Saab 99 Bosch K-jetronic rally engine.
- Detta ämne har 27 svar, 9 deltagare, och uppdaterades senast 2010-10-15 06:31 av
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I have just finished building and tuning the H series 8V engine in my ’83 99GL which is not a turbo, during development i came across power restrictions with the K-jet, i am curious to know if you guys in Sweden have come accross the same thing? From the information i have it appears that the Saab 99 rally cars back in ’76/77 using K-jet were limited to around 135bhp, would this be an accurate description?
I will post up details of my throttle bodied 99 later when i have more time, as it will be quite a long post.So maybe there is not much information about the works rally cars that used K-jet? Although i have since been informed about Per Eklunds 1978 Swedish Rally car (HGF641) that is reported to have 155bhp, although i do not have any details about the engine or if the K-jet was standard or modified or even from another car? Maybe Peter from the museum will have more information?
When i finally finished building my ‘fast road’ engine i took it to the dyno i always use which is quite accurate and consistant. The specification of the engine is as follows;
1. H series gas flowed head with 44mm inlet valves and standard injection exhaust valves.
2. Camshaft from Catcams, special profile 284*@0.1mm lift and 256*@1.0mm lift, the total lift is 12.2mm and the Lobe centre line angle is 109* (fairly mild cam) with adjustable sprocket.
3. K-jet from a 99 turbo and adjustable warm up regulator.
4. MSS 4-2-1 exhaust manifold attached to a 2” Jetex system.
5. Standard ignition.The cylinderhead and advice was from my good friend Dave Baker at Puma Race Engines http://www.pumaracing.co.uk
We carried out a few power runs on the dyno to get things fully warm. The engine starts to pick up from 2000rpm and climbs well to 5000rpm it then stops climbing and the line stays flat all the way to over 6500rpm, this peak is at 140bhp. At first we thought it could be a restriction with the exhaust, because this is what happens with an exhaust restriction, but this type of system has been used on other cars with higher power and no such symptoms. So next we fitted a calibrated vacuum gauge to a nipple on the inlet manifold to see what was happening at wide open throttle, the result was quite surprising, the manifold contained a vacuum of between -0.2bar and -0.3bar, i gave this information to Dave Baker and he explains what is happening very well;
In an ideal world a perfect induction system would have almost zero manifold depression at WOT. Any restriction there means a reduction in the amount of airflow into the engine. When American carb manufacturers started flow testing their carbs to give a CFM (cubic feet per minute) rating they settled on a flow bench test pressure of 1.5″ of mercury. The reason was that it had been found that if manifold depression exceeded that amount power started to suffer. In other words their flow figures were saying you can use this carb to supply that number of CFM of airflow and it won’t cause a manifold depression greater than 1.5″ of mercury.
Atmospheric pressure (14.7 psi) is about 30″ of mercury so 1″ of mercury is about 0.5 psi. 1.5″ of mercury is therefore about 0.75 psi and that’s as much as we ideally want to see at WOT. 0.2 to 0.3 bar is a huge manifold depression. 1 bar is 14.5 psi so we’re looking at 2.9 to 4.35 psi. That’s reducing the net atmospheric pressure feeding the engine from 14.7 psi down to 11.8 to 10.35 psi.
We can calculate the effect of this on power. Flow, and therefore power, is proportional to the square root of pressure drop. If we take 14 psi as being representative of a good non restrictive manifold i.e. about 0.75 psi below atmospheric, then we’re looking at a pressure ratio of between 11.8/14 to 10.35/14 = 0.84 to 0.74.
Taking the square root of those we’re looking at a flow and power ratio of 0.92 to 0.86.
In other words we’re losing between 8% and 14% of the potential engine power. That means the 140 bhp should really be somewhere between 152 and 163 bhp. The average of those is pretty much exactly what I originally calculated the engine should produce with a good induction and exhaust system.
So as you can see, either the throttle is causing the restriction or the K-jet, it probably is the K-jet, if we look at the history and evolution of the Saab 99 normally aspirated rally car we can see that the competition department stopped using K-jet and moved over to twin carbs, i think i have just explained why. Although i have finished using the Bosch K-jet system and moved across to throttle bodies and ECU, more about this later, i am still interested to hear about other experiences with tuned Saab engines using K-jet.
Hallo
Nice reading.
I have a paper on a rally engine 155 bhp. But they used Weber 45 and modified orginal exhaust manifold. I write down the exact number later.
Actually I dont know any big hp NA 8 valve 2 litre engines.
Ihav seen 190 bhp on a totally rebuild rally engine, Dellorto 48, Je piston, Verdi conrods.
I know that WV Rabbit (golf) Gti used Ford Granada 2,8(2,9) K-jetronic parts.Niklas
OK, i have my own thoughts on the limitations of the standard K-jet system….over the years i have heard many power figures given for tuned 8 valve Saab engines with K-jet, ranging from 150bhp to 180bhp, of course there is always the possibility that these figures have come about because of inaccurate rolling roads, but if these figures are to be true, then why did the Saab competition department change from a perfectly reliable quite modern fuel injection system to twin carbs that are giving out the same power?
Niklas, yes it is possible to reach this figure with carbs, but not on standard valve sizes. Lots of cars used K-jet parts, VW, Mercedes, Porsche and maybe improvements could be made by using some of these other systems, as we know Saab made a change with the 99 turbo rally car with a system from a another model.
After i removed the K-jet parts i fitted this system with an ECU and achieved some very good results…
I will post more specific details later.Hallo
Now I have read my pappers.
