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LS 6.2 L build list and advice

Hi folks, new here and new to airboats. Been searching and lurking quite a bit and I am leaning heavily towards powering the 15'8" x8' alumatech hull I have with a 6.2 l LS engine. Now might be a good time to mention I have never set up an airboat, or assembled an engine from scratch, but I'm doing it anyway. I've spent the last couple weeks watching engine builds on youtube and I'm comfortable it is something I can do, plus I have a few engine guys I work with to help if needed. I am a cnc machinist/fabricator/machinery design specialist by trade. I do have shop space, tools, and a good understanding of how things work, so I'm not going into this completely blind.

I am building this boat to use for hunting, and to take the family out on an occasional cruise. I don't anticipate a lot of dry running but don't want to get stuck if dry spot presents itself unexpectedly either. I would like to keep the engine budget in the 10k or less range. I do not have a prop or gearbox and would like to hear suggestions in that department as well. I do have SS cage, rigging and a motor mount.

With all of that said I am having difficulty deciding on what parts to buy. My hope is to get some specific recommendations for which block to buy, which rotating assembly, which cam, which heads etc. Any assembly advice is welcome. I will try to keep the thread alive with pics of the project as I go. Hopefully ending with a complete, properly running boat.
 
Welcome- here is my recommendation some will say differently but my research is from Proven combinations and proven engine builders
Not that it matters to this point but are you going carb or stand alone efi? On LS the difference can be a few grand. On to the assembly. Unless you are using the long block as Is, Get a good balanced rotating assembly I would suggest (lunati), Callie’s, stay away from eagle. If you are rebuilding throw your head, main, and rod bolts out they are Tq to yeald and should not be reused. If you upgrade to main studs make sure you have your machine shops line hone and bore using the new STUDS or you will be furious when it won’t rotate by hand or burn up some bearings
The build specs below are for a 500 hp 408 LS based off a L92.
Mains- .0024-.0026 in 50ft/lbs-out 60ft/lbs (ARP studs)
Rods- .0024- .0026 45 ft/lbs
Rod bolt stretch- .0055- .0060 “am for .0055” (ARP bolts)
Piston to wall - .0035
Bore finish-280
Crank end play- .004
Ring gap- use manufacturer recommendation for 150 hp shot of N02 mine is Top ring Bore x .0060, 2nd ring bore x .0070, oil ring min .0015 suggested use is .0035
That should get you started. Take it slow lay everything out and if something doesn’t feel right stop and recheck. Good luck and let us know how it turns out
 
The LS platform is very flexible. So need more info to provide better help. Here are some questions:

1. What is your HSP target?

2. What RPM at WOT?

3. Aluminum or cast block?

4. What type of hunting do you plan to do?

5. How many people do you plan to carry on the boat?

6. Are you more interested in push on the hill or top end speed?

7. EFI or carb?

8. What type of fuel and octane?

9. Do you plan to stroke the engine?
 
Thanks unforgiven,

Undecided about carb or efi, thats one reason I started the thread. Would it be reasonable to say if I buy a pull out engine that some of the stock fuel system can be re used for an efi build? If so is it worth it?
 
CarMotorBarge said:
The LS platform is very flexible. So need more info to provide better help. Here are some questions:

1. What is your HSP target?

2. What RPM at WOT?

3. Aluminum or cast block?

4. What type of hunting do you plan to do?

5. How many people do you plan to carry on the boat?

6. Are you more interested in push on the hill or top end speed?

7. EFI or carb?

8. What type of fuel and octane?

9. Do you plan to stroke the engine?


1. guy I bought the boat from said if I'm 350 + range I will be ok. To be safe I'm thinking I want to be between 400 and 500
2. I don't know, my gut says lower the better but this is something I came here to gain a better understanding of. Drives could be long so fuel consumption is something to think about.
3. Thinking aluminum, to dovetail this question in with #5 I have 3 kids so with me and the better half that makes 5. The kids are 9 (yes triplets) so they aren't huge but I balance that out by being a 270lb person. Wife isn't exactly wispy either. So I like the aluminum since its lighter.
4. Lake O, kissimee river and Big Cypress are all pretty close to me, want to explore all 3, and hope to get into some gator hunting and froggin too. Most of my hunting experience is hunting hogs and deer from stands over bait. I'm bored with it though so I'm trying to get into something new.
5. see 3
6. not looking to build a hot rod by any means, just looking for something reliable that will get me to some of the more remote areas I want to see
7. I'm juggling this, the engine guys I know know carb a lot better and all are encouraging me to go carb. Hoping this thread helps me make up my mind.
8. Pump gas, if I have to buy premium thats fine
9. maybe, if I'm putting it together anyway part of me says might as well. I don't want to sacrifice reliability either...
 
