I spoke with the "mystery" person again.

He threw some info at me, said he didnt mind if I shared it, also said one should test their own block to be 100% sure. He bases this on an idea that .100 cylinder wall thickness is the thinnest you would want (based on his SBF experience).

Two blocks were sonic tested, the third was cut at the cylinder bores and physically measured.




.125 doable? maybe .100




Anyone know of a "down draft" carb thats as reliable as a rolex, cheap as dirt, and can satisfy 50 cubic inches at low to moderate rpm all day long? That efi lower has me thinking...just a dream...but Id like to put the dream on paper.

 

I've passed that one through my grey matter some too. The projected best I have thought of is 3X2 progressive 2v's with each one feeding two of the intake runners...a bit more engineering than I want to get in to. I've also thought of a divided plenum on the lower intake supporting a 4v. There was a pic posted a while back at FSP with a 4v mounted on top of an upper intake but no comment as to how it ran.

 

I thought about the 3X2 setup. It would be easier.

Thinking about the six carbs, youd just need a plate, basically to adapt the carbs to the lower something to bold chit too, ...put six carbs on it....talk about a bitch to tune...wow...

Would be costly this route though, without a good vacuum source, youd need/want a mechanical ignition, guess you could tape the underside of the efi lower and run a hose to connect each, then be able to run vac advance??, then there is all those dang carbs...



All got started working on a little ATC I have for the nephews, kept thinking how simple that carb is...then the inline six came to mind, then....well you know....




Im fascinated with the idea of this overbore though...seems there would be some power to be had..

 

So why not chop the 90 degree turn off the lower and mount sidedrafts?

 

Yup...and then mount a side draft bike carb of choice to each runner...........

 

Lol, I wonder what the guys face at the bike shop will look like when you ask him for 6 carbs?

 

Certainly different than the looks on those biker's faces at closing time when...........

 

I thought about that too...I think down draught would be for me in this scenario...give it that munsters look. Way I envision things on the passenger side is everything vertical, on the drivers side horizontal.

Its the same viscious circle, I get to thinking about multi carbs, then a bulb goes off and says hey dummy it EFI now..then Im right back to a multi TB idea..there is the constant voice saying WTF cares but I try and ignore that one. I was thinking three TB's mounted vertical on top of the lower intake might be cool. You could put the linkage on the firewall side to hide the ugly, and connect them so they use a common linkage. Think going the TB route is more logical for me, it shouldnt affect function but would enhance form. Im still leaning towards the original idea, mounted on the drivers side of the upper.


I was searching ebay the other day, saw a used upper intake and lower, along with a throttle body.............starting bid was $200...guessing it was implied a loaded crack pipe was included?


So I started another want ad looking for a TB.


SS, what did you think about the block info I posted?

 

I think it's pretty optimistic, but without having a block sitting in front of me I couldn't say for sure. Using those numbers and knowing that the cylinders don't touch each other on the outside I'm inclined to say they aren't realistic. I seem to remember there being at least 1/8" between the outer cylinder walls in the block, and that would mean that the distance from cylinder wall to cylinder wall on the deck surface would have to be over 1/2" and it isn't. Like I said, there might be a block out there that will take the overbore, but that's cutting it close.

BTW, I never answered the original question. I think you'd need more than .1" of wall thickness. Probably .150" at least. .1" might be OK on a 302, but the cylinders in a 302 aren't nearly as long as the 300. Without having two blocks in front of me to measure, I'd guess the 300 cylinders are 20% longer than the 302 cylinders and that makes them harder to stabilize.

 

Optikal

Any luck trying to figure out how to share your files?

I had the timing events for crower and comp but for the life of me, I cant find them. Not even on their site(s) anymore.


I done a search, thinking I may have posted them here, didnt find them, did find we'd had this discussion three years ago though...history does repeat itself.



Right now Im liking the idea of a big bore engine/near stock cam...have to be one torquey sumbitch. DD dyno is showing 60+tq gain at the bottom and substantially more at the top of the stock cams rpm range. Thats w/t stock headflow, stock cam advanced 4 degrees with 1.7 lift, tweak the heads a little, consider there will more than likely be increased compression due to the use of v8 pistons to get that 4.1/4.125 bore.

I wonder how the bore would affect mpg, usually the smaller the bore the better for mpg but considering the substantial tq gain, I wonder if the added tq would offset that some, know what I mean?

Now to tend to that money tree.

 

DD2k is quite optimistic about your projected gains just from an overbore. If you bored the engine .100 over youd gain about 15 cubes, or 5%. You're not going to see a torque increase of 25% from a 5% displacement increase even with the added compression. You also won't see more pull on top with a displacement increase. The top end will actually suffer because the engine will run out of airflow sooner. As I have said before, there are only two reasons to increase displacement beyond just cleaning up the bores: If the desired power and torque output can't be had at stock displacement without compromising driveability; and if the stock rotating assembly needs replaced anyway because it can't live with the desired power or rpm levels. Other than those two things, building a big inch motor is nothing more than an exercise in building a big engine for kicks. When you do go big, it is a waste of time and money to go less than 10% larger than stock.

You would be better off spending the money it takes to get the pistons for a .1 overbore to work properly on other stuff.

 

think you misunderstood, DDK shown the gains get progressively less, lowest rpm being the best tq gain. it didnt show an effective rpm increase. it takes very little hp gain to show a dramatic tq increase at low rpm.

i dont get your logic, people have been stroking engines for years with success...how would 20extra cubes be ineffectitve in this scenario? If we were talking high winding engine, I could see your perspective, but added cubes usually helps low to mid range performance, substantially. In the 300's case, it would seem a larger bore would be more effective due to its crazy stroke, as compared to a shorter stroke engine aka any sb v8.


also dont understand how the top end would suffer. more displacement, demands more air, so at any given rpm, you demand more air be pulled through the cylinder head, it wont draw less air, more air/fuel = increased hp. if your trying to say more cubes wont give you a broader usable rpm range without headwork and cam, I agree totally, and we have a simple misunderstanding.


I was talking to another I-6 expert, he seems to think .060 is max overbore, he didnt really have the sonic test or mike data to explain why....so...Im not real sure how to take that info, other than to be a general notion in the engine world, that .060 is pushing your luck on older pushrod engines.


If you punch in .060 or .060 on the DD program, its not worth it, there are gains but not enough to do it for performance.

Maybe its early and my brain hasnt awoken, and Im comprehending what your saying *** backwards, it happens. Lemme know, also be pointed out, Im thinking street engine with kick, not how fast can I make my truck go.

 

I read over that to and agree, stroking an engine will diffently be a substantial gain, but as I read over it agian I wonder if he wasn't talking about increasing just bore size when he said upping the displacement, I agree there, you usually can't increase bore enough to ever get a substantial difference outta a stock engine, like he was saying on the 300, the only reason to go a little bigger is to save some money on flat-tops. I'm sure he'll chime back in and striaghten this out for us.

 

I agree but were not talking .030, more on the end of .125.

Now your dividing it up across 6 cylinder than the usual 8, and you then have to consider a 3.98 stroke, vs say a 3.5 on a 350+/- v8...thats alotta mechanical leverage.

I think we just had a misunderstanding, think we are on the same page.

 

Mine at .060 over is about a 304ish, at .125 over it should be around 309ish, you could really put the extra overbore to work if you could stroke it to. Otherwise your getting roughly another 10 cubes, plus more of a oversquare engine (not necerally a bad thing). If you stroke it with that thin wall though I imagine you'd really cut your durability down more then it would already be. I guess it comes down to the original question if it can be done safely or not, if it ends up right on the verge would the 10 cubes be worth the longevity?