370 OR 408 for boost?
Cubes don't matter when it comes to turbos...Unless you're going absolutely max effort. But an LQ9 block isn't what I'd consider 'max effort'.
They'll both make similar power...408 will have more low end torque. The 408 crank will be technically stronger.
It will come down to preference. I've always like the idea of smaller, more efficient motors. I'm a fan of the whole "doing more with less" thing.
They'll both make similar power...408 will have more low end torque. The 408 crank will be technically stronger.
It will come down to preference. I've always like the idea of smaller, more efficient motors. I'm a fan of the whole "doing more with less" thing.
I just said bigger cubes because you can make the same power as the 370 with less boost on the 408,but like i said,thats just what i would do,but its just my o2,everybody is guna do it diff from one person to the next!!
with a 76mm t4 turbo I would stick with the 370 for sure... No reason to go 408 with that turbo.... You will need the highest ar housing for the 370. You'll run into backpressure issues with anything higher than 370 cubes.. 370 is considered the maximum CI with a single t4 turbo.
That was going to be my hijack question between the two engine builds. im a 6 speed guy for LYYYFFE. I need the RPM's, to where i might almost stay with the smaller all bore engine. Plus im VERY limited on my rear end gearing since there are exactly 4 to choose from and 3.90 is the smallest,,, which i currently have...
Umm and what reasons are you basing this on..
My 408 is not a track car but a street car 99%. I went out of my way to make it very streetable. 3.54 gears now in auto but they were fine with the six speed. Streetable cam ,no noticeable lope ,easy to tune and no surge issues at lower speeds. 9.5 to 1 compression is still pump friendly enough if you run some alc injection or just keep timing down a bit. Lots of torque down low even with big afr 225 heads and can spool up turbos better than smaller engine. Still as said can turn a decent rpm ,feel pretty safe at 7000 for occasional track runs but do keep 6500 redline the rest of the time .
Cost more than a 370 because of the forged crank but aside from that don't see any downsides at all. In fact wish that had done a 427 or even bigger somedays.
As said haven't seen one shred of practical proof that a 408 is not a good boosted choice.
I used to hear the same thing about my 2.4 litre talon .Everyone was saying 2.4 was not good idea, 2.0 was better could rev higher ,rev quicker.rod to stroke ratio or someother junk science argument. But in reality the 2.4 is great for street. Spools up the turbo quite a bit faster than 2.0. Gives a broader more useable street power band and you don't have to spin it to 10,0000 rpm. Build 2.0 are spun to 10,000 sometimes although 9000 to 9500 is more usual rpm limit. Spin the 2.4 to 8500 or so but as said it makes the power and torque down lower in the more streetable range.
Only real reason I see for 370 is its cheaper. stock cranks are still pretty strong. But thats about only real reason I see for running one.
My 408 is not a track car but a street car 99%. I went out of my way to make it very streetable. 3.54 gears now in auto but they were fine with the six speed. Streetable cam ,no noticeable lope ,easy to tune and no surge issues at lower speeds. 9.5 to 1 compression is still pump friendly enough if you run some alc injection or just keep timing down a bit. Lots of torque down low even with big afr 225 heads and can spool up turbos better than smaller engine. Still as said can turn a decent rpm ,feel pretty safe at 7000 for occasional track runs but do keep 6500 redline the rest of the time .
Cost more than a 370 because of the forged crank but aside from that don't see any downsides at all. In fact wish that had done a 427 or even bigger somedays.
As said haven't seen one shred of practical proof that a 408 is not a good boosted choice.
I used to hear the same thing about my 2.4 litre talon .Everyone was saying 2.4 was not good idea, 2.0 was better could rev higher ,rev quicker.rod to stroke ratio or someother junk science argument. But in reality the 2.4 is great for street. Spools up the turbo quite a bit faster than 2.0. Gives a broader more useable street power band and you don't have to spin it to 10,0000 rpm. Build 2.0 are spun to 10,000 sometimes although 9000 to 9500 is more usual rpm limit. Spin the 2.4 to 8500 or so but as said it makes the power and torque down lower in the more streetable range.
Only real reason I see for 370 is its cheaper. stock cranks are still pretty strong. But thats about only real reason I see for running one.
TECH Apprentice
Joined: Aug 2006
Posts: 366
Likes: 0
370... for several reasons, some already listed...
for comfort here is the last dyno from my stock short block LS2 (364c.i.) obviously S/C and not TT but it'll let you see the 370ci FI potential, belt started slipping up top, thus the fall off...
for comfort here is the last dyno from my stock short block LS2 (364c.i.) obviously S/C and not TT but it'll let you see the 370ci FI potential, belt started slipping up top, thus the fall off...
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Verdad Gallardo Cubes don't matter when it comes to turbos...Unless you're going absolutely max effort. But an LQ9 block isn't what I'd consider 'max effort'.
They'll both make similar power...408 will have more low end torque. The 408 crank will be technically stronger.
It will come down to preference. I've always like the idea of smaller, more efficient motors. I'm a fan of the whole "doing more with less" thing.
