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Why so many people do iron block ls motor swaps?

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Old 03-11-2018, 02:26 PM
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dizwiz24
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Default Why so many people do iron block ls motor swaps?

im thinking about what future direction to head for my build.

i see tons of posts here about people putting iron block truck motors into their c4.

i want to understand why ? Are sbc and ltx rebuild parts just no longer easy to get anymore and thats why people do iron block lsx swaps ?

I thought the main goal of lsx swap is a weight reduction (and more modern engine mgt).

sure the ls3 heads flow better than lt/sbc heads, but afr makes ported 195 heads that flow ls3 (stock) numbers.

add a little bit of boost and which head flows slightly better prob becomes moot.

Help me understand the direction and reasoning behind the iron block (vs. alum block) lsx swaps so i can be better educated for my future build


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Old 03-11-2018, 02:42 PM
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..... The truck engines (iron block) are readily available and due to the laws of supply and demand they are cheap ! ... I can buy them all day long out of the local pick-n-pull for less than $500 including all the core charges for the accessories and all the necessary parts to make the engine "complete" ..... While the 1st and 2nd Gen SBC's have tons of support from the aftermarket , so too does the LSx ... the LSx has some very distinct advantages "in the box" that while they are available for the earlier engines they are expensive ... 12 degree heads ... cross bolted main caps ... higher cam placement in the block ... valve , port , and runner placement ... to name a few .....
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Old 03-11-2018, 04:15 PM
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Originally Posted by C409 View Post
..... The truck engines (iron block) are readily available and due to the laws of supply and demand they are cheap ! ... I can buy them all day long out of the local pick-n-pull for less than $500 including all the core charges for the accessories and all the necessary parts to make the engine "complete" ..... While the 1st and 2nd Gen SBC's have tons of support from the aftermarket , so too does the LSx ... the LSx has some very distinct advantages "in the box" that while they are available for the earlier engines they are expensive ... 12 degree heads ... cross bolted main caps ... higher cam placement in the block ... valve , port , and runner placement ... to name a few .....
Much stronger motors. . .

Hence nearly 1100rwhp on a stock bottom end motor w/ 250k miles. . and these engines can be had for stupid cheap. . .

http://www.lsxmag.com/features/car-f...ottom-end-lq4/

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Old 03-11-2018, 04:47 PM
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still stupid epensive out here. Guys want 2k+ for a worn out 6.0
BLocks are strong but they arent gods gift. Stock LSx stuf isnt that impressive you have to go aftermarket that gets pricy fast.
Cubes are cubes at the end of the day.
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Old 03-11-2018, 05:44 PM
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i think this is a fair question.

ive been back and forth about doing swaps.

what about all the wiring? and electronics to run the unit? and to make the extra power you still need to spend $ on aftermarket enhancements in an LS

vs a set of ported 113 heads (or aftermarket), cam, headers or even just Lt cast manifold with good open exhaust is becoming more appealing to me.

If all a guy wants is 350-375hp i think a stock 350 does that with all the goodies no? no wiring harness issues. stock computer with a custom tune? simple chip swap? do u even need a custom tune until u start stroking and increasing cubes?

seems wwaayyyyy easier to just stick with sbc.

but ive never done it. no idea what im talking about. mike holmen and other have done it. mike claims it is super easy and his car runs great.

the comment about strength on the ls. this comment interests me. if the engine can handle higher rpm and will last longer assuming equal maintenance and abuse, that would push me to an ls.

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Old 03-11-2018, 06:45 PM
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Because if I did a swap it would be an LSX iron block 400 with a big whipple and that is way more expensive.

We cant beat the head valve angle. 2 heads that each flow 300cfm can have vastly different characteristics due to valve angle. 12 or 15* will behave very differently than our 23*

Look at the Yates sbf heads. vast improvements over anything our at the time they came out.
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Old 03-11-2018, 07:13 PM
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most of your reply went over my head.Do you mean the geometry of the LS engine is different then the small block engine and the geometry in and of itself is a large horse power advantage due to increased airflow?
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Old 03-11-2018, 07:45 PM
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Like 409 mentioned the availability of the iron block/aluminum head motors from light trucks and SUV's is a major factor to swap to an LS block. But the great flowing stock aluminum heads make it a bargain for horsepower.
Myself I haven't performed an LS swap so I can't brag any experience. But those that have will argue it makes more sense for cost and power. But they tend to overlook all the headaches in the details of adapters, mounts, brackets and computer/ignition controls.

