331 vs. 351
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From: Temperance,MI
331 vs. 351
Hey guys, I have been doing some thinking. I just got my 400 built and getting ready to drop it in the 77. I have been kind of thinking about building a diffrent engine to have on hand for my 92. I have been tossing the 331 with stock rods and cut down sbc350 pistons around and a 351W with teflon coated pistons full roller valvetrain both would have a set of gt40p or maybe even aluminum heads. My biggest concern is efficency both would end up being SEFI MA but right now I get 20mpg out of my 302 but towing and all she lacks. What do you guys think? long rod 302? they make any diffrence?
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Curtis
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Curtis
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From: Bend,OR
for towing a 351w stock or with minor work will do better then a 331 will. the 331 is a car build and produces power hi in the rpm range which would hinder good towing characteristics. 20mpg out of a 4wd with a 302 is kinda pushing it. i know 300-6 can barely sqeeze that kinda mileage with a manual tranny. what size tires and gear ratio are you running? and what other mods have been done to the 302?
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From: So. California
The 351 W has a 5.956" connecting rod, that is a 1.7"1 rod to stroke ratio, the 302 has 1.697 rod to stroke ratio and less as teh 331. In low rpms a shrot rod to stroke ratio is just fine but it is a hinderance for mid range and upper rpms. I would build up a 351 W all stock 8.5:1 compression, 1.94"/1.6" valves, summit headers long tube. 250/260 duturation cam 110 lobe seperation angle and 105 intake centerline. As for lift anyhwere around .520" valve lift. I would port and polish everything from the throtel plate and intake manafold through the heads.
I expect this combination to make 450 ft/lbs of torque and 214 at 2500 and 375 ft/lbs of torque and 357 hp at 5000 rpm, with a 650 cfm carburater and I do not know how much it will differ for fuel injection but 291 hp and 437 ft/lbs of torque at 3500 is pretty good and if you kept the rpms low then you should still get good gas mileage.
I expect this combination to make 450 ft/lbs of torque and 214 at 2500 and 375 ft/lbs of torque and 357 hp at 5000 rpm, with a 650 cfm carburater and I do not know how much it will differ for fuel injection but 291 hp and 437 ft/lbs of torque at 3500 is pretty good and if you kept the rpms low then you should still get good gas mileage.
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Joined: Jul 2002
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From: Bend,OR
that build would only work in a car with a carb. even running mass air would have issues because of the cam.
if you port the heads an such to much you will lose all low end making the point of this build useless. plus building power in a heavy rig at 5000 which is rarely seen is a waste. you want peak torque in the 3500rpm range and peak hp no higher then 4500. this of course all being for a heavy 4wd truck or bronco.
if you port the heads an such to much you will lose all low end making the point of this build useless. plus building power in a heavy rig at 5000 which is rarely seen is a waste. you want peak torque in the 3500rpm range and peak hp no higher then 4500. this of course all being for a heavy 4wd truck or bronco.
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From: So. California
Your right Kemicalburns, but that suggested build had peak torque 450 ft/lbs at 2500 with a 250/260 duturation cam which is pretty small. I do not understand how polishing the ports in the heads would hurt low end. I thought a port and polish job was to speed things up by removing just the small edges that slow down the air. You have built more engines than me so I will just listen to what you say. I still think a 351 W is better all around than a 331- just my opinion and I do not think he needs to spend alot of money on this motor.
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Joined: Jul 2002
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From: Bend,OR
I expect this combination to make 450 ft/lbs of torque and 214 at 2500 and 375 ft/lbs of torque and 357 hp at 5000 rpm, .[/QUOTE]
this part confused me because of the 214 you had infront of 2500rpms.
so yes this build would be a good one. realize that the cam would be a carb only choice because most efi setup couldnt run on that.
were i was coming from on the port/polish if its done extreme or to the max of the head/intake etc.. can move the power up in the rpm range. to much flow can hurt ya similar to installing to large of exhaust will hurt low end.
this part confused me because of the 214 you had infront of 2500rpms.
so yes this build would be a good one. realize that the cam would be a carb only choice because most efi setup couldnt run on that.
were i was coming from on the port/polish if its done extreme or to the max of the head/intake etc.. can move the power up in the rpm range. to much flow can hurt ya similar to installing to large of exhaust will hurt low end.
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Hotshot
Joined: May 2003
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From: south louisiana
Not all 331's will lack bottom end. It depends on the heads and cam too. The one I built for my Ranger turned on at 1500 rpms. Plenty of grunt to pull a trailer. Just didn't have the radiator for it. Heads were 1.94 valved Canfields with a Z303 cam and 1.7 rockers. Dual plane intake with 3 x 2 bbl carbs. A 351 would be easier to build though. Build a 331 with conservative heads and cam and it'll tow anything a 351 will.
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From: Temperance,MI
My 302 is a 4x4 5speed 3.55s hedman long tube headers, off them 2 1/4"Yed into single 2 1/2" with a aero turbine muffler, Yed back out 2 1/2" then out at 45s. All depends on my shifting habits 2000-2200rpm I can pull 19.42-20.26 with city and hwy driving. 1600-1800rpm shifts it drops to 17-18mpg, just watching gas prices I don't want another one that gets 12mpg I'm hoping the 400 gets that much lol.
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