Why aren't our motors rev-happy? - The Saab Link Forums

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Performance Modifications for the NG900 / Old 9-3 This forum contains PERFORMANCE related Q&A's for the NG900 and 9-3. This may also include suspension.

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Old 05-13-2008, 06:03 PM   #1
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Why aren't our motors rev-happy?

I've always wondered why Saab engines seem to be less inclined to high revving than other 4 cylinders. Even the highly modded Saabs I've seen don't even make it to 7K. What is the reason for this? What makes some motors rev to the moon and others are all mid-range power? I just want to open up some discussion. Here's a list of possible reasons I could think of:
Head design, ports, cams, springs; Crank balance, short/square stroke; balance shafts, weight of rotating assembly....others?
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Old 05-13-2008, 06:12 PM   #2
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the lifters sucks you need solid ones to rev past 7250ish and stiffer valve springs.
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Old 05-13-2008, 06:22 PM   #3
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I didn't think about the lifters. It seems like it would be a pretty easy to manufacture solid lifters; it's a pretty simple design.
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Old 05-13-2008, 06:33 PM   #4
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I think its because most of our torque can be made fairly low. I don't think many have seen a point to high reving.
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Old 05-13-2008, 06:44 PM   #5
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if you had more range you could use a larger turbo. alot f those honday guys have lagre turbos because they can go to 9k so when they shift they would onlny drop down to say 6k.
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Old 05-13-2008, 06:51 PM   #6
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It also comes down to how the rotating assembly has been engineered and balanced. Saab choose to pursue driveable torque vs. high revving motors to produce power (low torque). It's all about preference of design and functionality. You could make a high revving saab but you'd need to redo the crank, rod, piston assembly as well as head work (or even a redesigned head for upper rpm flow).

Another thing to think about. When a fully tuned saab can an easy 300 torque even at the top of the rpm range it doesn't need the high revs to make the hp that the honda can make at 9k rpms with say 120 tq.

HP=(torque*RPM)/5252.



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Old 05-13-2008, 06:58 PM   #7
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SAAB engines tend to be longer stroke than most 4 cyl. engines. Rule of thumb is the longer the stroke the less RPM they turn. Short stroke engines will usually rev very high, such as Hondas. The long stoke engines tend to make most of their power at lower RPMs and tend to like to be lugged a bit.(lower end torque) In turn most of your short stroke engines will make most of their power higher in the RPM band.(high end torque)
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Old 05-13-2008, 07:17 PM   #8
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actually a lot of the honda engines are fairly long stroke, liek teh b18 is something like 81x87 compare that to a c900's 90x78.
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Old 05-13-2008, 07:21 PM   #9
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You take a 2.0 motor and put in solid lifters and a big turbo and cams and they will make 800bhp and rev on up to 9500rpm! They like to rev just fine, just have to get the head so it can handle it.

My motor wants to go past my 7k rev limit now and I have the 2.3 motor. I remember my 2.0 would sing to 7k and bounce against the rev limit with the gt3071. The hydraulic lifters will not support much past 7500rpm.

Check this out:

http://www.93ssr.com/engine/

http://videos.streetfire.net/video/s...ower_14401.htm

Made max power of 850bhp way on up there.....

John
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Old 05-13-2008, 07:42 PM   #10
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I tend to agree with John on this. I think our bottom ends should be fine, but its a matter of reworking the head and other HW to do something it wasn't originally designed to do. About the solid lifters, does anyone currently manufacture them or is it more of a custom thing?
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Old 05-13-2008, 07:46 PM   #11
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Last I know you could get them from trollspeed of sweden or possibly maptun. Those are about the only places I can think of.



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Old 05-13-2008, 07:53 PM   #12
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Long stroke engine has a lot to do with it. That plus at higher revs you have to worry about valve float.
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Old 05-13-2008, 08:15 PM   #13
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You can make any motor rev happy....take for instance the 8 valve motor we ran in our VW Drag Rabbit. In stock form, the 2.0L 8V would only make power up to 6200 rpm. After we worked the engine it spun and made power up to 9500 rpms with ease. I high reving motor is all about flow thru the head (large valves, high lift cam(s), lightened, balance, blue printed, etc).
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Old 05-14-2008, 05:34 AM   #14
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There is a big difference between being able to rev to XX rpm and actually making any toque up there.

With a turbo it is a compromise too. What works at 9K is not so good around town.
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2.0 GOOSE 500whp + 8500rpm = 11.06 @125 E85
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Old 05-14-2008, 08:32 AM   #15
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That is true, I have seen some of the guys that make that big power from 6500-9500rpm, they don't even start going until around 6-6500rpm and then they spool-up and make the power way up top.

We start at 3500-4500rpm and run to about 6500rpm, a turbo that would make power way up top, a t76 turbonetics or a gt42rs or something like that would not even start going until 6k or more. It would be a great race car, but be pretty bad around town...

John
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Old 05-14-2008, 10:01 AM   #16
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That is true, I have seen some of the guys that make that big power from 6500-9500rpm, they don't even start going until around 6-6500rpm and then they spool-up and make the power way up top.

We start at 3500-4500rpm and run to about 6500rpm, a turbo that would make power way up top, a t76 turbonetics or a gt42rs or something like that would not even start going until 6k or more. It would be a great race car, but be pretty bad around town...

John
selection of HW is the key. for instance a B204L with HX40 is capable of providing full boost to 4000rpm and revs happily to 7800rpm. Physical engine besides head is bone stock including cams and yes it will hold just as long as you hav the mapping in order.
General statement, select a normal "garrett" and for sure you registry will be limited to 2000rpm but with other choices its possible to extend much much further up.
So the fact that if you want to remain decent midrege and extended top with big power is more than possible, but it wont happen with a Gt3071 nor gt3076
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Old 05-14-2008, 10:11 AM   #17
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Im about to see what happens with a 9k aero gt3582R and 7300RPM redline....
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Old 05-14-2008, 10:43 AM   #18
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im not sure if anyone has mentioned this but the reason stock engines dont rev is turbo size and cams. these are kept as sensible as possible so the car almost drives like an n/a ie no lag or spool time etc. hondas with rev silly as they are designed to from the factory saabs arnt there designed for normal driving where 99% of the time your bellow 4000rpm.
if you are going to rev silly high past 7k rpm then you will need to look at lifters, valve springs and the oil pump, not to mention rod bolts, rods, pistons, cams, headwork etc. basically your completely redesigning the engine from what it was originally intended for. the 2.0 have a very oversqaure stroke and as mentioned when the above is done then can be made to rev 8000rpm plus. also remember the engine will wear out alot faster with increased revs another thing saab wouldnt want.

Last edited by crazybrightman; 05-15-2008 at 01:58 AM.
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Old 05-14-2008, 12:19 PM   #19
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Someone correct me if I'm wrong, but isn't the bore/stroke on a 2.0 90 x 78? That seems pretty short to me.
Nick makes a good point, with a turbo car it's all about what kind of powerband you want to have.
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Old 05-14-2008, 06:40 PM   #20
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Yes you are correct about the bore and stroke for the b204 at being 90mmx78mm. However they went to a 87x87 on the b207.



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