Strong possibility that the heads are coming off my 2L beast. while they were off, i figure i will bump up the CR to sneak some HP out.
MY motor has headgaskets and euro 94mm p/c (flat top mahles)
i think it is a tad over 8:1 currently.
been 3 years since i built it - runs great.
so my thinking is, remove the base shims and headgaskets -
I will CC the heads while they are out (cant recall the data when we built it 3 years ago)
How little deckheight can i run? what is max CR i can run on 91 premium unleaded?
If it matters, have mallory dizzy (can back off total advance if it detonates etc..) mallory CDI, and cool b7es NGK plugs.
AA
Full Version: How much C/R can one run on 91 octane pump gas?
here is a link to a compression calculator.
http://www.btinternet.com/~mezporting/header.html
ditch teh head gasket and lap teh cylinder into the head. teh factory posted a bulliten to eliminate teh gasket. are you running a stock cam? valve lift and how deep your heads and or chambers are cut will dictate how low you can set teh deck. 0.040 is a good starting point of reference for deck.
a compression quote might launch a huge debate...
my 8.5 CR did not ping with 89 octane
how thick are your cylinder base shims?
http://www.btinternet.com/~mezporting/header.html
ditch teh head gasket and lap teh cylinder into the head. teh factory posted a bulliten to eliminate teh gasket. are you running a stock cam? valve lift and how deep your heads and or chambers are cut will dictate how low you can set teh deck. 0.040 is a good starting point of reference for deck.
a compression quote might launch a huge debate...
my 8.5 CR did not ping with 89 octane
how thick are your cylinder base shims?
QUOTE(sean_v8_914 @ Apr 22 2006, 09:09 PM) 
here is a link to a compression calculator.
http://www.btinternet.com/~mezporting/header.html
ditch teh head gasket and lap teh cylinder into the head. teh factory posted a bulliten to eliminate teh gasket. are you running a stock cam? valve lift and how deep your heads and or chambers are cut will dictate how low you can set teh deck. 0.040 is a good starting point of reference for deck.
a compression quote might launch a huge debate...
my 8.5 CR did not ping with 89 octane
how thick are your cylinder base shims?
lapping cyl's to heads goes without saying.
i have a big cam, i believe a web 494 or an 86 grind. 3000 is about the beginning of the powerband. do nott recall actual lift numbers (had a folder with the build notes, and cannot find it)
base shims are anybody's guess without the build notes....
stock rocker ratio......
AA
yeah, you'll probably get a big debate.
but remember, physics dictate that more CR = more power = more heat.
Also remember that even with stock compression, 2L heads crack up pretty easily.
That being said, I was comfortable with 8.5 or so. (I think that's what it was, it was .5 over the Euro compression, whatever that is).
Drove the car a lot of miles with that using 91 and sometimes 89, never had any pinging problems or any other problems. But I didn't disassemble the engine to check how the heads were doing. (
I know that when it was disassembled during the first rebuild from the original engine, there were cracks that needed to be welded up)
but remember, physics dictate that more CR = more power = more heat.
Also remember that even with stock compression, 2L heads crack up pretty easily.
That being said, I was comfortable with 8.5 or so. (I think that's what it was, it was .5 over the Euro compression, whatever that is).
Drove the car a lot of miles with that using 91 and sometimes 89, never had any pinging problems or any other problems. But I didn't disassemble the engine to check how the heads were doing. (
I know that when it was disassembled during the first rebuild from the original engine, there were cracks that needed to be welded up)
car has a 7qt oil system.... (front cooler) so oil temps wont be an issue....
wonder what cyl head temps would do?
wonder what cyl head temps would do?
QUOTE(Aaron Cox @ Apr 22 2006, 09:26 PM)
car has a 7qt oil system.... (front cooler) so oil temps wont be an issue....
wonder what cyl head temps would do?
yeah, oil temps are easy to control and keep in the optimal operating range, but all things being equal, higher compression necessarily means higher cyl head temp and combustion chamber pressures.
AS, much as you want, 11 to 1 is a good number, and if it starts to ping, back off on the gas a little, than floor it. 
QUOTE(914-8 @ Apr 22 2006, 09:29 PM)
QUOTE(Aaron Cox @ Apr 22 2006, 09:26 PM)
car has a 7qt oil system.... (front cooler) so oil temps wont be an issue....
wonder what cyl head temps would do?
yeah, oil temps are easy to control and keep in the optimal operating range, but all things being equal, higher compression necessarily means higher cyl head temp and combustion chamber pressures.
agreed
QUOTE(Type 4 Unleashed @ Apr 22 2006, 09:43 PM)
AS, much as you want, 11 to 1 is a good number, and if it starts to ping, back off on the gas a little, than floor it.