They'll both make similar power...408 will have more low end torque. The 408 crank will be technically stronger.
It will come down to preference. I've always like the idea of smaller, more efficient motors. I'm a fan of the whole "doing more with less" thing.
Also you have offboost driving. Especially with bigger turbos off boost driving may make bigger cubes even more desirable.I barely see boost in the city in normal driving.
Also not sure abou the technically stronger cranks..you are saying forged cranks are not stronger than stock non forged ones? Many may not find the power limit of the stock ones but a little extra margin of safety is sometimes a good thing.
Strongly disagree. Bigger cubes equal faster spool up. You can of course play with ratios to affect spool up and other things like tuning can make some diff but generally bigger cubes spool up same turbos quicker. And bigger engine can make more power at less boost . Course max power is about same as turbos max out their airflow at lower psi on bigger motor.Making more power at lower psi may have advantages sometimes as well.
Also you have offboost driving. Especially with bigger turbos off boost driving may make bigger cubes even more desirable.I barely see boost in the city in normal driving.
Also not sure abou the technically stronger cranks..you are saying forged cranks are not stronger than stock non forged ones? Many may not find the power limit of the stock ones but a little extra margin of safety is sometimes a good thing.
Also you have offboost driving. Especially with bigger turbos off boost driving may make bigger cubes even more desirable.I barely see boost in the city in normal driving.
Also not sure abou the technically stronger cranks..you are saying forged cranks are not stronger than stock non forged ones? Many may not find the power limit of the stock ones but a little extra margin of safety is sometimes a good thing.
I took the guy that you quoted as saying that the forged 4" crank would be stronger only because it's forged, and that is correct. But the stock crank is plenty strong for the power levels he can expect for THAT TURBO.
For THE SMALL TURBO in question here, the smaller cubes would be better. Yes, on a bigger single, it would spool faster if it were a 408 but in THIS APPLICATION, the 370 would work better, and last longer IMO.
Staging Lane
Joined: Feb 2010
Posts: 73
Likes: 0
From: LI.NY
Ok guys. Sorry for being "That Newb" that brings up such an old thread. But i'd have to assume, there has been ALOT more testing, tech and builds that will shed more light on this. I was in the 370 vs 408 thing for a bit. Pretty set on the 370 w Procharger F1A/X. Only questions I cannot figure out is, why dose nobody mention a short stroke 390. Or a cubic inch between the two without the 4" stroke??? I also dont want a long stroke for my app. Rather up the boost, meth, timing and tuning. Is the 390" Lq out because of lack of good forged cranks? And before you say it. YES, I did search. ALOT! 
I guess you can say im trying to find that happy, but yet reliable middle ground between the stock cubes and the 4"??? All help is greatly appreciated. Thank You.
I guess you can say im trying to find that happy, but yet reliable middle ground between the stock cubes and the 4"??? All help is greatly appreciated. Thank You. Last edited by 89BANDIT; Jul 19, 2017 at 06:03 PM.
Why not do a fully forged 390ci..(3.825" Callies Crank).....best of both worlds. Thats what I did. 410 RWHP N/A. Gonna go 18-19psi. About 1,000 RWHP car.
I may put some good heads on first....then it should be around 470 RWHP N/A. It has garbage 1998 LS1 heads on it now.
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I may put some good heads on first....then it should be around 470 RWHP N/A. It has garbage 1998 LS1 heads on it now.
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Staging Lane
Joined: Feb 2010
Posts: 73
Likes: 0
From: LI.NY
^ Yes, thats what im asking about. Already chose AFR 225's. Anyone have any experices with the 3.825" crank and boost? Is it worth it over the 370"?
^^ Thats a Little cam you got there. On the lift side anyways. H/C You'll be good.
^^ Thats a Little cam you got there. On the lift side anyways. H/C You'll be good.
Staging Lane
Joined: Feb 2010
Posts: 73
Likes: 0
From: LI.NY
Would the power gain be worth the trouble of the 3.825" crank? Aiming for 900+RWHP on 93 pump. And meth. Also not sure about intake. Original plan was LSX102. But i'm see'ing alot of the Holley and other alternative short rams that MIGHT fit under a stock 3rd gen T/A hood.
Would the power gain be worth the trouble of the 3.825" crank? Aiming for 900+RWHP on 93 pump. And meth. Also not sure about intake. Original plan was LSX102. But i'm see'ing alot of the Holley and other alternative short rams that MIGHT fit under a stock 3rd gen T/A hood.
That cam is just what I'm using now.....running around N/A. I'm gonna have Martin Smallwood spec me a cam when my turbo kit goes on.
I'm also going to be at 10.2:1 cr and full time E85. So this 390ci will spool fast.
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Would the power gain be worth the trouble of the 3.825" crank? Aiming for 900+RWHP on 93 pump. And meth. Also not sure about intake. Original plan was LSX102. But i'm see'ing alot of the Holley and other alternative short rams that MIGHT fit under a stock 3rd gen T/A hood.
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