Big Block and 4x4 Question

[402Bowtie]

I have a 402 big block I would like to put in my '72 K20. There recently were a couple of threads talking about this, but I couldn't find them. If I remember right there was someone who had to cut out some of the firewall of their cab in order for the bb to fit. What is it about a 4x4 that creates a problem with a big block, and what modifications will need to be done in order for everything to fit?

[Yukon Jack]

I had to modify my firewall but some people have to do nothing, not sure why. You can see some pages on my website in my signature where I detail putting the bb in my 69 K20. Big blocks are taller and wider than small blocks.

[Longhorn Man]

A body lift will help quite a bit too.
not only does the size of the engine make it a PITA, but the 4X4 trucks have the engine sitting back further than a 2 wheel drive does...that's why you can get them in 2 wheelers, but was never an option in 4X4 trucks.

[402Bowtie]

thanks guys, that was exactly the info I was looking for. Why then do the engines sit farther back on the 4x4s....is it for clearance issues somewhere? Forgive me if this is an obvious answer, but I am a learning 18 year old...thanks...John

[kwmech]

Body lift to clear the rear of the cylinder heads, or you can move the x-member forward and redo the drivelines like I did. The only other modification would be the x-member itself for possible clearance of the oil pan--depending on the pan.

[4x4Poet]

Doesn't moving the engine xmember foward also move the oil pan's rear sump within shot of the axle and/or diff pumpkin cycling up?

[MAC67]

when i set the bb in my blazer i hardly had to do anything , the only firew wall mods i ddi was 2 eggsized dents i put into the firewall for valve cover clearance , it does have a 3 inch body lift which i dont like but it made it easier ,, you cant even see the dents when the motors in , they are very small

[kwmech]

Originally Posted by 4x4Poet

Doesn't moving the engine xmember foward also move the oil pan's rear sump within shot of the axle and/or diff pumpkin cycling up?

Still clears--may have a problem with the factory flat leafs, not with a 4'' lift

[special-K]

Personally,I keep the big blocks for street(2wd)trucks.You can get how ever much power you want from a small block for 4-wheelin`and they are lighter.I think the idea sounds cool,great braggin`rights,but I`ve never done it,never needed to.

[MAC67]

Originally Posted by special-K

Personally,I keep the big blocks for street(2wd)trucks.You can get how ever much power you want from a small block for 4-wheelin`and they are lighter.I think the idea sounds cool,great braggin`rights,but I`ve never done it,never needed to.

never gonna pull the same torque out of a small block that you will a big block , sure they are a little more expensive , the weight difference isnt enough to make to squirts , you really ooughta try it sometime ,

[Pont]

I'm also running a BB in my 4x4. Fit's tight, no firewall mods, no body lift and not enough room for an HEI so I opted to go with a Mallory Unilite dizzy. The stock exhaust manifold would not clear the passenger upper frame rail and it had to be notched (or ground) to clear. Same issue with the headers I now run. Hope this helps...

[special-K]

I knew I`d get a reaction from you,Mac67.Not trying to raise hairs.I just never bothered with it.I wanted badly to buy Bad4x4`s 454-powered K/20,too far.With 4wds I look for torque from gearing;axles&T-case gears.Ever wheel a doubler equipped rig?If I was to swap from a small block out for more torque,I`d run a diesel.Worth the added weight in torque(like a big block,just more).And,you get fuel injection,another off-road plus.I plan on this one day.Meanwhile,I`m content with the power from the 400,383,and even the 350 powered trucks I have.

[too much stuff]

Couple things i found out are: Corvette valve covers are notched in the back on one cover, this worked good on drivers side.
Exhaust manifolds are off a 77 454 pickup. Just had to grind a "nub" off the manifold to fit.
Stock hei fit to the firewall with a little caressing of the firewall.
Hope this helps. Mine is a 1/2 ton with no body lift.

[special-K]

That ain`t bad.At first it was sounding like alot of trouble:moving cross-members,oil pan clearance,body-lift(yuk!).You have to dent the firewall for HEI on a small block,too.

[mrein3]

Originally Posted by special-K

That ain`t bad.At first it was sounding like alot of trouble:moving cross-members,oil pan clearance,body-lift(yuk!).You have to dent the firewall for HEI on a small block,too.

The HEI in my small block clears my firewall fine. This last time it was in the engine when I installed it. However I originally installed it in a 350 in the factory location while the engine was in the truck. I pulled and installed the HEI distributor a couple of times.

You do have to remove the cap first. And it is a tight squeeze. But it makes it.