350/255HP Help please
 

Can anyone help me out a bit in knowing what my 350/255 stocker motor should be making for power and what rpm range it should be peaking at? I've been beating my head off the wall with this thing for a few years now and just dosen't want to get any better. I'm thinking I may have the wrong cam in it but really don't know where to turn next. Thanks.

Re: 350/255HP Help please
 

Assuming no obvious issues, a couple of pulls on a dyno can save you lots of time.

What kind of h.p. numbers are you getting when calculating from the E.T.?

Re: 350/255HP Help please
 

Made 387 @ 5600 on A&J dyno. 100% new engine except for the cam as it was like new and only a couple seasons old. The worn out peice I had before made 384. The slide calculator agrees with this. A little background info, it's got all what's supposed to be great gear, .065 over cp c6 Pistons with total seal advantage ring pack, Manley rods, new heads from reputable shop that flow quite well, pac 1409x springs, bullet cam, short travel lifters etc.eal down is 8-9% cold, we've had it apart again to make sure nothing is going away or getting tight and all is well. It's just not adding up, and it's beginning to make my head hurt lol.

Re: 350/255HP Help please
 

Are you saying the leakdown is 8 to 9%????

Re: 350/255HP Help please
 

Not trying to be ugly but that combo should make north of 430. How "new" are pistons? Most likely the problem is the ring package. Having said that I am not an engine builder nor do I build my own motors but I have been around stock for all my life and fairly up to date with what it takes to make them run.

Re: 350/255HP Help please
 

Yes 430 + with much higher peak than 5600 RPM. 119 MPH @ 3350 = 440 HP

Re: 350/255HP Help please
 

You're down 35HP or more, and your peak is maybe 600RPM or more low.

If you're really leaking close to 10% on an engine that is up to 160 degrees, you're not sealed up.

I seriously doubt that either Total Seal or CP has missed the mark on the rings or pistons, especially if you had them work together. I've used their stuff successfully many times.

Re: 350/255HP Help please
 

He said "Cold" Leak. That never has told me anything. I don't race Cold Engines... Could have bad ex seats and when it gets hot they go away..... Just Saying...

Re: 350/255HP Help please
 

Agreed. Cold leak down is useless. Honestly, on these engines, you need to be using a Dwyer gauge, or something, to test blow by on the dyno. Leakdown, even hot, can be misleading. Measuring blow by eliminates all of that.

Re: 350/255HP Help please
 

If its a junkyard block 384 is not that bad,if its leaking more than 6% you got problems, Call Greg at race rings get his ringpack give him the grove dept,and he will fix you up get it honed with a plate . Cam should be in at 103-104 with a three speed.spring pressure around 145 -385 with reg lifters. Bowtie should pick you up 20. good luck.Not all dynos are the same.

Re: 350/255HP Help please
 

I'll get it up to temperature and do another leakdown. Don't have access to a Dwyer guage. Cam is in at 103. What you guys are saying about 35-40 and 600rpm down is exactly what I have been figuring but can't find why. Engine is a factory block but fresh at .065 with plate. Pistons are a couple years old, Manley rods, (light piston heavy Rod)

Re: 350/255HP Help please
 

Is the block poured?

To the water pump holes?

Piston to wall clearance?

Hone finish?

Oil clearances?

Oil weight?

Oil pump type?


A Dwyer gauge is pretty cheap, find one online, probably for less than $100. They're easy to hook up. And they tell the tale about real ring seal with the engine running.

Re: 350/255HP Help please
 

-Block is not poured,
-.005" piston to wall as per CP
-Plateau Honed with torque plate, cannot remember exact grit but we spoke to total seal and did what they said
-Bearing clearances .0025 rods, .0037 mains
-Broke in and dynoed with amsoil break in 30 weight
-now running amsoil dominator 5w20
-M55A pump with stock spring,
-Champ CP40 pan

Cam specs
Bullet CHS 307/315-06H duration @.050 262/270

Re: 350/255HP Help please
 

Okay, in my opinion, for whatever it is worth, what I have highlighted above is problem one. There is no production block that I know of that will stay round under stress at 0.065" over. I've never seen an 010 or other block thick enough to do that.

If you want to run that big a bore size, you need to pour the block with Hard Blok or Embeco 885. At a minimum. You really need a BowTie or Dart to make it work well.

Ring seal is the most critical and fundamental part of restricted engine performance. You simply do not have one single solitary cfm to waste, the engine is suffering pumping losses just to breath, you cannot waste what it breathes. The bores have to stay round and straight, period.

