K-26 Twin Turbo Driving Impressions
01-07-2006, 10:58 PM
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K-26 Twin Turbo Driving Impressions
I hit the road today with the new K-26 twin turbo package on the 4.5 liter (ex-Callaway car). I must say, the twin K-26/6 makes for a very nice combo on the 4.5 liter engine.
The car runs and drives just like any other 928 that is not boosted, until you drop your foot. I have the 8 psig springs in the car right now, which yield about 6.5-7 psig at the manifold. In addition, I have the ability to cockpit adjust the boost at the turn of the ****. I've been running the car around on 11 psig. It looks like the boost control will allow about 14-16 psig at max deflection, though I have not tried those boost levels.
Now for the feedback. The car is simply a blast to drive. Crisp and sharp throttle response with a bunch of the good stuff (otherwise known as torque) up the middle and through the top end. Under WOT 2nd gear I got just a little light in the back end, but completely under control. I can be easily cruising in 3rd gear, drop to 2nd and open the throttle and full boost is on by 4,000 RPM or less and the car is rocketing onward. Lag on a twin turbo V8 is of about zero concern, in fact it is nice to have some delay to full onset of boost for control reasons. The response of the K26-6 is really nice, comes on hard enough to get you what you want, but not so hard as to get you into trouble. Nonetheless, a car like this is not a safe bet in the hands of a careless driver.
The nice thing I like about the turbo is that it has perfect street manners when you are out of the throttle. Just cruising back roads, you pull in say 1/4 throttle and the car simply blasts onward at speeds that would make many lift out. Just to pull in 5 psig from 3,200 up the car is exceptionally responsive. If you want to make a scene, simply pull throttle up to 3,500 and let the clutch out.
I'm not sure how much power the car is making just yet, but I don't think it is less than before. The 78/79 cams seem to allow more pull up over 5,200 RPM where the 80-82 camshafts fall off hard. The key point in this build was to make a really nice streetable package. The K-26 units I have installed do this far better then the older IHI RHB-6 units that were in the car. Spool times are down considerably and the K-26 compressors makes the IHIs look like a small toy by comparison. So faster spool with a more efficinet compressor...a good deal all the way around.
I'll see about strapping this car down next week sometime to get the results.
The car runs and drives just like any other 928 that is not boosted, until you drop your foot. I have the 8 psig springs in the car right now, which yield about 6.5-7 psig at the manifold. In addition, I have the ability to cockpit adjust the boost at the turn of the ****. I've been running the car around on 11 psig. It looks like the boost control will allow about 14-16 psig at max deflection, though I have not tried those boost levels.
Now for the feedback. The car is simply a blast to drive. Crisp and sharp throttle response with a bunch of the good stuff (otherwise known as torque) up the middle and through the top end. Under WOT 2nd gear I got just a little light in the back end, but completely under control. I can be easily cruising in 3rd gear, drop to 2nd and open the throttle and full boost is on by 4,000 RPM or less and the car is rocketing onward. Lag on a twin turbo V8 is of about zero concern, in fact it is nice to have some delay to full onset of boost for control reasons. The response of the K26-6 is really nice, comes on hard enough to get you what you want, but not so hard as to get you into trouble. Nonetheless, a car like this is not a safe bet in the hands of a careless driver.
The nice thing I like about the turbo is that it has perfect street manners when you are out of the throttle. Just cruising back roads, you pull in say 1/4 throttle and the car simply blasts onward at speeds that would make many lift out. Just to pull in 5 psig from 3,200 up the car is exceptionally responsive. If you want to make a scene, simply pull throttle up to 3,500 and let the clutch out.
I'm not sure how much power the car is making just yet, but I don't think it is less than before. The 78/79 cams seem to allow more pull up over 5,200 RPM where the 80-82 camshafts fall off hard. The key point in this build was to make a really nice streetable package. The K-26 units I have installed do this far better then the older IHI RHB-6 units that were in the car. Spool times are down considerably and the K-26 compressors makes the IHIs look like a small toy by comparison. So faster spool with a more efficinet compressor...a good deal all the way around.
I'll see about strapping this car down next week sometime to get the results.
01-07-2006, 11:11 PM
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Good work John, nice to see the project progressing.
When I bought my 79 track car, the 1st thing I noticed was how well it made power right up to redline vs my 81. Other than the cams, is this engine stock (well besides the turbo's).
When I bought my 79 track car, the 1st thing I noticed was how well it made power right up to redline vs my 81. Other than the cams, is this engine stock (well besides the turbo's).
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01-08-2006, 03:41 AM
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ditto mine will be turbo soon. herr is a very smart guy. your giving many of the older sharks hope. now the s4 guys (which iam now) can tell the older shark owners to get a turbo instead of telling them to just sell the shark and get the s4. like i did.