All of the OEM efi system can be reused however you will then be required to run a stand alone computer as the OEM computer will not work. That’s where it can get pretty expensive quickly. Then depending on HP/TQ goals, cam specs, cylinder bore, and stroke and NA, FI or No2 the OEM injectors will be too small so you will need new ones based off of specs. A pull out LS3 with Holley LS computer is hard to beat and can be had for under 10k, if your building from scratch a RHS block, or GM performance if it’s a brand new block still have it line honed and bored with the new hardware. And send the pistons with the block and check to make sure Piston to wall is correct. use the New Brodix LS heads, less than 3k and well worth it, but a few of the OEM heads are excellent, I didn’t speak of cam specs in previous post as that will be highly dependent on Hp/Tq goals, max rpm and Gear ratio. In no way is my above post intended to be a complete tell all step by step. It’s more than enough information to assemble a short block that’s bulletproof though
 
unforgiven11B said:
All of the OEM efi system can be reused however you will then be required to run a stand alone computer as the OEM computer will not work. That’s where it can get pretty expensive quickly. Then depending on HP/TQ goals, cam specs, cylinder bore, and stroke and NA, FI or No2 the OEM injectors will be too small so you will need new ones based off of specs. A pull out LS3 with Holley LS computer is hard to beat and can be had for under 10k, if your building from scratch a RHS block, or GM performance if it’s a brand new block still have it line honed and bored with the new hardware. And send the pistons with the block and check to make sure Piston to wall is correct. use the New Brodix LS heads, less than 3k and well worth it, but a few of the OEM heads are excellent, I didn’t speak of cam specs in previous post as that will be highly dependent on Hp/Tq goals, max rpm and Gear ratio. In no way is my above post intended to be a complete tell all step by step. It’s more than enough information to assemble a short block that’s bulletproof though

I don't think an RHS block and Brodix heads will fit within his budget of $10K.
 
oldscratch said:
CarMotorBarge said:
The LS platform is very flexible. So need more info to provide better help. Here are some questions:

1. What is your HSP target?

2. What RPM at WOT?

3. Aluminum or cast block?

4. What type of hunting do you plan to do?

5. How many people do you plan to carry on the boat?

6. Are you more interested in push on the hill or top end speed?

7. EFI or carb?

8. What type of fuel and octane?

9. Do you plan to stroke the engine?


1. guy I bought the boat from said if I'm 350 + range I will be ok. To be safe I'm thinking I want to be between 400 and 500
2. I don't know, my gut says lower the better but this is something I came here to gain a better understanding of. Drives could be long so fuel consumption is something to think about.
3. Thinking aluminum, to dovetail this question in with #5 I have 3 kids so with me and the better half that makes 5. The kids are 9 (yes triplets) so they aren't huge but I balance that out by being a 270lb person. Wife isn't exactly wispy either. So I like the aluminum since its lighter.
4. Lake O, kissimee river and Big Cypress are all pretty close to me, want to explore all 3, and hope to get into some gator hunting and froggin too. Most of my hunting experience is hunting hogs and deer from stands over bait. I'm bored with it though so I'm trying to get into something new.
5. see 3
6. not looking to build a hot rod by any means, just looking for something reliable that will get me to some of the more remote areas I want to see
7. I'm juggling this, the engine guys I know know carb a lot better and all are encouraging me to go carb. Hoping this thread helps me make up my mind.
8. Pump gas, if I have to buy premium thats fine
9. maybe, if I'm putting it together anyway part of me says might as well. I don't want to sacrifice reliability either...

Here are responses back to your answers:

1. Lets assume the goal is 500 HSP. This is easily obtained on any LS with a 4.0 stroke and a reasonable cam. A stock LS3 is 430 HSP.

2. Don't be scared of turning an LS some RPMs. Most people are turning 5400 to 5700 at WOT. Some are turning over 6000. I am turning 6100 to 6200 on mine. My recommendation is to get a cam that will make maximum HSP between 5800 and 6000.

