gs462

iTrader: (4)

Id like your opinions, Im building a LQ4 I have everything to do a 370 just need the crank for the 408, will all things the same except the cubes how much power is the 408 worth over the 370?? the motor will be 11-1 fully ported 799s, ls6 intake, TSP 1 7/8 headers, same cam in either one. Just want to know how much power im leaving on the table?

kinglt-1

iTrader: (26)

with those heads the power difference will be minimal, but the 408 will have a better tq curve.

gs462

iTrader: (4)

I know the tq will be better with the 408 but how much of a difference are you thinking?

streetknight2

iTrader: (10)

Ok, now take this with a grain of salt from me, but here's what I see wrong with your problem. You say you have "everything" to do a 370, just need a crank for a 408. Do you have 2 sets of pistons already? They would be different from each other due to the additional stroke I would think. I too was in a similar situation deciding between a standard LQ4 and 408, when I talked to a couple guys to spec a custom cam, they both said the cam choice would be different based on the cubes.

redtan

iTrader: (5)

That's the thing...you don't. If you have the rods and pistons for a stock stroke then you are going to demolish your heads/valves if you use those with a 4" stroke. You are going to need completely different pistons and rods for a longer stroke.

gs462

iTrader: (4)

I knew this was going to turn into a you need you dont have thing. I'm just asking for opinions on how much power is left on the table with a 370 vs a 408, you're right I have not ordered pistons and i will do that when i decide but either way as I stated the motor will be 11-1. So back on track HOW MUCH POWER am I leaving on the table.

redtan

iTrader: (5)

Ah ok, so basically you're saying you have the 4.030 bored block and that's about it. When you say you have 'everything' means you have pistons, rods etc.

Anyway, like it's been said before, with those heads and intake you will not be down more then 20-25 hp and torque. But the torque will come in stronger and earlier in the powerband.

gs462

iTrader: (4)

Nope I actually have a block, crank, rods, heads everything BUT the pistons, and I have a line on a deal on a Stroker crank, hence my ?

S10xGN

iTrader: (11)

Basically, the gains are linear. So if you increase the displacement from 370" to 408" (10%) you'll get an approximate 10% increase in power. As others have noted, variables can change this number to a degree...

red fury

iTrader: (1)

I vote 408. I am sure down the road you will increase air flow one way or another and the 408 will reward you even better.

PREDATOR-Z

It could reach up to additional 50 whp. with the extra cubes

JPH

iTrader: (2)

Pistons will be different also from a 370 to a 408 and not just the crank. Imo, your choice of cylinder heads would be the limiting factor on the 408s horsepower output (along with the intake to a degree also) and camshaft selection/design would be different between the two in relation to both of the engines crankshaft strokes and cubic inches.

hammertime

iTrader: (1)

With all things being the same, the 408 is at a slight HP disadvantage. Yes, it will make more power than the 370, but an optimum head/cam combo for the 370 will peak earlier in a 408, truncating the top end of the curve, but adding a bit more of a torque advantage on the bottom end.

That said, you never said what cam you are going to run, so we really don't have enough to go on. If you are running a small cam for stealth, the HP difference between the two could be minor. On the other hand, if you are running one of the popular donkey dick cams that are really too big for a 346 and marginal in a 370, a 408 might really shine.

01ssreda4

iTrader: (96)

I'd go 408 if it was me.

82cetuner

iTrader: (9)

if cost is not going to be much if a differenct definetly the 408 your talking a 40 cube difference so its a easy 50hp difference. consider that our engines make more than 1 hp per cube and even more than that with performance parts.

you will also have a broader powerband threw the RPMs, this was the reason GM went to a 6.0 litr from the 5.7 to begin with for the vette engine.

do youself a favor get the 408 you will kick yourself later if you dont.

Mike454SS

iTrader: (4)

I wouldn't blindly throw the same cam into either displacement engine...but I would say the 408, given the same general quality of parts as the 370, and the same general budget in the top end, would yield 40ish more horsepower, and probably significantly more low RPM torque...maybe upwards of 60-70 foot pounds more.

mark21742

Since I'm running s 408, I'll vote for the 408 too

gs462

iTrader: (4)

Well Funds didn't show up for the stroker crank so a 370 its going to be Eagle H beam rods with 2000 bolts, 11-1 (custom ordered pistons), fully ported 799s, cam in the ballpark of the TSP 233-239 on a 112 LSA (it's gotta thump) It will be custom spec'd, Have to use my Ls6 intake for now. I think I'm going to get the TSP 1 7/8 headers in case i go bigger in the future.