01-08-2006, 02:36 PM
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Cr is stock...I ccd at 8.1:1. The pistons look just like the factory units from the top side. I think this is a good CR for the older heads, specifically because of the wedge design. On the 32V I am certain it can handle more cr, maybe as high as 9:1 with substantial boost, but I'm thinking more like 8.5:1 for the new car. I always like some margin of safety in the design. As well, this setup allows for timing retard under boost, to a total timing of about 20-22 degrees at max RPM. It is crude, but works very well. Make no mistake guys, if you run boost you had better have given consideration to your ignition settings.
Lance, if I had my choice between a stock NA S4 and say and 84 twin turbo, the choice would be easy. There is no stock S4 that will hold a candle to a properly turboed 80-84 car. Of course the S4 does offer a nicer suspension and brakes, but that can all be changed easily. Myself, I can do without the racer-X wing on the S4, it looks teenager like to me. Unfortunately, the early 928s were never really respected thus they were not ever well kept. I have to say, mine is a time warp machine, possibly one of the nicest 81s in the country. I have yet to see a cleaner car of this vintage, though I have seen some just as clean.
I'll take some photos of the finished car sometime today after I give it a bath. The poor thing sat idle for like 3 months for this conversion.
Hey, can you believe I didn't say the "S" word?
Lance, if I had my choice between a stock NA S4 and say and 84 twin turbo, the choice would be easy. There is no stock S4 that will hold a candle to a properly turboed 80-84 car. Of course the S4 does offer a nicer suspension and brakes, but that can all be changed easily. Myself, I can do without the racer-X wing on the S4, it looks teenager like to me. Unfortunately, the early 928s were never really respected thus they were not ever well kept. I have to say, mine is a time warp machine, possibly one of the nicest 81s in the country. I have yet to see a cleaner car of this vintage, though I have seen some just as clean.
I'll take some photos of the finished car sometime today after I give it a bath. The poor thing sat idle for like 3 months for this conversion.
Hey, can you believe I didn't say the "S" word?
01-08-2006, 03:22 PM
#11
It is sunday... Great time to take some pics!!!
Very cool. Props to you.
Use the day of rest to document it a bit for us!!!
Are the turbos mounted low and in front of the timing covers .
How do they cool down there? Running separate oil system?
Do you see any mounting problems on later cars. I am putting a new electric fans in mine to free up some space. Wonder if I will be freeing up enough space.
Running any intercooler?
LO
Use the day of rest to document it a bit for us!!!
Are the turbos mounted low and in front of the timing covers .
How do they cool down there? Running separate oil system?
Do you see any mounting problems on later cars. I am putting a new electric fans in mine to free up some space. Wonder if I will be freeing up enough space.
Running any intercooler?
LO
Last edited by lorenolson888; 01-08-2006 at 05:20 PM.
01-08-2006, 07:09 PM
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Originally Posted by Herr-Kuhn
Cr is stock...I ccd at 8.1:1. The pistons look just like the factory units from the top side. I think this is a good CR for the older heads, specifically because of the wedge design. On the 32V I am certain it can handle more cr, maybe as high as 9:1 with substantial boost, but I'm thinking more like 8.5:1 for the new car. I always like some margin of safety in the design. As well, this setup allows for timing retard under boost, to a total timing of about 20-22 degrees at max RPM. It is crude, but works very well. Make no mistake guys, if you run boost you had better have given consideration to your ignition settings.
Lance, if I had my choice between a stock NA S4 and say and 84 twin turbo, the choice would be easy. There is no stock S4 that will hold a candle to a properly turboed 80-84 car. Of course the S4 does offer a nicer suspension and brakes, but that can all be changed easily. Myself, I can do without the racer-X wing on the S4, it looks teenager like to me. Unfortunately, the early 928s were never really respected thus they were not ever well kept. I have to say, mine is a time warp machine, possibly one of the nicest 81s in the country. I have yet to see a cleaner car of this vintage, though I have seen some just as clean.
I'll take some photos of the finished car sometime today after I give it a bath. The poor thing sat idle for like 3 months for this conversion.
Hey, can you believe I didn't say the "S" word?
Lance, if I had my choice between a stock NA S4 and say and 84 twin turbo, the choice would be easy. There is no stock S4 that will hold a candle to a properly turboed 80-84 car. Of course the S4 does offer a nicer suspension and brakes, but that can all be changed easily. Myself, I can do without the racer-X wing on the S4, it looks teenager like to me. Unfortunately, the early 928s were never really respected thus they were not ever well kept. I have to say, mine is a time warp machine, possibly one of the nicest 81s in the country. I have yet to see a cleaner car of this vintage, though I have seen some just as clean.
I'll take some photos of the finished car sometime today after I give it a bath. The poor thing sat idle for like 3 months for this conversion.
Hey, can you believe I didn't say the "S" word?
Nice work!
Can you post some pics?They way you described how this TT adds power is extremly simmilar to my setup. Regardless of the fact that I'm running a Paxton SC the description was very close.
