On a stock 318 ( it does have dual exhaust). Roughly how much power/ torque difference would going to a 4 barrel make? I'm asking because I was asked this same question and I said probably 15 horsepower, the person who I was talking to said that it was more like 50 horsepower and I don't believe that.
Not one hp more until the rpm gets up to where the two-barrel got to be too small, say 3000 rpm. from there to around 4000/4200 maybe 15 hp.
So lets say about 15/(1100/100)=
~1.36 hp per 100 rpm, if you jet it right. Let's say you free up the exhaust and get 20hp, which is
then 1.8hp per 100rpm.
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I know you didn't ask but;
But here's the problem I see;
with factory 2.76 gearing, and a TF trans, 4200 comes at about; 45mph in first, 76 in second, and 110 in third .
Whereas 3000 comes at; 32/54/and 79
Now don't hate me but, when you pull out to pass someone doing 55 in a 65 zone, and the trans downshifts; it will be too fast for first, and second will get you 3000 rpm, and the 4bbl just beginning to work., adding 1.36 hp per 100 rpm, approximately. Sooooo, don't hold your breath; By 60 the 4bbl is making plus 6.8hp, if your ignition timing is right, By 65, it is up to 13.6hp if you jetted it right.
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Best bang for the buck, off the line would be a modest increase in stall, I love the 2800.
Once moving the
Second-best bang is gears to keep the rpm up. If the Rs drop below 3000, then you're back into 2bbl territory.
Third best is a free flowing exhaust and I'm going with small diameter headers to help get the exhaust out in a hurry, and the biggest stinking pipes you can hang under your hotrod, that still clear the speed-bumps.
Fourth best is a cold-air intake system; the engine cannot make power with 240* plus temperature under-hood air.
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I recommend a 2800 & 4.30 gears, 3.91s minimum, but 4.30s was nice., headers and dual 3"pipes all the way, a spreadbore carb on a spreadbore intake, extra spring pressure to go to at least 5200, so you can get into Second at not less than 3000.
I already did all this, and more than once.
When it comes to the intake, get one with small runners that match the heads; and I highly recommend a spreadbore. Your throttle reasponse will drastically improve on that sucked out 135/140 psi engine.
The trick with this combo is to get the stock cam to pull a lil longer at the top so that when it shifts, the Rs don't fall into the dumpster. The 1-2 shift split is 59% . So shifting at 4400, the Rs fall to 2600. Whereas shifting at 5000, I got 2950. Shifting at 5400, I got 3200.
Obviously, by 5000 the engine wasn't pulling much anymore, but the payoff was coming into second, at way better than 2600, lol.
A different winter I installed an A998 with the deeper low, and it did ok with 3.55s.
I gotta tell ya, the standard TF 1-2 split of 59% is the stock-cam 318's weak spot.. She works waaaaaaaay stronger with a 4-speed and 72% splits, which is what I ran most of the time.
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But if you really want to have a good time with a stock318, run the Commando A833 with the GVod as a splitter. The first three shift-splits average around 78.5%, and with 3.55s, top of Second-over will get you to 4350 (about peak power on the stock cam) =65mph; how much more perfect can it get? That's two no-lift electric shifts and one pull.
I'll tell you how much more perfect; when you get to 65mph you stuff it into 4-over, the Rs drop to 2240; just as if you had 2.76 gears.. and you pussy-foot right past the cops.
This was, by far, my favorite stock318 combo of all time.
I could sell it to you.
I never checked the fuel-economy, cuz it was my winter-beater; but 318s with 2.76s in A-bodies, are know to get low>mid 20s right? Not great, but not bad for a 60yo design that burns 87E10 all day long.
The thing is Stock 318s will easily pull 2.20 gears for 65= 1800 ...... and 2.76 gears x .78= 2.15, so 65= 1740; oh yeah that is totally doable on a TQ. oh and
BTW
with 3.55s, 55mph in Second-over = 3640, not too bad for passing.
With 2.76s, 55 in Second is 3630, you see what I did there with the math. Either of those will get you to 4400 = 66 mph at full Power., wave bye-bye to Grandpa as you blow by him.
I'll tell ya, I sure had a good time in those winters, with that splitter; 5000 x .785= 3900, which is well above the 3000 basement, where the 4bbl gave you nothing. That 3900 is about plus 12 hp over the 2bbl .... by my guess. That's getting close to the power increase that the next bigger cam would normally get you, but without any loss in power below 3000.
To give you something to look at, here is the Command /GVod with 3.55s, my favorite, expressed as roadgears.
10.97/
8.56-6.82/
5.32-4.97/
3.88-3.55/
2.77; Gv in bold
Those are all useable ratios but not sequentially. Typically, I shift; first/second/third/third-over/then fourth over, for a short fourth/deep overdrive.
But at WOT, I shift, the first four ratios; then whatever, usually 4od which then looks like a drop to 52%.
And here it is with 2.76s; with the 3.55s under it.
------- 8.53/
6.65-5.30/
4.13-3.86/
3.01-2.75/
2.15
10.97/
8.56-6.82/
5.32-4.97/
3.88-3.55/
2.77
That 5.30/5.32 ratio will get you 65@4310, on a power-peak close to 4200.
I haven't found anything more versatile.
Ok bed time around here.
