Quote:
I never had the guts to simply rev it to 3500 and dump the clutch. 
Sam
I do that at every run down the Strip!! Sam
Greg
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| Author: | Dart270 [ Fri Aug 17, 2007 10:58 am ] |
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OK, sounds like you have your ducks in a row. The weird part here is still the cranking psi. Hard to see how you would get 210-220 psi with a 250 @0.050" cam with only 10.4:1 comp. I would probably start putting dial indicator on the valve spring retainers and measure actual valve lift and duration, overlap, etc. I ran 10.5-11:1 with my 250 @ 0.050" cam, albeit 106 LSA, and got 180 psi. I ran 11:1 with only 228 @ 0.050" for a while and got 210 psi. Lou |
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| Author: | Greg Ondayko [ Fri Aug 17, 2007 12:08 pm ] |
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Quote: I never had the guts to simply rev it to 3500 and dump the clutch.
I do that at every run down the Strip!! Sam Greg |
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| Author: | AnotherSix [ Fri Aug 17, 2007 12:29 pm ] |
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Stick with the thought that the math does not lie. I would not consider anything verified at this point, however. It's not working like it should, so thats reality. The idea that it not this or that because it was checked before is not valid at this point. I seem to recall that you did not know the cr, then it was 10.5, but now it's 12 something? Just start over with measuring and make no assumptions. Keep in mind that knowing something and thinking you know something are two totally different things. Many people do not know how to properly use measuring tools or exactly how or where to take the measurements on and engine. This may include your machinist. I would verify the timing mark at tdc. How was it done before? You can't even get close just by looking at it with the head off. The only accurate way to do it is with a positive stop, turn the engine both ways to the stop, mark both positions and split the difference. If your machinist does not understand this, I would not take the engine back to him, he's not qualified to build real race engines. Have you seen the equipment used to cc the heads? Can you really be sure it was even done? Also were the piston dishs cc'd or were the specs furnished accepted as correct. 9.5 to 1 is more realistic than 10 to 1. Pump gas is not getting any better, however. I think 9 to 1 is really more realistic for 91 or 92 pump gas on a good breathing engine. Yes an engine with higher VE will develope more pressure, and need more octane at any given point. Check the stroke as you noted. It just is not that hard to get all this straight. It looks like your machinist does not know what he is doing or is just not doing it. I've seen plenty of both. When the cam was out, was it checked in any way? At this point it might be a good idea to check it. Easy enough to do in the engine with the head off and a degree wheel. Someone here has no idea how to do things rite or is full of crap. You can get it right this time, just do it and don't accept any BS or do any rationalizing. I would really look at opening up the reliefs around the valves before thinking about doing anything to the short block. Why mess with it if you don't need too? Of course you dismissed this some time ago, I don't think you understood what I was talking about. Maybe you have a larger engine related vocabulary after all this and it makes sense to you now? |
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| Author: | Dart270 [ Fri Aug 17, 2007 1:41 pm ] |
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In my experience, the 225 can tolerate a lot of compression and not detonate. 11:1 is totally doable on 91 octane, and 10:1 is easy. Two things: You need to match your cam (duration) to your compression, and set up your ign advance/curve right. Lou |
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| Author: | argentina-slantsixer [ Fri Aug 17, 2007 3:40 pm ] |
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Quote: In my experience, the 225 can tolerate a lot of compression and not detonate. 11:1 is totally doable on 91 octane, and 10:1 is easy.
ditto!Two things: You need to match your cam (duration) to your compression, and set up your ign advance/curve right. Lou my car likes 15°BTDC initial 28° total, my compression is between 9 and 9.5 and my cam is in the 280ish ballpark (dont have blueprints or spreadsheets as I lost all my data due to a computer crash) and cranking pressure drops amazingly with a bad (or good ) lash. I have some sort of crappy hydro profile (wich is faster than I would like)EDIT: cranking presure with lot's a lash: 170~160 cranking pressure with practically zero lash: 120~100 all measures HOT, and I mean cherry red headers hot. When I test compression, I warm up normally, then beat the crap out of the car for about half an hour (take her to the road) I park on the side, remove all plugs and carb, and do the comp testing. |
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| Author: | Bren67Cuda904 [ Fri Aug 17, 2007 3:51 pm ] |
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Quote: my cam is in the 280ish ballpark
Is that @50?
