gretchen/jason Posted January 17, 2007 Share Posted January 17, 2007 I just purchased crate SBC 350 from jegs a Gm performance product . Well 6,000 miles latter i have 8% blow by on every piston and a whoping 12% on number 3 piston . What are the limits i should expect on a crate engine ? 5% or less or a bit more . I broke the engine in just like they said to do in the little manual that was sent with it . So i guess im looking at rebuilding a brand new engine that sucks with only 6,000 miles Of course they refuse to waranty the product as its not in a gm vehicel . I was even told my 78 280z put a strain on the engine as the engine wasnt made for a datsun . I asked what he meant by a strain on the engine he said the car is probably to heavy for the engine !!!!!!! Aparently a dumb ass so i spoke to someone else with no luck Just wanting to know what percentage of blow by i should be expecting to see or if all is normal basiacaly . Jason Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 17, 2007 Share Posted January 17, 2007 I'd say 5% or less IMO. I'll go out on a limb here and discuss cylinder hone finish abit. In my motors I like a smooth finish 550 grit with 28 to 32 degress of crosshatch. Looks nice and smooth when you get it from the machine shop. I use good brand moly rings, $150 a set, and I don't use zero gap second rings on the street. IMO the engine rings are seated in just a few hours and there is 2% to 5% leakdown or less, which I find acceptable. 13% indicates that on your engine either the rings didn't seat in that hole or that the ring end gaps are either incorrect, possible broken ring (typically the second ring) or the gaps are lined up in some fashion. Rings rotate in the cylinder bores during break in. I've experimented with ring end gap placement and after a short run period if you take it apart some are lined up or almost lined up, no matter where you place them to start with. Chevrolet even has a handy little chart depicting where ring end gaps should be placed on the left and right banks of a v8! The only ring end gaps that typically don't move are the oil rings. I try to line the gaps up 180 degrees opposed on the thrust faces of the piston skirts so that it leaves oil where I want it. With regards to your warranty, welcome to this world of "it's everyone elses fault except mine!" If you tear that engine down and piston to cylinder wall clearance is within tolerance, touch hone it as smooth as you can get the machine shop to do it, typically 440 or finer grit and put in some new moly rings of good quality. You'll end up with slightly more clearance, which doesn't help ring seal but if the clearance is .003 now, .0045 wont' hurt much. Cast pistons don't work very well with more than .004 although I've run them looser on circle track engines, hypers will work tighter or up to .006 or so. Forged as much as .008 depending on piston material, design and manufacturer, so ponder that. Forged pistons usually come undersized quite a bit so the finish bore size is the same for forged as is for any of the others in most cases. Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted January 17, 2007 Share Posted January 17, 2007 Jason, is this the same engine you have the roots blower on???? If I remenmber right you were going to up the boost from the stock blower setting. I personally would never put that blower on a crate engine. I spent the $$$ on my engine before running my blower at 10lbs. boost and I am Damn glad I did..... LARRY Quote Link to comment Share on other sites More sharing options...
Ledphoot Posted January 17, 2007 Share Posted January 17, 2007 OH and NEVER tell anyplace you buy parts from you are using them in anything but a GM car. I tell all of my part places they're for a 70 Camaro or Corvette. I learned long ago it voids the warranty if you claim it as anything but a stock fit. I've won't tell you what I've done with crate motor warranties.... let's just say a 300hp GM Targetmaster can take a .500 lift cam and a 150 shot of NO2 for a full weekend of racing before it starts knocking...LOL Quote Link to comment Share on other sites More sharing options...
jt1 Posted January 17, 2007 Share Posted January 17, 2007 In my experience it takes a really tight, fresh motor to leak down at 5%. After one has been beat on a while, 10% is pretty good. So my opinion is that yours is pretty good, and whether it's a problem depends on how hard you've run it those 6K miles or so. If it was mine, I wouldn't think about rebuilding it unless the performance dropped off. Also, the valve condition contributes to the leakdown as much as the rings. jt Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 17, 2007 Share Posted January 17, 2007 . I've won't tell you what I've done with crate motor warranties.... let's just say a 300hp GM Targetmaster can take a .500 lift cam and a 150 shot of NO2 for a full weekend of racing before it starts knocking...LOL Let's imagine all the retainers smacking the top of the guides, pistons swapping holes and finally somebody letting one of the rods out of the side of the block. You are too funny! Quote Link to comment Share on other sites More sharing options...
lbhsbZ Posted January 18, 2007 Share Posted January 18, 2007 up to 20% on a cold engine is considered OK. 20-30%, the motor was getting tired, over 30%...its time to rebuild it. The ring gap will close up substantially on a hot engine and your leakdown readings will drop. You've got to understand that it takes cylinder pressure to seal the rings against the cylinder. With most leakdown testers, you are only putting about 50psi or so into the cylinders, so the rings aren't going to seal very good. When the engine is running at WOT, cylinder pressure is ... well, a lot. I'm sure it could be calculated, but its a big number. Unless you've got 25% or more, I wouldn't worry about it. Quote Link to comment Share on other sites More sharing options...