IMHO nothing wrong with doing that swap but you better read up before you leap on it and don't look back once you do. I imagine you will become a electrical wiring geek if not already before your done.

Hope this helps.

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Old 03-11-2018, 08:34 PM
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dizwiz24
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Thank you for the civil replies

the intake and heads of lsx (both iron, and alum) is no doubt superior.

Everyone says the lsx is just so much stronger....

Is there any evidence the corvette 4 block main sbc has weaknesses under boost or high HP?

I mean the lsx is still cast crank ? Right? At what hp point does 6 bolt mains just become so much better than 4 bolt (or 4 bolt splayed) sbc mains.

Help me understand the fascination of an iron block lsx swap. I see guys super excited to take out their 5.7 and put in an iron block lsx 5.3 , or even 4.8 lsx motor....

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Old 03-11-2018, 09:23 PM
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The iron blocks are just a nice entry level LSx engine formula to make some great numbers for a street car. There was a C5 Z06 owner who plucked out his all aluminum LS for a 5.3 junkyard motor and added a turbo. He ended up wasting the engine by the time he got past 800 hp but it seemed be just fine at 700. Dirt cheap. Cheap, cheap, cheap. Never even cracked open the block to "do it right" and fortify the internals.

Guys get stupid CFM out of ported LS3 heads and I've seen a set of LS3 heads stock go for $400. You gotta spend $1500 or so minimum just to step into a nice AFR head that matches or outperforms the flow from the LS heads before they're even ported. Intakes are lighter, cheap as dirt and flow great for what they are. $75-$100 for a LS3 manifold WITH injectors and TB. Good luck finding gen 1 or 2 stuff for less than a grand that flows just as well...and it'll be heavier and not a dry manifold.

Newer stuff is just better and it's been out long enough that there are tons and tons of them to choose from at reasonable prices. For the money I spent on a gen 1 that makes 450 hp, I could've had an LSx that made about 600. Should've went that route but the whole hindsight 20/20 thing. Guess if that's the my biggest problem I have in life, I'm doing alright.

The SB2 stuff is ridiculous but it's fantasy babble in terms of $$$.
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Old 03-11-2018, 10:32 PM
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yeah 85, first world problems! haha.

Your response has some great meat thanks.

my only question is what are the extra costs with respect to a full set of ls1 accessories including functional ac, and the wiring harness situation.

i have to believe that by the time its all said and done, it will equal a superram/mini ram + ported or afr heads and a cam on the sbc platform.

a goo side by side comparison including everything would be great to see.
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Old 03-11-2018, 10:33 PM
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Originally Posted by cardo0 View Post
But those that have will argue it makes more sense for cost and power. But they tend to overlook all the headaches in the details of adapters, mounts, brackets and computer/ignition controls.

IMHO nothing wrong with doing that swap but you better read up before you leap on it and don't look back once you do. I imagine you will become a electrical wiring geek if not already before your done.

Hope this helps.
I did talk to a few shops that do LS swaps. Bottom line is that you are going to have to do a lot of that "details", where the devil lives, that you mentioned. In an F-body, it is EASIER since you don't have to worry about plugging into the rest of the ECM and BCM. Late model LT has Torquehead to help with that. I have talked to several speed shops that have put them in track cars. The question comes down to "How much do you love that car?". You want to get everything working without hacking, it will cost money at a time and materials basis. How much? Hard to say.

I did check with Torquehead if they were doing an L98 conversion. I was told to check back at the end of the year. They have done a late LT conversion and are working on the early LT conversions to an LS. Figure on $2500 to get their system, if it comes to fruition. Add that to the cost of the brackets and whatever else.
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Old 03-11-2018, 11:31 PM
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There isn't anything wrong with the sbc, that's been proven time and time again. But the nice thing about an ls swap is that a stock motor is about the same price but you're starting with parts on it that would be considered decent aftermarket parts on a 350. You can get them both to the end of a 100 yard dash per say, but with the ls it's like you're already staring the race 25 yards ahead. That's how I look at it anyway.
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Old 03-12-2018, 01:14 AM
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Originally Posted by dizwiz24 View Post
Is there any evidence the corvette 4 block main sbc has weaknesses under boost or high HP?
IDK what evidence there is that it has weaknesses...but in this vid, these guys blew my mind by showing it's STRENGTH! How about 25 un-intercooled PSI...765 hp/690 tq?





Or this 305 that made 620/570 with nitrous before the rings grew too much...


