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With no power adders the block is more than up to whatever you could try to make NA. I do think taking the bores to 4.125 is just too thin as you're going to want to really spin some RPM's to make great power in an NA motor.

I'm thinking 18 degree heads, sheet metal intake, 4 "stroke and a huge lift custom cam. 700HP from a SB of any kind is going to take some doing NA.

I would not worry about the block at all.
 

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If you want big stroke, and you do for torque to move these heavy cars or a truck, then the 7000 RPM limit should not be a concern as you really should not need much more than that with a 4" stroke. So there is your torque and like Frank said, now it's all about the top end to make the HP.

If money is really no option then go 18 degree and you will have a better top end than any motor you have seen on here. I know, no one makes an 18 degree LT head, right? Well I always wanted to do a set of 18 degree heads so I would alter a set to bolt on to your LT block. If you can't find anyone that could do it then I can. It's just some welding and cutting to make a set. Match that with a custom 18 degree intake and you can get to 700HP with an Opti at only 7K RPM.

I see the Opti is getting bashed again. It's not a problem if you buy a GM, replace the cap and rotor with the MSD replacement and lock tight the screws. They will last a long time even at 7000 RPM's. I test my car about every other week at the track and it runs the tach to 7200 on every gear change. The Opti is over two years old currently and has hit 7200 RPM's 100 times with no issues. If thats not good enough then take one apart and there is nothing in their to fail other than the optical sensor. It's not a complicated part.

I would love to build this engine for you if you want to do something different. I think if you do the above you can make the 700HP goal with equal or greater torque numbers to match from a 409 CID LT motor.
 

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I'm guessing I meant I change the cap and rotor to the MSD because that fixed the rotor issue that the GM rotor has.

The only keys I have seen to them living at this point is a GM Opti to start with, not a Summit or other cheap brands, change the cap and rotor to the MSD and use blue lock tight on the screws.

The more I think about it the last one I lost was at the LT1 Shootout in KC three years ago. The rotor screw came loose in the burnout box and a huge backfire followed by a dead motor.

We both are just saying what we have seen on these and I have no explnation for why it works other than what I said above. When you look at the Opti if it doesn't come apart then all that is left is the optical sensor to go bad. There is just nothing to these things.
 

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To make 700 with any of the options above is going to take some money going NA unless you use a power adder of some kind. I don't disagree the LT is not the cheap option and it really is just a reverse cool SB chevy at the end of the day.

It just what you want to do. You can get there with any of these motors if you're willing to spend the money to do it. There is a huge differnce in what it cost to make 500 hp NA vs. 700 hp NA.
 

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I think thats a great point. Look at your 385 motor and what has been done. No short cuts and it's still 200HP short of 700HP.

You will have to go extreme on air flow numbers with the heads on any motor or you will need to run a cam, and valve springs, that will be huge numbers and that will not last if you want to drive it. Those large cam motors also run like crap under 3K or 4K so as long as it's just a race car then it's fine but thinking you can drive it is out. Keep your flow numbers up on your heads and intake and you can run less cam to get the goal which would make it more street friendly. As many CID as you can get is also the right way to get to this goal.

Like I said, 700HP would be no easy task. I still think it can be done in a motor that you could drive but it's going to be high dollar parts to get there. To do this with a big block wouldn't be that hard, to do it with a small block is going to be a trick motor.
 

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Engines are engines for the most part. The LSX doesn't use a 23 degree head so fab a set of heads for an LT at 18 degree or better and it will make just as much power NA as a LS does. The LS engies just took what racing was already doing and made it a production engine. Put an 18 degree head on Mike's car and it will run 9's.
 

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I have never found anything that really makes big power changes is cheap to do. I run 23 degree so I can run the stock LT intake but if the time comes that I really don't care if I run that intake then 18 degree or better is what I would do.

Changing a set of heads to work on our blocks is really nothing compaired to making a block. I know what a set of these heads would do on anyone's motor and it would take you to the next level. If you want to play the LS stuff then you have to have what they have.
 

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One point on the LS stuff that I have not seen anyone talk about that makes an LT engine better in its stock form. You are aware those LS engine only have ten head bolts and if you push them much with a blower or nitrous they will not hold the heads on? You will blow head gaskets on those LS engine if you want to make more than mid level power.

You HAVE to BUY a LSX block to take those engines to the same level you can take a LT or small block on our stock blocks with only adding 4 bolt caps. Even with 23 degree heads you can make more power with the old small block when you jump to power adders in total cost than an LS engine.

I'm not an LS basher as they are better motors to the mid level because of the heads on them. But to stay on topic the LT block will hold more power than it's LS counter part because the heads will not stay on. A set of 4 bolt caps with a line hone is cheaper than an LSX block.

I'm still going to push Mike to get an 18 or even better 15 degree heads with a Wilson intake. Thats worth 100 to 150 HP and thats another level.
 

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I will clarify my last comment. Change to a 4" stroke to get the air flow up, change to an LS computer or after market and rev it to 7500 to 7700. It will stay together and make some big numbers. I know one guy using a normal SB doing an 18 degree setup with those specs on a 400 stock block and it works in that RPM band. Just don't over rev it as Im pretty sure he blew it up one time due to a tranny or drivetrain failure. With a setup like that if the load is removed it will rev to the moon before the rev limiter can stop it.

But it runs with the NA big blocks from what I have seen.
 

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If you are starting with a fresh motor build then I think the answer is the cost is not much more than your standard HP build for a high end motor. The cost is justified when you hit the wall in engine building and there is nothing else you can do. I'm with Mike on trying to get everything you can out of stuff before moving on, it's just more fun and rewarding in knowledge. It makes you think!! The cost is also justifed at that point by the amount of power you gain.

Following the same logic I can't understand why so many 383's are build when a 409 cost the same. The only difference is notching the blocks for the rods to clear and I have never hit water yet with an LT iron block. Really I do know the answer to that question and it's because a 3.75 crank will bolt in without notches, I don't know why notching blocks scares people. I have never built a 383 to date, every thing that comes from me has been a 409 because it was cheap, almost free, extra torque and HP over the 383's.

Way off topic and I have to stop but good sharing on the block issues including LS engines. I still think too many people think they can bolt an LS engine in their car and make big power they see in the mags they read. I can already smell the antifreeze coming out of the heads!!
 

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Ram Air 383

A 383 can be built with off-the-shelf parts without compromising compression ratio, etc. It has a higher reliability than a 408 due to a slower piston speed, more static piston height as well as reduced cylinder side load.


I'll give you the side loads are greater but that statement is ture when you look at a 383 from a 350? You can build a 409 with a piston kit that is a shelf item from Wiesco, crank from about anyone and rods as long as 5.85 from several different companies. Even the compression ratio is in the 10's on these combo's. A 409 is as much a kit as a 383 if you check. The level of the parts is what changes what this or any motor costs. I have seen little if any cost difference unless you buy the cheapest 383 kits that are out there and you get what you pay for. For a good quality engine a 383 is the same as a 409.

I'm not saying your wrong if you go cheap but not when you use quality parts that could live if you want to use a power added down the road.
 
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