ROFL
i dont remember the head CC's..... so ill have to do that.
i hear 56cc is common (gives me a baseline to work with) ((but mine have been decked at least once ugh....))
sounds like fun
Hey, I wasn't kidding.
Here's a tip:
Ceramic coat the faces of the valves, because the intake valve is fairly large, it's large area holds more heat, as the cold intake charge pases the hot valve, the hot valve heats up the intake charge, which promotes detonation, also ceramic coat the exhaust port, the exhaust port, is right next to the intake port, so as hot exhaust exits the port, it heats up the port, which inturns heats up the intake port, which inturns, heats up the intake charge.
By, Ceramic coating the valves, and exhaust ports, you reduce the amout of heat that is trans fered to the intake charge, which deters detonation.
Did , you know Porsche now Ceramic coats the exhaust ports on their production cars.
Do, you know why Nitrious makes so much HP, cause it's so cold.
Here's a tip:
Ceramic coat the faces of the valves, because the intake valve is fairly large, it's large area holds more heat, as the cold intake charge pases the hot valve, the hot valve heats up the intake charge, which promotes detonation, also ceramic coat the exhaust port, the exhaust port, is right next to the intake port, so as hot exhaust exits the port, it heats up the port, which inturns heats up the intake port, which inturns, heats up the intake charge.
By, Ceramic coating the valves, and exhaust ports, you reduce the amout of heat that is trans fered to the intake charge, which deters detonation.
Did , you know Porsche now Ceramic coats the exhaust ports on their production cars.
Do, you know why Nitrious makes so much HP, cause it's so cold.
QUOTE(Type 4 Unleashed @ Apr 22 2006, 10:17 PM)
Hey, I wasn't kidding.
Here's a tip:
Ceramic coat the faces of the valves, because the intake valve is fairly large, it's large area holds more heat, as the cold intake charge pases the hot valve, the hot valve heats up the intake charge, which promotes detonation, also ceramic coat the exhaust port, the exhaust port, is right next to the intake port, so as hot exhaust exits the port, it heats up the port, which inturns heats up the intake port, which inturns, heats up the intake charge.
By, Ceramic coating the valves, and exhaust ports, you reduce the amout of heat that is trans fered to the intake charge, which deters detonation.
Did , you know Porsche now Ceramic coats the exhaust ports on their production cars.
Do, you know why Nitrious makes so much HP, cause it's so cold.
im soo broke i can barely pay attention.... (rimshot)
not ceramic coating anything....
guess i should aim for 9:1 or so?
AA
Go for 10.2:1 or 10.9:1 !!!
QUOTE(Aaron Cox @ Apr 22 2006, 10:22 PM)
QUOTE(Type 4 Unleashed @ Apr 22 2006, 10:17 PM)
Hey, I wasn't kidding.
Here's a tip:
Ceramic coat the faces of the valves, because the intake valve is fairly large, it's large area holds more heat, as the cold intake charge pases the hot valve, the hot valve heats up the intake charge, which promotes detonation, also ceramic coat the exhaust port, the exhaust port, is right next to the intake port, so as hot exhaust exits the port, it heats up the port, which inturns heats up the intake port, which inturns, heats up the intake charge.
By, Ceramic coating the valves, and exhaust ports, you reduce the amout of heat that is trans fered to the intake charge, which deters detonation.
Did , you know Porsche now Ceramic coats the exhaust ports on their production cars.
Do, you know why Nitrious makes so much HP, cause it's so cold.
im soo broke i can barely pay attention.... (rimshot)
not ceramic coating anything....
guess i should aim for 9:1 or so?
AA
What a PUSSY.................... cat.
I think the answer to your initial question, "How much CR can you run on 91 pump gas" is ... Hellifiknow... My 944 runs fine at 10.9:1 on 89 pump gas. Dad's 964 is somewhere around 11:1, newer 996s are 12:1...
I guess your only worry at that point is valve interference
And, of course, having the timing set appropriately.
I guess your only worry at that point is valve interference
And, of course, having the timing set appropriately.
Can't answer your question or hypothesize without knowing the EXACTLY which cam and the REAL cam specs for starters...
I B thinking with the right cam, exhaust, intake, heads etc...
10 to 1 is very doable for premium.
