skinny z

I have a thread going regarding an LM7 swap with or without the OEM PCM. In an effort to ditch the truck manifold, a carbed intake is the cheapest most direct solution. But it looks like it isn't gong happen that way.
https://www.thirdgen.org/forums/ltx-...m7-w-carb.html
So, that puts me at a crossroads. What I'm looking for here is some dialogue that may help persuade me one way or the other. My target is an 11 second time slip.
Here's what I have:
Gen 1
Aftermarket iron heads. Intake: 229@.400, 250-255 from .500"-.600", Exhaust: 166@.400", 175-180 from .500-.600".
No cam spec'd at this point but have been running Comps XR288HR. Also the XR276HR.
Full roller valvetrain. Short travel lifters. RPM Air Gap. A few carbs to choose from. All of the tin including a Canton road racing oil pan.
With a 10:1 shortblock (forged crank and rods), I've seen 109 MPH trap speeds in the quarter. Best ET is 12.4 corrected.
Problem is I need to rebuild or replace the shortblock. I'd prefer to replace it outright and keep what I have as a solid core to rebuild whenever.
LS
LM7 out of my 06 Tahoe. Complete and running (but not recently). 240k miles.
I have nothing for the swap so at a minimum that means headers and engine mounts. I'd also need a flexplate (for SFI) to adapt my TH700.
That gets zero in the performance department. An intake and cam might add 100 HP over stock (or so I'm told). Rework the EFI or put a carburetor on it. A carb swap would mean an ignition controller. Reworking the EFI is another option.
I think the real deal here are either ported stock heads, which I've read can match what I already have (255 @ .500", and much better on the exhaust side) . Aftermarket heads are another option with a guaranteed improvement over most anything ported.
So, where does leave me regarding an engine that can produce 450 CHP and get me that half a tenth? I'd need about another 5 MPH all else being equal.
My take? Build a 383 and use what I have on top of it. I'd get a cam spec'd from the likes of Vizard or Jones. From a strictly cost standpoint, I think the Gen 1 might be half of what it takes for the same performance if only for the pile of supporting parts I already have. The LM7 would need a lot of work and that's not including any machining if required (the engine is high mileage even for an LS). I could run the stock shortblock as is but ultimately it would need some attention.
Anybody care to contribute?

Orr89RocZ

iTrader: (20)

skinny z

Interesting observation Orr regarding the underachieving. I think too (and know) that a more drag racing orientated chassis would put me in the 11's. A converter and some tires would go a long way. I can say the same for the shocks too.
What I know about combinations like mine, which are basically 350 Vortec variants with the inherently small intake (mine started out as 170 cc RHS Vortecs and have been ported by Charlie's shop up here), is that they are capable of 450 CHP. And that's not twisting them too tightly either. Under 6500 RPM. with the right cam as I mentioned above, that 450 HP mark is reachable.
As for the LS, yeah, I agree that a NA 5.3 would need as much attention as the Gen 1 for the same results. That and more dollars bringing the stock heads up to par (or aftermarket versions) and again as mentioned, all of the swap parts.

Orr89RocZ

iTrader: (20)

five7kid

iTrader: (14)

If it were me (and it obviously isn't me), here is what I would do:

Take the 5.3, keep the block. Get a 4" stroker kit intended for an LS1, bore the block out to the LS1 size (which will probably be .005"-.007" oversize). Now you have a 383.

Heads: Gotta do something here (by the way, I'd do different heads even if you keep the Gen 1...). 243s, AFRs, ported 706s - something. Of course better valves, and springs to match whatever cam you end up with.

Tranny: I have to confess my affinity for electronic shift. I haven't shifted on my own since 2013. Oh, and you'll need a converter to match your cam.

Induction: You may have noticed my affinity for self-tuning systems. There are two FiTech Ultimate LS systems in my "family". Honestly, they pay for themselves in what you don't have to buy and what you don't have to pay for. Even if you have a carb, you're either going to need wideband O2, or pay for a dyno tune if you want to get it right. You can get a complete EFI system with intake, TB, sensors, harness, injectors, PCM, for $1500-$2000 (depending upon HP level, and whether with or w/o transmission control). With wideband O2 no less (that alone makes it superior to an OEM system - or carb). Setup and what little tuning you need are from the included hand-held. Easy peasy.

