trevmust

I want to build a 400cid motor for my 1980 firebird and heard you can destroke an ls7 to that with a 3.75 crank. If i go n/a do i need the ls7 style crankshaft?

Patron

My question would be why de stroke a engine for a HEAVY car. Just because you see it, doesn't always make it a Good idea. So my question to you is so why Do you want to destroke just to be able to say you have a 400 cid engine. Pontiac made other Larger engine sizes aka 455/421...etc. If anything and I hate to say this Again Hate a little white collar lie in saying you have a 400 cid engine that's really larger wouldn't hurt. Torque moves heavy things such as a heavy FireChicken not RPM.

KCS or someone on here can tell you for sure but I think it's if you plan on keeping the Dry-sump system. 58x crank wheel is called for.

pantera_efi

iTrader: (1)

Hi, YES

I would keep it simple, A LS-2 Crankshaft with a LS-7 bore at 4.185".
I would keep it simple, A LS-7 Crankshaft with a Honda Rod, grind for stroke change to 3.75" with Heat Treat.

Your Choice ?

This would be a great high RPM engine !

Yes I UNDERSTAND the need for a "400" Formula.

Do you have a LS-7 engine ?
Do you want it to be Dry Sump ?
Do you want VVT ?
Do you want my help ?

Lance

KCS

iTrader: (20)

If you keep the factory dry dump system, you will need an "LS7 style" long snout crank.

FWIW, a 4.125" bore x 3.75" stroke combo is roughly 401ci. Your machinist will most likely recommend torque-plate honing it to 4.130" for new pistons and rings, which ends up being a 402ci engine. An LS2 based 402ci shortblock in comparison would be a lot cheaper and easier to get shelf parts for.

On the other hand, a 4.130" bore and a 4.250" stroke makes a 455ci engine...

trevmust

I don't have an LS engine yet. I'm removing the back seat and using fiberglass/carbon fiber parts for weight reduction. The build I saw the destroked ls7 with some addons was 600some HP and around the same for torque. It has a 305 in it now and it goes like a bat out of hell when it runs right, I just want an LS for added reliability and fuel economy. The engine would be brand new not used so it wouldn't need to be bored out.

tech@WS6store

iTrader: (2)

You want reliability with a dry sump use an ls3. They have both options dry and wet and we can get both for you. Brand new or hd built.

trevmust

It'll be bought piece by piece over time as I have to restore the body as well

tech@WS6store

iTrader: (2)

Even so i still stand by what i said. Id take an ls3 over an ls7 nearly any day, if not just for cost diff alone.

trevmust

i originally wanted an LS3, but if i was to go "ls3" I'd buy the LSA block.

KCS

iTrader: (20)

I'm not aware of any aluminum blocks that can be bored out. Honing is a different process though, and honing the cylinders is often needed to size the cylinders for the pistons and achieve the right surface finish for the rings, regardless of whether the block is new or not.

tech@WS6store

iTrader: (2)

Id still do that over an ls7 but maybe thats just me.

trevmust

i originally wanted an LS3, but if i was to go "ls3" I'd buy the LSA block.

tech@WS6store

iTrader: (2)

Gen4 5.3s are apparently popular to make into an alum ls1 at 3.898. Thats from customers asking us for parts because their machine shop recommended it and do it often. Quite a bit overbore, but they say itll work. Ive never tried that but i have seen and built a few ls2 408s and 370s. Both are better liners than ls1 or ls7 though

trevmust

ls7 block ships 4.115 bore and is finished to 4.125

tech@WS6store

iTrader: (2)

AFAIK and from Chevy Perf 2017 catalog they ship with 4.125 torque plate finish hone already.

trevmust

do you have a website, I can't find dry sump ls3 parts.

tech@WS6store

iTrader: (2)

We have 2, but those may not be on the site.
www.ws6store.com
www.rpmpseed.com

The dry sump ls3 uses the same oil pump, front cover, oil pan,timing set, crank bolt, crank pulley, oil tank, oil lines that the ls7 does and shares alot with the ls9 in that regard also.

Patron

trevmust: You'd do better Buying the short block of your Choice cost will be cheaper than piecing it together. 1st hand knowledge..Yet I did get to choose the best in every part needed. Could have done that with a assembled short block from a top notch vendor or builder. I was around $5k if not $5k in just short block parts and prepping along with assembly=Could have done a stroker Ls3 416-427. And this is just with a iron block Lq. Save and buy the short block with the parts wanted or needed.

Yet if you've got coin do as you wish or may.

tech@WS6store

iTrader: (2)

We have 58x ls3 short blocks for $3k....

trevmust

Lingenfelter 403cid ls2 for 5800. Is that a good deal? Short Block.