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Old 03-12-2018, 04:10 AM
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Originally Posted by 84 4+3 View Post
There isn't anything wrong with the sbc, that's been proven time and time again. But the nice thing about an ls swap is that a stock motor is about the same price but you're starting with parts on it that would be considered decent aftermarket parts on a 350. You can get them both to the end of a 100 yard dash per say, but with the ls it's like you're already staring the race 25 yards ahead. That's how I look at it anyway.
And if you want to make an increase on the 25 yard gain, it's going to be much easier.

Problem I have with the LS motor is the extra cost it takes to get it in. None of the professional people I talk to seem to think that it's a good idea unless I am in love with the car and idea.
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Old 03-12-2018, 08:37 AM
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Originally Posted by aklim View Post
And if you want to make an increase on the 25 yard gain, it's going to be much easier.

Problem I have with the LS motor is the extra cost it takes to get it in. None of the professional people I talk to seem to think that it's a good idea unless I am in love with the car and idea.
Both are accurate statements. LS parts are still a bit more expensive... just for comparisons sake getting a 350 for our 99 c3500 is a lot cheaper than getting the 6.0 in the 2500 Sierra or the escalade. The lq4 is in the 3 range vs the 350 which is around two, both being long blocks.

Speed always costs money and the ls upgrades are also a little more than smallblocks but it's not as drastic of a difference. Actually it's impressive really, from an engineering standpoint, the fact that the 350 basically went 50 years mostly unchanged is mighty impressive. The ls is a work of art but at the end of the day the sbc was mostly right from the start gate. The only real issue is size. To me the ls seems bigger.

As for liking the car, it makes sense on like a 68 camaro or something like that that was probably a 6 cylinder factory car that you're hopping up since it'll never be right anyway. On something like a c4 you really need to like the car because return on investment is around $5. You'll never get that money back.

I always had wondered why mercury didn't use ls engines for the boats. Then I saw the rpms needed to make power on say a 5.3... Thing would grenade itself trying to spin 6k. (Lower unit, not the engine) I know of a couple guys that went from 496s to 6.2s because they were rated close but there was no comparison. Made the thing a dog out of the hole and fuel burn was about the same. Then again when you're burning 5 gallons an hour or more anything helps I guess... I'm off topic lol. All I know is my 19 will eventually get a 350 to replace the ironduke 4 cylinder in it. Then that thing will be scary.
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Old 03-12-2018, 08:58 AM
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Originally Posted by 84 4+3 View Post
Both are accurate statements. LS parts are still a bit more expensive... just for comparisons sake getting a 350 for our 99 c3500 is a lot cheaper than getting the 6.0 in the 2500 Sierra or the escalade. The lq4 is in the 3 range vs the 350 which is around two, both being long blocks.

Speed always costs money and the ls upgrades are also a little more than smallblocks but it's not as drastic of a difference. Actually it's impressive really, from an engineering standpoint, the fact that the 350 basically went 50 years mostly unchanged is mighty impressive. The ls is a work of art but at the end of the day the sbc was mostly right from the start gate. The only real issue is size. To me the ls seems bigger.

As for liking the car, it makes sense on like a 68 camaro or something like that that was probably a 6 cylinder factory car that you're hopping up since it'll never be right anyway. On something like a c4 you really need to like the car because return on investment is around $5. You'll never get that money back.

I always had wondered why mercury didn't use ls engines for the boats. Then I saw the rpms needed to make power on say a 5.3... Thing would grenade itself trying to spin 6k. (Lower unit, not the engine) I know of a couple guys that went from 496s to 6.2s because they were rated close but there was no comparison. Made the thing a dog out of the hole and fuel burn was about the same. Then again when you're burning 5 gallons an hour or more anything helps I guess... I'm off topic lol. All I know is my 19 will eventually get a 350 to replace the ironduke 4 cylinder in it. Then that thing will be scary.
I think where people save money is getting a junked and car or truck motor for a couple hundred dollars, so they say but I'm not sure how good it would be at this point. You are talking more risk that it would go bad as opposed to a fresh build or rebuilding the junkyard core. Is the junkyard telling you the truth about the "slightly use" motor? IDK. I just know that it is a major problem if it breaks down in the middle of BFE. Any motor can break, even a fresh rebuild by a pro but an unknown entity is a higher risk.

It is leaps and bounds ahead, that is certain. Makes me think the LT is just a stopgap till they could produce the LS series.

