85mm x 85mm bore & stroke?

[hi-perf]

during a conversation sunday night with a gearhead friend of mine, we were discussing bore and stroke and how two engines with the same displacement, the one bored out more will usually win given same conditions such as cams OHC specifications and valves etc...

in particular the 4.6L DOHC Mach1 mustang engine and the 5.4L DOHC Cobra engine (without supercharger of course) (the 5.4 is a stroked 4.6)

and how the 4.6 will actually beat the 5.4 up high given same internals, and also how the chevy 327 (a destroked 350) will beat a 350 or even 400 (over stroked 350)

this basic concept held true with my 1.8L vs the 2.0L, the 2.0 beat me in the 1/8th mile but i pulled on him up high, ate him up for .3 sec on him after the 1/8th to beat him in the 1/4.


anyway getting to the point,

ive heard that we can overbore our pistons a little bit and having a slightly larger displacement. id like to get as square as i can (85 x 85) and running high compression with engine management later down the road.

im guessing that the question is directed towards twilightprotege but meh, anyone that can answer it, can out blocks be bored to allow an 85mm bore size?

thanks in advance and feel free to strike up a discussion

 

[twilightprotege]

the blocks can handle 2mm overbore yes. we're lucky we have a cast iron block that it can handle that. if the block as aluminium it wouldnt handle it as the wall between the no 2 and 3 cylinders is 6mm thick (so 2mm overbore you're reducing that down to 4mm).

with engines (and this is a fact), all engines with the same bore have the potential to make the same power, but a smaller stroke has to do that at a higher rpm and a larger stroke can get the power at a lower rpm.

fyi, engine displacment (use cm to get cc) = pi x bore/2 x bore/2 x stroke x no of cylinders...so 85 x 85 = 3.14... x 4.25 x 4.25 x 8.5 x 4 = 1929cc

personally i would have loved to have a 87mm bore x 84 mm stroke (1997cc) in my P5

 

[hi-perf]

right but i remember you saying we can have up to a 3mm overbore, so in reality it could be

86mm x 85mm = 1/2(3.14 x 8.6cm) * 1/2(8.6) * 8.5 * 4cyl = 1975cc

86mm x 85mm = (13.5088) * (4.3) * (8.5) * 4cyl = 1975cc


isnt there a big advantage to having an exactly square bore and stroke? what about slightly off like 86x85 or 83x85?

edit: fuzzy math lol

 

[hi-perf]

with engines (and this is a fact), all engines with the same bore have the potential to make the same power, but a smaller stroke has to do that at a higher rpm and a larger stroke can get the power at a lower rpm.

but preferably on the dragstrip you want all your power to be made so that your entire run will be high in the powerband. this is what i want, a fast car on the drag strip.

 

[twilightprotege]

^ yes and no. depends on the weight of the car mainly because hp is directly relative to torque and vice versa. a heavy car that revs to 10000rpm and has no torque wont do much...a light car with heaps of torque will just be wasted. there is a balance, but a higher hp figure is usually better.

any advantage to having a square bore? none. i've seen a few car manufactures advertise they have square bores to give maximum power...it's all a gimick. for high hp a larger bore is much better (think of the F1 engines. 1.5L 10cylinder engines...very little stroke and heaps of bore)

i'm hoping to bore my engine out to 85mm (giving 2088cc)

 

[hi-perf]

do you think that 86mm is pushing it? and of course i need new pistons if i bore this much right? what about 85?

 

[twilightprotege]

86 is the limit of the block for sure. i'd recommend going 85 because when you need to rebuild the engine down the track, you have room to bore out the block a bit more (ie 0.25mm) to get rid of any marks etc on the cylinder wall.

 

[hi-perf]

ok now i know what i want

now HOW DO I DO IT...lol

anyway where can i go to get my engine block overbored? and i will need new custom pistons right?

