I just want to see if there is anyone on here that can tell me the difference in HP on the same turbo,fuel etc.. setup going from 81-81.5mm bore to this extreme 84.5 mm bore?? the damn cylinder walls are so thin, the o-rings nearly touch, and i just dont see the big gains. i mean, yes there is no replacement for displacement but how much hp extra are you making going so big. to me its just not worth the risk or the extra weight on the rotationg assembly. 30grams or whatever it is x4 cannot help the way the motor revs. I do understand for those of you like laskey,jotech,jason hunt, all motor guys etc... you want every bit of hp extracted but i am referring to the guys on here that are lookign to make 500-600whp.so lets here some reasons... I think its personally all hype and to say "my motor is a 2.0l". just my .02

 

83x87.2mm seems to be a good compromise. I think 84mm+ is silly, because it doesnt leave too much room to rebore.

Suprdave

 

My current build is using 83mm slugs. I get a bit bigger bore, and god forbid something goes wrong I can still rebore. Plus I got a hell of a deal on my pistons

-Ryan

 

i think 83mm is a good compromise if you want to go big bore and you can get still get good off the shelf pistons for it. But there's nothing wrong with stock bore, plenty of 500whp runs have been made from the stock 81/81.5mm bores. Plus if you need a headgasket quick you can still get one from your local honda parts dealership.

 

I have to agree that if I would have bore the block and not bought it bored already I would do 81.5mm, but oh well my 84.5mm LSVTEC is still screaming... Well if it would stay in 4th gear that is...

 

Stock bore here. I did some more in depth piston measuring, and found that Im over 11:1 compression. In other words, with such high cylinder pressures, the more material, the better. I should be putting down 220 psi in each cylinder once I can get my car started and broken in. Imagine that with 15 psi of boost on top!

 

probably the same reason everyones car is slow unless it has 300+ whp.

 

I started with 81.5mm, but sicne I am changin pistons size and not wanted to take chance on having a loose cylinder to skirt clearance with the same bore piston size, I opted with 83mm, just becasue, 83mm is considered a shelf pistons nowadays with some mfg, unlike 82 is considered custom so therefore they are expensive. But first timer, 81.55 is perfect for me, I can use stock HG, no head work(enlarging combustion chamber) and over all cost effective

stan

 

what kind of timing curves and fuel are going into that? Not pump gas i hope...

 

the same reason people go high comp. w/ boost. they go big bore too. or big bore/long stroke. They want every bit they can get. The way I see it, build the motor to last, and use the turbo set up to make the power.

 

Im right there with you Mike. I dont see how 2.0 is worth it for a street motor that is built for longevity --meaning not rebuilt every 25 passes like 1320 cars.
I built my LS to stock bore with the idea in mind that Im gonna rev the **** out of it. Looking at added piston weight, pin weight and even ring weight, it all plays a part as to how high a motor likes to spin. Especially in my case where the LS doesnt have the best rod ratio and doesnt have any kind of bracing on the mains.
I like the idea that there is room for......gulp, I guess I'll say it----error. People pay good money for their sleeving and their motor work. Why throw it all away when a shitty titanium retainer outlived its life and broke through dropping a new expensive Ferrea valve into the chamber ( I also recommend stock retainers too )

 

OK real world dyno numbers from a friend of mine on his B18C Darton block, he went with 81.5mm bore for the same reasons mentioned above in case of damage he can still go up to 83,84,84.5mm etc. Well he did have a problem tested how far he could go on 116octane somewhat High compression 10.5:1 until a piston melted and there was damage to the cylinder wall, a simple .5mm overbore or even 83mm was not fixing the walls on this block so he went 84.5mm because he had too. Well here are #s 81.5mm 18psi=489whp and 84.5mm 18psi=506whp no other changes except he did lower the compression by .2-.3 CR so 10.2:1. When he went to 25-26psi on the 81.5mm bore made 591whp! Advantages of the bigger bore are of course more displacement and more torque, every little advantage you can get. Also the valve reliefs on the pistons can become more optimal instead of being at the very edge, unshrouding the valves and opening up the combustion chamber etc etc while keeping a good R/S ratio instead of going longer stroke and shorter rod, not talking about deckplated motors here though.

I myself have a B16A and I can use all the extra diplacement and help possible, I originallt went 84.5mm GE block that they bored and the tolerances were real loose looser than the Piston manufacturers specs but they were useable, after the sleeves sunk I had no choice but to go to 85mm but the sleeves sunk again! I now have a Darton sleeved block staring at 84mm so I still have room to play with as long as no MAJOR damage occurred. B16A needs all the displacement possible due to the short stroke which equates to less torque. so again

81.5mm 18psi=489whp
84.5mm 18psi=506whp also with .2-.3 lower compression

 

Awesome Info Terry

that should help quite a few people make their decision on bore sizeing.

 

I can understand on a b16 maybe going bigger bore cause the 1.6 does need all it can get to make 500-600whp. I just dont see the extra 17hp and 3mm of bore size being that rewarding. run 19lbs of boost and it will make the same power as the 18psi. the way i see it is, let the turbo make the power.

 

difference is torque curves and when peak power is achieved...remember.. drag races is won by torque.. not hp

 

correct the tq curve will change but torque will also be added by runnign 1-2 psi more boost. also, with the highe CR it wil change the curve also.

 

i fully agree.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Boostfed &raquo;</TD></TR><TR><TD CLASS="quote">
81.5mm 18psi=489whp
84.5mm 18psi=506whp also with .2-.3 lower compression </TD></TR></TABLE>

What was the diffrence in Torque??? I'd like to see each dyno sheet next to each other to see how much the TQ curve changed.

 

imho 20whp isnt worth the extra risk from sleeve cracking and from if a problem arises, the inability to bore further.

 

I once heard from a wise fellow, "the best engine is the best arrangement of compromises." I think that statement is so true. actually im putting that in my sig. lol

I think alot of people get caught up in all the "full boost by XXXX rpm" and "hp per psi efficiency" hype, that they forget what really counts. And thats building a motor that will last and having a set up that will win races. I don't think when u r making 500+ whp, 20 hp is what wins races anymore.


Modified by DIRep at 6:25 PM 6/24/2003

 

big reason -- 81mm and 84mm are the two most popular shelf pistons for the majority of the aftermarket piston suppliers. I am sure if there were 82mm and 83mm pistons available as readily there would be more people running those sizes.

 

A 75mm bore is the way to go

 

well mike as you already know i'm going 83mm bore now. I'm into the bigger bore for more low down torque, every little bit helps with this puny b16a2 motor. And since my car will be driven on the street and I want the car to be drivable. And it seems I sparked this thread since its right after we talked. heh

 

thats worth it to me 20 hp and the fact that the compression was higher with the 81 probably 40 ish horsepower we havent had any problems with 84.5 were boosting up to 30 lbs if it goes make an all motor 87 hehe

 

i'll keep it simple. the fastest cars out there right now in every class are 84mm or bigger. way better torque curve. if you have a street car, keep it gsr/81mm.....but if your racing, go 84/85 mm for forced induction.