Poleaxe

A bit off the subject but relevant to me. Is there a location for a listing of all the several head variants flow rates at .01"?
I've a '77 SB with, I believe, the 4A Heads and the 562299 Cam, all stock internally. This unit has all the available tuning done externally (tri-Ys, carb and dist, etc., etc.) done (by me) that seems to be providing me with approximately 320 ft. lbs at 3200 rpm (mathematically).
Hindered by a number of factors aside from money (low rise Toro intake, blocked, no clearance above carb, 11,300 lb. curb weight, desire to maintain some semblance of drivability (and near stock condition overall) in a GMC Motorhome with an effective final drive at ~2.8:1 behind a L-88 governed and valve bodied TH425), I am considering some means by which I can get a bit more bottom end out of this Bus Motor.
Windowed or no is not relevant here, since many locales outside metro areas don't even carry pump premium, my actual compression ratio is near to 7.8:1, and I don't have the need to run this engine above 4800-5000.
Seems to me that, barring some exotic inappropriate add-ons (blowers of any shade, A/M FI, low-dose nitrous or methanol, etc) that the best I can do is to advance this cam a couple degrees when I put the Cloyes set in it (we're at 80K, so it is time).
This machine has been quite competent running over most eastern mountains at about 7 ton GVW using the highest octane I can find or make, but I'm leery of 'doing' the Rockies as is.
Your thoughts would be appreciated. I've looked at a number of different gear sets and chain drive ratios, but that is for a different thread, and want to finish in the engine bay first.
Thanks.

captjim

If the engine is a 77 and is stock, you have a 403, not a 350. You could bolt on some smaller-chambered heads to boost the compression ratio, but to be honest, I doubt it really is worth the trouble and expense. If you did, and upgraded the cam, you would see an increase in low to mid range torque.

Poleaxe

Yes it is an L80. Will probably invest in the ~3.5:1 gearset before going after replacement heads or a custom cam grind. When it is time for a major I'll mull a 500" Cadillac (unless I find that this is a non-windowed Special, which then could end up with a home-made cross ram FI tailored to the lower rpm range).

oldsmobiledave

If it is a non-windowed "Special" as you call it be sure to pull the engine & sell it to Chris Witt. He is offering $1,000,000.00 reward for this unicorn.


No need to put a Caddy engine in this beast. A well built 403 can handle all of your needs & never rev over 4500 rpm.


Good luck with your project

Poleaxe

elsewhere in Forum the question was posed "can "a tenth", or, .100"" be removed from a small block head. Near as I could tell the question was dodged, so now I'll ask it. Actually, I was wondering if the 4A castings could get .135" thinner on the deck and intake mating surfaces without any issues. Again, this is for my "stocK' L80 in a '77 GMC MHC. Practicing machinist responses appreciated.

oldcutlass

I moved your posts to its own thread. Please, if you have a question unrelated to a particular discussion then start your own thread.

olds 307 and 403

The 4A heads have a terrible exhaust port that need a lot grinder time to flow. Just by adding early 68-72 heads will put you at 9 to 1 will Felpro head gaskets and flow better. Regular fuel should be no problem with the right cam.

Poleaxe

Yes yes yes… I know what I could use.The point of my question was an attempt to determine if there may be enough meat on the relevant mating surfaces to remove .100” –to- .135” and still maintain some sort of cyclical heat and shock loading robustness through the mating assemblies with these heads.I have not seen a blueprint of the head not sectioned one.One for the machinists out there.

Think Tractor.Think bottom end numbers. This unit will never see anything above 5,000.As it is, we’re right at 2,800 at 85. This is, pretty much, the top end of this RV due to wind resistance. Drag coefficient is something like a .9.

Again (see earlier entries), I am attempting to improve the “hill” climb competence of this Coach in order to stress-lessly “stitch” the Continental Divide.So, with the restrictions placed on the flow rate by the hyper-low plane Toro intake residing in and fully occupying the spaceclaim under the cockpit floor, and looking at something like 3400 rpm at 50-55 mph (in low pitch second) for hours at a time, I’d like to substantially improve the power band down there. Note the stainless tri-Y's are the same color as Dave's Cutlass. (Even if it installed the shortest gearset available for that final drive I’d still never see 5,000.And it already smokes a tire at an 80% throttle launch.)

So, since I’ve just discovered that it now [also] needs a head gasket, I’m going in.Still have not verified if this one actually has a solid bottom end (an early 4A, to be sure, possibly cast before implementation of thinwall light weight program).Upon reassembly, I’ll also be running 1.7 rockers on the intakes and keeping the stock cam, as the advertised alleged specs show me that it is the ‘right’ one (though I will likely advanced it 2 –to-4 degrees).See http://442.com/oldsfaq/oldsfaq.htm for more on heads n such.

Sure, I could re-engine it, and a 6.7 Cummins numbersappear just about right, but I’d like to see what I can do with what I’ve got.

Thanks to Dave for creating this as a unique post.This is way outside the scope of most all the GMC Bus folks.

olds 307 and 403

You can probably mill them .100. Another option is #8 heads, 5 cc smaller chambers and just need bowl work to flow decent. They also plentiful and near free.