Slant Six Forum :: xtream compression using a varible timing box ?

One item that will bollox this, is the engine design itself...even if you whack .125 off the deck, and .125 off the head and with stock pistons, end up at 13:1 compression, the intake valve timing event will limit the build because of the clearance between the piston and the opening intake valve chasing it...

This is where things get touchy and welding up the chamber or a set of dome/valve relieved pistons would help get there without the intake valve contacting the piston...this is why the turbo guys get the field because they don't need to get that close, but can pack the cylinder to get the power out of it.

But that being said, a cast crank engine in the 11-12:1 range would rev up fast and shove a 60's car pretty hard down the range with the right combination of gearing and intake with headers...

I had done this to my last forged crank engine, with the deck height being pretty low, and my chamber being about 36cc...the calcs put it at 13.1:1 SCR...once I mocked the engine up and degreed the cam the valves all marked the pistons...so I had to pull them and 'notch them'...the notches were deep enough (about 6-7cc per cylinder to have good clearance when hot between the piston and valve-I did it at a tight .187 at the peak of the notch which got me a .020 margin of whoops), that it knocked my SCR back down to 11.67:1.... I just took this engine out and the burn pattern on the pistons looked even and no contact with the valves even hot during a 6000 rpm launch. (Too bad the clutch didn't like it...)

Make sure to take the time to brush up on your geometry skills as there is a bit of head scratching and some number crunching when you get to this point even if you break out the clay and check everything...

Back to the original idea, I think if I were to build an 'unlimited' slant, I would opt for the MSD programmable that would adjust the timing per cylinder to get the best burn out of each bore coupled with EFI and Computerized timing curve. (Luckily SS racing doesn't have rules against the MSD-7 and up boxes luckily, but you may not be able to use your car in other classes if so equipped.)

-D.Idiot

Author:	USAJon [ Wed May 08, 2013 5:39 pm ]
Post subject:	xtream compression using a varible timing box ?
is there a variable digital MSD box so you can run extream compression and the timing will adjust @ idle= no ping. I notice they have built in rev limiter . this is all conjecture. I have that cast crank 1980's truck engine and thinking radical experiment...

Author:	Joshie225 [ Wed May 08, 2013 6:03 pm ]
Post subject:
The proper compression ratio with full timing makes more power than a higher compression ratio with retarded timing all else being equal. I suggest you find a copy of David Vizard's book Performance With Economy and read it from cover to cover.

Author:	USAJon [ Wed May 08, 2013 6:11 pm ]
Post subject:
OK but I thinking variable timing... uknow it strange but Mary's new bought 2006 outback 189Kmiles gets 29mpg HWY according to the onboard computer. it has variable timing, the mpggov web site states it should get 26 mpg NEW.

Author:	USAJon [ Wed May 08, 2013 6:20 pm ]
Post subject:	man there's one on ebay kinda
http://www.ebay.com/itm/MSD-8987-Start- ... 79&vxp=mtr

Author:	Fopar [ Wed May 08, 2013 6:24 pm ]
Post subject:
Did you notice it is for "single cylinder". Richard

Slant Six Forum https://slantsix.org/forum/

xtream compression using a varible timing box ? https://slantsix.org/forum/viewtopic.php?t=52003	Page 1 of 2

Author:	DusterIdiot [ Wed May 08, 2013 6:25 pm ]
Post subject:	one item of many to consider...
One item that will bollox this, is the engine design itself...even if you whack .125 off the deck, and .125 off the head and with stock pistons, end up at 13:1 compression, the intake valve timing event will limit the build because of the clearance between the piston and the opening intake valve chasing it... This is where things get touchy and welding up the chamber or a set of dome/valve relieved pistons would help get there without the intake valve contacting the piston...this is why the turbo guys get the field because they don't need to get that close, but can pack the cylinder to get the power out of it. But that being said, a cast crank engine in the 11-12:1 range would rev up fast and shove a 60's car pretty hard down the range with the right combination of gearing and intake with headers... I had done this to my last forged crank engine, with the deck height being pretty low, and my chamber being about 36cc...the calcs put it at 13.1:1 SCR...once I mocked the engine up and degreed the cam the valves all marked the pistons...so I had to pull them and 'notch them'...the notches were deep enough (about 6-7cc per cylinder to have good clearance when hot between the piston and valve-I did it at a tight .187 at the peak of the notch which got me a .020 margin of whoops), that it knocked my SCR back down to 11.67:1.... I just took this engine out and the burn pattern on the pistons looked even and no contact with the valves even hot during a 6000 rpm launch. (Too bad the clutch didn't like it...) Make sure to take the time to brush up on your geometry skills as there is a bit of head scratching and some number crunching when you get to this point even if you break out the clay and check everything... Back to the original idea, I think if I were to build an 'unlimited' slant, I would opt for the MSD programmable that would adjust the timing per cylinder to get the best burn out of each bore coupled with EFI and Computerized timing curve. (Luckily SS racing doesn't have rules against the MSD-7 and up boxes luckily, but you may not be able to use your car in other classes if so equipped.) -D.Idiot

Author:	USAJon [ Wed May 08, 2013 6:26 pm ]
Post subject:
Quote: Did you notice it is for "single cylinder". Richard wrong ebay list fixed link.

