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About a month or so ago my heads/cam 93 6 speed started knocking. The motor never quite ran right after I got a set of JPR ported heads, and Lloyd Elliot 231/239 .571/.587 109 cam installed. The car make 363rwhp with that setup through the stock exhaust manifolds despite a terribly rich mailorder tune. It was obviously lacking though because it lost about 100hp between 5800 and 6200rpm
Since that pull I installed OBX long tubes and got a new mail order tune. The car still ran ridiculously rich all the time (wide band read 10.x:1 under WOT) and still would not pull on the big end. After a couple months of just changing plugs every couple weeks because the kept fouling out I finally had some time around school to get a Moates cable and datamaster to try to log the car and get the tune fixed.
On the WOT pull the car was really struggling in 2nd and 3rd to get to 6Krpm and after I lifted just as I shifted into 4th and let the car engine brake, the moment I clutched in to let it coast the car died. It would no refire until I floored it while cranking to enable flood prevention. When it did refire it was clearly knocking and the car would no idle. I still managed to drive the car home but it was clearly down on power and I had to ride the gas the whole way across town.
The car then sat for a week or so until I could get it to my friends place where he had a lift to pull the motor. We finally got the motor taken apart Last weekend and found this:
One of the connecting rods was bent, the bottom of the piston was contacting the crank, 7/8 rod bearings were spun, and at least two pistons had piston to valve contact. There were deep grooves worn into the crank by the spun bearings as well so I'm not confident it will be able to be saved either. It currently looks like the entire rotating assembly is trash.
My initial plan before I saw the state of the rotating assembly was just to throw in some forged pistons, maybe some forged rods and keep the stock crank and use ARP rod and main bolts/studs. Now that it looks like I will probably need to replace the crank as well I am wondering what cranks are solid to hold power as well as what price differences I would be looking at for a standard 3.48 stroke crank vs a 3.75 stroke 383 crank?
Key factors:
I do not have the budget for a forged crank at this point.
I would like the motor to safely be able to rev to 6500rpm.
The motor will remain N/A at first but at some point after I graduate I would like to throw a plate system of spray at it (150-200 shot) so I would like the bottom end to be able to handle that.
I am going to talk to the machine shop on Friday but would like to have an idea where I am going before that.
Right now I am debating between A) finding another stock LT1 crank they seem to hold good power and can be found for about $150 shipped on ebay. B) Getting a Scat 9000 (or equivalent) 3.48 crank from Summit or the machine shop if they can provide it. C) Getting a Scat 9000 (or equivalent) 3.75 383 crank
Questions are: How much power can a Scat 9000 hold? If it looks unreasonable that I can find anything that will hold spray for a cheap budget I will just change my plans and not spray the motor.
Do I want to continue using a 5.7" rod or go up to a 6" rod? I know that 6" is lighter and better for N/A applications but dont know the affect of this with spray (150-200shot)
Any recommendations on what crank I should go with would be great.
Maybe do the figures on rebuilding yours and then compare it to buying a built short rotating assembly ? There will be a big time saving buying a built short motor.
I have the Scat 9000 in my 383 and it will spin to just over 6000 and hasnt fallen out the bottom yet !
I honestly would feel far more comfortable getting my own built. It is hard to verify how well the work was done buying a used short block. I like the reassurance of knowing everything was done right and the way I want it.
My opinion is based on what I have seen in other guys cars as well as my own experience with my rebuild. The questions you asked can only be answered based on your budget. Money dictates everything when it comes to higher performance. I'm sure you know this already, all I'm saying is the best parts cost the most money. So first decide how much money you will spend and then go from there as the budget will dictate your plans. Best of luck ! God knows it would be nice if money were not an issue and you could spend $8,000 on the engine build.
If you can do without the car for a bit somehow do the 383 youll forget about the 350;you need new parts anyway the cost difference its hardly anything
Keep the heads/cam if they are Ok, run it up a little past 6k tops. I bet a 9000 crank would hang in there although forged obviously is a good thing. 5.7 vs 6" rod do whatever you can afford you wont notice the difference. If youre going to spray absolutely forged but I bet wiht the longer stroke youll have enough traction issues already. Just an opinion youll hear lots
Check your valvesprings to make sure they are set up correctly; sounds like you were possibly losing valve control.
