I was playing around with my desktop dyno 2000, and a 4" stroke .030" over 408 actually made more tq and like 5 hp less then the 3.875"/4.060" 401. Would the .030" bore be more reliable? Now, if I could only find a good forged 4" crank.....
Let me know what you guys think

 

I am no engine builder, but going to a 4" crank either requires a small base circle cam or just play won't clear it because of the location in the block. You would need to do some serious work to the block to get it to work. But like I said, I am not an engine builder but I believe that there is a reason that a 396 (395) is pretty common.

Chris

 

I've heard of 409 LT1's before, but in my opinion, a 383/396 is about the best way to go. A 409 would costs serious cash, with limited gain over a 383/396. You would need custom pistons and crank for starters. And then you would need some serious head flow to pull any kind or horsepower out of the combo. There is a point of diminishing returns, and a 40x is past it.

 

yes a small base cam is needed, also you can only use block that have been checked over and over and clearance is a big issue.

 

As others have said, it's simply not worth it unless you are a skilled engine builder and just want to do it "because". The gain over a 383/396 is minimal compared with the hassle/cost.

Any LT1 block 0.060" over is an iffy proposition. I have seen them split cylinder walls as little as 0.030" over. If you have a lot of blocks to go through and the time/expertise to sonic check them you can probably find one with thick enough cylinders on the thrust side, but that's just one of the problems with this combo. Others have mentioned the issue of cam/rod clearance, which is not a trivial problem. As far as the block goes, there will also be an issue of getting into the water jacket when clearancing for the crank. This too can be solved (using block filler), but it's one of the many issues to deal with.

Like I said, not worth it.

 

Unless your last name is Musser I believe. Didn't he do his N/A 10 second pass on a 401??

Granted, if I remember right that was on a slightly overbored 396 setup (3.875/4.030 bored over to 4.040 if I remember).

 

Unless your last name is Musser I believe. Didn't he do his N/A 10 second pass on a 401??

Granted, if I remember right that was on a slightly overbored 396 setup (3.875/4.030 bored over to 4.040 if I remember).

 

With enough money, you might make it work.

 

now that's a big one....hahah...

 

It's been done.

You can make a 401 with the .060 over but that's a scary issue if you ask me.

A 4" crank would take alot of fitting of parts, and alot of block work with a guy who gets paid to do that with his time. I can attest that if that's your goal you better have deep pockets to do it because you would basically pay for my whole week for it to be done. Shop rates being $35-$90 an hour think about 40 hours of that, which is most likely going to happen.

One thing I've never seen is a sleeved block. Why not? You could build a 420 cube LT1 if you wanted to go thru the hassel of throwing 4.155" sleeves in one. I'm suprised nobody has gone that far yet. The scary thing is that to do that it's going to cost you more than running a CNC machined Bowtie block at $2500 a pop.

It's something to think about.

IMHO there is much more to be found in heads, INTAKES and valve train in a 383 LT1 than there is to be found in a larger cube LT1.

Bret

 

They make a kit for a 409. A couple of Impala owners run that set up running 11s and high 10s. They have been in several mags and even on hotrod tv a couple of years ago. One runs with a 400th and the other still runs his 4l60e. Very sweet rides. Illl search the Impalaforum and see if I can pull them up.
I also think John Moss built a 409 camaro too if Im not mistaking.

 

I've personally seen a 96 I believe SS with a 409 in it at Atco, a LONG time ago. Couple of years now.

The problem with the big bore LT1's I see is the supporting cast. What are our options for heads?? AFR, and that's about it. yeah, a stock ported casting would work, but you wouldn't make near the potential due to the restrictive intake runner size. Add in a set of AFR 220's and your total just went up about 3 grand with a top notch port job.

 

Apples to oranges.... Tons of people running 3.875" strokes. And there are plenty of people running 10s with 383/396 motors that are less than half the aggravation and expense of a 4" stroke 40x motor.

 

thanks for all the input guys, I think I'll just stick with the tried and true 383