How much can you "Frankenstein" an LS Engine? A thread about a possible project idea

Despite everything going on in my life, I can't help but dig through FB marketplace like a medicated prairie dog in a manure pile.

There's a Porsche 928 that's a few hours from me in -some- condition, an 83 that was used as an engine donor for another Porsche. Per the seller, the interiors ripped up but it still has it's 5-speed; few pictures of course, but it's been up for a month and a half for a grand. This would be just "interesting", except the seller has a SBC kit he's throwing in too- and last night I found someone in my city selling an L33 LS block (the aluminum one) for cheaper than the yards, which has sent the gears in my head a-turnin'.

My idea is based off of a build Curtis73 has posted before- bump the compression and tune for E85/91 octane as they're available in my area, and build the engine for reliable power and well-working parts instead of chasing a number. My idea is:

• L33 Aluminum block
• 6.0L crank
• 6.0L rods
• Some car oil pan, whoms't'v'e knows
• Head choices seem to be- "035"/"317" heads from the LQ9 (or are they L92s? So many pages of info...), "317" heads from an LQ4, and then "852" or "706" heads unless re-valving is easier than I think.
• Aftermarket pistons (not sure yet on the max compression I can run if I need to use 91 octane).
• Aftermarket Cam
• Stock Z06/500HP injectors (Or flexfuel truck injectors?)
• stock everything else possible, including ECU and flexfuel bits.
• Some kind of stock intake- LS6 if I can hack it, but unless it's a huge upgrade I ain't picky.
• Finally, cable-throttle if I actually go through with this Porsche idea.

My questions are, basically:

1. Just reading this, does it seem like this combination will work? Or is my research off?
2. Will I need new aftermarket, stronger springs? Or is there a stock spring that'll work just fine? 
3. Compression- it seems like 10.8 is the limit for 91 octane, is this true?
4. With it's kludged-together nature, I know some modules won't play nice if you don't grab the PCM and such. Should I source an ECU from a cable-throttle truck, or are there other options?
5. And finally, the cable throttles were a 4.8 thing. Will they be too restrictive?

Obviously, i'd probably be easier to just find a 6.0 LQ9, but I don't get to build baby's first V8 that way either (lol). So does my idea have any merit, or should I pump the breaks now? And when will we finally make an end all-be all LS thread

6.0 crank and rods are the same that are in a 5.3 so that's not doing anything for you to seek them out specifically.  L92 heads don't work on the 5.3 bore.  
 
243/799 heads commonly found on 07+ 5.3 are same as ls6/ls2 minus the valve springs.  You can get springs relatively easy from gm.  
 

cable throttles were on everything at first so it's not just a 4.8 thing, and 4.8-6.0 truck engines all used the same intake setup so I doubt you're giving anything up there.  
 

ebay is now chock full of sub $250 chinese clones of the holley 302-1 swap pan that fits most rear sump cars including my 240z, chevelle, and 57 chevy.  

you'll need a red/blue pcm and harness for cable throttle.  Some blue/green van pcm's have the ability to be switched from dbw to dbc, but unless you're pulling it from the van yourself i'm not trusting a seller online who is just going off ebay compatibility charts.

In reply to Patrick (Forum Supporter) :

I'd ask how the heck do you know all that but I'm afraid you'd tell us. And it's just too scary to contemplate. 

In reply to Jay_W :

All info easily available online, no big.

If you crack open a blue/green PCM you can see if the spots for the IAC hardware are populated or not.

I have no knowledge on LS stuff, but I strongly support this project.

Would a Vett transaxle be a thing? Is the Porsche transaxle strong enough?

Consider the VW 1.8T swap going into 944s? I know this one is sacrelige, but if it brought a 928 back into service, would be worth it.

In reply to wheelsmithy (Joe-with-an-L) (Forum Supporter) :

C5-7 Corvette transaxle is ginormously long because they stuck a diff to the back of a transmission.  You can bolt the normal bellhousing to them and bolt them to the engine, but for instance when i was measuring to put that setup in my 85 s10 the front of the engine was going to end up almost at the original firewall.  Curious to see what the dimensions are on the c8 unit and what can be done with one when they start getting wrecked en masse

I've read one of the most important things is matching your crank reluctor wheel, CPS and ECM.