Why I say all this:

My '82 with stock LS1 shortblock, shaved 317 heads (to 65cc), LS6 cam and springs, LS6 intake, 3600 stall in a LS 4L60E with Transgo shift kit, 3.73s in a 10-bolt with TrueTrak, mail order tune on the OEM system, 1-3/4" longtubes into single 3" - went 11.82 @ 114 at Heartland Park Topeka. At that time I had the passenger and rear seats, cargo cover, spare tire all removed; basically only the carpet, console, and driver's seat still in it aft of the dash. It weighed 3200 lbs with me going down the track. A 383 LS with better heads and cam should be able to do that pushing a couple hundred more pounds without even breathing hard. Will that be a "budget" 11-sec car? No. But, it will be a consistent car that you can drive on the street and not have to worry about something coming apart on you.

Another: My son has a '75 Vega he built with some old leftover parts I had laying around - stock LS1 shortblock, 241 heads, TH400 w/4000 stall (came out of my '57 in 2009). He added MS3 cam, upgraded the springs, 1-3/4" headers into 2-1/2" dual, got the FiTech Ultimate LS 450 HP kit, installed a 9" with 3.73s on a spool. Put in an 8-point roll bar. Weighs 3000 lbs going down the track. It has run a 12.05 at our 5800' altitude (corrected for altitude that equals 11.33) - with several things still not right on it.

To say the least, I'm an LS fan. My '57 has one, my wife's 2008 GXP has one, my 3rd gen has one, my '99 Silverado has one. The only thing I own that doesn't have an LS is the '96 Vette (unless you want to count the lawnmower and snowblower...).

(You could save some money by boring the 5.3 to 5.7, keeping the crank and rods, needing only pistons, rings, bearings, and ARP rod bolts (and balancing) - all the rest the same as above. It wouldn't be quite as fast, but 11's should still be easily achievable.)

skinny z

The 109 mph was with a custom spec cam. XFI lobes: .574/569, 274/282. 224/230, 110 LSA, 106 ICL. 205 cranking pressure with 10.4:1. 195 PSI at 10.1. Ran great with good mileage too but there was a probably with detonation. Especially at cruise.
With the 288 I was really short on CR at 10.2. I had it on a 102 ICL trying to build some cylinder pressure but I think by then the shortblock was toast. Spun it to 6800-7000 on the 1-2 shift and that may have been it's ultimate demise. That would probably be at the limit of my valvetrain I would think. Never made it to the track with that iteration which also included a better converter with another 500 RPM stall which would be about 2000 over stock. Maybe flash to 4000? Still wanting (and waiting) to test that.

skinny z

I fully understand the merits of the LS platform. But they all need something to realize their real potential.
And basically I'm working out the logistics (and expense) of 1) making the swap happen and 2) going for 11's.
What I already have Gen 1 wise is going to require a shortblock. Call it a forged 383 (with good forged parts thank you) and you have an idea of the cost. Probably an idea of the performance too. With the smallish heads, 500 HP isn't realistixc without RPM but 450 is.
Now, as you point out Mr kid modifying the LM7 is going to take some doing. I see heads, cam and intake in your lists. Not to mention the stroker. By way of comparison then, call the two different shortblocks a wash and add heads, inatke and valvetrain hardware to the LS mix. Plus the swap components. Both engines need a cam. (Leave the carb / EFI thing out the equation for now).
I do have a roller chassis sitting here waiting for the next project. Ultimately one chassis or another will be LS. The other old school. It's just what to do for (more) immediate gratification.
Getting the car on a diet would pay dividends too. I'm 500 pounds on the fat side of your heaviest vehicle. What's the saying? 100 pounds is worth a tenth at these power levels?

five7kid

iTrader: (14)

Taking weight off the car by removing things is free. After that, more speed requires more dollars. It doesn't really matter what platform you do it with.

There are several advantages to the LS platform - longer rods being one that isn't often considered. Roller lifters. Heads flow untouched (as pointed out). The list goes on (crank trigger, stronger block...). I just wouldn't leave the 5.3 a 5.3 with your goals.

FWIW, my heaviest car is 3850 lbs going down the track. It also happens to be the quickest car in the fleet (for now). Its powertrain would run 11.7's at altitude in the 3rd gen.