HR cams not a great idea to spin up that high. Not saying they cant be but the risk of them pumping up or having the issue you are having isnt any fun
Heck its all a roll of the dice
Check your valvesprings to make sure they are set up correctly; sounds like you were possibly losing valve control.
HR cams not a great idea to spin up that high. Not saying they cant be but the risk of them pumping up or having the issue you are having isnt any fun
Heck its all a roll of the dice
See thats what everything points to: valve springs that cant handle the cam. The fact that the heads were used and assembled when I bought them and didn't know what springs were installed further supports that.
However, when I bought the heads I had the springs measured per Lloyd Elliott's advice and they tested to about 150lbs seated and 400lbs open. Lloyd said this was plenty to keep the valves under control. I still plan to have the springs measured again though this time just for peace of mind.
As for traction issues the 315 NT05R's I have should be able to keep that in check no matter what NA setup I go with. The issue I'm seeing with a 383 is that you dont really seem to get that huge of a gain N/A 450rwhp vs 400-420 rwhp. This doesn't seem worth it if it would mean buying a more expensive cast crank like the Scat that wont be able to hold spray like the stock crank can (lots of guys on LS1tech i saw making over 700rwhp through the stock crank with nitrous).
At this point is seems like no one seems to have the confidence that a Scat 9000 crank will reliable spin to or above 6500rpm which the stock one will do no problem so it seems to be more worth while to get a cheap stock crank again and just build the 355. A 383 seems like it would be worth it with a Callies or Lunati forged crank but not on a budget like I have.
wouldnt trust a stock crank with 700rwhp
These guys are na with nitrous? At that point thats well over what the GM block is capable of holding
what the 383 will give you is plenty of torque gain everywhere in the range esp if you put some headers on it and let it breathe. Its not just a hp gain. There are some strong running 383s on the board. no way I could hook any street tire with mine, M/T full time is marginal
Wow. Given your hp goals, I think you need forged EVERYTHING plus a thick wallet to boot;
however that crank, if money becomes an issue, is probably salvageable; on my crank, magnaflux, check for cracks, grind mains and rod journal, new clevite rod and main bearings $287 total; done by a well known established machine shop, no handling and shipping fees.
if you go to a 6 inch rod, the lower end geometry is improved and basically you have a 350 that now wants to rev like a 327
If you want a motor to put out 600hp, you'll need to spend more than $2.5 on the bottom end unless you get a good deal on a used race piece. I'm somewhere around that level and I've spent much, much more than that on my motor. You want to built the thing right, not just to last a couple passes.
Forged Scat rods $250
Forged Speed Pro Pistons $400 (possibly mahles for $600)
Stock crank $200.
Will hold 600 hp at 6500 rpm all day long. Tried and true in the F Bodies. I was kind of hoping for some info here about the limits of the Scat crank but from more research on LS1tech it seems to not be comparable to the stock crank.
A few things, the installed height on the valve spring is critical, need to make sure you have proper clearance for that lift. If you get to close to coil bind the springs will relax faster losing spring pressure causing issues, or worse break and drop a valve.
The other thing to check is your oil pressure under WOT. Once you start revving the corvette ltx I have found it hit or miss of having oil pressure drop in the upper rpm. I battled this on a few motors and finally discovered the oil filter adapter was a restriction on some cars. Some castings are better than others, but all have terrible 90 degree unradiused turns. Couple this with a small oil filter and you can physically watch oil pressure drop in the upper rpm. This causes issues like you were seeing in your dunno graph, upper rpm power fall off occurs from the lifters collapsing when oil pressure drops, you lose a lot of lift therefore duration. Ultimately you wind up with spun bearings, and a mess.
If you have long tubes, ditch the oil filter adapter, grab a traditional oil filter screw on piece (few bucks from summit or Jegs) and spin on a Fram HP4 racing filter. They are made by WIX and are the best. Also, ask your machinist to radius your oil passage openings where the pump bolts on the rear main cap, in the oil filter boss side wall, and check the V-drilled path way from the pump to oil filter opening. There are plugs that can sometimes be set to deep and block off flow. This is the time to do these small but very beneficial miss and cost is negligible, you could even do it yourself with a die grinder and some sanding cartridge rolls.
