .