More RPMs

1521 Views 23 Replies 11 Participants Last post by scoobyrs25, Mar 8, 2002

scoobyrs25

Discussion Starter · Feb 5, 2002

Anyone know of a way to raise the redline while using the stock ecu? I will be using the new split seccond programable map.

1 - 20 of 24 Posts

Section 8

· #2 · Feb 6, 2002

Call someone who sells Unichip. I think that you can raise the redline by stretching out the fuel map. Weather or not this actually will work well I don't know. You are getting close to a programmable ECU price wise though combining it with other add ons.

Greg

scoobyrs25

Discussion Starter · #3 · Feb 6, 2002

Unichip is not an option.

8Complex

· #4 · Feb 6, 2002

I don't believe you can with the Unichip either.

I don't see it as being feasible without actually changing the ECU for a full programmable unit.

Graham

· #5 · Feb 6, 2002

I think that Larry Ganz is doing something like this, you send him your ECU and he's sends you back your new redline, or something like that. He did it for someone on "the club" (an RS of course) and his new redline was somewhere around 7200 RPM. He could tell you more about it.

Graham

RallyImprezive

· #6 · Feb 7, 2002

Thats an interesting idea. Any clue as to what RPM valve float would be an issue? Or complete engine failure? I don't think our engines like being revved particularly high.

-Andy

Graham

· #7 · Feb 7, 2002

Suppesedly the ECU that Larry Ganz did for that was guy had his stock valve springs in there and his redline was set around 7200 RPM. I can't be too sure though. If I raised my redline (all I want is 500 more RPM!) then I would probably get new rods, just to make sure nothing breaks.

Warp3

· #8 · Feb 8, 2002

RallyImprezive said:
Thats an interesting idea. Any clue as to what RPM valve float would be an issue? Or complete engine failure? I don't think our engines like being revved particularly high.

-Andy

According to Trey Cobb @ Cobb Tuning, 7200rpm should be fine with the stock heads. (He states this is a "conservative guess" based on their teardown of the heads.)

Here's the URL:
http://www.cobbtuning.com/tech/sohc/page2.html

MattC

· #9 · Feb 8, 2002

Regardless, you won't make any power. We have messed with higher RPMs on the dyno, only to see more lost power. My rev. limiter now is set to 6350rpms. Note, this is done with a TEC II. Shifting at 6300rpms is the optimal point for me, after looking at my dyno charts. However my car makes peak power at 5800rpms, as apposed to 5500rpms, and it does drop off nearly as quick as an N/A 2.5RS.

scoobyrs25

Discussion Starter · #10 · Feb 8, 2002

Hmm.. with my crappy Akimoto intake, I feel like I could use another 500 rpms or so.

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MattC

· #11 · Feb 8, 2002

Its very strange that way. I was convinced I was making power all the way to the rev limiter, but I wasn't. Only one way to find out though. That is, of course, to dyno it. Converting your car to 2wd isn't that hard. I have done it twice. You can get a Rwd kit from Cobb, or a welded center diff. from Rallispec. The later will make the car fwd, and a bitch to drive. My car would spin the front tires all the way through 4th gear.

MattC

Graham

· #12 · Feb 8, 2002

I thought the addition of COBB cams (mild or spicy) gave pretty significant gains in upper RPM all the way to redline?

The relatively low redline that the RS has is one of the disappoinments, to me. I think that if this car could pull hard all the way to redline instead of torque/horsepower dropping like rocks around 5500 RPM, the car would be much faster.

Matt- You mentioned that you raised your redline, and thus must have elongated your fuel/timing curve, but noticed no specific power gains? Do you have cams, as this seems to be one of the few ways to make some of the power back in upper RPM?

Finding more power up top and keeping it down low is something I would like to figure out, but right now there seems to be no one who can make significant increases above 5500 RPM.

MattC

· #13 · Feb 8, 2002

Of course if you go with a set of cams, or work the head gains are to be had. But, I don't know how much I would trust the bottom end. As you probably know the EJ25 has a very large bore, and utilizes in turn a short stroke. Well a large bore nessitates a large, heavy piston. This isn't the best combination for a high reving motor. It is the combination for great torque, and low RPM HP. I'm not saying you can't make high rpm HP. I'm just saying that if I was to go that route the first thing I would want to do is put in some aftermarket rods. Then build the head as much as your budget will allow.

This is just something I wouldn't want to do all together, because the motor loves being turbocharged. But, to each his own.

Here is a pic of one of my less impressive dyno pulls. These were done under low boost(5-7psi), and without the aid of intercooling. In fact the damn thing was heat soaking so bad I was seeing as high as 170F manifold air temps:

Keep in mind that we lose an average 45HP when measuring through the front wheels.

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scoobyrs25

Discussion Starter · #14 · Feb 9, 2002

Short stroke is one of the key ingrediants in a high reving motor.

MattC

· #15 · Feb 9, 2002

I won't say your statement is false, but I would like some facts to back that up. I haven't been building motors for that long, and am often wrong. But, I can't make much sense out of it. By utilizing a small bore, long stroke combination you take a lot of mass out of the equation. Specifically you take a great amount of mass out of the end of the stick. Also by using a very large bore, you make even air and fuel distribution much harder. This is why I believe that although F1 motors don't have a great amount of displacement, they still use many pistons. Maybe this isn't the best analogy, but hey its late and I've had one to many beers :barf:

Please give some evidence to back your statement. I actually do enjoy being wrong

Cheers,

MattC

scoobyrs25

Discussion Starter · #16 · Feb 9, 2002

This is going to sound silly, but bear with me, I had a great night last night, so I am still a bit fuzzy.....
Run in place only lifting your feet 6"s off the ground. High rpm stuff. Now, run in place lifting your knees to your chest. Not very easy to get the rpm's up is it? Short stroke, high rpm. The ideal setup would be a very square bore and stroke. Now if only someone made Ti rods.....

MrJosh43

· #17 · Feb 10, 2002

Now if only someone made Ti rods.....

Paeco makes them... www.paeco.com

scoobyrs25

Discussion Starter · #18 · Feb 10, 2002

Their website is totally useless. Have they already made them for the Impreza, or do they just do that sort of thing?

MrJosh43

· #19 · Feb 10, 2002 (Edited)

Yeah, order the catalog though, they should get it to you pretty quickly.

Not sure if they have made the Ti rods for Subies, but I'm pretty sure they've made the chromoly rods. If I remember right anything they don't have a template for they will make for you if you send them the part (i.e. send them a stock con rod). They don't seem to keep things in stock, but rather make parts as they are ordered.

I emailed them last year and they know their stuff, they've been around for quite awhile. Expect to wait for awhile though, they seem to have a heavy workload. They told me it would be about 2-3 months for a complete engine.

tydon

· #20 · Mar 6, 2002 (Edited)

reason short stroke is good for high rpm

a short stroke is good for rpms because it also means a slower piston speed. imagine at 10,000 rpm if your stroke is 4", then the piston moves at a maximum of 238 mph. a 2" stroke yields a max of 119 mph.

the gas produced in the combistion process can only expand at a limited rate, so at some rpm, the piston will start moving faster than the gas can push it. this essentially limits the rpm that an engine can achieve, because it is that expanding gas that pushes the pistion and makes power.

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