My long term plans for my car probably include a first gen aluminum smallblock, so this thread has more to do with solving some short-term power & maintenance problems. My heads/cam on a stock 350 LT1 bottom end probably won't live too much longer the way I drive it.

I've done some reading & internet searching. 396's are pretty common. But I haven't been able to find much on building a 409ci LT1 stroker shortblock (4.030 bore, 4.000 stroke). I see LS1 guys build these pretty frequently and get some nice numbers out of them, so I can't believe that the bigger stroke is really that big of a "wear and tear" issue. My basic questions are these:

1. The 4.000" crank costs the same $$$ as a 3.875 crank, so why don't we see more 409's?

2. Does the additional clearancing for a 4.000" crank significantly weaken the LT1 block?

3. Does the machine work necessary to make a strong 409 cost signicantly more than a 396?

4. Anything else I should know before starting on this project would be appreciated.

 

I can tell you what I was told about the 4" stroke motor.

One, the cranks put a good deal of stress on the block. So don't skimp on a crank. You'll want something that is as lightweight and has all the aero contouring. Not going to be a cheap piece but it doesn't need to be billet either. The extra clearancing on the block can't help it structurally but I don't know how much it hurts either.

Use rods with better bolt placement. These are usually a little pricier, but give the extra clearance you need.

Use a 5.7 or 5.85 rod. The rod/stroke ratio isn't going to be good no matter what you do. I wouldn't worry too much about it though. At 6500rpm the max piston speed with be a tad more than a 5.7" rod 3.48 stroke motor turning 7500rpm.

You want a 4-bolt block... preferably 4 straight but splayed is better than 2 bolt.

The 409 is going to need some good heads to make power to 6500rpm. Gonna need a small base cam too, but that goes without saying.

If you plan to put something together and get a year or two out of it, then the 4" may be what you're wanting. If your plan is to build a gen 1 sbc with the 4.125 bore, then you can use the crank for that build. The fact that you can transfer all the expensive stuff to a new block is always a plus IMO.

Your call.

-Mindgame

 

the LS1 can get away with it a lot easier because the cam is higher in the block. I'd venture to say that the LT1 block is stronger than an LS1.

Since you say that this LT1 will only be a short term motor, why put a bunch of money into it? You can make just as much peak power with a 3.75" stroke for a LOT less money than the 3.875 or 4.00 cranks. Average power won't be as high, but it'll be a good step up from the 350.

when you do the aluminum Gen 1 block, be sure to get one with a raised cam. That way you can fit a 4.125 stroke or possibly more if you want! 454 cid small block

 

So, do I need to pick up a four bolt block (Corvette?) or would splaying the mains on the 2-bolt that I have in there provide enough strength?

Smaller base cam? Does this mean that I couldn't use the Comp Cam I have in there right now?

Oil pan - would I need a new one to clear the 4" stroke? If so, can't LT1's use any of the (literally hundreds available) SBC1 pans?

As far as dumping money into this motor, I intended to re-use some of the parts on the SBC1 aluminum build (crank, rods, etc.). The thing is, those aluminum SBC1 blocks START at like $4500. I was hoping to get a 409 LT1 shortblock for a little less than that (AP Engineering has build 396 shortblocks for ~$3000). Doing a GEN 1 build could easily cost over $10K by time you have some nice heads, sheet metal intake, FAST or Accel EFI, etc. If I can put together a 409 LT1 for < $4000, it would be a nice temporary solution with the added bonus of being able to re-use some of the parts.

 

Can a SBC block be made to run LT1/4 heads and intake, that way, the car doesnt have to be rewired or setup for a full SBC conversion? Then you could run a 4.125 bore small block and also take advantage of using a longer stroke as well. Just wondering

 

Yes - but converting LT1/LT4 heads to standard cooling is rather counterintuitive. One of the MAJOR advantages to using a GEN 1 block (in addition to the potential for more cubic inches) is that you can use GEN 1 heads - 12, 14, 15, 18 degree, many different port configurations and sizes - which kick the crap out of LT1/LT4 heads.

