PilotOdyssey.com
http://www.pilotodyssey.com/PO/

Max compression on pump gas?
http://www.pilotodyssey.com/PO/viewtopic.php?f=1&t=13570		 Page 1 of 2
Author:  vwrule [ Sat Feb 01, 2014 11:10 pm ]
Post subject:  Max compression on pump gas?
So I just rebuilt my pilot Engine and cold before run in, I was getting between 185 and 190 psi on two different gages. Hopefully I'm going to start run in tommorow. Will my compression go up or down after initial run in? My squish is .055". What's the max psi I should be running on 94 octane pump gas?
This Engine was originally built by ATV racing. I noticed the new head gasket is .015" thinner than what was in the Engine before it threw a rod bearing.
Author:  Lonerider [ Sat Feb 01, 2014 11:28 pm ]
Post subject:  Re: Max compression on pump gas?
Not an expert, but doesn't the thinner head gasket bump the compression a bit?
Author:  B S [ Sun Feb 02, 2014 6:00 am ]
Post subject:  Re: Max compression on pump gas?
Isn't the max for 91 Oct around 186 ish?
Author:  hoser [ Sun Feb 02, 2014 9:07 am ]
Post subject:  Re: Max compression on pump gas?
Tell us more details about the Engine, what happen to the rod bearing?

If this is a ATV Racing Pilot Engine I would pitch the ATVR head and get a cool head, see if Speedchaser still has them.

At that static compression and a ATVR Engine build I bet that Engine wont last even on race gas.
Author:  B S [ Sun Feb 02, 2014 1:06 pm ]
Post subject:  Re: Max compression on pump gas?
hoser wrote:
Tell us more details about the Engine, what happen to the rod bearing?

If this is a ATV Racing Pilot Engine I would pitch the ATVR head and get a cool head, see if Speedchaser still has them.

At that static compression and a ATVR Engine build I bet that Engine wont last even on race gas.

Speedchaser is out of the heads
Author:  hoser [ Sun Feb 02, 2014 1:19 pm ]
Post subject:  Re: Max compression on pump gas?
B S wrote:
hoser wrote:
Tell us more details about the Engine, what happen to the rod bearing?

If this is a ATV Racing Pilot Engine I would pitch the ATVR head and get a cool head, see if Speedchaser still has them.

At that static compression and a ATVR Engine build I bet that Engine wont last even on race gas.

Speedchaser is out of the heads



He said anything about doing another batch, the cool heads are so much better than stock or modified stock heads for performance and cooling.

Has anybody checked with Duncan Racing http://www.pilotodyssey.com/duncanheadhtm.htm they use to sell cool heads for the Pilot I bought my first cool head from them, I also have bought a cool head from Pro Design in the past, been using the cool heads from Speedchaser ever since he first made them.

If you cant find a cool head I can sell you a stock Pilot head or a stock Pilot head that has already been modified to 49cc and will give about about 165 PSI static compression at about 600' elevation.

Have been down this road with the ATV Racing heads many times in the past they are completely clueless when it comes to head design, lost track how many of their Engine builds that never lasted and poofkaboom until they were hoserized to fix the ATVR problems.

viewtopic.php?f=25&t=3495
Author:  afastcar [ Sun Feb 02, 2014 2:29 pm ]
Post subject:  Re: Max compression on pump gas?
I have a spare speedchaser head I can part with.
Author:  vwrule [ Sun Feb 02, 2014 3:24 pm ]
Post subject:  Re: Max compression on pump gas?
Actually it wasn't so much the rod bearing that went, it was one of the thrust washers between the rod and crank that came apart and distributed its self through out the Engine.
afastcar I pm'd you.
Author:  hoser [ Sun Feb 02, 2014 3:53 pm ]
Post subject:  Re: Max compression on pump gas?
vwrule wrote:
Actually it wasn't so much the rod bearing that went, it was one of the thrust washers between the rod and crank that came apart and distributed its self through out the Engine.
afastcar I pm'd you.



