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+--- Thread: Compression ratio and valve clearance (/showthread.php?tid=507)
Compression ratio and valve clearance - ForcedInduction - 07-12-2009
By machining down the valve pits, one could reduce the compression ratio and increase valve clearance for longer duration and/or higher lift.
(Pictured is a .8mm oversize for a non-turbo 617)
RE: Compression ratio and valve clearance - GREASY_BEAST - 07-12-2009
(07-12-2009, 03:03 AM)ForcedInduction By machining down the valve pits, one could reduce the compression ratio and increase valve clearance for longer duration and/or higher lift.
(Pictured is a .8mm oversize for a non-turbo 617a)
What will that do to the strength of the piston?
RE: Compression ratio and valve clearance - ForcedInduction - 07-12-2009
A few mm shouldn't hurt it. The piston is thinnest in the prechamber cup.
You should see how the TDI guys hack away at their pistons and they still hold up to over 100hp/L.
RE: Compression ratio and valve clearance - GREASY_BEAST - 07-12-2009
(07-12-2009, 04:44 PM)ForcedInduction A few mm shouldn't hurt it. The piston is thinnest in the prechamber cup.
You should see how the TDI guys hack away at their pistons and they still hold up to over 100hp/L.
Cool. Fuel first!
RE: Compression ratio and valve clearance - Gross Polluter - 07-12-2009
What is the benefit of lowering the compression ratio?
RE: Compression ratio and valve clearance - willbhere4u - 07-12-2009
to add more boost
RE: Compression ratio and valve clearance - winmutt - 07-13-2009
I wonder if you could make enough space to do direct injection....
RE: Compression ratio and valve clearance - DeliveryValve - 07-13-2009
Soo, who grinds cams for higher lifter and longer duration?
RE: Compression ratio and valve clearance - GREASY_BEAST - 07-13-2009
(07-13-2009, 09:34 AM)DeliveryValve Soo, who grinds cams for higher lifter and longer duration?
Nobody. Grinding takes material away, in order to do those things you have to add material.
winmutt I wonder if you could do direct injection
Maybe but why? IDI engines can rev way higher than DI engines. I'm still convinced that's how we are going to make power in these 617s... make them flow air then crank the revs out.
RE: Compression ratio and valve clearance - winmutt - 07-13-2009
(07-13-2009, 05:00 PM)GREASY_BEAST Maybe but why? IDI engines can rev way higher than DI engines. I'm still convinced that's how we are going to make power in these 617s... make them flow air then crank the revs out.
CRD
RE: Compression ratio and valve clearance - DeliveryValve - 07-13-2009
(07-13-2009, 05:00 PM)GREASY_BEAST(07-13-2009, 09:34 AM)DeliveryValve Soo, who grinds cams for higher lifter and longer duration?
Nobody. Grinding takes material away, in order to do those things you have to add material.
Actually what I meant was exactly that, add material and then grind the cam lobes for higher lift and longer duration.
RE: Compression ratio and valve clearance - bigblockchev - 07-13-2009
When I dealt with gassers we used to increase the lift and duration of stock cams by reducing the base circle diameter giving more lift and more or less reshaping the peaks of the lobes to be lower and wider in a nutshell. This resulted in slightly different valvetrain geometry meaning the contact surface of the cam was in a different place on the follower. As long as there was a means of compensating for this with different thickness shims and followers and such it worked fine. This was not an answer for really radical cams, they had to be made from billets, but it did work for mildly hopped up cams. Usually welding the cam lobes up was not a great option as the metalurgy was hard to control. So my question regarding the 617 engines is how much adjustment is there in the valve adjustment area. Could this compensate for a small decrease in the base circle of the cam. Someone might like to test the theory. You kind of have to have access to a cam grinding machine but lots of cities have camgrinding shops. I am not sure how much power could be gained by this. Turbocharged gas engines were less sensitive to cam profile changes than Naturally aspirated ones. Also not sure of the difference in the whole gas vs diesel thing as the concept of fueling principals is different. More is always better but may not make a huge difference in one of these engines. With gassers the power difference between OHC and pushrod engines of a given displacement was reduced significantly once you started pressurizing them with the same pressure ratio. Anyone care to jump in here. Cheers Dan
RE: Compression ratio and valve clearance - willbhere4u - 07-13-2009
If you grind the back side of the cam lobe! you can re adjust the valve a bit taller and it will open farther! You never have to touch the lift side of the cam lobe at all! NO welding that is one way to grind a cam and just remove material and gain valve lift!
It will increase lift and duration by holding it open longer and farther!
RE: Compression ratio and valve clearance - GREASY_BEAST - 07-13-2009
The long and the short of it is we just don't know what the 617 head flows like, and where it's problems are. Maybe more duration/lift would help, maybe it wouldn't be worth the trouble. Its pretty darn certain that lower compression ratio would be good though.. but if the bottom end can't take the power what's the point? Again we don't know.
winmutt CRD
Okay, why not IDI "CRD"? Then you have the best of two out of three... You have stable burn at high revs, absolute control over combustion properties, and well... screw efficiency, you got power! And none of that problematic low-end torque that make high performance DI diesels such a pain to drive without breaking stuff.