 

396 and 409 are a waste of time and money in the lt1 field. you would get better results with a 360 or 383.

 

could you elaborate why you think it's better to do 360 or 383?
also, how would you get that 360? bore .060 over? that would be going a little overbored (pun intended) on the block wouldnt it?

 

.06 is about the farthest you want to bore a chevy 350. could really use power adders do to the thin side walls. okay say you have a 360 lt1 heads can supply a decent amount of air flow a smaller motor can use that air suppy to full advantage. now on the other hand you have a 409 lt1 the heads on a lt1 decent the but that added displacement sucks alot more are than lt1 heads can supply you would never see full potental

in short version a smaller displacement motor will make the same or if not more than a larger displacement motor not running at 100 potental.

 

So you get heads that will work with the motor you are building. Don't skimp on heads just to save money. And as far as building a 409ci LT1 for 4grand or less I think that's going to be harder than you think and I am just referring to the short block since I am sure that is what you are talking about.

 

This is really "LT1 Engine Tech". Moving it there......

 

First, a LT1 is not really going to like .060 since you would want to check the cylinder wall thickness.

It's really a 408.18 if it's a 4.030 bore x 4.00 stroke.

I would say a 383 is better bang for the buck.

Now the biggie on the 4" stroke crank is clearance for the rods in the block as Mindgame said. That and the counter weights might need to be turned down and have heavy metal added to the crank to balance it. This is going to mean your balancing costs will be higher, which sucks. The LT1 block has a deeper cylinder bore in the block which makes this a harder thing to do than a normal SBC block, but it's doable.

The larger stroke if done correctly will not weaken the block but the piston speed will be higher so crank stress will be higher. A straight bolt 4 bolt is a better idea, but it's not fun to machine.

Basically higher rod costs, higher balancing costs and higher clearancing costs.

Bret

 

Yes. Just shortblock. I already have heads flowing ~280cfm @ .600 lift on my stock cube LT1. I would be re-using them.

So what about a 396? Not worth the extra 13ci over a 383? They seem to be pretty common. Given that fact, I have difficulty believing they are as much trouble to build as a 409 (408.18, sorry). Could I get out of building one of these for < $4000? (assume forged parts & splayed main caps).

As far as "seeing full potential," that isn't necessarily all I'm going after. Right now I have a 350 with a lumpy cam and some nice heads. With the addition of some underdrive pulleys and an EWP, I will have done pretty much everything I can to it short of making it bigger. When I go bigger, I would retain the head & cam combination -- in an attempt not only to make more power, but to improve road manners.

 

[QUOTE=Elysian]Yes. Just shortblock. I already have heads flowing ~280cfm @ .600 lift on my stock cube LT1. I would be re-using them.

So what about a 396? Not worth the extra 13ci over a 383? They seem to be pretty common. Given that fact, I have difficulty believing they are as much trouble to build as a 409 (408.18, sorry). Could I get out of building one of these for < $4000? (assume forged parts & splayed main caps. [QUOTE]

As far as building it for under 4 grand I really doubt it if you want to use good parts. I am using an Eagle 4340 crank, Oliver 6.0 rods, Diamond pistons, Callies splayed 4 bolt main, block filled half way, cloyes doubler roller, canton 6quart pan and it was well over 4 grand to build this shortblock just to let you know since it seems like this is what you want to do.

 

The 408 is is going to be more expensive to build. The reasons have already been outlined. Bret mentioned the crank counterweights and the extra balancing. Add that to your cost.

Also look at the crank swap situation carefully. If you plan to use a Bow-tie 1-piece seal block you'll be ok. If you want to use a 2-piece seal block, then you need to buy a 2-piece seal type crank for your LT1 build and use a rear seal adaptor. That requires more machining and labor.

Use that 3.875 crank (396) in a 4.125 block and you're still sitting with 414 ci. You can make your goal with that.

FWIW, there's a less expensive Al block coming along from WP, in the Motown lightweight. Probably somewhere around $3500.

-Mindgame