The main difference between 317 and 243 (LS6) heads is the combustion chamber.  317 is a great way to get LS6 flow with a lower compression.  I chose to do the 243 heads with an LQ9 block to raise compression so I'll be at 11.3:1.  Do-able on 93 octane, better on E85 with a turbo 

By the way... the main difference between the LQ4 and LQ9 is that the 4 has dished pistons and the 9 has flat tops.  I think they had a slightly different cam as well.

You can frankenstein the crap out of LS motors as long as you stay in the same generation.  You can mix and match some things, but it's really hard to mix between the reluctor differences.

11:1 is easy on 93 octane from what I've read.  My 11.3:1 will be hairy, but I'm doing a from-scratch dyno tune with a factory ECM so we'll be able to monitor how much the knock sensors are crutching my combo.  You don't want to rely on knock sensors since it indicates that you've created a mismatch.  I can swap for a thicker head gasket, but not sure if the benefits would outweigh the perfect quench I would be defeating so time will tell.  

If you botch quench and/or compression, you can still typically get away with pump gas at the following suggested rates: compression minus one times ten.  So if you're at 9.8:1, subtract one to get 8.8, then multiply by 10 to get 88 octane.  This of course assumes you've made a proper cam choice.  Overcamming makes things a little more tolerant but kills torque, undercamming makes torque, but raises the octane requirement.

If you nail quench and compression, you can push things a little.  I'm pushing things a lot at 11.3, but time will tell.  I do have access to a few stations with E85, and I'll be using a flex fuel ECM and sensor, so I could fine tune my own mix or run all E85.  It's just that currently I would need to be more careful in my trip planning so I don't get stuck somewhere without alcohol.

I also chose to stick with ported cathedral heads.  They'll flow north of 310 cfm intake and 275cfm exhaust and still retain all that glorious velocity that the smaller volume ports provide.  I won't need to upgrade heads until I push it past about 600 hp N/A on gasoline.

Factory intakes are pretty good.  LS1 intakes are kinda unspecial.  LS6 intakes will pretty easily support 500 hp.  Truck intakes are actually quite good, but they are tall and ugly.

I opted for a Summit sheet metal intake (which is a copy of a FAST EFI intake) mostly because I'm going everything I can to mask the fact that it's an LS.  I want to pop the hood and have people need to take a minute before they ID it.

I also got some of these coil covers that make it look sorta BBC.  I'll paint mine charcoal (along with most of the rest of the engine).  The hope is with the intake and these coil covers (and a water pump pulley that doesn't look like a boobie) people won't be able to instantly identify it as an LS.

In reply to Curtis73 (Forum Supporter) :

I've always said that they should just make 351C-look valve covers for the engine and call it done.

What would be really cool, but impractical, and therefore perfect for the hot rod industry, would be an 8-in-1 coil assembly that looks like a distributor cap.

In reply to Curtis73 (Forum Supporter) :

How tall is that summit intake? 

In reply to yupididit :

Comes in a few heights.  I think mine was listed as a nominal 9" tall, but it's actually about 8-1/4".  The website is terrible at describing them.  They come in short/tall, black/satin polish, and 102mm/92mm.  They look identical to the FiTech intake (which is rumored to have been developed by FAST), so my guess is that Summit buys them and puts their sticker on them.

Plenums are all very similar.  The shorter ones have a slightly larger plenum, but from what my Summit rep said, he notice zero difference between the tall and short on the dyno.  Any differences in output could have been attributed to atmospheric conditions on the two different days he tested.  He suggested getting whatever will fit under your hood.  I got the tall, satin, 102mm, which I think is the part number in the photo I posted above.  Impressive finish, sexy TIG welds.

Just confirmed from my invoice.  This is the intake I got.  Looks more like the mid-rise, but like I said... the website is awful at its descriptions.