I wonder if we can check your cam specs with a dial indicator and a timing wheel??? (At Johns shop?)
Best to pull it and place it on a cam profiler. or find the markings on the cam.. (this assumes they are correct.) (cam cards can be wrong)
Like Jake says... it all in the .......................................
"Your uglier brother"
I B thinking with the right cam, exhaust, intake, heads etc...
10 to 1 is very doable for premium.
I wonder if we can check your cam specs with a dial indicator and a timing wheel??? (At Johns shop?)
Best to pull it and place it on a cam profiler. or find the markings on the cam.. (this assumes they are correct.) (cam cards can be wrong)
Like Jake says... it all in the .......................................
"Your uglier brother"
Hi Aaron
I can second the 8.5:1. I have Kobelsmitch (sp) euro specs pistons, and bumped down the shims, I think the number was 8.489 :1 . Never had a problem with pump gas. I think this is a very safe ratio for the type 4, more then that, I would suspect some sealing issues might arise.
Good luck
+Karma
Later
I can second the 8.5:1. I have Kobelsmitch (sp) euro specs pistons, and bumped down the shims, I think the number was 8.489 :1 . Never had a problem with pump gas. I think this is a very safe ratio for the type 4, more then that, I would suspect some sealing issues might arise.
Good luck
+Karma
Later
Aaaaron...
Grant has a 2056 with a 494 cam. He was running 9.5:1 with stock pancake cooling and a stock oil cooler. This was with 93 octane gas... 28deg of total advance.
He just added an external oil cooler and bumped it up to 10:1.
I'm gonna venture out on a limp and do some "shooting from the hip" engine building. Removing both the base shim and the top shim should be OK. If you're at 8:1 now, I don't see you getting over 9:1 with both of those gone. Even so, with the cam you have (either the 86 or the 494) you'll be OK. BTW - you didn't check which one it was when you replaced the oil pump????
Check your total timing and see where it's at. You may need to adjust it a little and bring the total advance down a little Do you have a mallory? If not, save your $$$ for one. That way, you can keep the base timing at 10deg of advance at idle and adjust your total advance to your liking.
"Bump it up to hear it thump"
Tom
Grant has a 2056 with a 494 cam. He was running 9.5:1 with stock pancake cooling and a stock oil cooler. This was with 93 octane gas... 28deg of total advance.
He just added an external oil cooler and bumped it up to 10:1.
I'm gonna venture out on a limp and do some "shooting from the hip" engine building. Removing both the base shim and the top shim should be OK. If you're at 8:1 now, I don't see you getting over 9:1 with both of those gone. Even so, with the cam you have (either the 86 or the 494) you'll be OK. BTW - you didn't check which one it was when you replaced the oil pump????
Check your total timing and see where it's at. You may need to adjust it a little and bring the total advance down a little Do you have a mallory? If not, save your $$$ for one. That way, you can keep the base timing at 10deg of advance at idle and adjust your total advance to your liking.
"Bump it up to hear it thump"
Tom
I'm running 10:1 on 91 pump gas with no pinging issues but it's a /6 so probably doesn't help you much....
Aaron
I'm running 9.8 :1 on 91 octane with a stock cooler and stock cooling. It hasn't been a problem. Head temps are not a problem but oil temps have me a little worried. I don't have any special coatings.
Remember that's a static number and it's influenced by other things. Cam for sure, driving style and exhaust too. Clock the cam so you have a pretty good idea of the cam specs then start talking about CR.
Here's a downloadable Degree Wheel I used to check my cam.
Dave
I'm running 9.8 :1 on 91 octane with a stock cooler and stock cooling. It hasn't been a problem. Head temps are not a problem but oil temps have me a little worried. I don't have any special coatings.
Remember that's a static number and it's influenced by other things. Cam for sure, driving style and exhaust too. Clock the cam so you have a pretty good idea of the cam specs then start talking about CR.
Here's a downloadable Degree Wheel I used to check my cam.
Dave
over 9 you should consider dual plugs......91 octane.....now with alcohol.....gotta love it.
to me, bumping the comp on motor with some miles sounds a little dicey. you can't just drive it and enjoy the car for awhile? i still don't understand why the heads have to come off. good thing the car has fresh paint. i plan to be a bit more conserative than 10:1 on the "new" onion.
k
k
street or track?
pull teh oil pump to read the cam. measure the base shims and cc the heads.
we must know what cam it is to determine min deck height
we must know base shim thickness to determine CR change when removed
different cams tolerate different CRs differently
oil temp and head temps are seperate issues
where did the "watch a topic" button go?
pull teh oil pump to read the cam. measure the base shims and cc the heads.
we must know what cam it is to determine min deck height
we must know base shim thickness to determine CR change when removed
different cams tolerate different CRs differently
oil temp and head temps are seperate issues
where did the "watch a topic" button go?