I do not know if you can salvage what you have by pouring that block. You could try it, and maybe open the clearance up to 0.006-0.0065. If you pour a block one side at a time with either cylinder heads or torque plates, it will sometimes get a little smaller. Not every time. And if you cannot get it back round and straight by 0.0065" clearance, you'll have to change blocks.

I run tighter oil clearances, and use a lighter oil ring with a Napier cut second ring. No more than 0.001" per 1.0" of journal size. Of course, the bearing bores have to be dead round and stay that way. But it allows around 10-12# oil ring tension with no oil consumption.

Next, with a cam ground on 106 and in at 103, you're going to have an early HP peak, especially considering low lift and relatively low compression. You might consider a cam ground on 108 and in at 104-105. You can try moving the cam you have around.

That's about all I can offer you on the forum. Take it for whatever you think it is worth. Good luck.

Re: 350/255HP Help please
 

Cam is in at 103 as per bullet's instruction. Really can't see the block being the issue, none of the other engines around here out powering me are aftermarket or filled blocks. I can understand where you are coming from there and if there was an extra 3k in the budget it would have got a dart or bowtie.

Re: 350/255HP Help please
 

Okay. Good luck.

Re: 350/255HP Help please
 

Chipper, where are you at with the intake manifold?

Cylinder walls on a non-filled production block can really rattle around at high rpms.

Re: 350/255HP Help please
 

I would listen to Alan. Everything he stated is dead nuts.

Re: 350/255HP Help please
 

This is a non filled '72 vintage block +.070 from my Nova Stocker that split the #4 cylinder. Will section the cylinder wall this week just to see how thin it really is. At high rpms, the walls in a block like this gotta' be shakin' like a female intern in the Clinton White House.......;)

http://img.photobucket.com/albums/v4...psswup8cfe.jpg

Re: 350/255HP Help please
 

OEM blocks vary a huge amount in hardness as well as wall thickness.

OEM blocks are often way offset from center on the cam and crank as they relate to the cylinders and other issues as well.

OEM blocks often have a lot of core shift......cylinders are thin on one side.


With the power levels being what they are even in stock engines and also the cost of the parts to build a good engine.....any OEM block considered for use should be hardness tested and sonic'ed for wall thickness....

We did this in the shop I worked at 30+ years ago.....and a soft block or a thin block was just not used....

I would not hesitate to fill the block no matter what.....but as was stated filling a block that is already machined and at size is not the right way to go....it should be done before the block was finished....

My last 350-255 was a stock 010 block at .040 over...filled block.....ran 11.80's in G/SA with TRW pistons....stock rings.....untouched heads other than old school legal VJ and CC prep and untouched intake.....old Lunati cam with std type lifters....that was 1996 and it was a good 4-5 tenths slower than the fastest cars....

I shifted that 350 at 6600-6800 and it was a powerglide trans. 3 speeds were not legal back then..

MPH was never better than 112....usually less

Re: 350/255HP Help please
 

Wrong cam

Re: 350/255HP Help please
 

I know what he's going through. I used to have a fairly good running car until I finally just wore my factory block out. I then went and put a Dart little m block in it and 4 years later I still can't make it run no matter what I do. Tried heads, all different kinds of ring packages(total seal luniac etc etc) cams and I've never had it leak less than 10%. Is it possible for a dart block to not be any good. Ive had some pretty impressive machinist hone the block and nothing seems to work. I'm about ready to go back to a factory block. Hope you find out what's wrong.

Re: 350/255HP Help please
 

"-.005" piston to wall as per CP"


This is one area you need to take a look at.

Re: 350/255HP Help please
 

Well, there you go, an expert speaks.

James, do you think that cam is 30-50HP and 600 RPM wrong?

Re: 350/255HP Help please
 

Bill, Dart makes a great product, although their customer service on some things can leave a bit to be desired. That being said, it is possible, but very unlikely, to have a bad block.

I will say that those blocks can drive even an excellent machinist insane trying to get the cylinders done correctly. Really good and experienced guys, way better than me, have struggled with them. A couple shared what they learned, and helped me figure out what I needed to do. I damned near ruined the first one I honed, the truth is, that one didn't seal up really well until we freshened that engine, changing pistons and rings, and honing it again.

