wardy18 33 1 Cars Posted April 23, 2008 What the lowest possible crank that will fit in a XU9 block?! To turn a XU9 block with 83mm pistons into a 1.8 you would need a 83mm crank, or with 83.5mm pistons you would need a 82mm crank, or can you do it using shorter forged rods?! Share this post Link to post Share on other sites
Anthony 1,003 Posted April 23, 2008 XUD11 crank is 92mm XU9/XUD7/XUD9 crank is 88mm XU10 crank is 86mm XU7 crank is 81.4mm XU5 crank is 77mm Shortening the rods will only serve to reduce compression and won't affect capacity. Only changing the bore or changing the stroke (or changing the number of cylinders) will change capacity. Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted April 23, 2008 excellent thanx Share this post Link to post Share on other sites
Batfink 201 Posted April 23, 2008 watch out as by reducing the capacity you will lower the compression! Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted April 23, 2008 well thats my next issue, because i will be running the same head which already has a big head skim of 60 thou takin the CR to 10.9, when fitted forged pistons they usually have a smaller dish so to increase the CR as this is the proper way to do it, would this mean ill be runnin way to high CR i know the engine can take higher CR's than 10.9 but i was told 60 thou was the maximum for a head skim for reliability so what else do i need to do so to get that higher CR with the lesser dished pistons to maintain reliability?! i dont what you need to do for teh engine to reliabily take high CR's?! Share this post Link to post Share on other sites
Batfink 201 Posted April 23, 2008 well when I worked out my engine spec to get down to a 1.6, I found with standard pistons it dropped the compression from 10.6:1 to 8.6:1 Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted April 23, 2008 how do you work out what the CR Ratio will drop to?! Share this post Link to post Share on other sites
Batfink 201 Posted April 23, 2008 compression = (swept volume + unswept) /unswept swept volume = bore x stroke unswept = combustion chamber vol + headgasket + piston dish Bore = liner diameter x liner diameter x 3.14159/4 example... bore = 8.3 (83mm) x 8.3 x3.14159/4 = 54.106 sq cm that should get you going Share this post Link to post Share on other sites
James_R 3 Posted April 23, 2008 Just use an Xu7 bottom end complete, need to double check head volumes, but I think 8v chambers are the same as the 16v head sizes (34cc's) and that's 10.4:1 so with the 60thou skim (1.5mm) you'll end up slighty higher, then again, the drop in capacity will balance it, based on 1905cc engine with 10.9 gives an unswept of 48.6cc (working backwards is swept/CR-1 = unswept which on the 1760cc of an XU7 gives; 10:1 workign forward again unswept+swept/unswept = CR) to keep to the 10.9 you have now you'd want to loose 3.7cc's unswept volume. 83.5mm pistons XU7 crank gives you 1780cc's 84mm pistons Xu7 crank gives you 1802cc's But then you could just say the bore is whatever you want, not something you can easily measure without stripping down the engine, and you'd have to win the class by miles to have to do that. got to wonder how many 88mm bore 2L engine's there are out there etc... Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted April 23, 2008 so because of the drop in CC would i be safe in running a flatter toped forged pistons with a head skim of 60thou an have no reliability issues?! The only issue i have with using the XU7 block as a whole is gettin one over here, im on Guernsey and so carriage for that would be well over £100 for a courier which is why i thought about stripping my XU9 alloy block (saving me weight being alloy) and getting a Lightened/Balanced XU7 crank sent over with a set of Forged Pistons/Rods/Liners and get it built over here!! What you think?! Share this post Link to post Share on other sites
Anthony 1,003 Posted April 23, 2008 which is why i thought about stripping my XU9 alloy block (saving me weight being alloy) Remember XU7's are alloy as well - it's only XU10's and XUD's that are iron block. Share this post Link to post Share on other sites
Sandy 191 Posted April 23, 2008 Stripping an XU7J4 and re-blocking it into the XU9 block would be cheap and up to at least 8000rpm, reliable from what I've seen using standard parts. You can create intruder pistons by machining XU9J4 (Mi16) ones to the desired size, I've seen that done before to great effect. Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted April 23, 2008 Stripping an XU7J4 and re-blocking it into the XU9 block would be cheap and up to at least 8000rpm, reliable from what I've seen using standard parts. You can create intruder pistons by machining XU9J4 (Mi16) ones to the desired size, I've seen that done before to great effect. So with forged rods and balanced crank would it be able to go higher than 8k?! ive got Double Valve Springs to compliment the Rally Catcam?! Whats "Intruder" mean ?! Sounds great Share this post Link to post Share on other sites
Sandy 191 Posted April 24, 2008 You shouldn't need to rev it much beyond 8k if it's working overall. Intruder is the opposite to a dish, a section of the piston crown that "intrudes" the combustion chamber at TDC. Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted April 24, 2008 You shouldn't need to rev it much beyond 8k if it's working overall. Intruder is the opposite to a dish, a section of the piston crown that "intrudes" the combustion chamber at TDC. 8k sounds good to me, im limiting mine at the moment to 7k and its got so much more left in the power band with the Catcam Ah ok, they sound perfect for gettin a high CR then, i would like to try and get hold of a XU10 head, cant afford a BV head just yet so this is the next best thing for me, i can then leave it to the intruder pistons to increase the CR and not a heavy head skim which my currect head has as this isnt the best way to do it. Will go for 3 angled valve seats and if i can afford it a light port and polish!! Do you know any XU10 heads going at the moment?! Share this post Link to post Share on other sites
wardy18 33 1 Cars Posted May 2, 2008 does anyone know what sixe mm the XUD9TE crank is?! Share this post Link to post Share on other sites