Wow that sucks I have never seen the thrust washers on a Pilot rod go bad like that, any history on the Engine, was it the original bottom end, plenty of oil on the parts when it was taken apart?
Author:  vwrule [ Sun Feb 02, 2014 4:08 pm ]
Post subject:  Re: Max compression on pump gas?
Nothing looked dry, it looked like an original honda rod, no history on the Engine or the pilot other than the guy I bought it off of said it was raced and it was ATVR built. If you go on their website almost everything they list as their mods has been done to it. Some one spent alot of money on it back in the day.
Author:  shoubadaba [ Mon Feb 03, 2014 12:50 am ]
Post subject:  Re: Max compression on pump gas?
165 is max on pump gas anything higher with most expansion chambers you will detonate. your pushing it with 170 and higher
Author:  nickRNR [ Tue Feb 04, 2014 8:39 pm ]
Post subject:  Re: Max compression on pump gas?
Is your existing head missing the indexing tab? If so, no doubt ATVRapin shaved the head.
Author:  vwrule [ Wed Feb 05, 2014 12:39 pm ]
Post subject:  Re: Max compression on pump gas?
I don't have the pilot in front of me but I looked at picture I have on my phone of the Engine, and yep, the tab on the head appears to be missing. You can see the head gasket tab and the cylinder tab but no head tab.
How much would ATVR have shaved off the head?
The Engine does have a CW racing cylinder with a .040" base shim.
So I'm guessing they would have shave off at least .040" to keep the compression up.
Did ATVR build all their Engine to run on race gas?
I ordered a Cometic head gasket which originally appeared to be on the Engine when I took it apart.
The Cometic gasket I pulled was .016" thicker squished than the Versah gasket I just put in and removed.
I wonder How many PSI the compression will drop with the .016" difference?
Author:  adnoh [ Wed Feb 05, 2014 12:45 pm ]
Post subject:  Re: Max compression on pump gas?
How about a little more info. Good info on original post and I would like a little more if you do not mind. I agree with the others on the 165 to 170 max.

For further discussion ,out of curiosity:
Did you increase the bore ?
If so from what to what ?
Did you alter the head for the new bore, if new bore?
New head gasket type and or ID?
Old head gasket and type and or ID ?

Any Idea on pressure reading from last build.

I will assume for a minute you were not running that high before. I will also assume you used a different head gasket.
If statement's above are accurate. Then lets look at what changed and raised it beyond what most refer to as OK.
#1 the bore area increased, larger dia. (due to new larger piston)
#2 the squish was reduced. (due to the thinner head gasket)
#3 the exhaust port was lowered. (due the port lowers as you over bore)

All the above will increase the pressure reading. In turn this will raise your CR (compression ratio)

Few thing to consider as well. When you over bore you also change the squish area ratio and it speeds up the MSV (max squish velocity).

I have seen several times where some one changes the head for 160 to 165 etc then start over boring without moding the head. When you get into the 81.5 and 82 then it gives you a real high rating. I have seen this take a 165 to 185 psi reading when an cylinder went from 80.5 mm bore to an 82 mm bore using the same gaskets and head. Something to look at is the head gasket ID and the head its self after 81.5. to much flat edge hanging into the cylinder.

Any way food for thought.

I will also say it to high right now for pump gas from what I have seen and ran.

Another item to consider is the head studs and the nuts your using. If you head has been milled down and the tab is missing and your running a thinner head gasket, you must shim the head stud with a washer under the nuts. If nut your acorn nut will pop it head open or at least distort it were it bottoms out. This may lead you to a miss torque on the head.
Author:  adnoh [ Wed Feb 05, 2014 12:49 pm ]
Post subject:  Re: Max compression on pump gas?
It appears you posted as I was typing. Call CW and ask him what he recommends. He most likely moded the head once the spacer was installed. It also may not be running the stock type piston.
Author:  vwrule [ Wed Feb 05, 2014 4:01 pm ]
Post subject:  Re: Max compression on pump gas?
I did not increase the piston size but I did put a new piston in.
The old piston was identical, to the new one, just a wiseco 81.5mm.
The bore looked and measured up good, just need a little hone.
Everything went back together the same, except for the thinner Versah head gasket.
Its been a while since the last compression check, (Last Summer), I think it was between 170 to 175 psi.
I should have wrote it down. Next time I will.
I ran 94 octane. Its available at the pumps up here. I'm in BC Canada.
What Octane do most guys run? I know when I go down to Washington state 92 Octane is the max I can find.
Author:  consol [ Wed Feb 05, 2014 4:06 pm ]
Post subject:  Re: Max compression on pump gas?
vwrule wrote:
I did not increase the piston size but I did put a new piston in.
The old piston was identical, to the new one, just a wiseco 81.5mm.
The bore looked and measured up good, just need a little hone.
Everything went back together the same, except for the thinner Versah head gasket.
Its been a while since the last compression check, (Last Summer), I think it was between 170 to 175 psi.
I should have wrote it down. Next time I will.

