Brings back not so fond memories.
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| High static (cranking) compression https://www.slantsix.org/forum/viewtopic.php?t=29533 |
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| Author: | madmax/6 [ Sun Jun 15, 2008 8:22 pm ] |
| Post subject: | High static (cranking) compression |
The guzzi twin motor is pinging big time, stamped on the block 10.5,but reading threads Doc posted he built it at 10.7, running 114 race gas,with still a bit of ping. Cranking compression is 222, to 230 psi with all plugs out, wondering if re curveing dist will at least let me run 112 race gas cut 50%, 114 race gas is $11.00 a gallon,mark,,,opinions????? |
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| Author: | emsvitil [ Sun Jun 15, 2008 8:34 pm ] |
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E85 has high octane........... but, you'd need to rejet and find it........... |
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| Author: | madmax/6 [ Sun Jun 15, 2008 9:32 pm ] |
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Running a 600 holley,new out of the box from Summit,plugs have just a touch , of color on them,,trying to be overly cautious,Mark |
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| Author: | LUCKY13 [ Sun Jun 15, 2008 9:45 pm ] |
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Thats a lot of cranking compression ( 222 to 230) for a 10.7 engine. Sounds like it needs a bigger cam. What camshaft is in th eengine now ? With no changes to the engine, I second the E85 change over. It will handle that much compression. Jess |
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| Author: | madmax/6 [ Sun Jun 15, 2008 9:53 pm ] |
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Erson 270 cam,mark |
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| Author: | Bren67Cuda904 [ Mon Jun 16, 2008 4:59 am ] |
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Brings back not so fond memories.
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| Author: | DusterIdiot [ Mon Jun 16, 2008 5:33 am ] |
| Post subject: | Err.... |
Quote: wondering if re curveing dist
What's your timing now? Plug your vacc. advance and see if it pings after that, if so then you will definately be limited to only a short amount of timing (not so good on economy...if it's a race only vehicle the vacc. advance will not be needed anyway, check your final numbers and see where your total advance is at..)-D.Idiot |
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| Author: | slantzilla [ Mon Jun 16, 2008 7:14 am ] |
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If it's pinging on 114 you've got some major issues going on.  10.7 motor should not be anywhere near 200, let alone 230, unless you put a stock camshaft in it. |
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| Author: | Dart270 [ Mon Jun 16, 2008 8:10 am ] |
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That cam is not much above stock. My guess is timing is off. Max advance should be 26-29 deg mechanical and I would shoot for 10 deg initial (at idle). Run without vacuum until this is figured out. You should not have pinging with 26 deg full mech adv on 114 octane. Lou |
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| Author: | LUCKY13 [ Mon Jun 16, 2008 9:14 am ] |
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What is the valve lash set at ? I would go as tight as the camshaft will allow on valve lash for the intake side. This will help lower cranking compression a little. Then really go over the distributor curve and make 100% sure where it is. Also you need to know, and make sure the engine is not running lean at all RPM's, plus also when you shift gears. A WBO2 sensor will be needed to check this when running at the track. A high compression engine like this may only need low 20's on the timing and will want to ge atleast 12.8 to 1 on the fuel mix. Although the cranking compression is high I agree with others, it should not be pinging when running 114 fuel. Pinging will kill a engine quicker than anything, it causes crazy stuff like beating the rod and main bearings out of a engine. Get it running without pinging before you even think about doing something like running a 112 50/50 mix or you will loose your engine. Have you done any run & cut passes so you can read the plugs and see what the mixture & timing are showing on the plugs. Jess |
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| Author: | madmax/6 [ Mon Jun 16, 2008 7:13 pm ] |
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Doc is sending me another recurved dist,I was still getting bad pinging at 16,initial,with the 112 50 50 mix ,just a hint now of pinging,at 16,and 90% 114.,will see if dist makes it tolarable,pretty sure I will need cam change to make the pistons live,set the vavles tight,14 on intakes,18 on exhaust,erson called for I think 22,22,mark |
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| Author: | Dart270 [ Tue Jun 17, 2008 7:01 am ] |
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I assume you have double checked the damper timing mark accuracy? How does it run if you retard the timing another 5-10 deg? What is your converter stall? Lou |
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| Author: | LUCKY13 [ Tue Jun 17, 2008 7:40 am ] |
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Yea if this thing is still pinging with 90% 114 fuel then something is out. Maybe Docs dizzy will take care of it because it sounds like your getting way more advance than you think, either becuase the balancer is off, or the dizzy is advancing to far. If the dizzy don tfix it, then the balancer may have slipped after getting hit with new power of the engine ( even though it may have checked out when putting it on). Jess |
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| Author: | Doc [ Tue Jun 17, 2008 9:25 am ] |
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The new distributor should help a lot, the first one was set-up to give 30-32 degrees total at 10-12 initial. Currently we are seeing 36+ at 2800 RPM... way to much, especially with the high stall converter (4000 stall and from what Mark describes, the converter is getting every bit of that) Bottom line, it's over-advanced right when you hit the throttle. The distributor I just set him is much shorter on mechanical advance (12 degrees) and I slowed down the rate a little... I bet that will fix most of the pinging issues, as long as some race fuel is mixed-in. Good thing this is "mostly" a race car.  We knew going into this build that the cam is too small for the compression combo. but we were working with an engine and a pile of parts Mark already had. The decision was to get a running engine into the car so the rest of the project could progress, rather then start over and build a motor from scratch. By running the lash down as tight as possible, some careful distributor recurving and the "right" mix of race fuel, we should get the car down the 1/4 mile with-out melting the pistons out of it. In hind sight, I should have used a thicker head gasket on this engine... we used a .020 shim gasket just to make sure it sealed... if we decide to spray it. DD |
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| Author: | Bren67Cuda904 [ Tue Jun 17, 2008 8:37 pm ] |
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Quote: Thats a lot of cranking compression ( 222 to 230) for a 10.7 engine. Sounds like it needs a bigger cam.
On my 10.4:1 Eileen I was cranking 230psi with a 240@50 110CL cam advanced 6*. I installed a 250@50 110CL advance 2* and cranked 205ish psi.What camshaft is in th eengine now ? With no changes to the engine, I second the E85 change over. It will handle that much compression. Jess I lowered the CR to 9.25 and put back in the 240 cam advanced 2* and I still crank 200 psi to this day.  Just some numbers to chew on. |
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