Blueprinting is the most widly mis-interpreted engine term thrown around the internet and in most cases get’s people in trouble.
Blueprinting a motor is a VERY exacting science, way moreso than what 99% of most engine builders follow. Every single piece is measured to EXACTLY what the orignial design calls for. Every part weighed in and balanced to the 10th of a gram. Time wise, it’ll bump the assembly of the typical motor from a couple days to well into a week, sometimes two. Most people don’t know the fact that you cannot BP a motor from even the factory manuals as they give a range. There is NO range in a BP motor, simply stated terms. 1st ring end gap = .007", connecting rod big end bearing clearance = .0013", etc. None of this ring end gap .007-.0015" stuff. You have to contact the factory to get the BP build plans to truely build a BP motor. Triples the labor cost on average.
If you’re building a motor for high performance use, or race bred use, you DO NOT want a blueprinted motor under your hood. Unless you plan to tear the motor down and rebuild it every ~20hrs or so. BP motors wear out faster, and generate upwards of 25% more friction and heat than a proper “loose” race motor. I’ve built many BP Porsche motors, but these were ~$20K dollar builds for either rare restorations or Cup Cars that were going to be torn down in a couple months time anyway for an overhaul(new bearings, rings, valve adj, etc.)
Typically when I’m building a motor that’s going to see a life of hard use, bearing clearances open up ~.00015", ring end gaps are towards the high end of the RING MANUFACTURERS tolerance(not the OEM ring specs), PTW clearances to the high end. Example…JClarks S52 has a factor PTW(piston to wall) clearance of .001"…nice for street stuff…wicked tight for a race motor. I open these up to .0025" and push the ring end gaps to the high side of the spectrum.
One other thing thrown around in bad nature is leakdown numbers…everyone expects low single digit numbers but again in a race motor really really low number = BP motor and it’s going to wear out quick or not make as much power as it could. Typical OEM street motor will run in the 15-20% LD range with some hard mileage on them. ~10-15% on a race motor is good. Jesse’s stock S50 with over 140K of HARD use still had #'s around 7-10%(again wicked tight .001 PTW and ring gaps)
I gotta say a lot of this info seems exaggerated and inaccurate. I really don’t want this thread to wander too far off topic though. An engine typically gets “tired” from worn out and poorly sealing piston rings and cyl walls that are scratched and out of round from heat cycling. That and the valves and seats get burnt and beat up over time and use
Please, go ahead and move this to a separate thread and point out my exaggerated and inaccurate info. I’d like to see it ;D My info is based on the hundreds of motors I’ve put together in my life, most of them high strung Porsche, BMW, Ferrari, Audi, various marine and aircraft motors, etc, etc and the R&D I do here at my shop and for Dave Hunts…
I don’t need to make a new topic, I disagree with some of your points. I don’t see us getting anywhere arguing about it in a seperate thread. The motor is tired and I was just trying to make a simple explanation as to what that means. ;D
I read import magazines where they build a race motor and the clearances are on the tight side especially rod and main journals. The author of one stated that tighter would be better because you would get more oil pressure… I sat there thinking to myself that if its too tight then you will have less oil film, less oil flow thru the bearing surface, and more heat/friction. It would negate the one advantage of having a very tight motor and more oil pressure. Does this sound accurate?
This perticular article I believe was on a 4G63 in Turbo Mag maybe 5 years ago
If I were building my motor for street and some track use. Not so much road race use, but I would like to do a few laps once in a while as well as hit the strip. Would I want it more to the lose side or tight? or would I want to try and stay in the middle?
just curious on your thoughts…
Paul(I think???) I really wasn’t trying to start an argument with you at all. I just wanted to see where you thought my information was exaggerated or inaccurate that’s all. :sad I understand you’re a smart guy when it comes to building motors and do know your shit. I’m in the business of building high strung race motors for many venues, wether simple endurance PCA mills to full bore offshore catamaran or aerobatic avaiation motors that run fullbore throughout the race, and have done my own personal research and R&D into this topic many times. I really only post what I know is dead fact from my own work and if you disagree with it that’s perfectly fine. I don’t want any bad blood here between us on some silly topic…
I requested a split because I didn’t want to put Jesse’s Evo fab thread OT with other talk that’s all. Not fair to him…
In reality, it all depends on the motor at hand and what the factory clearances really are. Subarus are notorius for running rod BE/main OEM bearing clearances quite tight and are good to be opened up a few tens during a build, due to the oiling path of those motors… Component choice must be taken into account as well. We have a '38 ChrisCraft marine here that was built last year by some shop with JE’s running too tight of a PTW clearance and under extended runs the motor would lock up as the pistons would expand farther than the bore would allow all because the factory bore clearances were used in the newly sleeved block with the JE pistons(Can’t get OEM slugs for this motor anymore). Got towed back to shore and by the time they got the there motor would turn over and fire up again, head back out and the same thing happens. Rule of thumb is if you’re unsure, it’s always better to run slightly loose than too tight, but avoid running so loose that you lose power and/or life of the motor(especially in a street motor).
And you previous post on oil film and too tight of bearing clearances is correct. If tha article was based on 4G63 construction whoever wrote it was smoking crack or seriously misinformed. 4G63’s have zero oiling problems and only benfit from a loose setup crank(rod clearance is actually good in those motors) I’ve built well over 40 4G63’s in the past and all were on the slight loose side. Some engines have faulty crank design as well where the oil holes actually scrap oil film away from the trailing edge at high rpm and starve the center of the bearing surface. Too tight and at extended elevated RPM the bearings can stave in the center, gall, and eventually shear the tabs and spin thus covering the oil fieed holes and completely starving the journal. High strung cranks benefit from a large trailing edge fillet machined and polished into the oil feed holes on every journal. OEM engines do come this feature however some are not up to par. It’s only takes a few extra thousands to make all the difference in most motors and has no ill effect on the crank itself if properly machined and polished to negate a stress riser. Not usually necessary on a street motor, even if double or triple the OEM power. Mostly suited for very high rpm race motors.