I think Richard Holdner included that intake in his huge LS intake shootout.
https://www.youtube.com/watch?v=6Ejbwy0srmY

I love that video, but he uses some nicknames for the intakes that kinda lost me a couple times.

Either way, I hope it does well.  It looks like it gives up a wee bit on the top end compared to a couple other intakes, but my cam is a bit smaller than his.  I think mine is 234/240 to keep things a little less lumpy to match the 6 speed.  Still, I'm hoping for 525hp.  I also don't really think I'll be spinning to 7500 on a stock shortblock.

Ah okay. Looking for an intake they'll clear the hood of an xjs lol

Curtis73 (Forum Supporter) said:

Factory intakes are pretty good.  LS1 intakes are kinda unspecial.  LS6 intakes will pretty easily support 500 hp.  Truck intakes are actually quite good, but they are tall and ugly

Trailblazer SS intake is also amazing but hard to find. And the LS2 intake manifold is garbage.

wheelsmithy (Joe-with-an-L) (Forum Supporter) said:

I have no knowledge on LS stuff, but I strongly support this project.

Would a Vett transaxle be a thing? Is the Porsche transaxle strong enough?

Consider the VW 1.8T swap going into 944s? I know this one is sacrelige, but if it brought a 928 back into service, would be worth it.

The 928's transaxle is mounted in the rear with the clutch (its an odd setup, but it works) and its pretty stout.  Its based around the 911 Turbo's parts.  The 928 was supposed to replace the 911 as the flagship model for Porsche (with the 944 and 924 filling the lower tiers), so its overbuilt in many areas.

This forum might help with any specific 928 swap-related questions:

https://944hybrids.forumotion.com/f9-928-ltx-lsx-sbc-conversions

NickD said:

Curtis73 (Forum Supporter) said:

Factory intakes are pretty good.  LS1 intakes are kinda unspecial.  LS6 intakes will pretty easily support 500 hp.  Truck intakes are actually quite good, but they are tall and ugly

Trailblazer SS intake is also amazing but hard to find. And the LS2 intake manifold is garbage.

If you're 450 hp and under, pretty much any intake will do.  LS6 intakes are not that hard to find for not terrible money.  The BBK intake in that review looked pretty good without much height.

After tuning lots of engines, 11:1 is a good practical limit for pump gas. It's dependent on the cam choice (IVC mostly) so you can go up a little bit with later valve closings, but down for under 93 octane. If it's flex fuel and you plan to tune it you can easily bump to 12-12.5:1 if you want to use E85 most of the time and only want it to limp along on lower octane if stuck without good fuel. 

Oh god there's so much info to go through

NickD said:

Curtis73 (Forum Supporter) said:

Factory intakes are pretty good.  LS1 intakes are kinda unspecial.  LS6 intakes will pretty easily support 500 hp.  Truck intakes are actually quite good, but they are tall and ugly

Trailblazer SS intake is also amazing but hard to find. And the LS2 intake manifold is garbage.

The *real* reason I speak of the LS6 intake is because of the low hood line of the 928- doubt the SS intake will fit. Plus, i'd probably use that intake with a turbo if I had one instead.

Thanks for the link Stefan; I'm not sure what the max on the Porsche transaxle can take, but I DO know people have ran them up to five-hundo without much problem.

One thing the 928 has going for it is that its engine has a similarly steeply-downdrafted port design, which made for interesting intake manifold choices.

I wonder if you could put the throttle body on an elbow to push it down, kind of like the late 5.0 Thunderbirds but on a different axis.

Regarding the trans, apparently they aren't THAT strong, with respect to how much power and torque one can make with an LS mill.  There's a guy developing a twin turbo setup for the 928 who bought the rest of Porsche's supply of 928 gears.  He was reliably shearing them at only 700hp-ish.

In reply to Pete. (l33t FS) :

Shredding gears at ONLY 700hp? That isn't strong these days? 

yupididit said:

Ah okay. Looking for an intake they'll clear the hood of an xjs lol

How you gonna make an LS intake work on that awesome powerful V12?