280zwitha383 Posted January 18, 2007 Share Posted January 18, 2007 Sorry to hijack but, how do you test blowby? Also what happens if you break the second ring (I may have done this)? Will it F up your cylinder? I.E. Should I fix this ASAP or just keep watching oil levels? Quote Link to comment Share on other sites More sharing options...
gretchen/jason Posted January 18, 2007 Author Share Posted January 18, 2007 Well the engine was at about 130 degrees . i tried to get it up to 180 by driving it but when its only 18 degrees outside it is hard to do so i guess that could be a factor . Also yes i run a blower , i waited for about 3,500 miles before i added the blower and im running 6 lbs of boost . I havent burned any oil a few leaks maybe but that is all . Im hoping i wont have to rebuild it till the end of the year . If so then ill have the block and head O ringed and a stroker kit added , H beam conecting rods etc . Im looking for about 500 horses . So ill leave well enough alone for the moment and wait for the power adders for a latter date . I have a set of heads to put on but not sure if i should do that now . i may do it just so i can see what the cylinder walls look like . Thanks for the info folks Jason Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 18, 2007 Share Posted January 18, 2007 Why are you wanting to O ring both the block and the Heads? At 500HP you should be fine with good quality head gaskets. I think the point in your testing is that you have one cylinder that is quite abit lower than the rest. Not bad for a crate motor that they assemble all 8 pistons and rods in just 2 minutes or so. If your serious about the blower, get quality parts, machined and assembled right and 600 or even 700hp aren't out of the question. Quote Link to comment Share on other sites More sharing options...
jnjdragracing Posted January 18, 2007 Share Posted January 18, 2007 Hey Jason, When I hurt my engine (Supercharged) I did a leakdown test and it was a big difference between cylinders, which showed the bad pistons. In your situation I would apply air to the cylinder that is off and listen to hear if it is escaping from the piston / intake / exhaust. This will determine the cause. If it is the cylinder you will hear if from a valve cover breather / dip stick. Could just be a valve to tight / burnt etc. John Quote Link to comment Share on other sites More sharing options...
icewtr Posted January 18, 2007 Share Posted January 18, 2007 Ya know on the leak down test ya do never know if it is rings or the valves. i had what i thought was 70% blow by with my turbo set up and i had new pistons and rings put in it after the machine work was done .. and guess what still had the bad leak down test .. it was the valve guides.. also i was wondering is this blower on cast or hyperuseless pistons or did you get a crate motor with forged pistons .. Quote Link to comment Share on other sites More sharing options...
gretchen/jason Posted January 19, 2007 Author Share Posted January 19, 2007 Well i determined it was rings as when i did the test i could put my hand over the breather hole for the PCV valve and it would build up pressure . As for Dr Hunt and his question i was told by a shop that specializes in blowers that you have to O ring the block and heads , they said they couldnt work on it unless i had it O ringed . Not sure if it needs it or not . I figured i could buy a stroker crank good conecting rods and good rings and pistons and then have someone machine the block and put it all together . Im sure i could assemble it myself but id rather not take the chance . And for ICEWTR the pistons that are in the engine are cast aluminum . What pistons and rings would be good for a blower aplicaition ? Jason Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 19, 2007 Share Posted January 19, 2007 Well i determined it was rings as when i did the test i could put my hand over the breather hole for the PCV valve and it would build up pressure . As for Dr Hunt and his question i was told by a shop that specializes in blowers that you have to O ring the block and heads , they said they couldnt work on it unless i had it O ringed . Not sure if it needs it or not . I figured i could buy a stroker crank good conecting rods and good rings and pistons and then have someone machine the block and put it all together . Im sure i could assemble it myself but id rather not take the chance . And for ICEWTR the pistons that are in the engine are cast aluminum . What pistons and rings would be good for a blower aplicaition ? Jason Well, your welcome to take whatever advice from your machine shop you choose too. Fact is there are people that make alot more HP than that out of a sbc with a blower without o ringed heads and block, which relegates you to using copper head gaskets, definately going to be a plus but at $$$$. Stroke has less of an effect on HP in boosted applications than bore does, but it still helps. Forged internals are definately a good decision in case you turn up the boost at a later date. I was over at Edwards Engines about 6 months ago, watching Tom Edwards dyno a blown SBC. Dart Block (350), LA Crank, Carillo Rods, JE blower pistons, Brodix track 1's unported, custom Comp blower cam (unknown specs), 6-71 BDS blower, 2 Demon blower carbs. Mind you this is with Cometic head gaskets, made 1050HP corrected at 7500rpm and was still climbing. I think the boost was around 20psi. Quote Link to comment Share on other sites More sharing options...
