i have a 1970 chevelle 454 (automatic), i was wondering whats the difference between a ls5 and an ls6?, i want to know if i could convert it to an ls6?

thanks.

I know there is a big difference between the heads.
LS5 heads are oval shaped.
LS6 heads are rectangled shaped.
There is more to it than that.

Heads,pistons,intake,carb,cam,lifters,steel crank vs cast or LS5,possibly con rods to because i believe they are the lager 7/16 bolts which should be the major items that are different.

But if you were to tweak your exisiting LS5 motors stock equip like doing some mild head porting,installing Manley undercut swirlpolished hiflow race valves,cam it up with an up to date better perf hyd grind ,(Stock LS5 cam is a very whimpy flat tap hyd with 214/218 deg dur @.05,.461/.480 lift,114 L/S so move up to a hyd cam with apporx 230-238/236-246 deg dur @.05,.550/.570 lift,110-112 deg L/S which will idle ok/decent in a 454),comp magnum roller tipped rockers for full/consistant valve lift and reduced valve guide wear. You should also have an experienced q-jet person tweak your stock LS5 q-jet with richer secondary meter rods and the high flow/high perf needle & seat to handle the higher perf & rpm,new street perf fuel pump with approx 7 psi fuel pressure max (q-jets dont like high psi) with the large metal high flow factory stock inline GF432 fuel filter that came on some BBC chevelles in 69 & 70,lighter high rpm fuel pump rod to also handle the higher rpm capability,headers through a good flowing 2.5 inch exhaust. You can also change to an edelbrock rpm intake to save a few lbs and gain a few horses but the stock intake does a decent job if your looking to keep the stock appearance and great driveability by retaining the q-jet and tweaking it for better perf. I know this from 1st hand exp,yes on the dyno the edel will out power the stocker by a few ponies esp on top end but it's hard pressed to feel in the seat of your pants for the extra bucks unless you looking to get every ounce of perf out of our motor if you race/drag it alot.

You can do all this on your exisiting LS5 if the bottom end is in good cond with good oil pressure,compression,and good ring seal . Doing all the above should conservatively increase your 70 LS5 454 from the 390HP factory rating to approx 425-450HP + due to mild the pocket porting/major cam improvement/headers/2.5 inch exhaust . doing all this helps the motor breath much better getting more air & fuel in and out a lot easier & faster along with the improvements to the q-jet and installing a H/P fuel pump with the stock GF432 larger high flow inline fuel filter to handle the higher fuel requirements of the motor after the higher perf mod's are done.

Accept for the headers the motor will still look like a stock 390hp LS5 454 but it will sound meaner than an LS5 (due to more cam timing & headers) while performing close or equal to a stock LS6 with better street manners than the stock LS6's had too.

You will also save some big bucks when going this route by not having to buy a new intake or an expesive used stock GM LS6 alm intake ,buy used LS6 square port heads,install higher comp pistons,and buy a vac secondary 780cfm(or maybe 750) holley.(Thie all saves you apporx $1k-$3k depending on the price of buying/building a used pair of true LS6 heads vs the cond/cost of rebuilding & doing some mild porting your exisiting LS5 heads)

Scott