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408CI boost question

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Old Feb 23, 2013 | 11:08 PM
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Default 408CI boost question

hey all,

i am wondering how much boost you could throw at a forged 408. im talkin the right rods, crank, pistons etc...

thanks guys, i appreciate the help
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Old Feb 24, 2013 | 12:23 AM
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Is the question you're really asking, how much power can you make and not blow up your engine? I don't understand the preoccupation with a certain PSI number.
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Old Feb 24, 2013 | 12:32 AM
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I throw 20 at my 402 every time I drive...been doing that for over a year.
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Old Feb 24, 2013 | 02:04 AM
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going to come down to what heads your running.
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Old Feb 24, 2013 | 09:53 AM
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Originally Posted by evo462
Is the question you're really asking, how much power can you make and not blow up your engine? I don't understand the preoccupation with a certain PSI number.
that too, but im really asking how much a lq4 408 can handle as far as boost goes. id like to se 800-1000rwhp if i go this route
Originally Posted by Atomic
I throw 20 at my 402 every time I drive...been doing that for over a year.
are u running an aluminum 402? i dident think the aluminum block could handle that much boost
Originally Posted by lmt0705
going to come down to what heads your running.
thats another thing, i have no idea what heads i would be running. ive always been an NA guy so this world of boost is all new to me. i guess id throw on sme L92 or afr 225s?? i really dont know. do u have an idea what a good set of heads are for a motor like that?
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Old Feb 24, 2013 | 10:17 AM
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20-22 lbs

1100-1200whp
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Old Feb 24, 2013 | 10:40 AM
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Nope, iron lq9 block. You want the best flowing heads possible with a turbo, just like NA.
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Old Feb 24, 2013 | 10:55 AM
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It's the 4 bolt heads that are the limit. When cylinder pressure get to high they flex and start pushing water. At 800-1000 you shouldn't have any problems.
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Old Feb 24, 2013 | 11:32 AM
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Originally Posted by 02sslayer
that too, but im really asking how much a lq4 408 can handle as far as boost goes. id like to se 800-1000rwhp if i go this route

are u running an aluminum 402? i dident think the aluminum block could handle that much boost

thats another thing, i have no idea what heads i would be running. ive always been an NA guy so this world of boost is all new to me. i guess id throw on sme L92 or afr 225s?? i really dont know. do u have an idea what a good set of heads are for a motor like that?
An aluminum block can handle 20-22 lbs Its not that much of an issue. You will lift the heads before the block gives you any problems. Mark Koehler of the Ohio Boys ran a stock LS2 block one year to 35 psi before the stock cylinder liner cracked and he ran 7.99 like that.

Stock L92's and AFR's are on different ends of the map as far as heads go.
L92's flow air but they have a thin deck and tend to lift when trying to throw alot of boost at them and when trying to get aggressive on the tune. AFR's flow a ton and have thick deck for boost but the price of them is double that of and L92. If you want a good flowing thick deck stock head it would have to be the LSA head. The aftermarket heads would be AFR, TFS, MAST, PRC, and All-Pro. The one thing about All-Pro, you are going to pay $$$$ but they are the only ones I know of with a 1 inch thick deck on some of their heads.
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Old Feb 24, 2013 | 03:44 PM
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Originally Posted by I8UR4RD
20-22 lbs

1100-1200whp
Originally Posted by Atomic
Nope, iron lq9 block. You want the best flowing heads possible with a turbo, just like NA.
Originally Posted by Cam72aro
It's the 4 bolt heads that are the limit. When cylinder pressure get to high they flex and start pushing water. At 800-1000 you shouldn't have any problems.
Originally Posted by 87silverbullet
An aluminum block can handle 20-22 lbs Its not that much of an issue. You will lift the heads before the block gives you any problems. Mark Koehler of the Ohio Boys ran a stock LS2 block one year to 35 psi before the stock cylinder liner cracked and he ran 7.99 like that.

