I remember on Swede saying that the piston skirts were real short, so short that at least one of the rings bisected the hole for the wrist pin.

I think the longer rods result in a smoother transition between the crank and rod when rotating (I forget the term for this but the angle between the crank and rod doesn't change as fast) which results in smoother revving, less friction, better reliability, more power, etc.

Also found this:
Short Rod is slower at BDC range and faster at TDC range.

Long Rod is faster at BDC range and slower at TDC range.

I. LONG ROD

A. Intake Stroke -- will draw harder on cyl head from 90-o ATDC to BDC.

B. Compression Stroke -- Piston travels from BDC to 90-o BTDC faster than short rod. Goes slower from 90-o BTDC to TDC--may change ign timing requirement versus short rod as piston spends more time at top. However; if flame travel were too fast, detonation could occur. Is it possible the long rod could have more cyl pressure at ie. 30-o ATDC but less crankpin force at 70-o ATDC. Does a long rod produce more efficient combustion at high RPM--measure CO, CO2? Find out!!

C. Power Stroke -- Piston is further down in bore for any given rod/crank pin angle and thus, at any crank angle from 20 to 75 ATDC less force is exerted on the crank pin than a shorter rod. However, the piston will be higher in the bore for any given crank angle from 90-o BTDC to 90-o ATDC and thus cylinder pressure could be higher. Long rod will spend less time from 90-o ATDC to BDC--allows less time for exhaust to escape on power stroke and will force more exhaust out from BDC to 90-o BTDC. Could have more pumping loss! Could be if exhaust port is poor, a long rod will help peak power.

D. Exhaust Stroke -- see above.

II. Short Rod

A. Intake Stroke -- Short rod spends less time near TDC and will suck harder on the cyl head from 10-o ATDC to 90-o ATDC the early part of the stroke, but will not suck as hard from 90-o to BDC as a long rod. Will require a better cyl head than long rod to produce same peak HP. Short rod may work better for a IR or Tuned runner system that would probably have more inertia cyl filling than a short runner system as piston passes BDC. Will require stronger wrist pins, piston pin bosses, and connecting rods than a long rod.

B. Compression Stroke -- Piston moves slower from BDC to 90-o BTDC; faster from 90-o BTDC to TDC than long rod. Thus, with same ign timing short rod will create less cyl compression for any given crank angle from 90-o BTDC to 90-o ATDC except at TDC. As piston comes down, it will have moved further; thus, from a "time" standpoint, the short rod may be less prone to detonation and may permit higher comp ratios. Short rod spends more time at the bottom which may reduce intake charge being pumped back out intake tract as valve closes--ie. may permit longer intake lobe and/or later intake closing than a long rod.

C. Power Stroke -- Short rod exerts more force to the crank pin at any crank angle that counts ie.--20-o ATDC to 70-o ATDC. Also side loads cyl walls more than long rod. Will probably be more critical of piston design and cyl wall rigidity.

D. Exhaust Stroke -- Stroke starts anywhere from 80-o to 110-o BBDC in race engines due to exhaust valve opening. Permits earlier exhaust opening due to cyl pressure/force being delivered to crank pin sooner with short rod. Requires a better exhaust port as it will not pump like a long rod. Short rod has less pumping loss ABDC up to 90-o BTDC and has more pumping loss from 90-o BTDC as it approaches TDC, and may cause more reversion.

III. NOTES

A. Rod Length Changes -- Appears a length change of 2-1/2% is necessary to perceive a change was made. For R & D purposes it appears a 5% change should be made. Perhaps any change should be 2 to 3%--ie. Ignition timing, header tube area, pipe length, cam shaft valve event area, cyl head flow change, etc.

B. Short Rod in Power Stroke -- Piston is higher in the bore when Rod-Crank angle is at 90-o even though at any given crank angle the piston is further down. Thus, at any given "time" on the power stroke between a rod to crank pin angle of 10o and ie. 90-o, the short rod will generate a greater force on the crank pin which will be in the 70-o to 75-o ATDC range for most engines we are concerned with.

stolen from here: http://www.offshoreonly.com/forums/general-q/120860-crank-rod-ratio.html

Went down to chris's shop today to replace the upper strut mount in my ng 900 today. Witht that done I tore into the 2.1 liter. I pulled the head off and cleaned up the block deck and found no signs of metal corrosion. I removed the harmonic balancer and the seal came out with it. Soooo I decided to just pull the engine completely apart and reseal it 100 % when it goes back together.

So making progress. Currently have: 16v headers, lightened flywheel, limited slip diff.


Next question concerns the intake on the later headsl I don't think the 2.1 intake will just bolt up to the later head. I have some ideas but any suggestions?

I dont have alot of experience with the newer stuff, but I recall seeing a manifold on a later SAAB that had rubber hoses connecting the flange to the plenum? Could you just cut the flange off the 2.1 intake and weld on the later flange?

I think the best option is to weld up and re-drill the mounting holes as well as re-shape the head ports. Everything is offset IIRC.

Welding and re-drilling was what I did, it wasn't too bad really, this gets you close, then a little port matching smoothes it all out. I could do the welding/redrilling for you when the time comes.

I have the 2.1 intake, which intake did you use for the Head side?

I used a 2.1 as well.

Luke wrote:I used a 2.1 as well.

did you graft the 2.1 to a 9-3/9-5 intake or did you just modify the 2.1?



Pulled the car out of its snowy tomb on Sunday, cleared all the snow away and took it for a short drive. The car had no power and sounded like it was running on 3 cylinders. When I got back I found that the #1 cylinder was dead. So I shut the car off and continued my snow shoveling. When I went to park the car again it fired right up and the engine was back to running on all 4. I suspect that either the plug was loaded up or the CIS line was frozen and thawed out. Either way I went out for another drive and had fun tossing the car around as it is so much better handling and much more predictable then my NG900. Even with the very worn Gislaved snow tires on it I still had amazingly good traction.

When mine was running on 3 I found a crack in the plastic fuel line was introducing air into the line. Replaced the line and it went away.

SwedeSport wrote:When mine was running on 3 I found a crack in the plastic fuel line was introducing air into the line. Replaced the line and it went away.

If it happens again the next time I run it I'll look the lines over. I think this might have happened because the car was sitting for a while.

8v cars don't seem to like sitting around.

SwedeSport wrote:I dont have alot of experience with the newer stuff, but I recall seeing a manifold on a later SAAB that had rubber hoses connecting the flange to the plenum? Could you just cut the flange off the 2.1 intake and weld on the later flange?

I think 1994 was the last year you could buy an NA Saab (at least, in the U.S.) and it was the first year of the so-called T5 head. The 1994 9000 NA intake had a two-piece flange/plenum design, as described above. So if you don't want to weld, and can find a '94 NA intake, then the flange > hoses > c900 plenum route might be possible??

I'm pretty sure you could buy an N/A SAAB up until the 9-3 series? I know there were N/A 900s up until at least '97.

You're right. I meant to write that 1994 was the last year for naturally aspirated 9000s in the U.S. (excluding the piece of $h!t V6s they sold toward the end of the run).

ok, time to get crack'n on this 2.5 deal again. get some parts and meet me at the shop.