rod ratios/ longer rod
 

So Im building a b18b in the fall for turbo and my girlfriends father is building it with me, hes a mechanical engineer and has been building racing street bike motors for years.

we got to talking last night about building the motor for turbo and what not and he starts talking about how were gonna calculate the ring thickness and rod ratio for the best piston acceleration rate for the motor.

I have been researching rod ratios and piston acceleration and I would like to add a forged rod to the motor that is 1 or 2 mm over stock less, this should minimise the piston acceleration rate 1.5-2% lowering the wear on the bottom end and allowing the motor to rev higher safely.

what is everyones knowledge about doing this, a longer rod and a shorter lower compression piston sould work fine in the block and work with turbo.

does anyone know where you can buy forged rods for the b18b engine that are 1 or 2mm over stock legnth? I can have them machined for me for a very reasonable price, but i would rather buy something off the shelf if this is available


rod ratios, piston acceleration and ring thickness's whats everyones opinions.... discuss

Re: rod ratios/ longer rod
 

holy ---- dude, you need to introduce me to your drug dealer :6


anyway, what is "high revs", seems like you may be getting a little too technical.

Re: rod ratios/ longer rod
 

umm high revs in meaning I would like to safely rev the b18 to 8200-8300rpm without worrying too much about blowing things... no worrys the motor will all be built to handle this as well

Re: rod ratios/ longer rod
 

Pretty sure the LS r/s ratio is the same as the D16, 1.52, which sucks. But people rev them to 8500 all the time. More important than investing in rods that nobody makes you just need to get ARP rod bolts and an upgraded valvetrain, then it will rev just fine. Don't get too technical, it's a honda.

Re: rod ratios/ longer rod
 

u want a better rs?
get a gsr

8300 isnt high really high for a honda

Re: rod ratios/ longer rod
 

i would love to skip technical stuff, but its just too interesting to skipp over... and my girlfriends father is dead set on building everything perfect..... which I dont mind at all seeing as he actually knows what he is doing and offering help for free

on the crower site they offer a b18 "stroker rod" with a C-to-C legnth of 5.564, which is over the regular 5.394 of the b18b, but i believe this stroker rod is for a Vtec b18 because the PE bore is 20mm not 21mm like the regular b18b rod...

Re: rod ratios/ longer rod
 

Stroking a motor makes the r/s ratio worse in order to increase torque. Seriously, I know it's a really fun topic but get some rod bolts and you can rev the bottom end all you want, seriously.

Re: rod ratios/ longer rod
 

just make sure you get an ITR oil pump and call it a day ::)

Re: rod ratios/ longer rod
 

Eagle sells the longer rods you desrie.......

Re: rod ratios/ longer rod
 

With a 2mm longer rod you are talking about a .03% decrease in piston speed, and 2% decrease in maximum piston acceleration. That's less than the difference between the B18b and B18c. It's not worth it. 8500 rpm's is not going to be that big of a deal if you select the proper components and build the engine properly.

The only way to really make a dent in piston acceleration is to decrease stroke. Im not completely familiar with Honda B-series engines, but (theoretically) you could use a b20 block, destroke it to 1.8 liters, use a custom rod, and custom pistons. You could play around with the rod length and stroke a bit, but you would probably end up with a rod to stroke ratio around 1.7:1. Is all of that time and money spent worth it? Probably not. There are advantages like less wear on the cylinders, and increased dwell time at tdc(which has multiple advantages in itself), but in a street application they are negligible.

Trying new things is great, but it rarely turns out the way it's supposed to. Concentrate on getting the clearances perfect, getting your quench area right, balancing, and matching parts that work well together.

Re: rod ratios/ longer rod
 

But that would require a custom crank which would be $$$. If your really worried about it run a gsr crank which is about 2 mm shorter stroke. Otherwise eagle does make the longer rods and someone does make pistons with the pin changed to the correct spot...i think its endyn but im not sure. But i dont think that its worth the money.

