Was curious if any of you guys are running cross drilled crankshafts in your engines.. I have read pros and cons and was curious what the high horsepower guys are doing. I have always run cross drilled cranks and standard type bearings with some oiling mods in block and haven't had any issues, but so far I have kept rpm's below 6500... Any input is appreciated along with the rpm you are turning... thanks for any replies
It's a hard call , that being the issue of keeping enough oil around the journal, and if using even just a half groove main Bearing how much of the very critical oil film support you give up/ trade off to get that groove in the Bearing , and also how much more heat gets put into that lesser width oil film! Oil control is hardly ever mentioned also and in regards to airation of the oil at high rev's it can take out even the best built bottom end ! All the oil volume and oil pressure in the world is useless with airated oil moving thru the motor, period! Oil being a liquid can not be compressed and a thin wedge / film .0025" thick can support a huge force, however oil with air in it can be compressed and then all bets are off! I have seen motors in Boats loose there bottom end at only 5000 rpm because of air in the oil. For me all but a true street stock motor that will never see more then 4500 rpm gets a Crank scraper and a windage tray, and yes to detractors of these two items in regards to them maybe not adding any HP, the help greatly in getting the oil out of the rotating mass and into the pan where air has a chance to get out of it!! In regards to Bearing width, keep in mind that up to 60 % of the heat generated by the motor gets drawn out thru the oil!
I'v never ran a cross drilled crank but I always groove the main saddles,run the bypass line,.003 clearance and turn close to 7000 rpm.don't have bearing issues either.
There is some talk in previous threads about cross-drilling the BBB crankshaft. I believe some folks feel that by cross-drilling the crankshaft that #7 rod bearing actually is starved at high RPM due to the rotational direction/ VS it's position with the original passage, pulling oil from that passage in the crank. I have not personally cross-drilled a BBB crankshaft, .... thus I can't say I experienced it. http://www.v8buick.com/index.php?threads/trying-to-keep-the-buick-alive.88751/ Larry
Actually, Buick recommended this in their "Service Recommendations for HD Application 1967 and later 400, 430, and 455 Cubic Inch Engine"
Interesting that Buick recommended. I would think it would weaken crank but then again it has some of the biggest main journals to begin with.
I can't imagine it weekin it any more than cutting .100 to .150 off the rods... I've always read that holes in things, if not crazy doesn't actual weeken. The forces go around the holes. Look at the supports on semi trailers, lots of holes to lighten the weight up.
my moldex has run crossdrilled since the 90's turns 7800 never lost # 7 # 3 usually is the problem but i would say nothig to do with cross drillng
Dave would you care to say how much oil pressure you run at 7800 rpm, and do you run a vacuum pump? thanks for the replies
Cost me my motor after 3 passes, from what I was able to find out. It is a low rpm solution if done per Buicks recommendation. It came from the diesel world and was perfect for the low rpm Buick racing motors of the past. The cross drilling works up to 7000 rpm and then from 7000-8000 it starts to reverse its effect. After 8000 rpm the oil is hemorrhaging out the other side of the main and not feeding the rods. Read this from Reher & Morrison http://rehermorrison.com/tech-talk-51-crank-calls-part-ii/ With that said my old bracket motor never went over 6800, it was CD and never had a oiling issue. So if keeping the rpm's low your fine, if building a Tomahawk block and your going to twist it, stay away from CDing your crank.
Some of the info from R/M is good,while other info,not so much,and proven wrong again & again. They also base their info off of a BBC. What is their experience with a Buick?
Ask 100 people get 100 answers? from 04 t0 09 we ran the hawk with stock blocks 2 of them . ( they both broke main webs with 200 plus passes on them ) We had no bearing/oil related failures. Blocks were full filled no water on alc. We ran our own priority oil system and halo girdle. we ran 15 -50 oil at 130psi + once fired the motor rarely saw less than 100 psi excessive maybe cost power definitely but stayed together that was with 3.25" main. motor ran 7600 + with 430 gear 7800 with 456 virtually every pass. Car regularly ran in the 7.90's back then that was enough to run top sportsman locally and qualify for ihra divisionals. The car was reliable enough that the last yr we ran it we finished 2nd for track TS championship RU at the divisional the same cross drilled crank ran in both blocks and is now in NBF for 5 years with main turned down to 3" in Tomahawk. Still running same rpms but at 75 psi. May be we have not hit the peak rpm yet???
It was a mess. I did a very extensive autopsy, paid for opinions on what caused the issue from BME, and 2 others which had no parts in this motor. All 3 came back with the same conclusion OIL STARVATION. This motor has a Dailey dry sump pump on it and the racepak still showed good oil psi right until it broke. We had put 20 pulls on this motor on the dyno up to 8000 rpm. Removed the crank and inspected everything to install the one piece rear main. Then another 18 pulls to test 3 different cams, pulling up to 8300 rpm, before this motor went in the car. The oiling issue showed up on the third pass. Broke a rod. In hind sight, I believe we would have seen the oiling issue had the motor been disassembled after the cam test and the higher rpm dyno session. This Motor goes through the traps at 8800rpm The only thing in this build that was not a proven clearance, or design was the cross drilled crank which I brought from the Buick world. The only thing changed to address the oiling issue on the 2ed build was the cross drilling being eliminated. The motor has since had over 35 passes going through at 8800 with out issue. The oil was clean when changed last week. My opinion, cross drilling as described in the Buick Bulletin: Up to 7000 rpm works great 7000 to 8000 effects are reducing but do not believe it will hurt at the finish line. Over 8000 you can save a lot of money if you do not cross drill your crank. The laws of physic's apply to all motors, Buick's do not get a pass or special rules.
Thanks again for the info Wayne.. I am glad you figured out what went wrong with your engine, and you can finally enjoy it. And in case nobody has told you, that car is absolutely beautiful... lol