The Vw that used Granada parts have 157 bhp in the engine at 6500 rpm. 142,5 on the wheels.The saab rally power.
rpm dhk hk
4000 92 106
4500 105 121
5000 122 140
5500 131 151
6000 135 155I dont know so much about the engine. Modified orginal exhaust. Weber 45. modified st rods.
10 at 1000 rpm
33 at 4000 rpm.Niklas
Niklas, thank you for posting the figures. But from my experience the wheels and engine figures do not quite look correct, are these figures from an official paper or from a dyno/rolling road.
I will explain why i think this, because on a rolling road we measure the power at the wheels, so if the dyno is set up properly it should read a good figure or there about, but for the engine figure the dyno will use software and coastdown losses etc to ‘estimate’ the engine or flywheel figure. On a front wheel drive car the formula that is used to get to a ‘ball park’ figure for the flywheel power is to add 10 to the wheels figure and divide by 0.9. So if we use the 142.5 + 10/0.9 = 169.4bhp, so this is quite a lot more than the stated figure. A good article too read is here http://www.pumaracing.co.uk/coastdwn.htm
But after saying this i personally think the power losses through the Saab gearbox are higher than on other cars with a more conventional gearbox.Please excuse my ignorance, i think hk = horsepower, so what is dhk ?
David, I would guess that DHK is short for DrivhjulsHästKrafter, i.e. horsepowers measured at the wheels.
Martin wrote:David, I would guess that DHK is short for DrivhjulsHästKrafter, i.e. horsepowers measured at the wheels.Ah Yes of course, i knew hjul is wheel, but i never thought about adding drive, thank you!
I know what I have done to my 99GL would never be allowed in historic rallying or racing, but it has been very enjoyable and worthwhile, my reason for this project was to get my humble 99’s power higher than that of a standard 99 turbo and to make it very user friendly and of course no turbo lag .
My first thoughts went to how and where to mount the crank sensor and 36-1 toothed wheel, I decided to have a custom crank pulley made so it would easily take the toothed wheel, I then just needed to make a simple bracket to mount the sensor. I needed to do this with the engine out of the car, because it is not possible to remove the pulley on the H series engine when it is in the car.
http://i147.photobucket.com/albums/r310/sonett_01/rearof90pulley.jpg
http://i147.photobucket.com/albums/r310/sonett_01/rearof90pulleyandtoothedwheel.jpg
The ECU I used is a DTA S40, this comes with several maps from many engines so it is quite easy to choose something similar to your specification, I used a map for a 150bhp Ford Zetec, the other very useful feature with this ECU is the built in oscilloscope, this enables you to see exactly where the ‘spike’ is for the crank signal and to enter the degrees into the spark map. The car started and ran well, not perfect but enough to be able to drive it to the rolling road to have it mapped. It looks very strange to see a Ford coilpack where the distributor should be.
http://i147.photobucket.com/albums/r310/sonett_01/DSC_0002.jpg
http://i147.photobucket.com/albums/r310/sonett_01/99onrollers.jpg
The result after a full day tweaking the map was to have a powerful ‘old timer’ that can be used very easily on the road and in traffic. The peak power is 167 bhp at 6400rpm and a torque of 141 lb/ft at 4800rpm, we could have taken the power above 170bhp but this is a fast road car and because I will be using ordinary unleaded fuel, it was mapped to a safe limit. An interesting note for those using carbs with trumpets, initially I had 40mm long trumpets fitted to the 45mm Jenvey throttle bodies, then fitted 90mm long trumpets and the torque came in 500rpm earlier which is very good, this sacrificed a few bhp at the top but it is worth it.
I have purposely limited the maximum rpm’s to 6500 because I am using standard valve train parts, except for the 44mm inlet valves, but on the dyno the power is still rising. The noise from inlet is beautiful and very addictive!
I just have one part that I need to experiment with, the 4-2-1 exhaust manifold, this is from MSS in the USA and at the time it was the only ‘off the shelf’ performance manifold I could find, the diameter of the primary and secondary pipes is the same and this is unusual, the primary pipes are usually smaller than the secondary pipes in order to keep the gas speed high, I will alter the primary pipes and watch the result on the dyno.
Krister, thank you for the link. I think one of those manifolds would be good for my EMS.
David,
Sounds like you have got yourself a very fun car. -Nice looking too. I would love to hear a high revving H-series with that kind of open induction system, I bet it really roars.
If you ever get around to filming it, on the road or dyno, maybe you could post the film on Youtube for us others to enjoy.
Thanks and have fun!
/EmilEmil Å wrote:David,
Sounds like you have got yourself a very fun car. -Nice looking too. I would love to hear a high revving H-series with that kind of open induction system, I bet it really roars.
If you ever get around to filming it, on the road or dyno, maybe you could post the film on Youtube for us others to enjoy.
Thanks and have fun!
/EmilThat sounds like a good idea, i will see what i can come up with.
Kanske en anden tråd med historic rallying ? … findes en så da ?
The MSS manifold fitted to the car during all of this tuning has been an unknown quantity to some degree, after talking with Dave Baker (Puma Race Engines) i decided to carry out some alterations, primary and secondary pipes were both 44mm od, it was easier to alter the primary pipes, so these have been reduced to 39mm od.
The first run on the rollers had the 40mm inlet trumpets fitted, peak power was down by a few bhp, no big deal, but then we overlaid the graph from a previous run with the old exhaust manifold and same size trumpets, low down torque up to around 3500rpm had jumped up, at 2500rpm it has increased by around 7lb/ft.
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