STR Redline

[DefeXion]

Something else I have been thinking about is the low redline on the STR. What is it about an engine that effects where it should redline. Is it just quality/strength of the block and piston, or is there more to it?

Sorry, I feel like an onslaught of questions atm.

[Kenneth]

There are a number of things that determine the maximum RPM

primarily the strength of the rods and crank play a big part. As you increase RPM you increase (by a large amount, not sure on the actual figures though) the stress on the reciprocating mass. This of course is related primarily to weight, the lighter the reciprocating mass the better. This is why 4cylinder 250cc motorbikes can have a redline of over 20,000RPM.

Then you get down to things like stroke length and cams. Shorter stroke is usually good to make the engine rev quicker and higher. Cams need to open the valves sufficiently to draw in enough air at high RPM to stop the power dropping off


To be honest it is a pretty complicated area. Best you can do is decrease reciprocating mass and increase strength :P

[bradc]

The FTO engine revs to 8000rpm and is obviously 2.0l instead.

The 6A13 DOHC Mivec engine created in perth has an 8000rpm redline, but it has a custom crank and pistons.

imho the stock 6A13 SOHC engine runs out of puff above 6000rpm anyway, probably due to the somewhat conservative cam's. If you got the cams reground you could shoot for higher rpm.

I don't have the gear ratios for a 6A13 SOHC auto at the moment, but I can tell you that with an exhaust and custom intake, Carsten's 25ST made it's max power at 105kmh in 2nd gear (93kw) at 120kmh it was down to about 83kw. Hence it isn't worth revving the nuts off the engine with the stock cams and or ecu setup.

[Subaru ETA]

valve spings play apart too. not good when you get valve bounce!

[DefeXion]

I felt that there wouldn't be too much gain without changing how the engine expresses its power. The upping the revlimit thing is more a "giving room for improvement" upgrade in my mind. Power seems to come on at 5k and finish at 6.5. I tend to rev to 7k though to put me back above 4k after changing gear (that's how i kept up with yous on the wellsford cruise), but theres still a bit of a slump before getting back to the power at 5k

A 6A13 DOHC Mivec engine? Have you got a link to any information about it? I didn't realise you could get a 6a13 mivec head :).

[Paul Beazer]

Sounds like a one off frankenstein job to me!

[bradc]

http://www.rpw.com.au/shop/index.php?option=com_content&task=view&id=144&Itemid=40

[DefeXion]

10 grand... pschh

[Turbo_Steve]

Also worth mentioning balance: If you want to raise your revlimit you need to ensure everything is as well balanced as possible: the better balanced it is, the simpler it is to work out how much stress the rods are under as the piston changes direction in the bore. If you're going to start raising the rev limit any more than marginally, you need to look at getting the whole rotating mass precision balanced.


Other than that: what Kenny said, really: everything needs to be as light and as strong as possible, your valves need to open and shut superfast (think gas filled instead of solid, with uprated springs, lifters, goodness knows what else) and then you need to start looking at dwell times on the ignition systems, plug temperatures, and also factor in the reduced lifespan on things like the oil/water pumps.
Oil may have to be different too

Overall, there's a reason why Honda VTECS are usually inline 4's.
They have done a couple of V6's but they're extremely pricey, and there's a reason for that. Sorry.

Saying all that, if you're looking at a smaller increase (say from 7500rpms-8000rpms) then you're probably at a lot less risk, but it's going to be a gamble. I'd certainly be thinking in terms of a "sacrificial engine" if you're going to start upping the rev limit at high loads.

Also, if you're going to get real benefit out of high to ultra high RPMs you need to think about port-work and/or cams to really see the benefits.

[Turbo_Steve]

I felt that there wouldn't be too much gain without changing how the engine expresses its power. The upping the revlimit thing is more a "giving room for improvement" upgrade in my mind. Power seems to come on at 5k and finish at 6.5. I tend to rev to 7k though to put me back above 4k after changing gear (that's how i kept up with yous on the wellsford cruise), but theres still a bit of a slump before getting back to the power at 5k

Just re-reading that, I'd suggest the following checklist:
1) Breathing (exhaust/airfilter, potentially better pipework)
2) Fuelling - Make sure your fuel is always super-top quality, and that your ECU knows it.
3) Ignition - Nice clean brand new plugs? HT leads? Perhaps check out new coil-packs (if they're cheap)
4) Cams. Changing your cams will have the single biggest impact on the power-curve of your NA engine.

What you describe is really that you don't have as much low-midrange torque as you'd like, rather than needing to raise the rev limit.
You could probably put an extra 250rpms on top, but it wouldn't get you all that much compared to a set of well sorted cams.
The problem is that I doubt anybody makes them...so you'd be looking at a custom grind.