Author:	Rick Covalt [ Wed May 08, 2013 6:26 pm ]
Post subject:
Ryan runs a fully programable MSD box on his Dart.

Author:	USAJon [ Wed May 08, 2013 6:32 pm ]
Post subject:
has anyone run larger exhaust valves then intake on a carb engine..in a hi comp motor with overlap cam the large exhaust should in my thought let hot comp exhaust gas leave earlier, thus u could run a higher comp...?

Author:	USAJon [ Wed May 08, 2013 6:45 pm ]
Post subject:	Re: one item of many to consider...
Quote: One item that will bollox this, is the engine design itself...even if you whack .125 off the deck, and .125 off the head and with stock pistons, end up at 13:1 compression, the intake valve timing event will limit the build because of the clearance between the piston and the opening intake valve chasing it... This is where things get touchy and welding up the chamber or a set of dome/valve relieved pistons would help get there without the intake valve contacting the piston...this is why the turbo guys get the field because they don't need to get that close, but can pack the cylinder to get the power out of it. But that being said, a cast crank engine in the 11-12:1 range would rev up fast and shove a 60's car pretty hard down the range with the right combination of gearing and intake with headers... I had done this to my last forged crank engine, with the deck height being pretty low, and my chamber being about 36cc...the calcs put it at 13.1:1 SCR...once I mocked the engine up and degreed the cam the valves all marked the pistons...so I had to pull them and 'notch them'...the notches were deep enough (about 6-7cc per cylinder to have good clearance when hot between the piston and valve-I did it at a tight .187 at the peak of the notch which got me a .020 margin of whoops), that it knocked my SCR back down to 11.67:1.... I just took this engine out and the burn pattern on the pistons looked even and no contact with the valves even hot during a 6000 rpm launch. (Too bad the clutch didn't like it...) Make sure to take the time to brush up on your geometry skills as there is a bit of head scratching and some number crunching when you get to this point even if you break out the clay and check everything... Back to the original idea, I think if I were to build an 'unlimited' slant, I would opt for the MSD programmable that would adjust the timing per cylinder to get the best burn out of each bore coupled with EFI and Computerized timing curve. (Luckily SS racing doesn't have rules against the MSD-7 and up boxes luckily, but you may not be able to use your car in other classes if so equipped.) -D.Idiot why not just cut the head drastically ..why touch the block deck?

Author:	DusterIdiot [ Wed May 08, 2013 6:47 pm ]
Post subject:	No need...
Quote: has anyone run larger exhaust valves then intake on a carb engine..in a hi comp motor with overlap cam the large exhaust should in my thought let hot comp exhaust gas leave earlier, thus u could run a higher comp...? The general rule on NA engines is to have the Exhaust valve about 3/4 the size of the intake as it is easier to empty the cylinder (piston pushing it out, and scavenging during the overlap event) than it is to fill it . If you run a larger exhaust valve you might increase the scavenging event, but during the long overlap event on a high duration cam, you can actually 'suck' the incoming air/fuel charge out the cylinder and into your tailpipe without using it (increasing your fuel usage, and if you get hot gases or a backfire, you might frag the exhaust pipes if loaded up). Some people do run a standard dual pattern cam which is heavy on the exhaust event to help the headers scavenge better. (Instead of the RPD cams we normally get to keep the intake open a little longer to hopefully fill the cylinder better...). Although I have not read the book Josh Recommended, I have David Vizard's other two books "How to build Horsepower Vol 1 and 2", I highly recommend them as a loose guideline in working up engine builds in general, he has a lot of good information in them (although the synthetic oil vs. standard oil section is a little dated...). 2 cents... -D.Idiot

Author:	USAJon [ Wed May 08, 2013 7:10 pm ]
Post subject:
looks like headers would stop the reverse flow of gases.. http://www.mazda.com/mazdaspirit/skyact ... tiv-g.html

Author:	Will [ Wed May 08, 2013 7:11 pm ]
Post subject:
I have run 11 to 1, 12 to 1 and 13.5 to one. same head same cam same intake,pistons ect... the car ran the same every time. MSD 7 al2 .. You do not need to beat up your engine with a lot of compression. It did however get faster with efi. Will

Author:	USAJon [ Wed May 08, 2013 7:15 pm ]
Post subject:
Quote: I have run 11 to 1, 12 to 1 and 13.5 to one. same head same cam same intake,pistons ect... the car ran the same every time. MSD 7 al2 .. You do not need to beat up your engine with a lot of compression. It did however get faster with efi. Will r u gona try this MSD 7531 Programmable Digital 7 Plus Ignition Control

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