If this is your toy and not your DD, I would consider an ls swap at this juncture, certainly opens your options up and you could drop some weight and make more power. Just a thought.
I have been making over 530rwhp on a stock crank, stock rod, summit cast piston rebuild kit with p1sc procharger setup with 12psi and 10.3:1 compression for years without incident and spin it to 6300rpm. If your tune is good, it goes a long way to what your motor will handle. Start detonating and it doesn't matter what parts your using, they will eventually fail.
I honestly would feel far more comfortable getting my own built. It is hard to verify how well the work was done buying a used short block. I like the reassurance of knowing everything was done right and the way I want it.
I meant the company's that are building engines,
they do short rotating assemblies and you can spec what you want in there, for example (not that Im recommending anyone in particular)
Thank you for the info on the oil filter adapter. I am wondering though if my oil cooler will still be able to hook up to the traditional sbc mount like it does to the curgent one? Or will I need a different size block to fit the new adapter?
What oil cooler? Aftermarket? I've had some of those also be a restriction...
You shouldn't need an oil cooler anyways, if you added one because of high oil temps it may likely be that the initial restriction was causing oil heating from metal to metal contact in your upper revs.
I would eliminate it and the adapter for the new motor. If you road race the car and that's why you need it I would look at a self contained cooling system seperate from the engine pressurized oiling system. Oil flow restrictions are motor life reducers.
I was one of the trailblazing pioneers with these motors going into uncharted territory making big power 939rwhp/861rwtq... Trust me when I tell you I have found the weak links in these motors and weathered the experience through financial trial and error.
At that power level I didn't need an oil cooler, I needed oil flow! Not many can say they have gone where I have, I know that nobody on the corvette forum has even come close with the lt1. The f-bodies weren't burdened with that adapter like we were. Two motors identical builds, same parts one in an f-body that lived and did great, one in a Vette that kept eating bearings and wiping out motors... Finally figured it out.
The adapter is 100% a restriction. The oil cooler is not necessary, the vettes with high oil temps.... Guarantee its because of the adapter... If you have headers, ditch both adapter and cooler, do the flow mods I listed and go with the HP4 filter and you will make more power, Pull higher revs safer and have lower oil temps. Oil pump isn't working as hard either which keeps it from cavitating and heating the oil from frothing.
If you are having the engine built locally, make sure you vet the builder well. Has he done Lt motors? And ensure when he does your balancing, you take him your balancer and flywheel/flex plate so he can get a true balance with all reciprocating mass installed. If your using the dual mass flywheel still that won't work as the two pieces move and will throw the weight off. It also is extremely difficult if not impossible to zero balance the dual mass which is counter weighted and not for a zero balance motor. May also be a good time to do a single mass flywheel conversion so you can get the balance dialed in and have the motor silky smooth in the upper rpm!
Most builders will zero balance the rotating assembly and using a neutral balanced flywheel and balancer is a must!
I battled this on a few motors and finally discovered the oil filter adapter was a restriction on some cars. Some castings are better than others, but all have terrible 90 degree unradiused turns. Couple this with a small oil filter and you can physically watch oil pressure drop in the upper rpm.
If you have long tubes, ditch the oil filter adapter, grab a traditional oil filter screw on piece (few bucks from summit or Jegs) and spin on a Fram HP4 racing filter. They are made by WIX and are the best. Also, ask your machinist to radius your oil passage openings where the pump bolts on the rear main cap, in the oil filter boss side wall, and check the V-drilled path way from the pump to oil filter opening. There are plugs that can sometimes be set to deep and block off flow. This is the time to do these small but very beneficial miss and cost is negligible, you could even do it yourself with a die grinder and some sanding cartridge rolls.
Chris
thank you for sharing your experiences.
I've got to agree with you 100%; those adapters and small filters just look wrong....and to paraphrase, if it looks wrong, it probably is wrong; too often people just assume that the stock small block oil system is "bulletproof" as it came from the factory....no, far from it. Some of my favorite reads are from the "bad ole day's" when NASCAR (and others) actually ran stock motors and the multitude of modifications that were done to stock chevy small block engines to get them to survive at those performance levels.....believe me it was extensive.
04-21-2015, 08:43 PM
355 vs 383