Re: rod ratios/ longer rod
 

DART tall deck, what the eagles were made for :)

Re: rod ratios/ longer rod
 

i actually saw something like that done in a magazine. They de stroked a b16 to 1.5 liters to run it in a certain class and it also made it over square so they could have a crazy high rod/stroke ratio

Re: rod ratios/ longer rod
 

if u wanna make the b20 a 1.8 use the b16 crank with custom rods

Re: rod ratios/ longer rod
 

AEM's Bonneville car

Re: rod ratios/ longer rod
 

Or just get a b16 bottom end and call it a day. Yeah, 0.2 liters less, but awesome r/s ratio...1.74:1 i think. You can rev a b18 block pretty high, as long as you upgrade your rod bolts on the stock rods, but since you were already talking about buying a set anyway, just get a decent h-beam or I- beam rod and call it a day. The killer on the LS motors is the valvetrain...anything above 7600rpm and the rocker arms like to pop off ;)

Re: rod ratios/ longer rod
 

yep, fucker was nasty

Re: rod ratios/ longer rod
 

WOW! thanks for all the awesome replys... i know you can rev a LS motor to 8500 easily with rod bolts, but I dont feel comfortable doing that and I have pleanty of time to build the motor and have a mechanical engineer/race engine builder helping me for free.... I couldnt ask for more! this is a prime situation to be doing what I am doing

the rod ratio of a stock LS motor is 1.54, with an added 2mm on the legnth of the rod it will give me a rod ratio of 1.71.... not bad in my mind, and yes i know this will hardly slow the piston at all if any (0.03%), but the 2% decrease in maximum piston acceleration is what I'm looking for, this will essentially give me 2% less load on the bottom end of my motor... the amount of stress once put on the bottom end at 8000rpm will now come at 8160rpm..... not much you say? well combine that with the added stronger rated rod bolts, all fresh bearings, dual valve springs, thinner rings, head work, valve job and new head bolts...... and I feel safe revving my LS to 8500


Many would say this is a waste of time..... in fact it may be, but I feel like building a motor and learning as much god damn engine tuning information and theory as I possibally can..... so stay tuned for a complete thread of the build up and how to's

thanks for everyone's comments so far, please keep commenting, positive or negative... I would like to hear may comments... maybe some piston sudjestions?

Re: rod ratios/ longer rod
 

I plead the 5th :)

Know the class records, smaller can be faster.

Re: rod ratios/ longer rod
 

they sell longer rods that are designed to be used with special pistons that have the wrist pin moved up. they give you a GSR r/s ratio which is a perfect r/s ratio IMHO for 8500rpm redline. www.theoldone.com -> under components

Re: rod ratios/ longer rod
 

thanks, that site has a lot of good info as well!

okay, i found local a b18 head a b20 head, a b20 crank and some b18 cams.... i know the b18 and b20 heads are similar but are they identical and interchangable? also I probably wont use the b20 crank due to the longer stroke...

Re: rod ratios/ longer rod
 

b20 stroke: 89mm
b18a/b: 89mm
b18c: 87.2
b17a: 81.4
b16a: 77.4

as far as heads, non btec b18/b20 are all the same if they have the p75 casting, only b20 head that is different is the p8r and thats not compatible with 81mm blocks.

as far as the cams use either b18b or b20z cams, they are the biggest non vtec cams

honestly i dont think many people worry about r/s ratio when it comes to turbos and i dont think you should either. i wouldnt look to re-invent the wheel here, no disrespect to you helper but ask people that build hondas for help with hondas. only reason to look into r/s ratio is for NA IMHO were you care less about low end and more about making every pony you can near redline. and your also lookin to rev as high as you can.

take a b18b block, skunk2/itr style intake manifold, some crower turbo cams and valvesprings, get a good port job (notice i didnt say "and polish") and throw in some fresh bearings, and a set of forged off the shelf pistons and eagle rods. rev the bitch to 8k with a gsr tranny and call it a day. its a simple and a well proven setup.

Re: rod ratios/ longer rod
 

Your math is a little off. That would give you a 1.56 rod ratio. I read somewhere about somebody using a B20 block, B17 crank,GSR rods and custom pistons. That would give you your 1.8 liters and a 1.7 R/S ratio.