The Sword

how is the longevity on such a set up? 84x95

is that kind of stroke/displacement useless on a big boost set up?

my buddy is a brian crower vendor, hence me asking. lol

RedneckRicer

Only seen a few and those were on DART Tall Block setups. Dont think the R/S Ratio is good in the standard deck. Unless u get a Raised Pin piston to match crank and rods.

The Sword

the BC kit optimizes rod length. im just wondering if there is a drop in longevity from say an 87.2 or 89mm crank, and if there is, is it so drastic that the gain in tq and spool up isnt worth it.

TheShodan

iTrader: (14)

It's really a torque maker when it comes to 89mm+ stroke, and less rpm needed for the same power. Most use a sleeved 84mm bore with this engine. The only disadvantage I've ever seen is one some rare B-series engines, the crank just doesn't clear correctly. (InlineR is a member that may be able to explain more) This may be a "longevity" concern, but that's about. In general, if an engine is built and tuned correctly, then longevity is rarely an issue.

HiProfile

I personally know someone who did a 85mm x 95mm setup NA with the longer rods, and the extra weight really negated the expected gains - although low/mid range was much improved. I think Roger McDaniels also has used a tall dart w/95mm (boosted), and IIRC the same deal happened.

I honestly think the best deal is to use the shorter rods. You'd then treat it like a normal bigger motor - expect a little more peak power at a lower rpm (lower the redline), but also whole lot more low/mid range power.

Longevity is one other issue. Not only is it not OEM Honda quality, but you have expotentially more stress working on the crank with the longer stroke. 7% longer stroke makes far more than 7% extra stress at the same rpm.

FWIW, one of the original papers on detailing how the GSR was designed based on the LS shortcomings, the piston speed was one big factor. They considered 8k rpm with the 89mm crank to be 'stratospheric', hence the shorter stroke. They also narrowed the rods for weight savings... Food for thought.

steven_highet

Here are some figures on my setup.

Rod Length = 137.000
R/S Ratio = 1.442
Maximum Engine RPM = 8021
Maximum Piston Speed (fpm) = 5298.556





As you can see a bigger stroke will make the piston accelerate away from TDC alot quicker. It also will decrease piston dwell time which is a good and bad thing. With the piston been at TDC for a shorter time it helps in detonation control but it also forces you to run more ignition advance as you need to increase the cyclinder pressure sooner in order for the piston to recieve the maximum amount of force before it runs away from the flame front. The piston speed is also something else that need to be looked at very closely. My piston speed is on the bleeding edge. Every component on the rotating assembly needs to be balanced and blueprinted in order for this kinda setup to hold together. Another problem with such a high r/s ratio is the increase side wall loading on the cylinder. The rod is at such an extreme angle that it is basically pushing the piston into the cylinder wall. So I wouldnt recommend this setup on a stock block. I also went with teflon coating in order to decrease piston to wall friction. Another downside is the engine ability to rev. But if you build your engine for a certain reason that factor doesnt really matter anyway. If you look on evans-tunings website there is a dyno sheet of a 95mm stroked engine that jeff said feeled like a small v6 off boost. This topic could be debated all day long so it basically boils down to what you want. Hope some of this info helped. I have lots of spreadsheets with formulas which can help you work out a good setup to go with such a extreme r/s ratio. Just let me know if you want them

The Sword

im going to find out the exact rod length of the BC kit, then we can more accurately throw numbers around.

blinx9900

I never understood the desire to increase low end tq so much on a fwd car. Some of the fastest guys use an 89mm crank.

The Sword

what if the desire is to smooth out the power curve and transition to boost? could that not be achieved with a flatter tq curve and peak power at lower rpm?

RedneckRicer

Im pretty sure that would increase the sideload on the piston which would decrease the life of the engine. Honda's make there power at high RPM's 9-10000 RPM's. i think with the stroker motor and the decreased rev limit you might fall out of Vtec in between shifts (depending on what transmission you used) so the higher reving motors of the 87 and 89mm cranks seem to be doing there job just fine.

blinx9900

Thats all in tuning and having an efficient turbo like a dual ball bearing, a larger engine would just make it all happen earlier which i personally don't want, i like having a car i can drive off boost around the street and then plant my foot in it and scream the **** to 9000rpm. Honda's are known for having great top end power, its easier and more satisfying to me to improve on that than focus on improving its shortcommings.

quicksilver1689

^ i totally agree, i usually focus on working with what we got, tight gearing, high rpm powerbands make the most of it.

steven_highet

Has anyone on this thread ever driven a 95mm stroked 22 psi boost b series? If you havent then you have no idea what you like! It is a completely different ball game and it will still roll with a b16 all day long its just alot more fun to drive!!