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Poor performance 351c

10K views 14 replies 6 participants last post by  Big Block Ford 
#1 ·
Hi there, I need advice from someone who is an expert on Ford Cleveland engines please. I replaced my standard 302c engine with a 351c engine in my 1975 F100. The 302 was a little weak, poor acceleration but a nice cruiser. I wanted more pull away power (torque) so I fitted a "new" 351c engine (done by engineering company, new .40 oversize pistons, bearings, rings all of that). We fitted the Aussie 302 2V closed chamber heads, new aluminium Performer intake manifold, and a 4bbl 600CFM Holly carb. Standard cam shaft. The results were shocking. No increase in power!!?? I might as well kept the worn-out 302, same power. How is that possible? I actually think the Performer intake and 4bbl Holly worsened the situation because I first fitted that to the 302 and the drop in performance was obvious. No torque low down, but seemed to rev better. Does anyone know, a 351c fitted with Aussie closed chamber 2V heads and the Performer intake with 600Holly, is it supposed to be powerful? I was expecting a huge increase in power, but nothing. What am I doing wrong? :help::help:
 
#2 ·
Hard to tell, it sounds like you have a good combination, but a lack of power could be caused by many things. Is the carb jetted correctly, or is it running lean or rich? What kind of compression ratio are you getting? Many of the engines after 1973 have really been choked and have really low compression ratios. Timing may come into affect. What size exhaust? If you stepped up on what's flowing into it, you have to let it flow as freely from the exhaust. With it being 40 over, you should have upped your compression ratio, your timing may need to be a little more advanced than it's default. You may also need to step into a higher grade of gas.
 
#3 ·
I ran a set of the Aussie 2V heads on a Clevor years back, they worked quite well on it.....but, I also had a bit more cam then stock along with upgraded valve springs... I've never been satisfied with the Performer intake on anything!! Tried one on my 351W in a pickup....if anything the power was down from the stock cast iron intake! Went to a Performer RPM, some upgrades on the ignition and woke the engine up considerably! Got any cam specs, and what ignition are you running?

Those heads do need to breathe good on the exhaust side, also, are you running headers or stock manifolds? Dual exhaust on the truck or single?
 
#4 ·
you have a " new " engine and it is tight. Give it it's break in time, about 500 miles then
start your tuning. Your engine may have been put together on the tight side. Minimum
clearance. My 460 was so tight i had trouble getting it to 60 M.P.H. in the first 100 miles.
 
#5 ·
Thanks for the responses. To be honest, I actually did not check the carb's jetting, I fitted it out of the box, fine tuned it on the engine and there it is. I also did not check the compression ratio. What should it be? Or what would be acceptable compression ratios with these heads?

The exhaust size is decent, dual 2" diameter pipes but using the standard exhaust manifolds. The drop in performance was very obvious when I installed the Performer intake on the 302 so yes, it would seem as if that is definitely not working.

The engine is very tight, I had to service the starter motor that started the 302 with ease, to be able to turn the 351. I thought the battery was finished and replaced that, but only after a new solenoid was fitted, the engine turned over and started. But yes, very, very tight in comparison to the old 302 engine.

Maybe I should look at an upgraded cam, but something that will produce more low down power. Any suggestions on what will be a good cam to fit? Should I put my 2V intake and carb back on or rather replace the Performer with something else like you said, Performer RPM? I do not want something that needs high revs to perform, I would like to be fast on pull away and cruise 50 - 60 mph
 
#6 ·
Sorry, I forgot to mention, I fitted an electronic ignition system, can't remember what it is called, but from the USA. It has it's own module on the side, small silver box fitted away from the engine. The distributor is grey in colour and I use 8mm high performance ignition plug wires, also from the US.
 
#8 ·
If the motor is that tight, guess I'd have to be suspicious of the entire assembly of the engine!!!! If the bearings and rings were fitted properly, no reason an engine will require 500 miles to "loosen up"!!!

What are you running for timing on the engine, and how do the plugs "read", fat, lean, or just right?
 
#9 ·
Wingman1. For one thing your exhaust pipes for that size engine are too big. 1 1/2" is
plenty. Dave. No offense but seems you haven't run too many engines. EXP. A boss 302
and most high output engines are " maximum clearance " Very little bearing and ring friction = high and instant R.P.M. but not much oil pressure. A " tight " engine is minimum
clearance. It will take as much as 500 - 1000 miles breakin depending how it is driven.
Problem is when a " boss " motor blows there is not much left of the motor to rebuild.
There is not much metel left. I spend over half my life working in an engine rebuild shop.
I hated the older Ford Flatheads. The block, bell housing, and started mount were one
piece. Cast iron. 1942 - 48 was nice if it was a car engine. the bell housing was steel and two piece not part of the block. Nice and light. The truck was still cast iron though.
I think you remember. A very tight engine usually means a very good machinest with very good machinery and new cutters. A loose engine usually means high R.P.M. very fast, early piston slap, and low oil pressure. Yes there are both kinds. No offense. Just my experiance. Merry Christmas to all.
 
#14 ·
Yes, I have run a considerable number of engines..... The tight side of a clearance is less then half a thousandth.... other then rings seating, what is it that is accomplished after 500 miles, that much wear on the bearings and pistons already??? The only difference I've seen on piston clearances are because of the makeup of the piston, cast, hypereutectic, or forged, then a couple different manufacturer clearances on forged pistons if they are 2618 or 2619.... Curious what are you suggesting to set clearances at????

Tell me what I'm missing, bearing clearances are bearing clearances, I don't like to deviate from them, as ring gaps are ring gaps....except on the zero end gap and some low friction rings... I like to run the zero gap second rings, makes for incredibly low leakdown numbers throughout the life of the engine!!!!

Not meaning to offend anyone, just curious how tight it is you think this engine may have been set up??? For that matter, unless you or I did the engine, anything we would say are the clearances is little more then a guess!
 
#11 ·
Thank you all for your advise. I will use the engine as is for now, clock-up a good few hundred miles and then if no improvement, I'll be back for more advice. Otherwise the engine sounds good, starts easily and idle very smoothly, looks good in my truck (I have posted a picture under "photo gallery" for those interested to have a look. Green metallic F100 and picture of the "new" 351 motor. Thank you all again, hope you have had a great Christmas and may all of you have a fantastic 2015!! :hy:
 
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