***ignore this, I misread your post, I thought you went to a thicker gasket
I'll leave the original content for egg in my face though

Someone else will need to chime in, but I see a few issues here

If you were getting 170-175 before, and now after a hone and re ring your getting close to 190 (assuming the same gauges), the old piston/ring was letting too much blow by through and now after the build, your way up there. I also think your compression should go up some after the rings settle also, so you might be looking at a 200 p.s.i. build

I'm not sure what happened, did you blow up the old piston? If so, I'm guessing the old setup needed some serious octane race gas to support a 190-200 psi build

I'm with everyone else on max psi for pump (91) gas at about 165
Author:  adnoh [ Wed Feb 05, 2014 9:45 pm ]
Post subject:  Re: Max compression on pump gas?
Interesting on your numbers. I will be off work tommorow so I will enter you numbers into a spreed sheet I have and see what the difference is. Based upon the difference in head gasket thickness. It a CR based formula however I have Static compression numbers for a variety of Cr numbers to compare it to. I my self use 92 octane pump gas. I did lower my CR on my current Engine rebuild due to a change in rpm and port timing.

Measure your cosmetic and see if it has an 82mmm ID, volume is volume. I have the versah numbers.

Ok did some quick math you decreased the volume by 2.066 cc roughly based on what I have for both gaskets. this will bump you Cr about .291. so if your at 6.9 for 175 than 6.9+ .291=7.191 or 7.2, That will take you to around 185 psi

I will work over tommorow to be sure. You can use any online calc to figure you area decrease by measuring you two head gaskets using ID and thickness. I need to double check the cometic as I thought it was thinner than versah and the versah had a smaller ID than cometic.
Author:  vwrule [ Thu Feb 06, 2014 12:37 pm ]
Post subject:  Re: Max compression on pump gas?
"adnoh" That would be awesome. Thanks.
In a earlier thread a member called "stix" said "The Athena head gasket measures .077 at the ring uncrushed. The edge of the gasket measures .067. It is a three layer."
Can anyone confirm this?
Does anyone know what that gasket ends up being after crush?
Author:  adnoh [ Thu Feb 06, 2014 8:10 pm ]
Post subject:  Re: Max compression on pump gas?
Ok did some number crunching. I had to start with your 175 and work around that number to formulate a guide to base my results on since I did not have all you Engine numbers.

I would advise you call CW and ask him as he was the builder of the Engine as a safe guard.

Remember this just some hacker math.

I will start with the stock numbers and known number to me and what I have done and then work my way through.

6.18 CR at 150 psi (Stock)
6.76 CR at 160 psi
7.17 CR at 171 psi
7.40 CR at 185 psi

I then took your bore and gasket numbers and matched them to what I have. I then came up with the following results.

VW RULE:

7.23 CR at 175 psi, Head Gasket cc of 5.809
7.55 CR at 185 + psi , Head Gasket cc of 3.685
Gasket diff of 2.124 cc

I can only assume the base gasket numbers did not change.

I would recommend the following:
Call Cw and verify
Remove cylinder and head and replace with the same gaskets you were running.

If you post up the exact ID and thickness I can simply enter into a calc and tell you the diff.

Also be aware altitude, cranking rpm and ring condition plays a part in the Static psi reading. It does not in the CR. So there is a margin of error in the numbers. Also be aware you can not interpolate the psi numbers based on CR.
This being said the increase in cc will for sure put you over pump gas based on your original psi number converted to average CR than decrease cc to new higher CR.

Please let us know what CW says and if you get a chance let us know the numbers of you head gasket and type are.

