Hello,
I just completed an LS swap into my 2003 S10 and I'm extremely disappointed with the performance. I have a long history with the old small block chevy engines and I don't see much notable difference between the LS and old school SBC in terms of performance...

Is there anyone that also has a long history with SBC and also personal experience with LS swaps that can give me your own perspective on this? I am right that the LS is not really much more powerful without power adders?

Engine: L59 (flex fuel version of the most common LS the LM7)

I've made similar modes to the LS as what I did to my SBCs in the past and the performance is basically the same, maybe a little bit better but not more then plus 20 horse.

I do know that the LS is a much better engine, capable of much more power with power adders and likely more power if I changed the cam but right now it seems like I've wasted my time choosing the LS (with all the additional complications that come along with the LS swap compared to the simpler SBC).

 

The reason the LS didn't gain as much as the SBC did is because there was so much to be gained with the SB that is already there in the LS.
The LS has far better heads than even the high performance SBC's had. The lowliest LS truck engines START at 255HP! From 4.8L!
SBC's in full smog gear couldn't do a major fraction of that.
Many of the SBC mods are already there on the LS.
All an LS needs to gain major power is a good cam.

 

Yes, I get that but...
My old SBC was advertised at 190 HP and the LS I got is advertised at 320 HP but with the exact same mods they seem almost identical in terms of speed and performance (butt dyno).

Anyone else experience this?

I expected the LS engine to just blow the tires off the S10 very easily but actually it seems totally comparable to the SBCs I've been running in the past. That's the part I can't figure out...if the old SBC actually had 190 HP compared to the 320 HP Ls the difference should be HUGE and it's just meh

I am comparing totally stock long block to totally stock long block (just bolt on intake and exhausts on both so same basic mods).

 

I'd would suggest to list your setup. Lots of things could be holding it back, if not setup correctly, or components working against each other.

Vehicle setup, Engine setup/mods, transmission setup, axle gears, and how are you controlling the engine?

 

The SBC has good low end torque due to the small port heads that choke it off at higher revs. That is what your butt dyno is feeling. A real dyno would tell a far different story.

 

Hello,
totally stock long block to totally stock long block, similar weight cars, similar geared cars (mostly factory 3.73s same as the S10)

One difference would be the tranny - I always ran auto with SBC and now I'm using a 5 speed manual with the LS

For the SBC I've modified more then ten of them ranging from 305s to 400s. In my mind I would compare the power of my LS to a 1972- 350 stock long block with a torquer 2 open plenum intake, Holley 750 (vacuum secondaries) headers and dual exhaust

For comparison the LS I have now is a 2003 5.3 liter L59 from a Suburban, Holley open plenum (single plane) intake, MSD ignition, 850 CFM carb with vacuum secondaries, headers with two into one exhaust but decent performance muffler (just a temp exhaust to get it driving).

So yeah right out the gate the LS has a disadvantage with the single exhaust I put on it and I admit I am comparing a 325 CI to a 350 CI engine but I can't imagine that would make such a huge difference top make the engines seem basically the same.

this is really a generic question though, like generally speaking (for people who have gone from SBC to LS) is there a huge difference that you see and feel immediately or did you have the same experience as me...disappointment?

Don't get me wrong, I have big plans for the LS (sloppy turbo) and I'm not moving backwards to the SBC but so far It's not what I expected

 

Good point, very good point, it is mostly the torque I am able to compare but while spinning up to 6,000 RPM, in first gear in the S10 I expected traction to be a major issue and it doesn't spin the factory sized tires at all except below 3K where the torque lives (just like the old SBCs in G-body cars I've had).

Anybody actually do the swap from SBC to LS in a similar car/with similar modes to the engines and see a better result or did I just over estimate what I was getting when I did the swap?

Who knows, maybe my jetting on the secondaries is still off (new carb) and maybe the tune files in the MSD aren't very good but before I spend a ton of time fine tuning this I was hoping to get some feedback from others that have already done this. What was your results from doing this?

I actually thought my ignition advance wasn't working at all and spent a lot of time confirming that it is advancing properly and I did already enrich my secondaries in the carb (that helped but not like OMG it so fast now). So now I think I am at the point of fine tuning and need to know if I'm chasing 10 more horse power or if there actually is most likely much more power to be found....like did you do an LS swap and got blown away by how much better the LS is or...you know

 

First off these are simply air pumps and you are comparing an old style to a newer style both very similar in size. The advantages of the LS are the strength of the short block, The flow of the heads, the factory roller cam and the weight loss in factory form. With the stock cam you do gain some hp over the old sbc because a hydraulic roller is good for about 30-40hp over a flat tappet. Flow makes the heads more efficient, but you really wont notice that much until that cam gets swapped. LS motors REALLY wake up with a cam swap.

Not exactly sure what your trying to do with your setup, but it's completely wrong if you are trying to make good power from a stock LS motor. Single plane intakes are for high rpm horsepower which you will never see with the stock camshaft and the 850 carb is way to big for that little motor. If you want to run good with a stock cam then run a dual plane and a smaller 600-650 carb.

Apples for Apples you are correct with the exception of the hydraulic roller they are pretty much the same. The thing is the bolt ons helped the sbc tremendously while the LS was already over 300hp stock. The bolt ons probably did nothing for it over the factory setup because it is already so efficient.

 

I noticed you running a single plane and 850cfm carb on a 5.3L engine.
If using a stock cam, it is WAY over-carbed, and a 2-plane manifold will give it a lot more low end torque.

