So I've been toying with the idea of building a 408 to do something different. I'm not concerned with what's been proven but more of what is possible. So I wanna slap a 4" crank in an LTx. Now I'm sure that's been done, but I wan to do some deviating here. So I've been looking into what heads I wanna top this thing with. Now since I'm pretty much restricted to a .030 overbore due to structural reasons (I don't want the cyl. walls getting too thin at the base of the bore with the large stroke). So anyway I'm tossing up the idea of getting some Dart 220 CNC heads. They've got 248cc intake runners and flow 324 cfm at .800 lift (this is advertised from dart). Now I'd have to convert them for the reverse flow cooling, but the intake pattern will remain with the idea of installing a magnacharger (to be determined later )on top of it. Then again I can always go with the 215 Trick Flow's from AI. So the real question comes down to how much is 15-20 cfm going to hurt me? Now I know, I know, numbers aren't everything, but they are a good indicator to what's going on. I'd really like to get numbers up to the mid 300cfm area if possible, but I'm not going to hold my breath for anything anytime soon. Anyone have any viable opinions/ information on this issue.

BTW.....plans are a 408 rotating assembly, SR cam, And a modified magnacharger base with a TVS 2300 unit similar to the LSx variants, all normal bolt-ons, and 1 7/8" headers into a 3.5" or 4" Mufflex system. If anyone really wants to know.

 

Register on www.impalassforum.com and search for user Jeff Green, and PM him. He's converted a Donovan aluminum block for LT1 cooling and is pushing about 1600 hp with a Novi SC. I think he's been there, done that, with just about everything you're wondering about for your seup.

 

if you want to stay 23 degree, AFR 227's would be a good choice. Well ported they should flow 330. Otherwise I would convert a SBC head to reverse cooling.

 

+1 on those AFR227's. In fact, Jeff Green is running those ported.

 

sorry to hijack here but im curious.

How does one convert and SBC head to reverse flow cooling?

 

Proven and possible are two words you used to describe putting a 4" stroke crank in, but you forgot one. Expensive. And while there have been successful 4" stroker LT1 motors, I'd say it's not a good option for someone who cannot afford to watch a motor blow because a real thin spot ground for clearance failed and happened to let a gallon of coolant into the motor. The cost/benefit ratio, IMO, is just too high.

I think a well-built 396 will deliver what you're looking for.

 

The clearancing required is understood. Plans also call for short filling the block to take away the risk of the water jacket being cut. Plans also call for an auxiliary oil cooler (not like the factory setup, more like a trans cooler) to be installed to avoid possibly over heating the oil. Aside from that the clearance required for 4" stroke crank are not that much more than what is required for a 396 if the correct rods and rod bolts are employed. I'm more curious to know weather or not heads that flow 30 cfm less at .7" lift are going to cost HP in a roots type blower application. I know it's going to cost money to accomplish what I'm planning, that's not the issue as this is going to be a lengthy build, not something done in 2 weeks. Either way it's more of a curiosity than anything else.

 

sounds very interesting

 

i'd think you'd want more compression height from the piston in a blown application than what a 4" stroke is going to leave you with....

 

im very interested in seeing what you end up with - especially the maggie part. Thats another thing Ive always wanted to do.

 

Sorry, I love LT1's as much or more than the next guy in here, but right now I have to be "that guy".

I have to be that guy that says, dude simply buy an LSX block, 6.0 liter block, or L92 block and build a big inch stroker MUCH cheaper than you will be building this LT1 for.

Throw some boost at it, and hold on...

You will likely go faster for much cheaper than a 408 build like you described and the options you will be given are 1,000 greater than that of the LT world...

JMHO.

 

Wicked, you're right.....I may want more compression height as it leaves me about 1.175" for compression height at a zero deck of 9.025". Now I know I could run N2O on it, but I want something different....it's that easy. I'll just have to limit my boost numbers which shouldn't be that hard (then again, I'll probably get greedy). But if I am conservative to start and have a good tune up I think I should be fine. I'm not planning on spinning it to the moon, but I may do the LSx PCM swap depending on what the engine likes for a powerband. Either way it'll just require some constraint, which again I'm not really known for......but there is a first for everything.

JoeliusZ28, the only real thing holding it back is getting the rear inlet charger from Magnuson with the correct length jack shaft. Then you can mount it on their base for a carbed SBC, have injector bungs put on it and cut off the water neck (just like most single plane conversions), and bolt it to a Gen I SBC head. Now either way I go I'll have to add material to the top of the runners to facilitate mounting to the raised runners of the heads....again nothing really major. This will also allow the use of a LSx throttle body which as we all know can flow some pretty serioous numbers for the HP department.

gregrob, you sound like a buddy of mine that keeps telling me to buy an LSx with the harness and pcm for $2500-$3K and slap it in. Truthfully, I've always wanted to be able to say "I've done something different." In today's world it's getting harder and harder as everyone has tried almost everything. This is one thing I have yet to see someone do. It may cost a bunch of money, but hey you only live once. If it doesn't perform like I'm thinking it will, then I'll move to the LSx, but I won't be happy unless it's a breathed on LS9. So either way it'll cost some coin......

So these are the plans, I'm just wondering if the difference in CFM is going to hurt under these circumstances......maybe it's time to call Duttweiler and see what he thinks.....then again he'll probably tell me to do it to a LSx and make twice the power