351W Overbore Maximum?

auto10x · #1 (**permalink**) 05-02-2003, 08:29 AM

I have located what appears to be a sound 1971 stock bore 351W block. Does anyone know what is the generally accepted overbore allowance on these blocks.
Thanks,
auto10x
Bill

Cobra20646 · #2 (**permalink**) 05-02-2003, 09:24 AM

I'm pretty sure that stock OE 351 blocks can take a .030 overbore, max. Some of the aftermarket Ford MotorSport (and possibly others) can go out to .180 with siamese cylinders. 427 cu in. small block......

DAVID GAGNARD · #3 (**permalink**) 05-02-2003, 12:39 PM

Bill;

My 351-W had to be bored .040 to clean up the cylinders... I have a little over 17,000 miles on it now with no problems,but I do not like to go more than .030 on a 351-W block. At the time I was building this engine that's the only block I had,now I have a few more for spares for my next project....

I have seen some dirt track racers go .060, but they usually go thru a block a season and do not care....

I have two 1972 blocks that I checked and will easily clean up at .030 and a complete 69 engine coming,it's still in a 69 Cougar running today with about 70,000 miles on it. The owner is rebuilding a 351-Cleveland to put in his car and I have bought the Windsor from him,he should swap out later this summer.... A buddy just picked up a 69 351-W for his 67 Mustang. He took it down the other day and we checked the bores and all it needs is to be honed,doesn't need boring.... The motor was in a wrecked Cougar with 64,000 miles on it and he got the complete motor for 50 bucks,some guys have all the luck...

David

auto10x · #4 (**permalink**) 05-02-2003, 12:49 PM

David,
Thanks for the information. I've heard that the 69-71 blocks have a higher nickel content and what you're saying seems to bear that out. My '71 block has very little wear in the cylinders. It will obviously need more than a hone job, but should clean up with probably a .030 overbore. The one I have now has a .040 with no apparent problems.
My reason for asking about the max overbore is that this engine apparently sat for quite some time and has one deep rust pit in the cylinder. I'm surprised there was not more rust (sat out in the open for who knows how many years), perhaps it's low rust can be attributed to the high nickel content. Who Knows??
Thanks again,
auto10x
Bill

DAVID GAGNARD · #5 (**permalink**) 05-02-2003, 01:15 PM

Bill;

I can not verify this,but have been told up to and including 1974, the blocks were a little "thicker or beefer" than the later blocks... Mine is a 1972 in my Mustang.... Also, spoke to a guy that drag races a late model Mustang with a 351-W,he usues whatever block he can find. He told me the later ones last just as long as the early ones for him. Do not know,but he claims they are just as strong.

I have enough old blocks that I'll just stick with them.. Around here,up to 74 blocks can still be found without too much looking and I get most for no more than 100 bucks,the last two I got for 50 bucks each...

David

klayfish · #6 (**permalink**) 05-02-2003, 02:49 PM

David,
I'm curious. What size is a 351W bored to .040? Is that a big increase in displacement? How much power does a moderately built .040 over 351W make? Reason I ask is I'm looking at buying one.

Steve

DAVID GAGNARD · #7 (**permalink**) 05-02-2003, 05:15 PM

Steve;

Using one of the many cubic inch calculators,it comes out to 358 cu. in....Mine is fairly "mild", I built it using the same specs as the Ford SVO crate motor advertised at 350 hp...

385 to 425 hp is not too hard to get,but you may lose some bottom end and driveability.... I am very pleased with my setup,get 23.5 mpg on the highway and still runs 12.90's in the quarter mile fully street legal with mufflers and street tires... In fact, before I got a trailer,I'd drive to the track (100 miles) race and then drive home in the car. Now I trailer it,just in case I brake something racing,but that's the only time it sees the trailer,to go racing...

My cam is fairly mild with lift at 484 and duration at 272,so it idles just fine at 700-800 rpms pulling 17 on the vacum gauge...

My next engine will be a 393 stroker with aluminum heads shooting for 475-500 hp. It will have after market rods and a lot of other goodies in it....

David

machineman · #8 (**permalink**) 05-02-2003, 06:12 PM

auto .060 isn no problem but most engine builders like to take out as little as possable

Steve R · #9 (**permalink**) 05-03-2003, 03:10 AM

Bill,
Can you post a picture ofthe main webs on your block? I have an early block that has casting provisions for 4bolt main caps. I have never heared anyone talk about this feature on a 351 W.
Steven

auto10x · #10 (**permalink**) 05-03-2003, 04:43 AM

Steve,
Unfortunately I cannot post pictures, but as opposed to 75 and later blocks, the earlier ones have a completely flat surface on the whole web surface from the main cap to the oil pan rail, with lots of "beef" below for a splayed 4 bolt cap. My newer (89) block does not allow a 4 bolt cap to be installed.
auto10x
Bill

ted · #11 (**permalink**) 05-04-2003, 06:22 AM

Concerning overbores, sonic testing will help determine how much can be safely bored from any block. There are enough variances in cylinder wall thickness either due to core shift or the particular mold being used to mandate this if boring a block over 0.040". The good thing about knowing where the core shift is in the block is that the cylinders can be offset bored into the thicker side of the cylinder so that the cylinder wall thickness can be equalized while also gaining some additional overbore that would not have been available otherwise.

As a rule, unless you're just going for the biggest, baddest boy on the block, then always bore to the minimum amount possible. I like starting with .020 which then allows the next build to be .040, the one after that .060, and so on.

auto10x · #12 (**permalink**) 05-05-2003, 04:41 AM

Are there any generally established guidelines on minimum wall thickness?
auto10x
Bill

ted · #13 (**permalink**) 05-06-2003, 04:28 AM

I haven't seen any specific guide lines regarding minimum cylinder wall thickness and that's probably because of different block constructions and the different materials being used.

I try to maintain at least .090" for the minimum thickness and the more the better. There is the major thrust side in the cylinders that takes the most abuse and subsequently these should be left thicker than the opposite or minor thrust side. The Major thrust sides would be the outside of the cylinders on the passenger bank and the intake valley sides of the cylinders on the driver's bank.

Where you run into a problem is when the major thrusts in the block are already thinner than the minor thrust sides. This is where sonic checking really proves it's worth as you can weed through the less desirable blocks.

Ted Eaton.

auto10x · #14 (**permalink**) 05-06-2003, 04:41 AM

Ted,
Thanks for the good information. Time to dust off the sonic tester.
auto10x
Bill

auto10x · #15 (**permalink**) 05-06-2003, 10:31 AM

Checked the wall thickness. Both major and minor surfaces check out at about .250 - .285 inches. Looks like there is plenty meat for a rebore
auto10x
Bill

stengun · #16 (**permalink**) 05-11-2003, 02:26 PM

hey dude,
U can safely bore it to .060" os without any trouble. We have ran a '72 block bored 60 over in a truck for over 100,000 miles and most of the time it was during the summer while pulling a bass boat. Good luck and just bore it!

toopoor · #17 (**permalink**) 05-11-2003, 05:44 PM

I do not know the numbers, but Flat Lander has a stroker kit for the 351 W that results in 454 ci. I think the max RPM is 2000.