 

[twilightprotege]

yes, custom pistons.

make sure (an old school trick but very very very worth while) that when they over bore the block that they make a plate like thing that sits over the bores and is tighened to the block with the same torque as the head. that way the bore is perfectly aligned with the head when the head is on (can flex a tiny bit when the head is on compaired to when it's off)....does that make sense?

 

[hi-perf]

yes, custom pistons.

make sure (an old school trick but very very very worth while) that when they over bore the block that they make a plate like thing that sits over the bores and is tighened to the block with the same torque as the head. that way the bore is perfectly aligned with the head when the head is on (can flex a tiny bit when the head is on compaired to when it's off)....does that make sense?

no.

who is they? where can i go to get it overbored is what i meant.

 

[03MSP]

no.

who is they? where can i go to get it overbored is what i meant.

lol, I didn't quite understand that either.

 

[hi-perf]

where do i go

where i can take my engine block

and have some dude use his machine or whatever to overbore my block

so i can have bigger pistons (bore) and have higher displacement and go faster and make more power

 

[twilightprotege]

i have no idea who can bore the block out for you because im a crodocile hunting aussie, arh no that's steve irwin.

anyway, when i said they i was meaning the place you get to bore the block out for you.

i was just meaning there is a wrong way and a right way to bore a block.

i found the name i was looking for. torque plates. here's a link for one for sale : http://www.goodson.com/g5-bin/client.cgi?G5genie=1;G5button=1&item=P3799

as it says the idea of them is to bring the block into the same shape it will be when the head is connected.

is that better?

 

[hi-perf]

like any machine shop? or a mechanic?

is it possible to do this myself?

 

[p5sundevil]

superstreet just did a little article about choosing who does your internal work, the interview or story was from a guy who does all the port and polishing and all the boring for the drag cars like the streetglow drag cars. The article was more on porting but about the where to go part he said there really arent questions you can ask someone to make sure they are trustworthy for doing the job, seeing how much experience they have is your best bet.

 

[charles]

Generally you'll want to find a machine shop that has good knowledge of your engine or engines like it. Don't go to a place that does big-block Pontiacs, for example. I'm going to send my head to somebody who specializes in Miatas, as mine is nearly identical. Fortunately (for me) good work done on Miata motors isn't in any real short supply, from what I can tell.

 

[iluvmacs]

any advantage to having a square bore? none. i've seen a few car manufactures advertise they have square bores to give maximum power...it's all a gimick. for high hp a larger bore is much better (think of the F1 engines. 1.5L 10cylinder engines...very little stroke and heaps of bore)

You're right, but they're 3.0L V10 engines. 1.5 L with 10 cylinders would mean smaller bore and much smaller stroke than motorcycle engines that rev to 15k already.

I have a friend rebuilding an old TVR engine. He found a machine shop that specialized in engines. Scope out some machine shops and ask them how they do their work to see if they're quality. Find the highest quality shop that charges a fair amount for the work.

Let us know where you get your pistons and connecting rods. Are you de-stroking the motor, or simply adding bore to make it square? I'm sure the 1.5 and 1.8L protege engines have crankshafts that would fit and destroke the 2.0L. I wonder if any parts from a turbo protege engine could be used, because they should be quite a bit stronger than the N/A version.

 

[hi-perf]

the 1.8 is the 2.0 but the 2.0 is just simply stroked out. different crank and rods.

the 1.5 will not fit, its a Z series engine while the 1.8 and 2.0's are F series which will fit.

the msp engine has no forged parts (except for the crankshaft which is forged on all F series engines), it is just a stock motor with a turbo slapped on it.

 

[iluvmacs]

I meant the 1.8turbo. I think it was a J-spec only engine. A strong 1.8L crank, with an overbore would be pretty cool.

Maybe that's why the MSP only makes 170hp...

 

[hi-perf]

the bp engines were very smiliar to the f series engines, they used the same bore. id imagine they can only be overbored to the max of 3mm per cylinder like the f series engines.