General Jack

iTrader: (4)

I could use a little advice. I'm replacing my 346 with something larger, most likely either a 408 Ls1 or 427 Ls3. I plan to have a sponsor build this engine for me so all I have to do is the swap itself.

I've done a little bit of research, but there are still a few things I'm not sure of... any help would be appreciated. My goals out of this motor are 525-550 rwhp through my Moser 12 bolt. This will be a weekend/track car, so driveability doesn't have to be outstanding. I would like it to last for a long time though (30k+ miles plus couple hundred drag strip passes minimum), I don't plan on doing this again. I don't plan to use power adders. Finally, I would like for it to rev very quickly, as much like a pro stocker as possible.

So, do I need to go 427 LS3 or should the 408 LS1 suffice? My impression is that the 408 would be a little cheaper and easier to swap.

99blancoSS

iTrader: (115)

More cubes makes more power easier but thats not to say that 550 isnt within a comfortable reach with a 408, we've seen 408's with 600+ (solid roller) but just goes to show it can be done. The power is made in the heads so your going to want a real good set, TFS 235's would be my first choice I think.

I offer competative pricing on my long blocks and would love to work up an estimate for you. I'll pm you with some information to help.

LSGunZ28

iTrader: (8)

You guys are overlooking that his 427 is with a LS3 and not LS7, a LS3 427 has a 4.100" stroke I believe and thats not a great idea for a fast revver, If Im not mistaken... ZIt already doesnt have to be a very driveable car he is saying, so I think he can get 550+ real easy from a 418....

why not go with a 416/418?

Light as a 427, more cubes than 408 and way lighter... and larger bore than 408...

If I were to do it all over again, id go 418 vs my 402 that I havent even put in my car yet...

james562

iTrader: (35)

408/402 LS1/LS2 + AFR 225's, TFS 235's, or ET 225-245's, with11.1-11.5 Compression or better and a Ported FAST 90/90 Setup will make 550-580RWHP ALL DAY behind that six speed 12 bolt car of yours

If it were me I'd buy the best possible heads available then purchase whatever is the largest shortblock you can afford afterwards.

The 427 isn't necessary but would be nice.

You could always bore that iron 6.0 block .060 with a 4.125 stroke and have a 427 for ~3000

MY vote is 402/412/415 LS2(All cost the Same) with a pair of ET or TF heads FTMFW

General Jack

iTrader: (4)

No reason I've overlooked the 416/418 really... and thanks for the info. I would like a fast revver (although the shorter stroke would reduce torque, correct?), so maybe the LS3 427 isn't a good option for me.

General Jack

iTrader: (4)

Does the LS2 require an adapter harness like the LS3?

I definitely like what I've been hearing about the TFS heads, I'll probably goes with those. And I agree, the 427 is nice, has a sex appeal that the others lack... but at the end of the day it probably isn't worth the extra cost, especially if the LS3 isn't best suited to what I'm going for.

abbaskhan

id go with the 416 ls3 based N/A........
or a 408 in case you change your mind about the power adder

98Z28CobraKiller

iTrader: (17)

The LS7 block features a longer sleeve. My understanding is that the LS3 has the same sleeve as all the rest of the LS series blocks. A 4.0 stroke is already notorious for using lots of oil unless done just right because of how far the piston comes down in the bore. I would think that a 4.1" stroke would make the oil consumption even worse. The LS3 is supposed to be better aluminum and improved oiling so I will be going to the 416/418 option myself. I think it's better to get the cubes from the bore than the stroke IMO.

Stang's Bane

iTrader: (22)

The reduction of torque comes from less cubic inches, not stroke length.

General Jack

iTrader: (4)

I thought I remembered from way back that longer stroke would create more torque than shorter stroke if cubic inches were held equal? And by the same token, larger bore versus smaller bore, cubic inches held equal, would tend to be more of a rev happy engine?

