so how much power does your stroker have?

[Dr. Dyno]

Those speed pro pistons wont work on a stroker.

Mmmm. That's interesting. I wonder how I've managed to make my Speed Pro 677P pistons work just fine for the last 35k miles in my stroker? It must have been a fluke.

He's blowing smoke up your a$$, I bet it makes no more than 180 rwhp on an actual dyno (remember those things, they don't work on theory but fact?)
I've still never seen a printout from a real live dyno where a stroker makes more than 200 at the wheels.

Then I'll dyno my strokered Jeep and be the first to break 200rwhp. Yes, I've seen others make a lot less but they all had bigger tires than stock. It also depends on the type of dyno that's used. A Mustang Dyno or a Dyno Dynamics dyno will absorb more power and show ~8% lower numbers than a Dynojet.

 

[Frank Z]

Interesting thread and very timely (for me at least). The one thing I was hoping to see here is a printout or attachment showing actual dyno numbers.

Anyone?

FWIW,
My stuff is at the machine shop waiting on a new set of pistons. The shop cc'd the H825CP dish volume and found that it was off by 7cc's. The spec's for the piston are 22cc's but the actual volume was 15. The 677CP had a volume of 18cc's and the pin height is .010" lower on the piston. This will bring the compression down to 9.4:1 with the other work that's been done to the block and head.

 

[muddshutter]

My stroker has MORE power than i could ever need.

 

[stever6kid]

funny thing is...dynos do work on theory! have you ever looked into the development of the dyno industry? the methods used and the numbers that are spit out are all based on some arbitrary crap. they started up using drums of a size and weight that was simply enough to make the engine work hard. then they use computer programs to spit out a number that sounds about right! it's nothing like the way the OEMs test the crankshaft horsepower, but it is a good method to test for real life power gains from modifications. the big problem is that no 2 dynos spit out the same numbers all of the time for the same car. there are other factors such as temperature, fuel, etc. that change these numbers, but the fact is that dynos are just tuned to spit out relative numbers...not necessarily accurate numbers

That's right infact most of the time you can gain afew horsepower number just by tweaking the dyno. Does it actually build up more power in your engine, NO, but the dyno will show different numbers from one run to another.

 

[MudDawg]

On the dyno thing....depends on what dyno, how accurate the calibration of the dyno and how accurate the peripherals are....no two pulls are the same, even back to back pulls...the conditions change...barometric pressure goes up or down, oxygen content, moisture content....hell on a chassis dyno, how tight the axle is strapped down makes a difference. When you read a dyno chart...it should show the correction factors...and even that leads to an assumed (albeit close) power output level.

In all reality, any dyno measures torque....how long it takes to accellerate a known mass relates to how much power is being produced...or in the case of a water dyno, it's the engines ability to maintain rpm against a known constant resistance.

Short rod vs long rod motors....long rod motors have less frictional losses and longer piston skirt life...short rod motors are cheaper....

However you set up the motor...quench design plays a huge part in combustion efficiency....stock rods are made of iron, not steel....careful preparation is in order to assure reliability...they are ok if properly prepped since the max revs are not all that high...personally, I would spend the extra bux and build a long rod motor.

 

[JJacobs]

Then I'll dyno my strokered Jeep and be the first to break 200rwhp. Yes, I've seen others make a lot less but they all had bigger tires than stock. It also depends on the type of dyno that's used. A Mustang Dyno or a Dyno Dynamics dyno will absorb more power and show ~8% lower numbers than a Dynojet.

Do it! This crowd seems almost (should I say it, oh why not) ricer-ish about dynos. "Oh, those things aren't accurate. It's not going to show my true 300Hp, so I'm not going to waste my time."

Prove me wrong, please.

 

[philip_g]

Do it! This crowd seems almost (should I say it, oh why not) ricer-ish about dynos. "Oh, those things aren't accurate. It's not going to show my true 300Hp, so I'm not going to waste my time."

Prove me wrong, please.

with a name like dr dyno, who can argue

 

[Dr. Dyno]

Well guys, I ran my 4.6L "poor man's" stroker on a Dastek Dyno today at MOCA Performance in Dubai. It was late in the afternoon so there was only enough time for one pull, and for some strange reason my rev-limiter was cutting in at only 4500rpm so I couldn't get a full run. The pull was done in 3rd gear of my 5-speed AX15 and the dyno applied load to the rear wheels to hold the rpm steady at 500rpm intervals to get HP/TQ readings. Here are the rear wheel numbers that I did get (STP correction):

1500rpm: 63.2hp, 221.4lbft
2000rpm: 88.1hp, 231.3lbft
2500rpm: 114.6hp, 240.8lbft
3000rpm: 141.3hp, 247.4lbft
3500rpm: 166.6hp, 250.0lbft
4000rpm: 190.4hp, 250.0lbft
4500rpm: 206???
5000rpm: ???

Peak rear wheel torque plateaued at 250lbft from 3500-4000rpm. Unfortunately I couldn't get the true HP peak but the HP curve was still climbing up to 4500rpm.
I've disconnected the battery and I'm going to leave it overnight so the ECU can reset itself. Maybe the rev-limiter will also reset so I can go above 5000rpm again.

 

[Frank Z]

Nice!

