Gee, that's too bad you ordered that TC.
That TC will very likely cost you more gas than keeping the A999 with the 2.74 low(Assuming you have an A999), and moving up one gear size, to 3.55s.Unless you are cruising hiway a lot, AND at much higher speeds than 65mph.
Here is some math;
Currently with the A999,you're starter gear is; 3.21 x 2.74=8.8
With the A904, your starter-gear will be 3.21 x 2.45=7.86
So you have lost 1-(7.86/8.8)=10.7% torque multiplication. If your previous TC was a 2200, and your new one comes in at 2600; that is a 400 rpm increase. So your engine will have to make 10.7% more torque at the new stall, JUST to break even from the Gear loss. That means if your 360 currently puts out 150FtLbs at 2200, then it will need to put out 150x1.107= 166 now at 2600,again,just to break even. Chances are very good that this will happen. The compression increase alone will bring in a good part of that, perhaps 3 to 4 %. But if you delay the intake closing event by installing a bigger cam, then the torque will drop again. All-in-all, I think it is a
poor trade. The new TC will gain you very little snap, over what you had.And in the mean time you have to cruise at a higher rpm to best drive that non-loc-up TC, and just to heap insult on injury the thing will heat up the oil.And as a parting shot, if you do lose low rpm torque, you will,of course, have to step harder on the pedal to move from one speed to the next, with the same authority that you did before the loss; and that burns gas
So if fuel mileage is that important,and your old A904 has the 2.45lowgear set; then I stand even stronger on the closed chamber heads. You will essentially be building a long-stroke,big-bore,teener. I will want the smallest cam you have,and the smallest dualplane intake, and a small vacuum secondary or air valve secondary carb.I would try to stay away from the Holleys, cuz it's been my experience with the older ones, that they are quite fat on a hotted up engine, never mind on one that is about to pull major vacuum. Any metering rod carb is IMO a better choice.But as with most things spending money to replace what you already have is false economy.What I mean is; how far can you drive on the gas you could save going from a Holley to say a TQ or AVS, and including the purchase price?Yeah that's a poser..... And once more, the Holley being fat, can be changed. It ain't that easy, but if you already have one, say a 500 or a 600,just bolt it on;we can lean it out later.
You will want to run that engine as hot as you dare.If the cooling system is up for it, I would try to run it at a minimum temp. of 200*F, so long as it doesn't run much past 220, and only occasionally. Do what you have to ensure the cooling system is up to the task. This temperature will get you a nice reliable maximum output, and maximum fuel-economy. There is one
caveat; do not let the engine get into detonation under load. If you cannot keep out of detonation with timing curve changes, then you can reset the minimum running temp to say 190*F, and re-start your timing curve tune. Try to run as much Vacuum advance as possible,under cruise condition.With 3.21s your cruise speed of 65 is about 2600 rpm.
With your new TC, you will want to run a cruise rpm that is about 50 to 100 rpm higher than your stall rpm.Otherwise the TC will cook the oil on long trips. I highly recommend a temp.gauge on the transmission, and if the oil temp gets over about 220*F, you will need a cooler.Try not to let it get up to over 235ish.By 250 the oil is cooking.
The small-port heads will like a smallport intake.
I get that the AG is one of the finest DP manifolds out there, for a hotted up 360. But most of it's advantage will be lost on small-port heads and a small cam. It really works best on big-port heads, and using much bigger cams. There are two schools of thought as to how a big-port manifold might work on a smallport head, and I have no experience with what you are about to do. My gut feeling is that since you have never had a smallport manifold on your combo, you will be non-the-wiser. I also know that I would not run that situation. I would sooner run ANY small-port intake, on a small-port head.
Here's
the truth of the matter;
If you had chosen to put proper pistons in there, NONE of these shenanigans would be needed. You could have left the original TC and tranny alone. You could have left the big-port heads on. You could have gone DOWN one cam size, or down one gear size.You could have run any intake and carb. You could have made more torque, more power and more MPGS. But as I recall, you said
Rear end is 3.21:1 the rear end is not changing and I am not pulling the engine out again.
You started the thread with the wrong question. You probably should have asked something to the effect of how to increase fuel economy and without losing torque. The number one answer would have been to increase the compression and reduce the gear. You kindof tied our hands by disallowing both.Now you are spending money on performance band-aids, that will do nothing for your economy. The AG was designed to extend the operating range of the base manifold , allowing the use of a cam with a higher operating rpm.And of course the 770 will follow. The Higher stall TC is an attempt to cover the hole in the torque curve that a bigger cam usually suffers from. So all of these items are designed to up the operating rpm, for more power, and have NOTHING whatsoever to do with increasing fuel economy. Bruce, I'm sorry I didn't catch your post in time to try to steer you away from the path you have chosen. But now you are on it,the money has been spent, the parts are on the way. You have more or less locked yourself into the big-port heads and kissed economy good-bye. If you stick to the cam that is in there now, at least the hit won't hurt all that much.Unfortunately none of those new parts are gonna amount to any performance increase, unless the cam IS upsized. So if you thought you were in a quandary before.......
The way I see it, because of the cost involved in the procurement of those parts, you really have only a few escape paths; #1 is to resell the parts when they get to you and start over, or, #2 is bolt those parts on and let the mileage be what it will be,or, #3,is to up the compression now,properly,and add a cam to take advantage of those parts, and thus you have a hot-rod.
Upping the compression is likely only about a 3to4% power increase. But the economy increase is often double that,mostly because of the low-rpm torque boost. So you can still recover from this situation.
Now this is a good place to inject another of my experiences.
In 99 I built a very nice
Hi-compression 360.And I was able to gear it up and lean it out, to the point that it returned 32MpgUs, (yes,thirty-two)on a certain hi-way trip of over 1500 miles;point to point and traveling at speeds of 75 to,dare I admit, near triple digits for over 20 hours.Hey, that was the speed of the traffic.
And I used a 270/280/110 cam with .050 specs of 223&230, and a Holley 600.The final drive was just about 2.0
And the same exact combo, (with the exceptions of a carb-swap to a 750DP,and a timing reset),went 12.9/106 in the qtr.; no other changes.
The Scr was about 10.9; Now you know a little about compression, gears, power, and tuning.
BTW; that 600 was set up to cruise pretty lean at 75 to 95 mph, which was 1860rpm to 2230rpm.And the timing was adjusted to the max,that the engine wanted. That carb was not used for anything else;only cruising.
