1940 Buick Special Bus Cpe. Warm up?

[Guest glcalstoy]

I would appreciate any pros and cons on increasing compression, dual exhaust, cam or carburetor  changes on my 248 stock engine.  My apology s  to all my purist friends. Just curious as to what experience  other members would  share.  My first post here.  Thanks 

[Matt Harwood]

I have a 3/4 race camshaft, 7.2:1 compression, and a few other tricks in my '41 Century's 320 engine. Doing anything more radical isn't productive simply because of the intake and exhaust manifold designs and the shrouding of the valves. I expect to have about 200 horsepower when I'm done, up 35 from stock. Not huge, but a bit more grunt. A lot of people install dual exhaust using the '41-42 dual carb system, which has two separate exhaust manifolds that make it easier (easier, not easy). You won't get a lot more power, and maybe not even enough to make much of a difference unless you're driving around with your foot on the floor. Remember, most driving is at part throttle when you're not even using a significant portion of the power you have, so think carefully about modifications that you may not even use but a few seconds at a time, if that. I was already in my engine, the work had to be done, so it didn't cost any extra (OK, the cam was $750), but if you already have a running engine, tearing it down in search of horsepower is probably a mistake.

 

Think about how you'll be using the car, what most of your driving will be, and then decide if you really and truly need more power, because the power-per-dollar ratio on an old engine like this is kind of steep.

 

Hope this helps.

[Guest glcalstoy]

Thanks Matt,  your answer is pretty much along what I thought.  I would like to hear that dual exhaust though. . 

[Buicknutty]

 I rebuilt the 320 in my '41 Roadmaster a few years ago and the two main modifications I did was raise the compression, and went to insert bearings. The guy that did the machine work is an experienced local builder of stock and mucho modified engines, and its' estimated the compression is about 3/4 of a point higher by milling the head and going to the thinner head gasket. Not huge, but it is quite cheap to do it when the engine is apart for a rebuild, and touching on what Matt said above, it is a modification you can use all the time, for a bit more performance and economy. Porting is a bit of a risky procedure, time consuming, and I'm not sure in regular driving it will help much.

 Depends on your point of view though.

 Keith

[Guest glcalstoy]

Thanks Keith, do you recall how much you milled off the head?  One article I read suggested as much as .125" (1/8th"  That sounds like a lot.  Any thoughts?

Gordon

[DonMicheletti]

As always, I suggest going through the old Torque Tube magazines. There were several performance enhancement tricks noted. Taking 1/8" off the head is a quick and easy way to get the compression a touch up to take advantage of todays better gasoline (no bitching about ethanol please).

Remember, you are driving an old car and it wont match your new Toyota no matter what.

 

My stock (I believe)  '38 Roadmaster gets 11.3 mpg on the road, but performs and accelerates well  and I am satisfied with that.

 

I'm old enough to remember the Centurys at the drag strips dusting flat head Fords - both of which were cheating like heck!

 

There is lots you can do to a big Buick engine to make it a real performer, but the stock manifolding is a real negative

[Buicknutty]

 Gordon, I am pretty sure we took about 50 thou off of the head, my machinist did not want to take any more than that, so if the head needs more off at a later date, there's still lots of "meat" remaining on it. That plus using the thinner head gasket, which is 20 or 30 thou less, I cannot remember for sure. I did have to shim up the posts on the rocker shaft, to be able adjust the valves properly.

 Keith

[Guest]

Greetings I had .080 milled off the cylinder head on my 1940 Super coupe 248 eng. I used push rods from a 41 engine I had for parts, as the pushrods were a little shorter, if memory serves, which is not a good bet these days. You can mill alot off the heads and blocks off these engines, but two things to consider, if you take too much off you can't use stock pushrods, becuz they are then too long to adjust the rocker arms to get proper alignment "geometry". If they end up too long, they push the rocker arm end way up and also rub on the sides of the hole in the cylinder head they are supposed to be centered in and you run out of adjustment. The other issue is if one were to overheat these straight eights with such a long cyl.head, it could warp, needing to be milled again. I recommend leaving some metal available just in case. I have heard of stories of .125 off both cyl. head and block, but unless your going to Bonneville it might not be worth the risk. I run pump gas with ethanol in it. Many worry about valves burning and recession,spelling?, anyway, burning valves with the added compression and I haven't experienced any of that. The engine runs sweet and is plenty powerful, course I haven't replaced those damnable stock 440 rear gears yet. The Buicks use smallish valves and relatively light spring pressure, cuz they engineered the system to rely on high velocity intake charge not big valves to pack the cylinder. Add that to the fact that Buick and Cadd used a higher nickel content in the cast iron, cuz believe it or not they seemed to want the customer willing to step up and spend extra to have an engine that didn't wear out as fast. A concept seemingly lost today. When they had harder cast iron they could also grind valve seats right into the cylinder head without the need for valve inserts. Any thoughts, contrary or otherwise are welcomed!

Edited December 6, 2015 by Guest (see edit history)

[jenz38]

With my original 248 engine i had drove with a 4mm (=0.157 inch) milling on head without problems, of course with compund carb manifold and 2 aav1 front carbs with straight linkage and 2,5" exhaust...

runs perfect.

actually i have a 263 with a 0.080 milling on head an the same on deck because of the little bit shorter 84mm BMW pistons inside.

M2C

Edited December 10, 2015 by jenz38 (see edit history)