See5

iTrader: (53)

An LS3 based 416 probably is the best bang/$ and should do >500 RW in a relatively mild state with ported LS3 heads. Lots of torque.
4" stroke is max IMO given the shortish sleeves of the LS1,2,3.

LSGunZ28

iTrader: (8)

your mean piston speed will be too fast with a long stroke.. Im not 100% sure on if It will also be slower to rev... but logically it seems like it will because the piston has more contact area with teh cylinder walls and more friction, etc..

A rule of thumb is the longer the stroke, the more it helps for low end torque, although it will also have to do with what type of heads and what cam you use... a longer stroke should help with a lower revving, low end tq applications.. while a short stroke is a more rev happy and higher peak tprque maker...

again this is generally speaking..

if what I have said is wrong in any way, correct me.

zjt

iTrader: (1)

torque = R x F, where R is the radius and F is the force (this is a cross product, not just multiplication). Longer radius w/ same force => more torque, simple physics.

I agree, but I also considered the increased the moment of inertia to rotate the crank.

Again, correct us if we're wrong.

Stang's Bane

iTrader: (22)

I understand the physics behind it, but sadly every test performed on an actual engine and not on paper, says otherwise.

Hot rod Magazine did the test years ago. Two SBC's within 1-2 cubes of each other. One was a bore heavy motor and the other was a stroke heavy. Same top-ends, equaled same results.

zjt

iTrader: (1)

okay, I stand corrected. Learn something new everyday

LLC

The most common problem I see with the LS3 427 builds are the rod lengths used and the rings used.

I've seen many configurations of this build that include 4.070 bore and 4.100 stroke (426.7 cid), 4.080 X 4.100 (428.9 cid), 4.080 X 4.085 (427.2 cid), and a 4.080 X 4.090 (427.7 cid). They all achieve around 600 flywheel horsepower.

One of the problem area's is all these builds use a 6.200 rod which compacts the ring pack. Because the ring pack is so tight the top ring is already so close to the piston deck that everyone just uses a super-light piston suitable only for N/A use. To gain even more horsepower from the build, most are using low tension top ring and oil ring with a standard tension second ring.

If you want a reliable LS3 427 that will take on a power adder use a 6.125 rod. Have the piston pin moved down the .075" lost from the rod length and have that .075" added to the piston deck but retain the ring pack orientation (.043" X .043" X 3mm). Use a loose fit top ring but use a standard tension Napier style second ring, and a standard tension oil ring. Also have the piston skirts bulked up and made thicker to reduce piston rock in the bore.

By design and configuration the engine will make a little less HP/TQ N/A. With the added 150 shot of nitrous your competition will say' "WTF just happened?"

99blancoSS

iTrader: (115)

His goal is 525-550 with a 427... there is no need for a custom piston or nitrous. Why complicate things when you dont need to.

LLC

It is my experience that no matter how much N/A power you provide a customer with, they always want a little more. This being said for racers and street cars alike. By building a strictly N/A motor, 99% of the customers feel "locked in". I choose to build engines that are reliable, makes huge power, but are open for that little more. Most everyone likes an advantage. Who am not to offer the room for such?

A custom piston of this nature would cost around $100 more than the off the shelf.

LSGunZ28

iTrader: (8)

Im not saying you cannot be correct, but 1 - 2 cubes is a very close displacement...

remember the 455 rocket engines from the olds 442? Why did they make heaps and heaps or torque at low rpm but very low HP?

I understand they revved very low and valvetrain has LOTS to do with it, cam profile, runner length, etc... but the amount of torque it made for a 455cid engine on pump gas was abnormal... Im fairly sure we wouldnt have seen those numbers if it was a larger bore, shorter stroke making that 455ci displacement..

Stang's Bane

iTrader: (22)

It is all in the runner length, cam profile etc.

As a matter of fact I can take the same engine and change the exhaust, intake manifold, and camshaft and they will act like 2 completely different engines. Not to mention the cylinder heads....