calemoses Posted September 10, 2013 Report Share Posted September 10, 2013 ive brought a 7k for my ke10, planning on supercharging it was thinking to get custom made rod shafts for the pistons to lower the compression for the supercharger and also giving me a stronger rod shaft, most of all giving me a bit more rev range, does anyone see any problems this might cause?? Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted September 10, 2013 Report Share Posted September 10, 2013 Not that I can think of- how much shorter are we talking?? 2mm? The top of the cylinder becomes part of the combustion chamber and the piston is down further out of the block at bottom dead center. Certainly lets you run a high-lift cam! The stroke and the piston speed remain the same, I can't see it changing the rev range. Nearly everyone who talks about changing rod length is going to change the stroke Quote Link to comment Share on other sites More sharing options...
ke70dave Posted September 10, 2013 Report Share Posted September 10, 2013 What is the compression ratio of the 7k standard? Nothing better than high compression turbo..... Quote Link to comment Share on other sites More sharing options...
calemoses Posted September 10, 2013 Author Report Share Posted September 10, 2013 ohk so whats the best way to go about making a shorter stroke? and can it be done on the cheap? otherwise i'd just get the head machined I am pretty keen to get more revs out of it Quote Link to comment Share on other sites More sharing options...
Twincam16seca Posted September 10, 2013 Report Share Posted September 10, 2013 More RPM would come from a bigger cam, not too sure on this but wouldn't a 5K or 4K have a shorter stroke, or is it bore size opposed to stroke length with K series? I also would have thought shortening the stroke would effectively reduce the capacity of the engine making it more like a very low compression 5K. The point of having a 7K would be for the higher capacity and EFI, so a turbo may be easier but not cheaper and but a supercharger will be instant, eitherway would require ecu tuning for max benefti. For lower compression I would get a thicker head gasket maybe, or dished pistons would help a lot i would think. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted September 10, 2013 Report Share Posted September 10, 2013 (edited) The capacity should remain the same I thought- A short rod will pull the piston down further and push it up less, so you effectively move the same stroke down the bore. I think the 7K block is heavier than the smaller K's, maybe that is an advantage in boosting. Dished pistons would drop the compression for sure, so the D-dish 5K pistons should fit and drop the compression, cheaper than custom rods. The stroke will be 87.5 compared to a 5Ks 73, so its a lot more and there's not much you can do to make it rev. Its all about long-stroke torque in there. A shorter stroke comes from a different crank swing, so if you regrind the crank off-center you alter the stroke. I don't know if a 5K crank would fit in the block, but that would obviously shorten the stroke to 73mm and give you the 5K's 1500cc. I haven't heard of other cranks that would fit the K block, nobody bothers to hot up that motor... Edited September 10, 2013 by altezzaclub Quote Link to comment Share on other sites More sharing options...
kickn5k Posted September 10, 2013 Report Share Posted September 10, 2013 If you're wanting to put a positive displacement supercharger on, I'd definitely leave the stroke where it is. When you see the torque curve of a blown K motor you'll understand. I had a big blower cam in my old 5k, it would never pull power past 5,500rpm but geez it had some torque. Dyno sheet is in pdf somewhere in here. http://www.rollaclub.com/board/topic/9733-my-white-ke-11/page__st__45 Quote Link to comment Share on other sites More sharing options...
calemoses Posted September 10, 2013 Author Report Share Posted September 10, 2013 thanks people, yea ill be leaving the bottom end alone then just machined head, has anyone had a blown 7k? any info would be good what kind of power ect. Quote Link to comment Share on other sites More sharing options...
altezzaclub Posted September 11, 2013 Report Share Posted September 11, 2013 Stuart, on the dyno run, what gave the nasty dip in the original torque curve around 4500?? Yu lost about 75nm from 3500 to 4500.. Did you find out? It looks like ti was dying from leaning out and then the cam suddenly cut in... Boosting it certainly sorted that out. Quote Link to comment Share on other sites More sharing options...
japlish Posted September 11, 2013 Report Share Posted September 11, 2013 doesnt 7k's and 7afe use the same rod's? if so get some SPOOL rods. Quote Link to comment Share on other sites More sharing options...
kickn5k Posted September 11, 2013 Report Share Posted September 11, 2013 Stuart, on the dyno run, what gave the nasty dip in the original torque curve around 4500?? Yu lost about 75nm from 3500 to 4500.. Did you find out? It looks like ti was dying from leaning out and then the cam suddenly cut in... Boosting it certainly sorted that out. Are you talking about the blue lines Keith? That was my first run/tune. It had std 7k injectors and fuel pressure reg. You're bang on the money had a massive lean spot, it was lean everywhere but that point was the worst of it. I had all corresponding tune pots maxed and had the max timing set to 18deg btdc. The red lines were my second dig at it with a rising rate reg and a set of bigport 4age injectors fitted. Timing was lifted to 28deg btdc and had plenty of fuel! Both runs on 9psi. In hindsight I should have kept that setup and fitted a proper ecu with ignition control. Geez it was fun! It made 5th pull like 3rd in my old twin su 5k! Quote Link to comment Share on other sites More sharing options...
kickn5k Posted September 11, 2013 Report Share Posted September 11, 2013 doesnt 7k's and 7afe use the same rod's? if so get some SPOOL rods. Yep. 7k conrods look fairly fragile compared to 5k ones. Not sure if they are weaker or just look skinnier, I've never owned a 7k. Quote Link to comment Share on other sites More sharing options...
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