3. Aluminum blocks are about 100 lbs lighter than the cast iron blocks. They also cool about twice as fast. I would recommend an LS2 block or LS3 block. Both are aluminum. The LS2 with a 4 inch stroke will make a 402. The LS3 with a 4 inch stroke will make a 416. The LS2 is cheaper, but the LS3 has a larger bore and will make more HSP and torque.

4. Doesn't look like you are talking any serious dry running. A 500 HSP motor should be fine. Just keep the boat as light as possible.

5. See 3.

6. I would recommend using a 2.68 ratio with a wide or super wide prop. The 2.68 will allow you to get to extra HSP so you can turn more prop. The wide and super wide props push really good on the hill. The only disadvantage of the wide and super wide props is the increased vibration versus skinny blades.

7. Carb will give you the best chance to get under $10K for the entire engine. I personally prefer EFI, but there are a ton of boats that run really good with a carb. Just make sure you use an AFR meter to ensure the AFRs are correct at various RPMs.

8. I would get flat top pistons and use 93 octane. The flat top pistons will get you around 11:1 static compression.

9. A 4 inch stroke does really good on an airboat and is extremely reliable under 6000 RPMs. I would get a forged crank, forged rods, and forged pistons. This will cost about $2,500 and doesn't include any machine work. Also the CNC LS3 heads from GMPP are really tough to beat for the dollar.

Hope this helps.
 
unforgiven11B said:
Welcome- here is my recommendation some will say differently but my research is from Proven combinations and proven engine builders
Not that it matters to this point but are you going carb or stand alone efi? On LS the difference can be a few grand. On to the assembly. Unless you are using the long block as Is, Get a good balanced rotating assembly I would suggest (lunati), Callie’s, stay away from eagle. If you are rebuilding throw your head, main, and rod bolts out they are Tq to yeald and should not be reused. If you upgrade to main studs make sure you have your machine shops line hone and bore using the new STUDS or you will be furious when it won’t rotate by hand or burn up some bearings
The build specs below are for a 500 hp 408 LS based off a L92.
Mains- .0024-.0026 in 50ft/lbs-out 60ft/lbs (ARP studs)
Rods- .0024- .0026 45 ft/lbs
Rod bolt stretch- .0055- .0060 “am for .0055” (ARP bolts)
Piston to wall - .0035
Bore finish-280
Crank end play- .004
Ring gap- use manufacturer recommendation for 150 hp shot of N02 mine is Top ring Bore x .0060, 2nd ring bore x .0070, oil ring min .0015 suggested use is .0035
That should get you started. Take it slow lay everything out and if something doesn’t feel right stop and recheck. Good luck and let us know how it turns out

Is the .0035 piston to wall clearance something I should just assume from the get go I will have to have a machine shop bring to spec for me? Assuming I just use main bolts and not studs is it flat unrealistic to think I am just going to buy a block, and a rotating assembly and put it together without getting a machine shop involved?
 
carmotorbarge, sounds like the 4" stroke is worth it. I realize I will have to verify this as I assemble, but generally speaking if I buy a 416 stroker rotating assembly for LS3, gm ls3 block, will I have to cut any rod clearance in the block ? How about valve clearance with the flat top pistons you suggest?
 
A quality machine shop isn’t going to bore a block without the pistons being used. This allows them to set the piston to wall clearances in each cylinder. A lot of times a used block and SOME brand new blocks are not perfect, Many shops will upon request but it’s highly advised against. For instance if you have block bored .030 over, depending on the aluminum used in the pistons the piston to wall clearances will change so your final cylinder bore is for each slug will be slightly over .030 and not all the same.
It is 100% UNrealistic to think you can assemble without machine work. New castings are not perfect and you will want to ensure everything is square and true prior to assembly. Neglecting this part and have severe consequences. I would not risk $10k in new parts and cut corners. On a side note I have and have buddies pull an ls out of a wreck or bought from LKQ complete pullouts and nothing other than a new wiring harness/computer and a oil change and put it in and go and have zero issues after years of use.
 