Hopefully I'll get my block and parts from the machine shop this week and can get my stroker assembled and installed ASAP. Dyno will have to wait till the motor is broken in though.

 

[philip_g]

Nice!

Hopefully I'll get my block and parts from the machine shop this week and can get my stroker assembled and installed ASAP. Dyno will have to wait till the motor is broken in though.

I'm in the same boat but don't have a cam, rods, pistons etc sourced yet either.

 

[JJacobs]

Not bad.. any reason they didn't do it in the industry standard, 1:1 gear ratio, which would be fourth with that trans?

 

[Frank Z]

I'm in the same boat but don't have a cam, rods, pistons etc sourced yet either.

Have you asked your machine shop to quote the parts? You might get a better rate on the machining if you the parts from them.

FWIW, here's a link to my Stroker thread at CO4x4...

http://www.colorado4x4.org/vbb/showthread.php?t=80410

 

[Dr. Dyno]

Not bad.. any reason they didn't do it in the industry standard, 1:1 gear ratio, which would be fourth with that trans?

Yeah, the top speed limiter cuts in at 122mph on the speedo which is only 4350rpm in 4th gear, so that wouldn't have given me a full run to 5000rpm. As it was, I didn't get it anyway even in 3rd.
I disconnected the battery overnight to reset the ECU as per the dyno operator's suggestion. I drove the Jeep again today and the rev limiter still insists on cutting in at about 4500-4600rpm. I'm stumped and so is the dyno operator, and this is a guy who custom programs Unichips on the dyno so he knows his stuff. The engine still pulls hard and sounds happy up to 4500, there's no "check engine" light, and no fault codes.

 

[philip_g]

Have you asked your machine shop to quote the parts? You might get a better rate on the machining if you the parts from them.

FWIW, here's a link to my Stroker thread at CO4x4...

http://www.colorado4x4.org/vbb/showthread.php?t=80410

I told him I'd give him a crack at it.

the cam I'll get from delta, they'll custom grind a comp cams knockoff for 75 bucks with core and the lifters are something like 45 bucks so that's nice and cheap.
The rods I'll get refurbed and the pistons I'll see about getting from the machine shop, plan is to use the cheap speed pro pistons since I'm not going FI.

He also mentioned something about paying a local shop 100 bucks to pull engines for him so he doesn't have to muck with it, I might see if they'll pull my old one and swap in the new for 200 or 300 for me, as I just plain don't want to
Oh he's even going to cut down the crank nose for me.

The real question I have is to dish the pistons or not, and to weight match the rods and pistons or not. It's my daily so I want reliability and to keep the cost down. Just want to be able to drive up the hill out of castle rock on I25 in 5th

 

[Frank Z]

The real question I have is to dish the pistons or not, and to weight match the rods and pistons or not. It's my daily so I want reliability and to keep the cost down. Just want to be able to drive up the hill out of castle rock on I25 in 5th

I suggest using the spread sheet at www.maxj.com to get a handle on the compression ratio. Keep in mind that every block and head will require varying amounts of milling/decking inorder to get them flat. My block was sagging in the middle and needed .018" removed to get it flat. The head required .008" decking to get it flat. Six cylinder heads will sag/warp a lot easier that a v-8 head simply due to the length. (Speaking of which, I learned that storing a 6 cylinder crankshaft horizontally for a long time is not a wise move either. Keep that mutha standing tall.)

Be carefull when you have your pistons milled out. Too thin on top and the piston won't last very long.

I'm probably going a bit overboard on my motor, but then again this isn't a project I care to repeat because I took the wrong shortcuts. Yes it's possible to build a very low-buck motor and have it perform adequately, but that's not my approach this time. I'm willing to go a bit over budget and get better quality parts and hopefully a better motor in the long run.

 

[philip_g]

I just don't care that much, it'll be close enough. I'll slap together as is and leave the pistons stock.

 

[northernxj]

Do you guys gain a lot of engine noise doing the stroker build, or just gain noise from increasing exhaust flow? Thanks guys

 

[jeepinwi]

My stroker is nearly as quiet as the 4.0, but I'm running it through the stock exhaust still...which is a restriction for even a 4.0L. I do hear a faint valvetrain ticking most of the time due to the higher lift camshaft.

 

[Dr. Dyno]

Do you guys gain a lot of engine noise doing the stroker build, or just gain noise from increasing exhaust flow? Thanks guys

The engine itself shouldn't be any noisier than a 4.0 but if you use a high lift cam and stiffer valve springs, you can expect a bit of valvetrain noise at idle up to about 2000rpm.
The stock exhaust is very restrictive for a stroker but if you make it free-flowing, it shouldn't become substantially louder as long as you have a cat and a muffler that's at least as big as the stocker.

 

[BlueCuda]

Dynos should only be used as a tuning tool. The numbers will vary by dyno manufacturer and vary from dyno to dyno. Comparing dyno numbers accross the world is pointless IMO. The only reason I care to dyno my jeep is for AF ratios, I would like to see what it looks like. With heavy tires, 8.8 axle etc I am sure the numbers won't look great. I know my stroker makes decent HP because it runs at least as quick as a bone stock Xj but it wieghs a good 700-1klbs more.