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| Author: | argentina-slantsixer [ Fri Aug 17, 2007 4:07 pm ] |
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Quote: Quote: my cam is in the 280ish ballpark
Is that @50? |
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| Author: | argentina-slantsixer [ Fri Aug 17, 2007 4:10 pm ] |
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you should (emphasis on should) be around 170~180 if you had 10:1 with that cam. (maybe 190 with an avdanced cam?) This is based on experience and not in measuring your actual engine. As the guys remarks, something must be way off and assuming things ain't gonna help. You've learned, maybe it's time for you to look over the shoulder of your machinist...  you never kept us posted on this: different lash settings accounted for some change in cranking pressures?????? |
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| Author: | Bren67Cuda904 [ Sat Aug 18, 2007 9:52 am ] |
| Post subject: | Re: The numbers check-out... |
Quote: Calculate Engine Displacement and Compression Ratio
Above are the old measurements. There are two differences:Bore Diameter (inches): 3.591 Stroke Length (inches): 4.250 Number Of Cylinders: 6 Combustion Chamber CC: 64.5 Piston Dome(-)/Dish(+) CC: +6 Deck Height (+/-inches): -.007 Head Gasket Thickness (inches): .038 Head Gasket Cylinder Dia (inches): 3.66 Displacement: 258.2628 Cid Displacement: 4232.1693 cc Compression: 10.0184 :1 1.Is that the valve reliefs don't add 6 they add 4cc. 2. The headgasket compressed is .048 The new CR calcuation is 10.0503 :1 My plan is to mill the pistons .060 for a CR of 9.0250 :1 Anybody see a problem with this? One more thing. There was a bit of carbon buildup (1cc worth) in the cambers. Is it likely that it built up while I had the old rich running carb on it? I know that carbon can glow hot and cause detonation. I know I could go for a 9.5 :1 CR, but I refuse to tare it down again. Besides, I can always mill the head a bit to bring it back up if I so desire. I doubt that I will ever desire though. |
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| Author: | slantzilla [ Sat Aug 18, 2007 10:04 am ] |
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Is the top of the piston thick enough to stand an .060" cut?
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| Author: | sandy in BC [ Sat Aug 18, 2007 10:06 am ] |
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I dont get it..... My car is 9.25:1 and runs fine on 87. BUT in order to do that I had to recurve the dist. Your cranking pressure does not work with your math. I dont think the cranking pressure is wrong....your use of race gas shows that. I think your math is still wrong......milling pistons wont make it right. 60 thou off the piston tops will make them weaker.... Id cc those chambers again 64 sounds small for a chamber that has been swept.... |
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| Author: | Bren67Cuda904 [ Sat Aug 18, 2007 10:11 am ] |
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Forgot one other thing. The exhaust head pipe (old one). http://tinyurl.com/yp8k5v This pipe has been replaced with a similar design. I cut the back of the old pipe (pictured) open to view the transition and all I could was laugh. The openning that the exhaust guy made was about the size of two quarters (1"x2"). A new head pipe has been made because the old one in my opinon is a total loss. The new one is 2" into 2 1/4. Not 2" into 2" like the old one. The back was also cut open and die ground out to the full opening. Back panel was then welded back in. New head pipe. http://tinyurl.com/328c2r Aside from power loss, what other effects would this have. Can this cause or promote detonation? |
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| Author: | Aggressive Ted [ Sat Aug 18, 2007 5:50 pm ] |
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If you got 3 cylinders running free and 3 as bad as you say with that small of a hole for the exhaust to escape I would think it would idle ok, but not much more than that..... heck half of your power is gone! which is quite a in balance. I am surprised it could do 50! If it did, I am sure grumbled, popped and shook allot. Not fun, sorta like putting a potato up your pipe! |
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| Author: | LUCKY13 [ Sat Aug 18, 2007 6:23 pm ] |
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Quote: Forgot one other thing.
The exhaust head pipe (old one). http://tinyurl.com/yp8k5v This pipe has been replaced with a similar design. I cut the back of the old pipe (pictured) open to view the transition and all I could was laugh. The openning that the exhaust guy made was about the size of two quarters (1"x2"). A new head pipe has been made because the old one in my opinon is a total loss. The new one is 2" into 2 1/4. Not 2" into 2" like the old one. The back was also cut open and die ground out to the full opening. Back panel was then welded back in. New head pipe. http://tinyurl.com/328c2r Aside from power loss, what other effects would this have. Can this cause or promote detonation? Yes , causes = Detination, Rich Conditions, High EGT's, Tunning problems, Low RPM power Peaks , reversion back into the intake (which is black soot in the heads intake port, extreeme cases even get all the way up in the intake) , and more. Do you have pics of the pipe cut open, or did I just miss it. Looking at the pic of it in one piece it looks fine. But if it was closed off as much as you say, that is a total joke. As a matter a fact, I dont see how you expect it to breath through the DD mannies with a build at this level. Much less with even more restrictions. I would have to have Headers. I have seen engines that simply have to small a primiary header tube do this, like a Big Block with 1 3/4 pipes before the collector. Then a change to 2" primiary cure the reversion & tunning problems. Jess |
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| Author: | Bren67Cuda904 [ Sun Aug 19, 2007 7:56 am ] |
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The pistons where speced for nitrous. (heavy top). http://tinyurl.com/2jzqnu Looking at my slide calipar, .060 looks like a shade under 1/16". This dosen't look like much compaired to the piston tops. Maybe add some CC's to the head and cut less? Maybe add 5cc to the cambers and only take .030 from piston tops? I don't have any before pictures of the restricted pipe inside. Considering the exhaust restriction, it ran pretty good. (14.97 best) Maybe with three more cylinders working hard I'll be in the 10's. 
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