A couple of things I can suggest. First, it is necessary to use extremely soft stones, it is near impossible to get them too soft. Second, flood the cylinders with hone oil, good clean fresh hone oil, it is near impossible to flow too much. Third, use light to medium pressure, never more. Finally, use coarse stones right up until the last 0.001" or so, then use your last two finish stone sets for only that last bit of stock removal. Dart blocks are extremely hard, they will glaze over, and load up a set of stones in an instant.

Once you get the bores correct on a Dart block, they'll hold up well and last forever, you can literally touch them up with maybe 5 light strokes of soft 400 grit stones and a finish pass or two with the Total Seal suggested finish technique.

Re: 350/255HP Help please
 

Alan there is no doubt the wrong cam and being in wrong can cause this in a 255. This is several times Bullet has advised putting a cam pretty far off from where we have foud them to run best. I would really suggest Chipper call Woodro and get one of his grinds and degree it per his instructions. A 255 is almost cookie cutter to make run.

Re: 350/255HP Help please
 

Painter, I have no doubt the wrong cam will hurt one. I don't have a ton of experience with the 255-350, just thinking that they had to miss that one by a country mile to cost him 30-50HP and 600 or so RPM, that's a lot of power and RPM from a cam mistake. Bullet is not necessarily my favorite brand, but that's a huge miss.

Re: 350/255HP Help please
 

Alan the 9-10 cold leak down doesn't catch my attention as much as the lack of rpm's does. Those thing run pretty good, pretty easy.

Re: 350/255HP Help please
 

Oh I agree, I think he has more than one thing seriously wrong.

Re: 350/255HP Help please
 

Painter,
I'm with you on the cam deal. It would make sense that the RPM is down if the intake or Ex lobes were not in the right place. (not just the intake C/L)
I still stand by the hot vs cold leak. If your looking for a problem look at all parts of it as the engine runs. The bad ex seats could kill the RPM, too. I would pull the intake and look for signs of bad reversion. That would point to cam and or a couple other issues as well as ex diluting the intake charge. OH, if you can't find an exact cause go slow and just make one change at a time. don't dig yourself deeper in the hole.
Good luck..

Re: 350/255HP Help please
 

Alan, could you describe how the Dwyer gauge works?Is it basically installed like a vacuum gauge? I've never heard of one.Looks like there are several different calibrations.Which is correct to use to measure ring seal as you described? Thanks,Mark

Re: 350/255HP Help please
 

Mark, if memory serves correct, you want one that reads 0-10 scfm. The 12" tall model is probably the best.

What you do is connect the gauge to the only outlet where any crankcase pressure can escape from the engine, everything else must be completely sealed. The easiest way is to connect the gauge to a breather with a tube outlet, such as the one used in a crank case evac kit. The gauge must be mounted perfectly vertical.

You then make dyno pulls as you normally would. We normally use our vacuum and or evac system for a while to seal the engine up, then after we've got it where we want it and tuned, we make a couple of pulls with the Dwyer gauge on it to make sure it is sealed up.

Re: 350/255HP Help please
 

The one I used was a Fisher-Porter same one Chryser Race Group used was about $300.00 30 years ago. I could hook it up as Alan described and if it was bad enough the weight in tube would bounce just spinning on starter. We would check engine every time we loaded car to come home by hooking up meter and just free rev engine to 6500 rpm if Blowby was over 2 cfm engine would come apart we we got home. Difference on a 740 hp engine on dyno at 6 cfm down was down 60 hp to 1 1/2 cfm. Ted Flack showed us how to use it.

Re: 350/255HP Help please
 

OK , I get it now.All I could find online the other day was a round gauge with a bunch of NPT fittings and hoses stickin' out of it.Thanks Guys!

Re: 350/255HP Help please
 

Look at a Dwyer Model# RMC-121. 1 to 10 Cfm range, 10" tall, 1/2" fittings.

Re: 350/255HP Help please
 

What I don't know about building engines seems to outspace what I know.

Re: 350/255HP Help please
 

Same here. I have learned so much in two years of lurking on ClassRacer.

Rick Thomason
GTOMayhem

Re: 350/255HP Help please
 

Finally got time to do a hot leak down. All cylinders are 5-6% both at tdc and approximately halfway down, at 150 degrees. No access to a dwyer guage here to check that.

Re: 350/255HP Help please
 

Great testimony! Lurk on!

Re: 350/255HP Help please
 

What would the fix be after you tore it down? I know, probably a novice question. Also how would a supercharged engine change what you would be looking for as far as ring seal and blowby?

Rick Thomason
GTOMayhem