Combustion Contraption

All points taken. However in reading the original post in this thread, it was never stated that this was a race-car only. I always assume, since we're not all rich, that this car would also maybe be functioning as some sort of daily driver. And if you read my posts youd see that i said if its a drag only motor to go ahead and do it. Since it wouldnt be a pain to rebuild constantly.

As far as r/s ratio, i think its a little overrated in its importance to a motors health & longevity. In hondas it has a little more relevance due to the open deck cylinder design. I however believe piston speed is a better tool for determining the longevity of a motor. R/S ratio moreso determines where the motor likes to make its power as stated by previous posts due to the extended amount of dwell time at TDC and BDC.

colt45.5

Well maybe i better restate myself in better reguards. This car will be driven on the street more often than a race only car. I just have more leniancy towards whats streetable and whats not. As far as streetability, i want to be able to drive it to blockbuster and rent ernest goes to camp, and at the same time not have to worry about it overheating or breaking a rod in the process..

However at the same time, i dont need cup holders or a dashboard, or hell even mind lwatching the cv axle turn through the holes for ac and heater core lines from the drivers seat


Modified by colt45 at 3:35 PM 8/11/2004

Veris

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">As far as r/s ratio, i think its a little overrated in its importance to a motors health & longevity. In hondas it has a little more relevance due to the open deck cylinder design. I however believe piston speed is a better tool for determining the longevity of a motor. R/S ratio moreso determines where the motor likes to make its power as stated by previous posts due to the extended amount of dwell time at TDC and BDC. </TD></TR></TABLE>

Peak piston speeds are a great way to determine longevity of a motor. Average piston speeds are an ok way to determine longevity. It doesn't give you the whole picture. It is very effective at comparing motors with similar R/S ratios (ie: most stock motors). It is not very effective when looking at stroker motors.

Here is why:

The formula you use simply finds the AVERAGE piston speed via stroke. The formula is akin to driving across the city in stop and go traffic, then taking the distance travelled and dividing by the time the trip took to determine what speed you drove.

It is the peak piston speed and acceleration which causes problems. Stroke and R/S affect these peaks. Shorting the rods and increasing the stroke is a "double whammy" in regards to peak loads. If you do both and only look at the stroke's effect you are missing much of the picture and the point of piston velocity analysis.

Many people misuderstand R/S ratio's and its importance. Either thinking R/S is not important at all (LSVTEC raving crowd) or thinking that it is the most important part of engine design (anti LSVTEC). As with most things the truth is somewhere in the middle; it should be a consideration when choosing RPM limit and engine componets to completement the motors breathing.

Combustion Contraption

yea, and as you probably guessed i built an ls/vtec for myself. I never take it past 8k, but i dont really have to. Theres enough hp there for me. It is my daily driver so id rather not flirt with disaster.

197hp
144 ft/lb tq
dynapack #'s

Veris

I run a B20VTEC and run mine up to 8500 with eagle rods. 9000 is probably safe, but I need long term reliability as it is also my daily driver.

Combustion Contraption

stock LS rods here, shot peened with ARP bolts.

Veris

My old setup used stock B20 rods with ARP rod bolts. Max rev was 8000 then.

Used2beAb16

b18a vtec no problems 9,000+ rpms at times.

Combustion Contraption

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Used2beAb16 &raquo;</TD></TR><TR><TD CLASS="quote">b18a vtec no problems 9,000+ rpms at times. </TD></TR></TABLE>

Thats great for you, but youre flirting with disaster every time you rev that high. Id rather only take it to 8k and have it last thousands of miles longer.

colt45.5

Indeed. i agree. I wonder sometimes what camshafts people run.

You say your reving it to 9k, do you make any power at 9k or is it just for street racing someone and staying in gear longer.

In the long run, ive ran into more transmission issues id think from high rpm. Anyone ever notice how **** clutches work with above 9k daily. Ive broken about 4 pressure plates and im nearly positive its from this. I think the centrifigal force from such rpm causes the clutch to not disenguage correctly? Maybe its absurd, but i do most definately notice how much easier the pedal is to push above 9.

I could see it also wearing bearings, and parts in the trans not engineered to spin that level of rpm?

Like i said i have no idea, im just guessing at that.

colt45.5

I think im scratching the entire idea, just keeping the r crank, and going 85.5mm bore. That way i can beat the **** out of it, and use the car for roadracing rather than a drag race car with less reliability

Combustion Contraption

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by colt45 &raquo;</TD></TR><TR><TD CLASS="quote">I think im scratching the entire idea, just keeping the r crank, and going 85.5mm bore. That way i can beat the **** out of it, and use the car for roadracing rather than a drag race car with less reliability</TD></TR></TABLE>




now youre talkin

90teg

before my teg got jacked i had 85mm bore, crower 95mm crank and rods with 12:1 c/r pistons. this was an LS but man did that thing pull.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by LsVtec92Hatch &raquo;</TD></TR><TR><TD CLASS="quote">big bore short stroke is where its at. when will people reliaze this?</TD></TR></TABLE>

Combustion Contraption

how long was it running before your car got stolen?

90teg

i finished it in september and it got jacked this march. ran like a champ with no probs.

CallMeJesus

pullin an lsvtec past 6500 rpm's is not necessary. it loses its breath above 6000 rpm's, and when you go above that, you are putting unneeded shock on the rods. you'd see that during drag runs you would pull just as quick time slips runnin it to 5800-6000 as opposed to 7500-8000 rpm's, and the engine would last longer because you are essentially taking it easier on the rotating assembly.

Combustion Contraption

Im going to have to disagree with you on that one. Lets take a look at my dyno graph...



now looking at that graph, what do you think would happen if i shifted around 6k?

90teg

nice numbers

Combustion Contraption

Thank you.

OEM cams, as well

CallMeJesus

you gain 30hp over 1500rpm's, so youre wasting your time by stickin in that gear. drag racing is all about keeping momentum up, and by staying in the gear after the "peak" of the powerband has hit only slows you down. take a look at how quickly you gain hp/torque between 5500 and 5900 rpm's. you make almost 40hp and 20ft-lbs of torque in 400 rpm's. and after 5900 rpm's your torque falls off too dramatically while you arent making significant hp.

so if you shifted at 6k, you would keep vehicle momentum, stay within a more efficient breathing range, and probably shave time off of your time slip.

just because a vehicle makes hp to 7800 rpm's doesnt mean you stay in the throttle til you run into redline. you want to bang thru the gears more quickly, and if you keep vehicle momentum up, and stay at the "sweet spot" of your powerband, you are gonna run quicker 1/4 miles.

just because i dont dyno my cars doesnt mean i cant read dyno results.
nice powerband though, not a lot of peaks and valleys.

90teg

i don't see why you would shift at 6k?

CallMeJesus

to keep momentum up and the engine in its ideal breathing range. if you were to sit down and plot the hp/torque curve at every 100 rpms you would see above 6000 rpm's it doesnt have the same pitch as it does from 4000-6000 rpm's. take a ruler to a print out and look at it, compare the two by placing a ruler in line with the curve from 2000-4000 rpm's and take a look at where the curve from b/w 6000-8000 rpm's rises and falls against it.

by lookin at that graph it should be obvious where that engine breathes the best. it just takes time, trial and error, and driving technique to really understand all of this.

Combustion Contraption

You have to remember exactly what horsepower is and it sounds like youre forgetting. Hp and gearing have a greater effect on drag racing after you shift from first to second. Here, have a read.

http://www.speedoptions.com/articles/3519/

90teg

That was a great link, learn something new everyday.

colt45.5

What type of pistons would you suggest running? And do you have any advice as far as cam to use?