Adnoh
Author:  vwrule [ Fri Feb 07, 2014 3:55 pm ]
Post subject:  Re: Max compression on pump gas?
I got ahold of Chris from CW Racing.
Great guy, answered what he could about my Engine and his Engine builds.
I Highly recommend him if you have any questions.
Basically the way my Engine was set up before was correct and he recomended keeping it the same.
The Engine ran great before. THe Engine wasn't predetonating. The top of the piston look good. The plug chops looked good and the exhaust temps were good when I got it jetted correctly for my area. The guy before me and I both ran this Engine on pump gas with no problems.
The worn out thrust bearing that came apart was not caused by the compression ratio so I know it was correct.
So I'm going to change the head gasket to the thicker Cometic head gasket.
I ordered two head gasket sets and I am waiting for them to arrive, so I can check their thicness.
If they are not thick enough ,Chris at CW Racing said I could phone him up and get thicker ones from him.
He gets Cometic to make different thickness of head gaskets for him and has them in stock.
Author:  hoser [ Fri Feb 07, 2014 6:15 pm ]
Post subject:  Re: Max compression on pump gas?
vwrule wrote:
I got ahold of Chris from CW Racing.
Great guy, answered what he could about my Engine and his Engine builds.
I Highly recommend him if you have any questions.
Basically the way my Engine was set up before was correct and he recomended keeping it the same.
The Engine ran great before. THe Engine wasn't predetonating. The top of the piston look good. The plug chops looked good and the exhaust temps were good when I got it jetted correctly for my area. The guy before me and I both ran this Engine on pump gas with no problems.
The worn out thrust bearing that came apart was not caused by the compression ratio so I know it was correct.
So I'm going to change the head gasket to the thicker Cometic head gasket.
I ordered two head gasket sets and I am waiting for them to arrive, so I can check their thicness.
If they are not thick enough ,Chris at CW Racing said I could phone him up and get thicker ones from him.
He gets Cometic to make different thickness of head gaskets for him and has them in stock.



Good info I am glad to hear he is still in business.
Author:  Dave-Co [ Sat Feb 08, 2014 4:02 am ]
Post subject:  Re: Max compression on pump gas?
i know vw engines about 8.8 to 9 to 1 is as high and into the danger zone with forged pistons, cast pistons no more than 8.5 to 1. the figures i gave are to the point they start detonating pinging when they are warm. a pilot stock is about 6-1 so it seams to me it figures about the same consider a stock 1600 vw came from vw with a 7.5 to 1 and was supost to run 92 octain. my 68 bug i drive all the time is about 6 to1 so i can run California shitty gas with out pinging. my race vw engines are 12.75 to 1 and run 117 octain to keep them cool and ping free. i have not read threw this thread but thought i would chime in on what i know, the higher the octain the cooler the burn that is why you use race gas with high compression. My Vws rave engines would knock them selfs to death with 92 octain and burn a piston before 2nd gear. I have seen it happen! Race gas on a low compression Engine will not give you any performance advantage at all but the reason it gives performance and horspower on high comp engines is the heat control the fuel has in (burn) I ran race fuel all the time when I had 350 air cooled and the heat difference in the Engine from pump gas to race gas was incredible. the air cooled engines loved 115 octain. Try it sometime, you wont believe the temp difference in the Engine compartment from 92 to 115 octain. My 350s ran forever with no teardowns or brake downs with maxima super M race formula at 50 to 1 with 115 octain leaded race fuel. If I owned 1 today I would do the same thing. I run the same combo in all my pilots, they run so much cooler and love the taste of that blue fuel. California fuel I tried 1 time on a weekend, they ran noticably warmer, the fans came on a lot more, all the engines are stock, so it is real difference between the 2 fuels. Do I need to run high octain, no not at 6 to 1 but I love the smell LOL
Author:  King Kx [ Fri Feb 14, 2014 10:48 pm ]
Post subject:  Re: Max compression on pump gas?
Octane is the resistance to gasoline detonating. It does not burn hotter or colder than another fuel. Your ignition timing is the number one thing that affects the cylinder temps. While cranking compression is important, running compression is often overlooked and will be the determining factor of the performance of an Engine. BTW, I run a 9.8CR with 22psi of boost on 93octane. Put that in the calculator and it comes out to something around 18:1CR. For pump gas, that has been my limit. 28-30 psi with 116. The cylinder head design is the limiting factor. The better and more evenly distributed air charge mix you have, the more compression you can run and the more power you can make.
Author:  adnoh [ Sat Feb 15, 2014 3:40 pm ]
Post subject:  Re: Max compression on pump gas?
King, was that for a pilot Engine?
That's pretty impressive.
FYI on my post I used CR, I should have used CCR.
Page 1 of 2 All times are UTC - 5 hours [ DST ]
Powered by phpBB® Forum Software © phpBB Group
https://www.phpbb.com/