unforgiven11B said:
A quality machine shop isn’t going to bore a block without the pistons being used. This allows them to set the piston to wall clearances in each cylinder. A lot of times a used block and SOME brand new blocks are not perfect, Many shops will upon request but it’s highly advised against. For instance if you have block bored .030 over, depending on the aluminum used in the pistons the piston to wall clearances will change so your final cylinder bore is for each slug will be slightly over .030 and not all the same.
It is 100% UNrealistic to think you can assemble without machine work. New castings are not perfect and you will want to ensure everything is square and true prior to assembly. Neglecting this part and have severe consequences. I would not risk $10k in new parts and cut corners. On a side note I have and have buddies pull an ls out of a wreck or bought from LKQ complete pullouts and nothing other than a new wiring harness/computer and a oil change and put it in and go and have zero issues after years of use.

Well I will certainly plan on sending it out then, just to further clarify, if I plan on using pistons for 4.065 bore and don't plan to bore over, one could assume there will be material to remove from the cylinders to accomplish the .0035 clearance you recommend, assuming a new gm performance block?
 
If you buy an LS stroker kit buy a balanced assembly the lunati is like $25-2700 and some change we’ll worth it, no you will not have to cut for rods, I would have the machine shop chamfer the bottom of the cylinders slightly or you can with a die grinder prior to final cleaning. Valve clearances will be dependent on Stoke, piston, heads, cam ,push rods and valve size staying in the parameters of a normal stroker nothing will have to be messaged to work will all go together like a stock motor.
 
In some areas it can be hard to get good balance work so that sounds like good advice. One of the best in my region just closed up shop.
 
Oldscratch- the Piston to Bore or Piston to wall clearances is going to change based on Pistons! Forged vs hypereutectic. A 2618 expands more than say a 4032 so the Piston to Wall will be slightly looser however both will be exactly same size once up to operating temperature. The clearance I suggested are used in a 6.2 aluminum block L92 base with Forgerd slugs. Had this been iron block and hypers the clearance may need to be adjusted. If the PtW clearance I gave falls within the manufacturer recommended specs for you performance then use it. But to answer your question yes there is plenty of cylinder bore for you to get the clearance you need.
 
For what you want why not just buy a WaterThunder Performance 408 or 418 Ls? Complete carb motor can be had for under $10k and efi probably close to that maybe more maybe less. I know at one time Dave was doing economic 400-425-450-500 hp engines and believe they were under 10 grand. My next one will be a WT due to cost by the time I buy everything to build one identical I’ll have spent more or right at the same Ammount without the headache
 
ok so getting close to pulling the trigger on block and rotating assembly. Stroker kit looks like


LUNATI 416 LS3 STROKER KIT, BALANCED 11.5:1 CP PISTONS


LS3 Stroker Kit, Lunati 4340 Forged Crankshaft 4.000 Stroke, 9.240 Deck Height, Lunati 6.125 H-Beam Rods with ARP2000 Bolts, CP-Carrillo Premium Forged -2.7cc Flat Top Pistons, 11.5:1 Compression Ratio, Balanced Assembly


which reluctor wheel should I go with?
 
unforgiven11B said:
For what you want why not just buy a WaterThunder Performance 408 or 418 Ls? Complete carb motor can be had for under $10k and efi probably close to that maybe more maybe less. I know at one time Dave was doing economic 400-425-450-500 hp engines and believe they were under 10 grand. My next one will be a WT due to cost by the time I buy everything to build one identical I’ll have spent more or right at the same Ammount without the headache

Thats a thought, I was under the impression his stuff was a lot more than that. I did drop him a line a couple weeks ago and didn't hear back. He might have just missed my email or something. I'll try him again.
 
I don’t speak for Dave Hartz or water thunder performance however it’s well known he don’t get on email often but usually a phone call can get him. He hasn’t been on SA in years lol I know I’ve sent a few emails and never heard back but could reach him by phone. In no way am I trying to push another’s product but unless you have a good build able base to start the price just is justified building from scratch when I can have a 2 warranty and no build stress for the same loot
 
oldscratch said:
carmotorbarge, sounds like the 4" stroke is worth it. I realize I will have to verify this as I assemble, but generally speaking if I buy a 416 stroker rotating assembly for LS3, gm ls3 block, will I have to cut any rod clearance in the block ? How about valve clearance with the flat top pistons you suggest?

You will have to clearance the block for the longer stroke. Also you can get pistons with valve reliefs for higher lifts and/or durations.
 
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