260pos Posted January 19, 2007 Share Posted January 19, 2007 Just doing my part" myexperience@jegs.com I guess it wouldn’t be wise to do business with your company. I was considering buying a crate motor from your company, not a very good review I must say. If a 2400-pound vehicle has too much weight for your product. I guess a pick-up truck would cause one of your motors to just melt in the driveway. http://forums.hybridz.org/showthread.php?p=726746#post726746 Quote Link to comment Share on other sites More sharing options...
icewtr Posted January 19, 2007 Share Posted January 19, 2007 (What pistons and rings would be good for a blower aplicaition ? ) Well forged is the only way to go .. my crate motor i am running now is hyper whatever they are ... i do have a small amount of NOS but to go more i really need forged pistons ... and i have a nice 76mm turbo sitting here that can't go on due to the same prob.. even if ya don't need the forged stuff the difference in money is not that bad so do it and down the road ya will already be set up for what ya wanna throw on the motor Quote Link to comment Share on other sites More sharing options...
COZY Z COLE Posted January 19, 2007 Share Posted January 19, 2007 My engine build.... AFR 195 race ported heads. Comp Cam bee hive springs. Comp Cam 1.6 Pro Magnum roller rockers. Cometic .040 head gaskets. Special machined spring locaters. .512 lift The engine was balanced / blueprinted and has 8.5-1 comp. in a 355 SBC with the 144 WEIAND blower at 10 lbs. boost. Forged steel crankshaft 3.480 stroke. Forged TRW blower pistons 4.030. Engel custom hyd. roller cam. Plasma - Moly rings. Ignition system MSD 6 BTM. Blaster SS coil, Pro Billet Distr. Holley 700 cmf Supercharger DP carb. Mallory Race Comp. 5 ported adj. fuel reg. IMO forget those O rings. LARRY Quote Link to comment Share on other sites More sharing options...
jnjdragracing Posted January 19, 2007 Share Posted January 19, 2007 The Cometic head gaskets are top notch, if you run them you do not need to o ring the block or heads. Most of the Turbo guys around here run them and they are supposed to be the best you can get. Before these head gaskets and if you were putting out alot of boost then oringing the block and running copper gaskets were the way to go. But thanks to Cometic you do not need to do this. You do have to make sure your block and heads are straight and clean. As far as pistons and rings we run the Speed Pro forged blower piston ( same as TRW L2441F) and file to fit rings. If you are planing on bumping up the overdrive of the blower you will need a good bottom end. We are presently pushing 14psi, but soon to be more. We run a Callies steel crank, Eagle H beam rods, Balanced rotating assembly. Hope this helps... John Quote Link to comment Share on other sites More sharing options...
260pos Posted January 19, 2007 Share Posted January 19, 2007 I got a reply: Good afternoon, I guess I would like to know engine he bought from us. As I’m sure you are aware GM makes 9 different versions of a small block that we carry. I don’t know what difference the weight would make, plus you don’t know what radiator he is running it might not have enough cooling surface to cool the larger motor. Good luck with your project. Please remember that GM crate motors are exactly that. They are put together on a GM assembly line just like any new motor that you would by from any GM dealer in the United States. Again, good luck on your project; Les Lewis Mail order manager 800-345-4545 ext 534 614-851-9763 fax Les.Lewis@jegs.com Quote Link to comment Share on other sites More sharing options...
dr_hunt Posted January 19, 2007 Share Posted January 19, 2007 My TT motor is; gm prod. block +.030 and hard block short filled. GM steel crank (balanced rot. assy.) Eagle H beams with L19 bolts TRW blower pistons, +.030 Speed Pro File fit moly rings Clevite H bearings Custom Comp solid roller, 240/250 ..630/.618 114LSA AFR full cnc 227 cc heads gear drive too much else to list oh, and cometic .040 head gaskets. Quote Link to comment Share on other sites More sharing options...
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