Stock L92's and AFR's are on different ends of the map as far as heads go.
L92's flow air but they have a thin deck and tend to lift when trying to throw alot of boost at them and when trying to get aggressive on the tune. AFR's flow a ton and have thick deck for boost but the price of them is double that of and L92. If you want a good flowing thick deck stock head it would have to be the LSA head. The aftermarket heads would be AFR, TFS, MAST, PRC, and All-Pro. The one thing about All-Pro, you are going to pay $$$$ but they are the only ones I know of with a 1 inch thick deck on some of their heads.
thanks to everyone for all the info. i know alot more about boosting a motor thanks to you guys.

i wonder if i could have extra holes drilled in the block to accept the 6 bolt heads? do you guys think i could get away with 18-20 PSI on the LQ4/9 or on the aluminum block? id rather put boost to an aluminum block 402 instead of a 408 if i coud still reach my goals
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Old Feb 24, 2013 | 04:32 PM
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It would be best to grab an lsx block from the get go, then skip straight to 427 or 434 anyways. Thats what ill be doing next go around.
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Old Feb 24, 2013 | 04:36 PM
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Originally Posted by 02sslayer
thanks to everyone for all the info. i know alot more about boosting a motor thanks to you guys.

i wonder if i could have extra holes drilled in the block to accept the 6 bolt heads? do you guys think i could get away with 18-20 PSI on the LQ4/9 or on the aluminum block? id rather put boost to an aluminum block 402 instead of a 408 if i coud still reach my goals
You can't just drill the holes. Material would have to added to the block to make it a 6 bolt setup. ERL does it to stock blocks all the time. I would do an aluminum ls2 block as a 385 setup from AES. It would get you a better piston in the bore and trust me, you won't miss the 17 cubes under boost.
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Old Feb 24, 2013 | 09:16 PM
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Originally Posted by I8UR4RD
It would be best to grab an lsx block from the get go, then skip straight to 427 or 434 anyways. Thats what ill be doing next go around.
i am leaning more toward the lsx 427 with an F1 procharger. just thought id check inti the 408 to save some money on the build. if i dont go boost route ill probly build an LSX440 NA
Originally Posted by 87silverbullet
You can't just drill the holes. Material would have to added to the block to make it a 6 bolt setup. ERL does it to stock blocks all the time. I would do an aluminum ls2 block as a 385 setup from AES. It would get you a better piston in the bore and trust me, you won't miss the 17 cubes under boost.
thats some good info. im finnaly learning about boost lol. i would love to buuild on an ERL block but i do not wana spend that kinda cash. some people say the LSX block is no good but ive heard alot of good about it too. so im gonna go that route
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Old Feb 25, 2013 | 08:53 AM
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Just want to give you an idea of price difference of the 6 bolt superdeck and an LSX block. You might find an LSX for around 2200 at the cheapest (that was awhile ago I looked at that so it might be more now)and an ERl superdeck is 3500.

The ERL block comes with ARP main studs and the LSX does not. That's a little over 300 bucks right there. The ERL block is hand honed on the deck surface and the LSX is not. Plus there will be alot more machining than just that on the LSX compared to the ERL. So, now the price gap is a little closer and one more thing, the LSX block is 140 lbs heavier than an ERL block. Reckless, a mod on here weighed all the GM blocks and the 6.0L truck blocks were 110 lbs heavier and the LSX was 140.
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Old Feb 25, 2013 | 10:13 AM
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Did he make a thread about it? I couldnt find one, and that sounds like an interesting read.
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Old Feb 25, 2013 | 10:27 AM
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Originally Posted by Atomic
Did he make a thread about it? I couldnt find one, and that sounds like an interesting read.
x2 I also would like to read.
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Old Feb 25, 2013 | 10:32 AM
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Originally Posted by Atomic
Did he make a thread about it? I couldnt find one, and that sounds like an interesting read.
He said he made it a sticky. Here ya go.

https://ls1tech.com/forums/generatio...ls-blocks.html
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Old Feb 25, 2013 | 03:09 PM
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Originally Posted by 87silverbullet
You can't just drill the holes. Material would have to added to the block to make it a 6 bolt setup. ERL does it to stock blocks all the time. I would do an aluminum ls2 block as a 385 setup from AES. It would get you a better piston in the bore and trust me, you won't miss the 17 cubes under boost.
Ultimate power is dictated by blower for the most part, not cubes.

IMO I'd prefer to keep nice thick bore walls for a more rigid block, and you simply dont need a 4" crank.

Plus with a shorter stroke, the piston doesnt drop out of the bore as much at BDC.

One of AES 3.825" cranks and an LS2 block would make plenty of power and be a strong affordable platform.

As for the 4 bolt argument. ARP make a much stronger head stud in standard M11 size. or you could go for 1/2" studs.
Both easier and cheaper than 6 bolts, and will be a good improvement over normal ARP studs

That's assuming you might have an issue with them in the first place. Many push very hard with regular ARP stuff and have very few problems.
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