 

hello,
I appreciate your thoughts about the two engines being similarly sized air pumps and I suppose I should not expect to see such a drastic difference because they are similarly sized, I suppose the original advertised HP ratings are what really made me expect more of a difference between the two engines, they must use a different kind of rating system now
As far as the setup goes though I have to disagree, I've been running low rise single plane intakes on the street/strip for 20 plus years and I've run plenty of dual plane intakes to compare them to. The one I have on the LS is rated from 2500 to 7000 RPM. I shift at 6000 - the idea is to move the torque curve up into the power band as much as possible with the stock cam and a low rise single plane works great for that purpose. Sure I lose off idle and some bottom end torque but I'm focused on peak torque and top end power personally . The 850 CFM carb has vacuum secondaries so it's not really too big, I could make the secondary springs tight enough to choke the engine if I wanted to. The idea there is to find the perfect amount of vacuum at wide open throttle by making the secondaries open easier or harder. With a big carb I can adjust it and let it eat as much as it can without under or over carbing it. I do admit that the LS is much less responsive to that approach then the old SBCs...with the old restricted heads I could set the secondaries very loose and drop the vacuum very low (like 1.5 HG at WOT!) at the carb and they liked it but the LS is so much more efficient it clearly likes to pull more vacuum to run well. I would have agreed with you if I had put a high rise single plane and 850 double pumper of course but in this case it's planed and I know the positives and negatives to consider.
I do realize that on paper a 600 CFM might be a good option for a 5.3 liter but in the real world its not big enough. I'd be chopping the power off around 5 to 5500 RPM with a 600 CFM. I'd rather put a bigger carb and be forced role into the throttle then bottle my motors up like that...but then again with the vacuum secondaries its not a problem

 

A naturally aspirated 5.3 is bottom of the food chain in the LS engine family. It's not the kind of engine spoken of in LS folklore. And you made it worse with your modifications. Somebody with a ZZ4 would clean your clock at the moment.

The 5.3L is legendary for boosted builds though.

 

1) why did you take two steps back and put a carb on it? Thats mistake #1
2) I'd put money on it the carb is holding you back. I'd bet its not tuned correctly and a vacuum secondary carb sucks bootyhole casserole anyways.
3) If you are going to continue with this Bassakwards way of doing it, ditch the single plane, put a dual plan like a performer rpm (if they make that intake for this...I dont keep up with carbed **** anymore) and a holley 750 double pumper. That intake is killing your bottom end tq.
4) you probably dont have a timing map worked out correctly for this engine
5) these motors LOVE a small cam. It picks up tremendously. You know how you pick up tons of power with a head swap on a sbc? Well thats how the cam swap is and the head swap on an LS makes alot less difference.

Ive had LOTS of sbc experience and carb experience. A vacuum secondary carb is much less responsive than a double pumper. I tried a plethora of different carbs and a 750 dp was by far the best.

I had a daily driven 3rd camaro with a sbc that made 447rwhp and 479tq with a LT1 style intake and haltech ecm. Thats stout for back in the 90's to have a NA car that was daily driven, not stripped down and ran low 11's on nt555r tires, trapping 122mph. I was a kid when I built it.

 

yea, its fairly anemic in NA form.

 

At similar compression as my old 406" SBC.... 42 ci smaller LSx, way smaller cam @ 23X/24X Vs 25X/26X in the 406, HR Vs. the SR in the 406. This little CARBED LS stomps mud holes all over the 406" I had.

You have WAY TOO MUCH carb to start with. 650 would be a very good start.

 

Actually I could tighten the secondaries and run that 850cfm on a four cylinder , it’s a spread bore with vacuum secondaries and it’s infinitely adjustable by simply turning a hex bolt and screw , never been a fan of two plane intakes because I personally shoot for mid and peak torque mostly moving the torque peak up in the power band at wot

 

1. Nostalgia and the knowledge that they work fine properly tuned
2. Personally I think vacuum secondaries are ok if your using an automatic transmission but yeah they are not good for manuals.they don’t seem to respond fast enough in cars that require letting off the gas while shifting
3. Single plane for the win. Why limit yourself with a dual plane? Probably put this on the bottle and it will make more sense then. I was also thinking 750 dP but worried it will be too big by a small fraction
4. Yeah there’s a weird dip in the out of the box MSD tunes, need to fix that but it’s still within “pretty close”
5 I think your right about a CAM and springs of course

I think I get it now, everyone’s feedback helped me. I was just expecting to much. I knew going with a carb would not increase the power so its really comparing a stock 5.3 engine to a SBC engine with full aftermarket high performance intake, fuel delivery and complete exhaust upgrades.....that totally explains it.

i see a 750dp and nos kit in my future

 

Kinda disagree. Richard Holdener took a LM7 stock bottom end 5.3 motor to 501hp with a 228 cam/fast intake/TFS 205 heads.

 

I think he just meant in terms of a starting point as if to say it’s not an LSA what did you expect

 

I agree with you Tusky. A 5.3 is 325 ci. The 327 was a great engine back in the day, and the 5.3 is a better engine than the 327 in every way. Flamers, the line forms to the right...

 

off topic but sorta on topic, I remember seeing a thread where somebody was asking if ported heads get better gas mileage and the answer was no.....more air needs more fuel meaning ported heads will eat a little more fuel.

so pretty certain the ls gets noticeably more mpg in fuel injected form, and a little bit better than sbc in carb form, but I wanted to bring this up because I believe modded sbc struggle to clear 10 to 11 mpg highway, while carbed race ls1 cars (th400, 9 inch, all that wasteful stuff) still can see 13 to 15 highway.

so my question is, if the heads flow weak on sbc, why are is mpg still low compared to the better flowing ls stuff?