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

Shaving Head--increasing compression
https://slantsix.org/forum/viewtopic.php?t=21408		 Page 1 of 3
Author:  Daddiojoe [ Thu Jan 11, 2007 11:58 am ]
Post subject:  Shaving Head--increasing compression
What's the best/simplest way to increase compression? I'm going to switch to propane, and will have 103 octane to play with, so I'm figuring I can increase the compression ratio.

I'd like to get it up to 10:1 or even 11:1. What's the best way to do it? Can I do it all with the head? I've also got some oversize valves--are they going to cause problems with banging into the pistons?

Finally, I haven't been able to find a whole lot out there about propane and higher performance. I'm assuming that a higher compression ratio would be beneficial. Is my thinking correct?

Also plan on Dutra Duals. I currently have a Super Six on a 727 AT.

Thanks for your thoughts and theories,

Joe
Author:  BigBlockBanjo [ Thu Jan 11, 2007 12:28 pm ]
Post subject: 
I would say the best way($$$) would be a set of custom pistons.
The cheap (easy) way to do it would be to mill the mess out of the block and head......I still don't know if you'd get to 11:1 or not. Your chamber size should be conservative....but the pistons are sometimes .250 or more down in the hole, and milling has its limits. :shock: In that case...I'd use the custom pistons. Forged material wouldn't hurt anyway on a blown application. :)
My .02....
BBBanjo
Author:  Doc [ Thu Jan 11, 2007 12:51 pm ]
Post subject: 
High compression with-out milling or custom pistons can be done easily with a set of 198 con rods. :D
The hard part... finding a set of 198 con rods. :(
DD
Author:  Daddiojoe [ Thu Jan 11, 2007 12:56 pm ]
Post subject: 
OK--interesting tips. So how much should I be able to safely take off from the head.

What's the best way to tell if an engine is a 198? Are used connecting rods going to be in good shape generally?

Thanks,

Joe
Author:  70valiant [ Thu Jan 11, 2007 2:59 pm ]
Post subject: 
I had 0.100" taken off of my head resulting in 39cc chambers which I feel are too small. If I were to do it all over again with a different engine I would take 0.050" off both the head and block, use a steel shim head gasket and, use oversized valves. My engine is bored 30 over and using a felpro head gasket I have a measured 9.8:1 ratio. My biggest bottle neck is my cam though.
Author:  Ron Parker [ Thu Jan 11, 2007 5:48 pm ]
Post subject: 
Me being a dumb azz why are you going to propane . Usually propane does doint have as much bang for the buck as gasoline. Its the burn rates. Hell you will have to ask Lou or Charlie for that answer. Thanks Ron Parker :D









It Aint Over Until I Win











It Aint Over Until I Win
Author:  mpgmike [ Thu Jan 11, 2007 7:50 pm ]
Post subject: 
It is generally accepted that 0.100" off the head is safe and that typically gets you about 11.5:1 compression. Of course that varies from one casting to another. I milled one 0.055" and got a 10.25:1 ratio. Unless you go "Charles Manson" with the "killer" cam, you should have no clearance issues, even with oversized valves. I have a power adder (turbo set-up) listed in the For Sale section right now. Still available. Propane injection is rarely used on gasoline engines. It's a diesel sort of thing.

You might want to look into milling the head and block to get your compression up to around 12:1 and running a water/alcohol injection system. That will knock out the detonation issues. Of all the tricks I ever tried on the slant (and I've tried nowhere near what DD has), the absolute best power adder is a well ported head...period.

Mike
Author:  Avenger2040 [ Thu Jan 11, 2007 8:47 pm ]
Post subject: 
How much you can mill the head and/or block also wich would be the biggest cam you can put without needing new rods or pistons?.
Author:  Charrlie_S [ Fri Jan 12, 2007 2:58 am ]
Post subject:  Re: Shaving Head--increasing compression
Quote:
What's the best/simplest way to increase compression? I'm going to switch to propane, and will have 103 octane to play with, so I'm figuring I can increase the compression ratio.

