383mazda

iTrader: (2)

Hey guys, here's the deal...

I have an LM7 my father and I are about to put in an rx7. We were going to do the normal budget build with the 317 heads, '20+ zo6 cam, LS1 intake, good valve springs, 60# injectors and ~12psi from a t70 ot t76... proven combo for 600rwhp.

However, our search for a good deal on 317 heads has led us to two complete LQ4's, one for $800 one for $500. We have a computer out of an 2000 camaro, and we do not have a wiring harness. Both motors come bare (no ecu / harness).

Is it worth getting one of the 6.0L and selling the 5.3? What kind of boost / hp can the 6.0L take? If the numbers are the same we might as well keep the 5.3 and toss on the heads and start building... I can't find a solid combo for a 600rwhp 6.0L build (although I'm sure they're out there...) The 5.3's seem to be getting a lof of attention lately cause they're $250 out of a junk yard!!!

mxman

iTrader: (1)

you can get the painless harness, i think you may need an antitheft delete with hp tuners, it may have a module, also you may be able to source it from a stereo shop

CBIII

iTrader: (6)

are the lm7s iron or aluminum? In a car like an rx7 that are already light, id want to avoid throwing a heavy iron engine in there (even more weight with the turbo setup) plus in a car that size you wont NEED alot of power (ask skinnies) if you HAVE the 5.3, id stay with it.. or look for a good deal on any aluminum lsx

Jimmy P

iTrader: (177)

LM7 is iron. I personaly would go with the LQ4. They have proven themselves again and again to be able to make a lot of power reliably.

skinnies

iTrader: (33)

Just keep the 5.3, no need to swap heads or anything, just throw in a z06 cam/springs/pushrods and let it eat. See my sig for my rx7 tc78 5.3 numbers, that is on 11lbs and ~550rwhp.

DamianN.

iTrader: (11)

what's advatages does the LQ4 have?

1BAD_LS1

iTrader: (36)

i think you should just keep the 5.3 throw on the 317's so you can run high boost on pump gas with no meth.

i made 528hp at 14 psi with a slipping 4l60E.... I have a th400 in there now and am running 16psi on 91 octane pump gas no meth.... looking to get dyno numbers soon, sure its well over 600hp with 2 more psi and a tranny thats not slipping!

383mazda

iTrader: (2)

I figure the main difference is the displacement of the LQ4 is bigger, but it's CR is like 9.4:1, while the smaller LM7 will have 8.6:1 with the 317 heads... so it might still be the better boost motor. If all the stock internals stop around the same max hp, might as well keep the little motor eh? If both go "pop" around 700ish it's better to replace the cheaper motor.

Can anyone chime in with a better reason to keep the 6.0L??? There's a guy I've talked with that grinds his own cams, has one in his 6.0L with a t76 running 10.3's in colorado with his truck! That would be nasty in a 3000lb car!

383mazda

iTrader: (2)

Just to confirm some numbers. The LQ4 would have 39 more cubes (364 vs 325) and 0.8 more compression than the LM7 with the 317 heads (9.4 vs 8.6).

So which would you pick for a boosted motor, cubes of compression?

The other diff would be the TB; the stock LS1 (which I have now for the LM7) is 75mm, the stock LQ4 is 80mm...