[DefeXion]

At least I can check three of those off the list.

1) I just fitted a VR4 air intake box with a K&N panel filter. I have really noticed the difference. Accelleration is less jerky and the pickup after changing gears is much better.

2) I run 98... no questions asked. I will need to plug evoscan in and check out what the ecu thinks of it

3) You might be onto something with ignition. I had a suspicion that one of the cylinders wasn't igniting because I had a repeating poppy feeling on low idle. The STR has a dizy instead of coil packs, but HT leads sounds like a good idea.

4) Cams = dream!

[Kenneth]

3) You might be onto something with ignition. I had a suspicion that one of the cylinders wasn't igniting because I had a repeating poppy feeling on low idle. The STR has a dizy instead of coil packs, but HT leads sounds like a good idea.

When was the last time you took a look at the plugs?

[DefeXion]

mid last year ish. I don't have a spark plug socket handy to do it whenever I want.

[bradc]

I was told cams would be $750 for a VR-4, and thats for 4 of them! That would be a regrind of existing cams from Kelfords

[DefeXion]

Well, that's something I was just thinking when steve said regrind. The VR4 cams are quite agressive where they slap the valve open, and shut rather quickly. I was thinking it might be a good platform to make an NA cam from.

I'd just be concerned about timing though. I think turbo cams are set to open close quite early... or is it late... I'm not sure, but I know theres a considerable difference and it won't suit NA without any heavy modification.

[bradc]

yeah they wouldn't be suitable. I'd say that a regrind on your existing cams is the best option

[Subaru ETA]

my dads mate owns a car yard. one day i was there looking a cars (think i was looking for an evo at that stage) and he had a 97 mirage mivec. he started telling me how he got it in from japan and it was a race car there. he got another one and put the racecar back to std interior wise (and panels that wouldnt comply).

it looked pretty lame real, then he said take it for a spin, and ill come out in the evo you are looking at.

ill tell you what i jumped into it and the thing had a 10000rpm redline according to the dash!

we pulled out onto the northern motorway and well lets just say that that dash wasnt just for show! IT PULLED AWAY FROM THE EVO 4!!!!

however to do this it had some major $$ spent on it!

standalone engine management
cams
crank etc
1800cc stroker kit
everything lightend and balanced
beefy valve springs

i had the list he gave me but i dont know what i have done with it.

guess what im saying is that you can get high rpm and power out of N/A but damn does it cost alot!

[bradc]

and it is cheaper to get a VR-4 than getting all the stuff done to an STR

[Turbo_Steve]

!!!!

http://www.superchargersonline.com/product_detail.asp?PartNumber=PAX1016125

Still more expensive than a VR-4, though, but if you can find a smaller one at this price, and a 5th injector driver, you would see a significant increase in output power, with more torque accross the range too, an no need to fiddle with the rev limiter or anything.

It'd have to be a small one at light pressure.

[Turbo_Steve]

In fact, from memory, Vortech is probably your best bet, if you can get a small one at the right price.
Alternatively, keep an eye out for Wrecked SLKs....they have a lovely little unit on them which would be about the right spec for the 2.5.

[N9nebar]

sorry to butt in on this thread ,but i'm gettin a 1.8gdi 4g93 legnum ,and i've asked this question on a couple of other forums so i'd like to get more opinions .i've been told its possible to put a mivec head on the 4g93 or to turbo the gdi .what are the pros and cons of both? all opinions and comments appreciated......

[Kenneth]

sorry to butt in on this thread ,but i'm gettin a 1.8gdi 4g93 legnum ,and i've asked this question on a couple of other forums so i'd like to get more opinions .i've been told its possible to put a mivec head on the 4g93 or to turbo the gdi .what are the pros and cons of both? all opinions and comments appreciated......

Do a search for: GDI Turbo

In short, you are better off getting a VR-4. Probably going to be cheaper and definitely much much less hassle.

[DefeXion]

I'd like to see a GDI go Mivec. Where were you told that you could do that? linkies...

[bradc]

just buy a VR-4, it's cheaper than modding a gdi

[DefeXion]

I'm not planning on doing it myself :). I'm just interested.

[bradc]

it's cheaper for you to buy a VR-4 as well :)

[N9nebar]

I'd like to see a GDI go Mivec. Where were you told that you could do that? linkies...
not a site as such , a bloke on another forum told me its possible ,says he's done it before to lancers but he just not sure of the wiring loom on the legnum,he'd have to have a look at it first.