We'll see, won't we? IIRC, someone was selling a 700 or 800 hp Mercedes and he has a string of tickets to prove that it was able to get up and go on his eBay page.
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Old 03-12-2018, 10:53 AM
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Just my 0.02c here:

Disclaimer: Modded and hot-rodded many cars but Corvette history - '72 350 4-spd mostly stock, '73 350 auto all stock, '85 L98 all stock, '04 LS-1 rarely lifted the hood, currently have '93 40th auto, PO replaced opti just prior to selling, it crapped out a week after I bought so new good opti + thorough update to basic maintenance, runs like a top.

So, LS swap into a C4: the way I see a decision tree can be built to account for the following factors:

L98: Great platform but dated. That's why GM phased it out. The basic engine was revolutionary in 1955, that's why it lasted to the '90s but it has some dated architecture that was specifically addressed with the LS series. A big continuing problem with the L98 that will probably never be adequately addressed is the intake. The TPI was made for the 305 and GM never updated the design. Nothing short of total induction replacement will fix it. IMHO a stand-alone system is the best replacement for multiple reasons but pricey. Makes the LS swap financially closer.

LT-1: Last gasp to eek out a few more years from the SB platform before the LS was ready for prime time. GM fixed a few of the long-standing SB issues but left most alone, and in the process created a few more (i.e., opti-spark).

Both SB based C4 engine platforms have the same basic problem: bypassed by newer and better tech. Heck, back in the early '90s I can remember that it was tough to find a rebuild-able 350 short block because everybody wanted one. Now it's tough to give one away - everyone wants an LS. When the time comes for an under-hood refresh of the C4 the question can be asked: the SB platform at 300 to 330 hp was essentially maxed in factory trim. The LS started there and rapidly left the SB in the dust. If we are comparing cost apples to cost apples, does the LS swap cost significantly more than rebuilding the existing SB and is that extra cost justified? Realistically, every one of our cars is not economically a valid rebuild candidate. The cost of a (good, reputable) SB rebuild will come close to the retail value of the car. So spending the extra coin for the LS might be justified.

Next issue: Electronics. All the OBD-1 platforms have the same basic problems - lack of tuneability, lack of new replacement parts, and diminishing quality of available replacement parts or repair services. These problems are not going to improve over time, they will continue to deteriorate as the remaining C4s continue aging. The LS swap, though there is an integration issue, fixes most of these problems.

Next issue: drivetrain. Transmissions - whether it's a 4L60, ZF, 4+3, etc., we're limited to a transmission that can support the C-beam. All the C4 transmissions have issues of some type and there is no way around them. Rear-ends: D44s are becoming rare. D36 is hp limited. This is not going to get better. Which begs the question - can I really use the extra 50, 100 or 150 hp the LS is capable of?

Personally I like the idea, concept and feasibility of the LS swap. It's an elegant engineering solution. Having said that, I want my '93 to continue chugging along as-is until the LS swap decision has no financial bearing, i.e., I'll do it and not bat an eye at the cost. Hope I get there someday!

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Old 03-12-2018, 11:01 AM
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Originally Posted by aklim View Post
I think where people save money is getting a junked and car or truck motor for a couple hundred dollars, so they say but I'm not sure how good it would be at this point. You are talking more risk that it would go bad as opposed to a fresh build or rebuilding the junkyard core. Is the junkyard telling you the truth about the "slightly use" motor? IDK. I just know that it is a major problem if it breaks down in the middle of BFE. Any motor can break, even a fresh rebuild by a pro but an unknown entity is a higher risk.

It is leaps and bounds ahead, that is certain. Makes me think the LT is just a stopgap till they could produce the LS series.

We'll see, won't we? IIRC, someone was selling a 700 or 800 hp Mercedes and he has a string of tickets to prove that it was able to get up and go on his eBay page.
Exactly. The late truck vortecs imo are better than the lt-1 only because it uses a traditional distributor. And 4 bolt main. By the end GM had the 350 dialed but with everyone else updating they did too so.... The LS will get to where the 350 was soon enough. My only real complaint is that you have to pull the damn heads for a cam swap. But if that's the only complaint I have I guess that ain't that bad.
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Old 03-12-2018, 11:05 AM
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Originally Posted by cuisinartvette View Post
still stupid epensive out here. Guys want 2k+ for a worn out 6.0
BLocks are strong but they arent gods gift. Stock LSx stuf isnt that impressive you have to go aftermarket that gets pricy fast.
Cubes are cubes at the end of the day.
You say worn out, I say properly gapped rings for forced induction.
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