Ultimately, it's your car(s), your money, your decision.

skinny z

The advantage I can see with swapping in the 5.3 is just that that. Getting it in there and running. That's half the battle and it opens up a lot of options . The other half is making it quick enough. Having said that, I'm thinking I could reach that goal with the current platform. And for less expense. I do like the idea of the stroker 5.3 though. Hadn't considered that. But that's outside the current budget as is a supercharger, which, by the way, was something I'd always thought of a way to have terrific performance and keep the driveability.
I'm not about to take this on, in either direction, anytime soon. (That's a personal choice). But I'll continue to work it through on both levels. FWIW, LS3s are going at a discount up here with one having arrived at a friends shop for less than 7k USD (complete less PCM). There's your 450 HP right there. How does that stack up against a modified LM7? Id say it going to be close.

QwkTrip

iTrader: (22)

Why not sell the 5.3L and get a used 6.0L LS?

skinny z

Selling is something I've considered although having it in hand at least allows me to move along with the swap in general, performance notwithstanding. Then upgrades or replacement from there.
And a 6.0 L is less likely than a new LS3...but that's another story.

Orr89RocZ

iTrader: (20)

skinny z

Agreed on both counts.
I had a brief discussion with Coan regarding a converter in that spec but their reply was
that with a lockup function it wasn't possible. Didn't think that was all of the truth but that's as far as that went.

QwkTrip

iTrader: (22)

I think you said in one of your recent threads that you have two Camaro's, one for the track and one for the street and both are toys. I'll just say this.... two project cars will make a man poor and neither will be what he wants. I see an easy way to maybe get money for the engine you want.

skinny z

Well, not exactly. At least not at this point in time. I've the gray SC that's served as a street and track car for the last decade or so (which was preceeded by the 86 IROC) and as a DD recently (when the truck was disabled) and has since gone **** up. Still a driver but not a racer. Recently I picked up an 82 Berlinetta that to me, for all intents and purposes, is an SC and would be either a track car or a cruiser depending on which chassis is in the best shape. The new purchase is still somewhat of an unknown but it will have to be really clean to beat the current 86. It's yet to be disassembled. I can see developing the 86 chassis and then moving all of the good stuff to the 82 if it's warranted.
Anyway, yes, I can see how two projects could be a drain. This is primarily why I've been discussing what I'm going to do next as I'd like to put a cap on the 86, establish a performance threshold and then get on to the 82 if it's in as good shape as I anticipate.
One will be Gen 1. The other an LS.
Or electric.

91ls1t56

My stock(besides headers for the swap)140,000 mile LS1 got me a 108.75 mph trap speed in my 3rd gen with all season radials. As mentioned above 243 or 706 heads, look at your 5.3 they may already be on it. The 243 heads came on ZO6 vettes, along with the ls6 cam and intake they had a factory rated 405hp. That was back in 2002-2004 now those same heads are on most truck engines. The 706 heads can be found in the garbage, they have the same runner volume as LS1 heads but smaller chamber and slightly smaller intake valve. Chevy High Performance has done a few dyno comparisons of factory heads over the last year and the 706's actually out perform or are on par with 243's. 25 years ago I didn't want this computer junk either, now it's the only way to go. Those ugly truck intakes really are not that bad, you have a harness and probably good heads already. To me the LM7 is the way to go especially when you have one. I just built myself a iron 5.3 with LS6 heads, cam and intake.

skinny z

I appreciate the real world examples. What they're showing me is that the LM7, in it's stock form with intake and heads, wouldn't be a performance upgrade from my current Gen 1. The calculators put the average RWHP in or around the 320 HP mark. That's probably close to 400 CHP at peak. The 06 truck engine version is rated at 295 bhp. I would say that at least another 150 HP would be needed to get an 11 second et. That same math says that about an 112 mph trap speed with all else being equal. That puts the engine build at heads, cam and intake. There's probably an argument to say the heads would be OK, but the cam and intake would have to go. Getting 400-450 CHP out of 325 c.i.d. is going to take either some serious RPM or really good low engine speed torque. As it is, the savings with the swap would be in re-using the stock bottom end. That in itself would lower peak engine RPM. While 7000 has probably been achieved on more than one occasion by more than one racer, I wouldn't want to venture in that direction. Besides, without at least upgrading the valve springs, it wouldn't be reliable enough to repeat. I should mention that in addition to my target 1/4 mile goals, I have to have a go at some open road events. Or a flying/standing mile where the high RPMs are going to held beyond the less than 11 seconds the dragstrip demands.
Dollar for dollar, I think I'm still ahead with the Gen 1. Starting from scratch? I'd go LS. Take what I have and do the typical HCI upgrades.