4.6 Gems with 4.0 pistons
- Thread starter WILL.TILLERY
- Start date
If you want to see a reason to keep the compression low, here's a very backyard built 4.2... with an M90 Eaton blower 
I believe you are correct. I looked in to this last night. The stroke is changed with the 4.6 crank so it's likely the 4.0 rods would be too short so it doesn't matter if they fit or not. You take the 4.6 crank and rods and pair them with the 4.0 pistons. This will give you a 4.6 with slightly higher compression. The longer stroke gives you more torque, the higher compression helps you maintain it.
So start with an older (better?) 4.0 and change the crank, and possibly rods, or start with a 4.6 from a P38 and change pistons? Is one option preferrable for any reason?
Starting from scratch, I'd buy a 4.6 motor and a set of 4.0 pistons. Then I'd have the motor machined and top hat liners installed. Keep everything else stock other than your basic improvements.
Agree but for a low budget option, I’m using a 96 4.0 block with the crank and rods sourced from a 4.6. I suppose an early P38 4.6 paired with 4.0 pistons would be an equal low budget option.
I already have the 96 4.0 and the 4.6 crank and rods, so that will be my assembly. All are still within standard spec, too. I paid next to nothing for all of it, so it’s extremely low budget. All new bearings, camshaft, gaskets, new heads found on Facebook marketplace, and a mint timing cover / oil pump I have been saving will all be utilized. I’m trying to decide what do for a cam. I have time to figure that out as it is a back burner project.
I like that rotating combo, but have never used a 4.0 block. There was some discussion about unused firing deck height that makes a 4.0 block less likely to have issues, at least theoretically. I follow the quality paint code method, and only use 4.6 blocks.
I guess I'm spoiled by my machine shop, as apparently their prices are lower than some places (one very thin silver lining about Atlanta), but a 4.6 greatly benefits from head work too. The exhaust ports are the worst. Heck, as handy as you are you could probably work them yourself with a Dremel. My go-to cam is Crower's 229, but their lifters can intermittently tick at idle. Some people find it annoying, and I've heard some builders won't use them anymore. With the 229, I think you could run New stock lifters. I recently found TWD's hardened pushrods. Never had a problem with stock, but will be using the hardened units in my next build.
An intermittent tick probably wouldn’t bother me. But, I do have a new set of OEM lifters set aside that I purchased from Turner Engineering when I was leaning toward a stock cam. But, now I am not. I will definitely look into the Crower 229. Years ago I used an Isky cam (can’t remember the specs) and it was awesome. I definitely see your point on the exhaust ports. I have always been puzzled by the decision to use rectangular ports with an awkward path and they are small. Old Buick engineering… Rectangular ports just seem like they would create a lot of turbulence. I worked in a machine shop as a teen. I saw a lot of heads with round and much better routed ports. The Italian high revving engines were the best, even Fiat did a nice job. I suppose you are right about giving a go on porting them myself. I’m retired and certainly have the time to do such tedious work.
When I lived in St. Louis there were a couple of good and reasonable machine shops. I just dont know much about the places here. I spoke with fellow enthusiast and he told to stay away from the places here. There is a machine shop next to Southwest Rovers in ABQ. I may look into them but it is 3 hours away.
Great thread!
I'm still interested in the details/realities of the 3.90" tophats with the 4.0 pistons. Is seems odd that the 4.0 slug's deck hight gives a slight bump in compression [no pun intended]
Here is a great description of fitting a 350 crank into the 300 block. Note: the 300 block has the same deck hight as the 3.9/4.0/4.6.
It gets cramped in there but it works. 348cu:
www.britishv8.org
I'm still interested in the details/realities of the 3.90" tophats with the 4.0 pistons. Is seems odd that the 4.0 slug's deck hight gives a slight bump in compression [no pun intended]
Here is a great description of fitting a 350 crank into the 300 block. Note: the 300 block has the same deck hight as the 3.9/4.0/4.6.
It gets cramped in there but it works.
348cu: Aluminum Buick Monster Motor, by Kurt Schley (British V8 Newsletter - September 2002)
Bored and Stroked: Building an Aluminum Buick Monster Motor
Great thread!
I'm still interested in the details/realities of the 3.90" tophats with the 4.0 pistons. Is seems odd that the 4.0 slug's deck hight gives a slight bump in compression [no pun intended]
Here is a great description of fitting a 350 crank into the 300 block. Note: the 300 block has the same deck hight as the 3.9/4.0/4.6.
It gets cramped in there but it works.
Aluminum Buick Monster Motor, by Kurt Schley (British V8 Newsletter - September 2002)
Bored and Stroked: Building an Aluminum Buick Monster Motor
I'll consider this thread derailed, so here it goes
it works. I built one and it screams as much as a rover v8 and 5000lb truck can. it absolutely must have the highest octane fuel available.
87 makes it sound like a rock tumbler. I found this out when in the upper peninsula and all they had was 87.
Since I like driving to that truck in the boonies Im currently rebuilding it with regular pistons.
Interested in the motor. Only question I have is would you be able to provide the additional equipment necessary for it to run in my 94 D1? Feel free to PM me to keep the thread on track. Thanks!
For your Boonies/85-87 octane trips...
A little "Girl Scout juice"(Coleman fuel) in the tank seems to calm things down and clean them out too.