Finally, I haven't been able to find a whole lot out there about propane and higher performance. I'm assuming that a higher compression ratio would be beneficial. Is my thinking correct?



Joe
You are correct about raising the compression ratio, when using propane.
When changing from gasoline to propane, with no changes to the engine, you will have a power loss in the neighborhood of 10-15 percent. Propane has less heat (BTU) content then gasoline. By increasing the compression ratio, and using a more agressive ignition timing curve, Power levels will be about the same or slightly higher then with gasoline. Propane will work well with a turbocharger, without raising the compression ratio. I have most of the parts to do a propane/turbo installation. Just need to get the time.
Do you have a particular reason for going to propane? My reason is just to be different.
Author:  sick6 [ Fri Jan 12, 2007 4:03 am ]
Post subject: 
if you have your heart set on a particular comp ratio, cc the head first.

just for reference:

on my head and block, .090 off of the head + .060 off of the block gave me 10.4 to one (with a head gasket of .040).
Author:  70valiant [ Fri Jan 12, 2007 1:39 pm ]
Post subject: 
Quote:
It is generally accepted that 0.100" off the head is safe and that typically gets you about 11.5:1 compression. Of course that varies from one casting to another. I milled one 0.055" and got a 10.25:1 ratio. Unless you go "Charles Manson" with the "killer" cam, you should have no clearance issues, even with oversized valves. I have a power adder (turbo set-up) listed in the For Sale section right now. Still available. Propane injection is rarely used on gasoline engines. It's a diesel sort of thing.
That is incorrect.
There is no way you removed 0.055" from the head only and got 10.25:1 CR
It is generally accepted that removing 0.100" results in a CR of approximately 10:1 with a steel shim head gasket of 0.019"
I took 0.100" off the head in my car and there is now way I am over 10:1. I can still run 87 octane with an initial advance of 10*
Author:  Daddiojoe [ Sun Jan 14, 2007 9:26 am ]
Post subject: 
Thanks for the tips. Any ideas on how aggressive the re-curved timing should be, Charlie? Also, should I be switching from the blue box to the orange box on my electronic ignition, then?

Top 10 Reasons to go Propane

10. Chicks dig it

9. Hank Hill gives it a big thumbs up

8. 50 gallons of fuel w/o the big weight increase

7. No cold starting problems

6. simpler and more efficient fuel metering

5. hi-performance possibilities

4. cool blue diamond sticker

3. who else has done it?

2. lower emissions, cleaner burning-The Environment

1. Because I can.


I guess I'll be cc'ing the head to see how much should be taken off.


Joe
Author:  DusterIdiot [ Sun Jan 14, 2007 10:00 am ]
Post subject:  At least one person did it...
Quote:
3. who else has done it?
Someone over on the East Coast had a Ram truck that they had "converted to dual fuel" so they could run Propane for highway use and gas for starting and in town a few years back, don't remember who it was though.

Changing to the Orange box is only necessary if you think you're going to be revving the mill into the 4000+rpm range quite often...unfortunately the new MP boxes aren't as good, quality wise as the one's offered 10-15 years ago...

-D.Idiot
Author:  Daddiojoe [ Sun Jan 14, 2007 11:22 am ]
Post subject: 
Thanks for the orange box tip, D'idiot. Good to know. It doesn't make much sense to warm up your engine on propane. That's one of its beauties--it's already a gas and as warmed up as it needs to be when it hits the engine.

Joe
Author:  Daddiojoe [ Sun Jan 14, 2007 11:23 am ]
Post subject: 
Thanks for the orange box tip, D'idiot. Good to know. It doesn't make much sense to warm up your engine on propane. That's one of its beauties--it's already a gas and as warmed up as it needs to be when it hits the engine.

Joe
Page 1 of 3 All times are UTC-07:00
Powered by phpBB® Forum Software © phpBB Limited
https://www.phpbb.com/