To recap;
I have a 318 getting finished up and will be needing to upgrade my carb. Currently the engine is a stock 318 HD in a 1976 D100 that was ordered for Cal Trans. It has a 360 intake on it and I've always been curious if the HD designation had it built with 360 heads and intake in 1976 or if these were add-ons. The engine had reportedly had the oil pump replaced by the previous owner. After a few months of ownership and the truck running like **** I was tuning on it and decided to buy an Edelbrock AVS 500 cfm carb to use on the current engine. It ran much better with this carb.
The good times didn't last as it started knocking pretty bad and parformance dropped off so bad that I could barely get up the hill on my driveway. With the report of a previous oil pump replacement I decided to just have a different 318 built with a '73 340 cast crank I had laying around. Around this time Speedmaster (alloy heads) was having one of their salse so I got a pair of bare heads and an air gap intake.
Specs on the new engine are .060" + for "328 cu in.", '73 cast 340 crank, Eagle SIR rods, KB167 pistons, GJ oiling mods, HFT 224/230 @.050 lift on a 110* LSA, Competition Camshafts adj. rockers, bowl blend on the SM heads and gasket matched intake. I am thinking about an FBO ready to run distributor. Fresh 727 with mild work, the shifts are a little firmer but nothing crazy that is annoying for street cruising. Stock converter, 3.23 gears. This is just a SWB, parts chasin'/run around town "sport truck".
Any ideas on HP and the main question of what carb? I really like the AVS. I was flirting with doing a Fi-Tech but leaning toward sticking with the AVS style since I was liking it in the 500 cfm form with the 318.
With 28" tires.( 88" roll-out), and 3.23s, your hiway rpm will be
75=2900@zero-slip, perhaps plus 4% pushing the brick, so 3020 ish.
What that means is that you can run a stall-Rpm just under that and not lose any fuel mileage, but, compared to the stock TC, pick up a ton of bottom end torque. Say you picked up 20 ftlbs@2800, that would be 11hp, nearly the equivalent of one cam size. And it comes at an rpm that you can really use it.
Now, this is about 4 or 5% higher at 2800 than at 2200. So, because you have 3.23s and 28s;
here's the deal;
in first gear, at WOT your roadspeed will be
at 2800 =~26mph(15%slip).
at 3300 = ~31(12%),
at 3800 = ~36(10%),
at 4300 = ~42(8%)
at 4800 = ~47(8%)
at 5300 = ~52(8%)
The point is that your engine is rapidly running into wind-resistance now, so when you shift into second, the rate of acceleration will drastically diminish. Firstly because the 1-2 split is 1.45/2.45=59%, so shifting at 5300 will drop the Rs to 3140, and the engine is well off the 110LSA cam. And secondly, now you are are bucking the wind at 3140 rpm. So the point is this, and this is MY Opinion; since performance in second gear is going to diminish anyway, and there is nothing you can do about it without major changes; You might as well make first gear a killer first gear;
do you agree?
If no, then what's your idea?
If yes, then follow along.
Wiki says San Diego is at 60ft or so above sealevel, so you got that going for you already.
If you want killer with the parts you have, then the first thing you need is way more cylinder pressure.
With an Ica of 61*(on that 224/110 cam), the Wallace Calculator predicts
just 162psi. But my alloy heads do support up to 185psi, still on 87E10, AND, I see no reason why yours wouldn't.
Now, since you already have adjustable valve gear, let me suggest a switch to a SOLID lifter cam-kit, one size smaller at .050. This should bring your Ica down to say 53* with which the Wallace predicts
174 psi. and now yur talking.
This represents an increase in low-rpm (stall to 3300ish) performance of ~16%, which is in the ENTIRE speed range below 31mph.
That 16%, represents the gear difference from 3.23 x1.16=3.75s OR you could look at it from the other side; 3.23/1.16=2.78s.. What that means is that with the earlier Ica, you could run a smaller gear, and not loose the usual low-rpm performance.
So, that will change your cruise-rpm
from 75= 3020(3.23s),
to 75= 2750(2.94s)/70=2570, or
to 75= 2580(2.76s)
Ok so say you went with the 2.94s, giving up 9% of that 16% performance. That looks like a fair trade. , leaving you with plus 7% below 3300 with the solid lifter cam. Now, since your cruise rpm has been reduced to 70=2570@4% slip, lets go with a minimum 2600stall, and a max of 2800.
Either of these will not cost you steady-state fuel economy, over 70mph.
And, the short-period solid lifter cam with it's Ica of 53* versus the Comp Cams 61*, will pump up the Fuel-economy potential still more.
But, there's no free lunch; the smaller at .050 cam will give up power over the nose, of maybe 10hp, beginning at perhaps 2hp at 3800rpm(guessing). So, the top of first gear WILL go soft sooner ot later, but the new pressure of 174psi versus the pre solid lifter cam pressure of 162psi, is gonna soften the hit quite a bit.
The ET, from zero to 50 mph will be quicker off the line, (with the solid/ 2.94s/ 174psi); but slowing slightly towards 52 mph.; versus the 224FTH/stock stall/3.23s/ and 162psi ...... I can't say which way it would go.
It has been written that you can expect a fuel-economy percentage increase of 50% of the rpm decrease. So from 3020 to 2750 is a decrease of ~10.1%, so you can expect an increase in fuel economy of 5%, due to the rpm change.
But the biggest change will be to the solid lifter cam, opening the exhaust valve way later, which means that at cruising speed, more energy CAN be extracted from the combustion process, with proper tuning. But even better is that you can run 87E10 full-time, saving you money at the pump every day, all year long.
The bonus is that pulling out to pass someone at 70mph with 2.94s, the KD into Second will get you 70=3940 rpm, on the fattest part of the torque curve, and Second gear goes to 4800=87 mph, so let 'er rip.
I mean, jus saying,lol.