RE: Compression ratio and valve clearance - Motorhead - 07-13-2009
What I will do is send my cam out to my friends cam shop and have him put it on the cam doctor and see what it is, I first need to degree the cam and see where the factory parkes it and see the actual rocker ratio. If the geometry will permit it I can cut down the base circle of the cam and add duration or lift and maybe both, there are things we do to the heads to compensate for rocker/follower geometry. I run into this problem now and again and so I am not that concerned, when we get more information like cam profile and head flow we can then decide if any change to the valve events are needed.
RE: Compression ratio and valve clearance - ForcedInduction - 07-14-2009
MB increased the lift in 1980 to gain an extra 10hp with the same boost psi.
I'm not sure how much free thread is left on the valves to adjust them up. Might be something to check out in the junkyards.
RE: Compression ratio and valve clearance - Motorhead - 07-14-2009
If there is not enough thread then we could mod the adjuster or sink the valve in the seat and do some back-cut to keep the port flow up.
RE: Compression ratio and valve clearance - Jdmills - 08-14-2009
(07-14-2009, 03:57 AM)ForcedInduction MB increased the lift in 1980 to gain an extra 10hp with the same boost psi.
I'm not sure how much free thread is left on the valves to adjust them up. Might be something to check out in the junkyards.
Ok Question here: how is it that MB gained 10 HP with a cam grind, was there a change in fuel delivery?
does that imply that port and polish work around the valves, would gain some as well with out touching the fuel delivery???
would a "street and strip" (what ever that means) port and polish make a difference in power, with increasing fuel delivery?
RE: Compression ratio and valve clearance - willbhere4u - 08-15-2009
You really don't want to polish any thing in the head! except maybe the combustion chamber to help eliminate carbon build up!
you wanna keep the ports a bit rough to keep to make power! Just grind them for some more flow and call it good!
RE: Compression ratio and valve clearance - willbhere4u - 08-20-2009
I just striped down a 617 turbo and man the pistons have a lot of material to play with! they are 3-4 times beefier than a gas engine of the same displacement!!! very impressive! thEy are almost 3/4 inch thick up top!
RE: Compression ratio and valve clearance - Jdmills - 08-21-2009
(08-15-2009, 12:37 AM)willbhere4u you wanna keep the ports a bit rough to keep to make power! Just grind them for some more flow and call it good!
how is it that rough intake ports, and rough exhaust ports make power?
I would think smooothhhh would be best, unless there is fuel in the intake port that needs to be kept in suspension, then a rough intake port may help.. but that is just my guessing and not knowing..
RE: Compression ratio and valve clearance - willbhere4u - 08-21-2009
That's what I learned form some people that port heads at two different race shop's one for gasser's/bikes and one for diesel/cummin's and they both said the same thing that the air floes better if it is a little rough and not polished you want to make it bigger with less bends! some thing to do with the way the air goes in to the combustion chamber around the valves
RE: Compression ratio and valve clearance - tomnik - 08-22-2009
Shark skin!
The ports should be free from edges and should be smooth concerning diameter changes. But "shark skin" surfaces create turbulent cover directly on the surface and the main flow runs on this cover like on grease.
Then there is also some thing with condensing humidity on polished surface (but this is not too clear for me).
Tom
RE: Compression ratio and valve clearance - willbhere4u - 08-22-2009
that sound like what I have heard!
RE: Compression ratio and valve clearance - Motorhead - 08-22-2009
When I do the port work on my 617 head I will have the finnish as smooth as I can get it in the intak & exhaust ports, I may break the edges in the piston chamber but that is about it. In a diesel with direct or inderect injection there is no need to suspend the fuel in the intake ports, exhaust ports on a gas or diesel like to be smooth.
RE: Compression ratio and valve clearance - shredator - 08-23-2009
(08-22-2009, 02:06 AM)tomnik Shark skin!
yep. by forcing flow to be turbulent with a rough surface, you can help prevent it from separating from the body that it is moving around as it goes past sharp curves in the body. This is why golf balls have all those dimples, frisbees have ridges on the top, and some airplane wings have all those miniature fins and crap attached to the tops of their wings. Those that are interested should look up 'boundry layer'
RE: Compression ratio and valve clearance - Silberpfeil - 09-12-2010
Re: custom camshaft
Sorry I'm a bit tardy in this response (about a month I think)
Anyways if anyone ends up being interested in a custom camshaft these guys are some of the best in the business, plus they do lots of other really neat things. Try www.lsmeng.com
The block lightening they do is outrageous. My friend got a 383 aluminum block down to 41 lbs (56 lbs with steel cylinder liners). Or... how about a 650hp 383 Chevy small block with a total weight of about 200 lbs.
Check these guys out-they're amazing!