I am curious about this,can someone explain what you'd gain?Is there a certain range rpm for example over stock 351 where the difference would show up?For example,I have a 63 Ford p/u that turns 26-2800 RPM's at cruise speed (60-65 mph),probly see's 35-4000 max very seldom(maybe goin thru the gears).I have a 69 351/auto out of a 69 LTD that I've been thinking of redoing and putting in my truck,and am curious if this would be a worthwhile/worthless mod.Any advice/info on this would be greatly appreciated,as courious minds want to know.Thanks,Al
I'm not the sharpest knife in the drawer but I'll take a stab at your question until the real engine gurus get here. It sounds like you're talking about building a stroker motor out of the 69 351. The biggest gains you'll see are more low end torque and horsepower lower in the rpm band. A longer stroke produces more torque.
Engines that have a shorter stroke turn up faster than one with a long stroke (ex. a fast revving 302 vs. a 351W) but produce less torque and their horsepower comes higher in the rpm band.
There are threads in this forum on stroking a 351W that are very informative and may held you decide if it's what you want to do.
Hi Ron,thanks for the reply,not talking about stroking,just long rod conversion(400M rods swapped for the stock 351's)which I believe changes the rod ratio.The reason for my original question is because of the rpm's the truck turns at cruise,I was basically wondering if I would gain anything.A gear swap is out,since this is a 4WD,so I was just weighing my options.I don't know how this would apply to my application(just a well built truck motor,with some goodies).Truck is 5000lbs,3.92 gears w/33" tires.Al
My bad Al, I read 351 and assumed Windsor. You know how us Windsor guys are, we think the world revolves around us. lol
Maybe one of the gurus I mentioned earlier will stop by and give us some input.
Question so I know we're both talking about the same thing; you have a 351M engine (shouldn't that be a 351C due to it coming from a 69 LTD?) and want to put in 400M rods, is that correct? If it is, we need to move this to the modified forurm where the right gurus can find it.
Rod length directly effects how an engine breathes because it controls the speed of the piston during both the intake downstroke and exhaust upstroke. Longer rod motors also tend to run cleaner as the piston dwells longer at TDC, creating a more complete mixture burn and increasing combustion pressure efficiency. A side benefit of that is that the motor becomes less detonation prone for a given fuel octane. Longer rods also decrease piston thrust against the cylinder walls during the power stroke so more force is sent to the crankshaft. The horsepower and torque ranges of a motor are more dependent on camshaft timing than rod length, however.
Yeah, what he said....lol. According to Wayne's Engines(they do a lot of the long rod setups), they are claiming 50-80 hp increases over similar 351w setups with just the stock rods. I have seen 3 on dynos, the 302 was pushing 400 hp(with mild components), and both 351's were over 450 hp(with big low rpm torque, flat all the way to 5000 rpm), and both 351's were able to run 11.1 compression on pump gas and aluminum heads. I will be building either a long rod 302 or 351(351 takes priority) for my Mustang, and eventually redoing the 351w in my van with a long rod engine. Speedomotive has a couple of dyno sheets on both engines,(click on the long arm kits). I am impressed with both, especially the 302 with low compression.
Thanks for the replys,guy's.Yes Ron,this is a 351 Windsor(first year production I believe)we're talking about.Forgot to mention that little important detail(didn't even think of the 351M when I first posted).OK,now that I have an idea of what benifits the long rods would give me,does using the '69 block present any problems since it apparently has a lowwer deck height?My game plan is something around 9-9.5 cr,is this possible using the 69 heads?Also,would a camshaft with 214 @ .050 on the intake side be to much for a truck motor(ex-Isky dual pattern 264 Megacam)?This is all in the thinking plan right now,just trying to gather info.Thanks guy's for any advice.Al
Originally posted by Quantrex Rod length directly effects how an engine breathes because it controls the speed of the piston during both the intake downstroke and exhaust upstroke. Longer rod motors also tend to run cleaner as the piston dwells longer at TDC, creating a more complete mixture burn and increasing combustion pressure efficiency. A side benefit of that is that the motor becomes less detonation prone for a given fuel octane. Longer rods also decrease piston thrust against the cylinder walls during the power stroke so more force is sent to the crankshaft. The horsepower and torque ranges of a motor are more dependent on camshaft timing than rod length, however.
A trick I've used in building 5.0's is putting pistons in backwards. Because of the offset wrist pin it essentially gives you a few thousanths more rod length. Joe Sherman, who is a Ch*** guru taught me this and claims near 20 HP on a modified motor.
The draw back is less cylinder loading on start up which is supposed to cause cold start rattle. But with the TRW forged pistons @.003 clearance I haven't noticed.
Getting back to the original post; the 351M/400 rod-late 351W would use the same compression height piston as a 331ci SBF stroker (1.17"). You'll have to rebush the rods, (check with Scat Cranks for rod bushings) for the smaller pins. The new r:s ratio would be 1.88:1 vs. the stock 1.70:1. In the early 351W block, you might have to deck the pistons to get zero deck height. With a mild cam and stock heads, you should wind up with a very wide powerband/high-torque motor. The longer rods will help overcome(not cure) the restrictive porting of the stock heads.