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Discussion Starter #1
Hi all,I have an alfa boxer 17 16v engine which is stock except that i converted to run with carbs.I was very happy with it until it decided to give up.I already have worked out its heads and now it has ported ports+inlet manifold,three angle,lightened stem valves etc.i havent tried it out since.Now im thinking of having a set of forged 88.5 or 89mm pistons,lightened,polished and shot peened stock rods and polished crank.But now im asking myself if it is worth doing such work or if its better to have the engine stock as it is but only with the heads i already have with carbs.What do you think?any help would be appreciated,thanks
 

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Got the money = mod
Don't have the money = stock

Seen quite a few promising projects left undone because of running out of money.

and no... It's probably NOT worth it, but if it makes YOU happy, then go for it ;)
 

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Discussion Starter #3
Heh on the contrary i dont have much money to waste.Can anyone give a rough estimate of how much bhp will a set of forged 89mm pistons gain compared with the stock 87mm ones?thanks
 

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I am looking at some thing similar - the 1.7 8v carb engine out of my s2 cloverleaf sprint 33 is currently being rebuilt - should get it back next week. Polished/ported race heads, fast road cams, balanced bottom end etc etc.. Have a second 1.7 8v that I have stripped down and intend (eventually) to bore out to approx 1.9, get everything balanced again, then take the existing heads/cam carriers off the first engine and put it on the 1.9 - that should be fun - long term project.
 

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In order to have 240 you must change the entire engine internally plus gearbox. 180-190 is more realistic although very hard to achieve if the engine block is not in top condition. You can ask Chris with his oversized pistons and Omex system how difficult it is so far....
 
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Dave from Brunswick Motorsport and i spoke some time ago, i think Johnboy is correct, i'm pretty sure he can pull approx 240 bhp from a race perpared 1.8 16v.

That kind of engine will cost around £3-4k in parts alone, plus the labour to work the heads, strip and rebuild.

Then, as Greek mentions, you'll then need a gearbox that will cope with double the power it was built for, as AHM will testify from the metal he has swept off the dyno previously, even a reinforced stock gearbox simply lets go in a big way at this sort of power!!!

its all down to use, and justifying the budget, even if the budget is there in my opinion.

but that doesn't stop me dreaming of 200+bhp, awesome street sleeper!!!

shrew
 

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but that doesn't stop me dreaming of 200+bhp, awesome street sleeper!!!
Why not just buy an old skool bmw 325i ?:lol::lol:

Brother-in-law had one and that thing shifted like crazy but then he wrote it off at a junction!!
 

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The question was how much the piston alone would increase power... Not with all sort of other mods.

AFAIK increasing the piston width doesn't give that much alone. a friend of mine who has done race engines (not alfa thou) said that increasing piston size is the last thing you do when tuning an engine. First being optimizing everything else that's slowing it down ;)
 

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Capacitywise I guess it would be like the following.

(pi*(Bore/2)^2)*stroke*number_of_cylinders

Stroke: 72mm

Bore: 87mm gives 1.712 litre (dm^3)
Bore: 88.5mm would give 1.772 litre (dm^3)
Bore: 89mm would give 1.792 litre (dm^3)

How much do I have to multiply the engine capacity to make it 1.792?
1.712 * X = 1.792
X=1.0467

So, an 1.792 litre engine is about 5 % larger than a 1.712 litre engine, so, if a standard 1.712 L 16v gives 132bhp, then a 1.792 would give about 138 bhp, which is not a lot, but any other mod will give about 5% more with it being 1.8, compared with it being 1.7.

I might be wrong about this, but mathematically it would be like this.

This is of course the case if the compression is left as original. Often, I guess, the compressoin will be raised with many forged pistons, and with the engine mapped against the higher compression the power hike will of course be higher.
 

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Discussion Starter #16
I see,so i guess its not that much worth doing,as i didnt told you before the car use will be street driving and a little drag.So in other words what is the best bang for buck set up on a 17 16v with carbs?i mean mods.I think some will argue to leave it stock.It will be installed on a sud ti 1981 or an alfa 33
 

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I think I read somewhere that it you jus tune the carbs and put a mod exhaust on you should get an increase of 6-30 horses...
The thing is, I can't remember were I read it. :p haha
 

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Have a quick look at Guy Crofts forum. He has nice examples of tuning engines to get the peak torque out of engines.

Again some mods are not cheap at all, but some little adjustments/mods can make a difference.
 
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