in other words this can be translated to that a stroker kit will not be significantly better

 

good write up. makes for something to keep me awake on another cross country flight from rhode island to washingtin state.

 

No, not at all.

Scorke

 

I want your opinion on which way you would go, given these 2 choices I'm about to mention and why.
Build a 4G64 with 100mm crank, 156mm rods and std. stroker pistons. Or..build a 4G64 with 159mm rods and custom stroker pistons. Is it worth having the pin shifted up another 3mm in the custom stroker piston, just to bring the rod up to 159mm and increase the rod stroke ratio from 1.56 to 1.59? Keep in mind that the cost of the rods will be the same and the cost of the custom pistons will be $650.

Thanks

 

Basically a longer rod makes more torque with the same piston force, because it is longer the load angularity??(is that a word?), reduces sidewall loading and decreases friction. All of this adds up to more power. Longer rods also give the piston more time in a state of dwell, or rest, at the top and bottom of the stroke, which is good because it means more time for intake air to come in and more time for energy to be capture during ignition, all good things.

To keep the same overall length of the piston/rod combo you are going to have to move the pin height as you mentioned. As long as you and or your engine builder is confident that you have enough "meat" above the pin placement (area of exposed piston above the pin before the rings) I would say going with a longer rod is without a doubt going to be a better performing engine, if not at the expense of a lower rod/stroke ratio or seriously weakening the pistons.

The only reason to go with a shorter rod IMHO is to get some low end tq, everywhere else the long rod is going to win out.

VERDICT- 600 bucks on top of few thousand to piece together and assemble a stroker motor you might as well build it as aggressively as you can without compromising safety, as long as your custom pistons are up to the task throw all the rod at it you can.

Scorke

 

What bore are you going with?

Scorke

 

87mm I believe, same as I will be, though I am going with a 94mm stroke.

MirageEvo- I didnt get back to the internet soon enough but scorke did a good job of explaining it.

To take the layman explanation one step further though, the intake port becomes the ultimate restriction as the airflow approaches .6 Mach and higher. As is pointed out in the article the ideal airdlow speed seems to be .4 or .5 for best results. As the mach number increases and the choke flow is reached, vacuum forms just a head of the port inhibiting airflow. All in all it makes a brick wall, so what we were talking about the other day about larger valves becomes important. That and porting the Bejezzus out of the head.

I use for an example Paul Nelson's Evo. Year before last it put down 1014 at 55psi on a 4202. Just recently it put down 1050whp on the same turbo (we arent counting the 4508 for this comparison) at 44psi. To me there are 2 reasons this happened...and possibly a third.

Reason 1- Ported head. The valvesize was a constant between the 2 trips to the dyno at 1mm over. The change was a mildly ported head to a CNC ported head from GSC.

Reason 2- Intake manifold change. Though both tests were done on SMIM, the 1014 pull was on a smaller plenum which will tend to keep velocity up as the air has less time to stack inside the plenum. I am going to incorrectly compare this to a garden hose versus a firehose. The firehose has alot higher flow in FPS (something we are trying to keep away from to a point) vs the garden hose and will reach .6+ Mach sooner. The tradeoff is it does with significantly more mass (lbs/min) than the garden hose at a given port velocity.

Reason 2.5- Camshafts. While I cant directly say that it has anything to do with port flow (because it doesnt) that is going to be some of the power gained at lower boost. S2 to S3s for those keeping track.

The other night I found an awesome portflow calculator on SlowGT.com that can show the relationships mathematically a little better than I can explain them.

On my engine the R/S ratio works out to almost stock (1.72) so it seems my job of tuning and math is going to be about what it ends up on a 2.0.

Hopefully some of that was in english

Cheers

aaron

 

Aaron after replying to the Mach question I did some researching myself and learned a lot about how valve area, numbers of valves, and the angle of valves play a part in the way air fills the cylnder..... How much of this differs between FI and NA setups, with pauls car wouldn't any modification to the intake piping/ports/heads/valves that allows more volume regardless of changes in the speed of the intake charge?

Scorke

 

Scorke,

I cant directly answer the question about differences between NA and FI applications, but it would seem to me that it would be negligible Because once air pressure has reached a set limit the motor is for all intense purposes NA. Anything that directly affects VE will have the same overall effect though at a greater magnitude since its breathing at higher pressure. I look at applications where the car is really airflow limited (like Rally cars or the stock turbo competition) and the solutions to make more power is to build the rest of the motor like its a high powered NA application.

Ted B and I will refer to Subaru WRC cars where the static compression ratio is 10 or 11:1, its on 40psig of boost, and runs on 98RON but the actual airflow numbers are really low. For reference a 38mm restrictor (38mm for 3mm over a 50mm span) flows something like 130cfm and thats it more or less.

On Paul's car I agree with you. Anything that slows or speeds the intake charge velocity is going to be the ultimate power and rpm limiter. Obviously Paul's car wasnt at the exact limit for RPM because the car has turned 10,400 both times but I would bet dollars to pesos that it was taking more "push" from the higher boost to push through the vacuum that was forming in the port on the mild ported head. It would be interesting to see a head on the flowbench and see what the air is doing by using smoke or something. I am sure somewhere on the internet someone has done this and put the video up. I am very visual so I guess I have some research to do.

 

Yes, John Bradley was correct. I am boring the 4G64 to 87mm, unless I end up getting a new block which I will leave it at 86.5.
I was also looking into the Cosworth M3 Mivec Cams. A question for both of you guys...Do you think it would be a good idea to have my head cnc ported and have +2mm oversize supertech Intake & Exhaust valves installed? I plan on running a full race twin scroll header and a borg warner 91-79 turbo ie. equavelant to the Garret GT40.

 

dude, you really like to hear youself talk....you typed quite a bit, but really said nothing..which get's you a

if you have something good to say, say it..if not, just lurk and learn, boy

 

Pot meet Kettle.

#1 That was a quote from the whitepaper you apparently did not read

#2 It was Aug 8th

#3 Look at the convo that has developed since then

 

On a 2.6 liter 4G64 stroker with a rod stroke ratio of 1.47 (106mm stroke & 156mm rod) I was planning to CNC Port the head, but what oversized valves would you recommend for the intake and exhaust? Also what cams....was planning on the Cosworth M3 Mivec. I plan on running a Borg Warner S300SX 91-79 twin scroll turbo set-up and revving to max 8000rpm.

 

I would go with 1mm over valves to be sure, and possibly larger if you can get them to fit. The main issue is of course shrouding, but 1mm should be sufficient. That is a big motor

 

There is a company called CNC Port that does a standard +1 intake and +2 exhaust. Here's the link to their website...what do you think? Seems like the +2 exhaust might be a good idea for a stroker motor.

http://www.cncport.com/applications.phtml#

Mitsubishi Lancer EVO 8-9
5-Axis CNC Head Porting, CNC Chambers, SERDI Competition Valve Job Bronze Guides. +1mm Int & +2mm Exhaust. Call for Flow Details. (888) 797-3773

$1195.00