I am WAY overwhelmed.... GMPP LSX in a 70 Chevelle

[The WidowMaker]

im in the process of building a PT 70 chevelle and looking at a GMPP lsx block. original plan was for a gen 1 dart block based 434, but ive seen the light with the gen 3 and 4 stuff. ive tried searching, but i have too many questions and im not getting anywhere. if i can just get a start with these, it will help relieve the overload.

is it necessary to cut the crossmember when using a tko 600 and only ps and the alt (no ac)? i dont think i will have the same issues on the front of the motor since im not using ac, but im not sure. frames been based and cleared, so id rather not have to cut. who makes the best mounts for this application?

im looking at over a 4" stroke, so who makes a pan that will accept this? anything stock that will fit?

since im waaaaay new to the efi stuff, who makes a good computer for a ~650 hp na motor? what is needed for electronics (coil per cyl, ???)

how much more $$$$'s are involved to go with efi vs a carb (different manifold, rails, computer etc.) plus what is my etc?

what judges whether its cable or tps? can it be either?

do all the sensors have to be hooked up for a carb application? what can be left off a non smogged efi?

i can build a bad ass gen 1 434 for right around 9k. just not sure i really want the extra headache and the extra money for a like powered gen 4.

thanks, Tim

[matty b]

GO WITH THE LS!!!! The LSx family you pretty much make more hp everywhere with smaller cubes and when you find heads that flow comparably to ls7 heads in the Gen 1 family for the same price lemme know. First your dart block cost twice as much before machine work. Heads for the LSx are off the shelf ls7 pieces and will cost a fraction of the SBC heads. Cost is a wash for the reciprocating assembly and depending on the brand of crank and size that could also be a wash. Trade off is weight in the LSx block but it may be close to the dart block. Id say build a wet sumped version of the ls7 which is a 427 and throw a cam at it and some nice headers. I can almost assure you that itll have better street manners and durabilty is better for the LSx. So obviously you can probably tell Im biased but when I started seeing what these engines can do my mind was set and anything else is a waste of money. Oh and as far as computer goes, you cant beat the stock PCM they are just amazing and can do magic, well almost. Use the stock sensors and a harness for an LS based motor and youre good to go. If you wanna go carb, all you need is the msd box for LS1s plus a few sensors and the carb stuff. As far as the oil pan goes, if you build a 427, youll be fine with a conversion pan to fit early gms. You may come out slightly cheaper depending on how you do it but they will probably be close to the same cost but one will run way better that the other. And think of it this way, if SBC were so much better you wouldnt see every one going to the new stuff now would ya this stuff isnt as hard as you think so take a moment, gather you thoughts and start build the best v8 available!!

[The WidowMaker]

thanks for the reply... so far ive gathered some more info and im looking at the following...

gmpp lsx block

somewhere around 440ci - ill have to research this a little more. the bores are short and i dont want too high of a pin. its also able to go to 4.25, but i dont want to push it that far. id like at least .060 to keep going.

afr or ls7 heads

autokraft pan and mounts

msd box

holley carb

not sure what else yet?!?!? any ideas?

Thanks, Tim

[WS6]

hold off on the LSx block for now. Supposedly GM is having issues and is looking into the problem. I don't know much beyond that unfortunately. If you dig I am sure you can find out specifics on that.

[matty b]

430 hp 70, thatll be a monster of an engine and easy to tune to boot!!. I havent heard anything about the lsx block personally so couldnt tell you about that but you will be very happy going this route. Only thing that is pretty expensive for these motors is rocker arms. Jesel wants a ton more for ls stuff than for sbc but if you can stick with the stock rockers and just upgrade the springs and pushrods youll be fine..

[The WidowMaker]

i have heard about issues, but i thought they were related to labor and not the block itself. ill look into it though. thanks for the heads up.

how are the afr heads. expensive yes, but is there a big advantage?

anyone use the autokraft stuff? mounts are expensive, but they look really clean. pan is awesome and nicely priced since you dont have to relocate the filter.


thanks, Tim

[68topls]

Log on to ls1tech.com. Thats the best site for information on the gen 3 and gen 4 stuff. The big thing now is to use the l92 heads in stead of the AFR heads as the flow numbers are better at a lower price point. I would stay away from the lsx or at least wait a while.

i have heard about issues, but i thought they were related to labor and not the block itself. ill look into it though. thanks for the heads up.

how are the afr heads. expensive yes, but is there a big advantage?

anyone use the autokraft stuff? mounts are expensive, but they look really clean. pan is awesome and nicely priced since you dont have to relocate the filter.


thanks, Tim

[The WidowMaker]

68topls - why would you stay away from the bowtie lsx? have you also heard something?

thanks, tim

[Trevor @ Texas Speed]

The LSX blocks are currently back-ordered from GM. They did have some issues with the blocks, so they put them on back-order until they can get them worked out. I have heard as bad as April before they are available again. It's not an issue where they are failing after running. The biggest problem has be porosity in the cylinders. Literally half of the LSX-based engines we have built had to have the blocks replaced when the machine work was being done. It would have porosity problems while boring the block. If the block bored fine you're okay. We're running a 431 cid LSX solid-roller in our '00 back-halved Camaro with two stages of dry nitrous and a 440 cid LSX in our '00 back-halved twin turbo Corvette. Both cars have made over 1,000 RWHP with power-adders, and the turbo car has not been pushed past 17 psi.

For stock GM oil pans past 4.000" stroke, you can use a 2005+ Corvette pan. We've run the C6 Corvette pan on some of our 454 cid LSX engines, and they are a 4.200" bore and 4.100" stroke. We have installed the Milodon oil pan for a few retrofit customers, and while we have not tried it on a 4.100" stroke engine it looks like it would clear. You have quite a few choices with EFI tuning, but Big Stuff 3 is a popular choice. We have used both the FAST XFI and Big Stuff 3, and the Big Stuff 3 is more user-friendly. You also have the options of running a factory GM LS1 f-body PCM and having a company like Speartech build you a harness specific for your application. The LS7 composite EFI intake manifold uses a newer-style fuel injector connector, so a custom harness would be ideal. GM sells the LS7 intake manifold as an assembly with the electronic throttle body, fuel rail, and injectors. However, you'd be better off purchasing the intake and fuel rail separately and running a cable-driven throttle body with a set of FAST fuel injectors. FAST now makes an LS7-specific fuel injector in larger sizes, which you'll want. We maxed out the factory GM fuel injectors on the engine dyno with our 454 cid LSX. They were maxed out at 680 FWHP, so it took a larger injector to support the 750 FWHP that it made with our PRC ported LS7 cylinder heads and more aggressive camshaft.

Feel free to give me a call or shoot me an e-mail at [email protected] with any questions or concerns.

Trevor
Texas Speed & Performance