Sean, in the top right corner there is a box that says Options, click it and choose Track this Topic.
Aaron, take out the seals and run it. I don't think you'll bump a full point in CR. But if you've got it apart, I would take some measurements and work with real numbers, not guesses.
Aaron, take out the seals and run it. I don't think you'll bump a full point in CR. But if you've got it apart, I would take some measurements and work with real numbers, not guesses.
I have to agree with Mark. Take out the seals and run the snot outta it. You'll like the compression bump.
My 2270 had 9.5:1 and it was a ball. I love the sound of a high(er) compression motor. It seems to have a nicer "snap" to the sound.
Tom
Aaron, take out the seals and run it. I don't think you'll bump a full point in CR. But if you've got it apart, I would take some measurements and work with real numbers, not guesses.
My 2270 had 9.5:1 and it was a ball. I love the sound of a high(er) compression motor. It seems to have a nicer "snap" to the sound.
Tom
QUOTE(McMark @ Apr 23 2006, 01:00 PM)
Aaron, take out the seals and run it. I don't think you'll bump a full point in CR. But if you've got it apart, I would take some measurements and work with real numbers, not guesses.
QUOTE(McMark @ Apr 23 2006, 10:00 AM)
Sean, in the top right corner there is a box that says Options, click it and choose Track this Topic.
Aaron, take out the seals and run it. I don't think you'll bump a full point in CR. But if you've got it apart, I would take some measurements and work with real numbers, not guesses.
tis my plan.
sounds like i need to work with real measurements
so - I'll CC the heads, degree the cam, etc
Why ya tearing it apart again?
Dont do it. lotta work for neglible gain. 
Want speed? get a sportbike: 0-60 3+ sec, split lanes and go where you want when you want. park it wherever. 50mpg... just dont die.
Want speed? get a sportbike: 0-60 3+ sec, split lanes and go where you want when you want. park it wherever. 50mpg... just dont die.
QUOTE(Headrage @ Apr 23 2006, 10:18 AM)
Why ya tearing it apart again?
might need guides..... (loonnnnggg story - it may not becoming apart)
might need guides? does it smoke a little when you take your foot out of the throttle at high rpm?
k
k
Do you think this is the source of your smoking issue?
Any plans on how to lap the cylinders into the heads when you are just pulling the heads off?
I guess you could pull the cylinders far enough out to get to the wrist pins, yank the whole works, lap the loaded cylinder into the head, and then put it back together.
Good luck. You've got this purty paint job and now have to pull the motor? Sad.
Sounds like its time to sell some body parts and just -6 that sucker.
Tom
Why ya tearing it apart again?
might need guides..... (loonnnnggg story - it may not becoming apart)
Any plans on how to lap the cylinders into the heads when you are just pulling the heads off?
I guess you could pull the cylinders far enough out to get to the wrist pins, yank the whole works, lap the loaded cylinder into the head, and then put it back together.
Good luck.
You've got this purty paint job and now have to pull the motor? Sad. Sounds like its time to sell some body parts and just -6 that sucker.
Tom
QUOTE(Aaron Cox @ Apr 23 2006, 01:25 PM)
QUOTE(Headrage @ Apr 23 2006, 10:18 AM)
Why ya tearing it apart again?
might need guides..... (loonnnnggg story - it may not becoming apart)
QUOTE(rhodyguy @ Apr 23 2006, 10:33 AM)
might need guides? does it smoke a little when you take your foot out of the throttle at high rpm?
k
it is one of 3 things due to all the fuel being dumped in the cylinder.....
1 ) rings
2 ) guides
3 ) or glazed cylinder walls....
so when the carb parts come, we will drive the piss out of it and look for smoke on accel, and over run... (rings vs guides )
QUOTE(Aaron Cox @ Apr 23 2006, 01:35 PM)
it is one of 3 things due to all the fuel being dumped in the cylinder.....
1 ) rings
2 ) guides
3 ) or glazed cylinder walls....
Ooohohohoh... I pick 3. That's the easiest to try and fix.
Yeah, just go give it the Italian tuneup and see what happens. Worst case? You glaze the other 3 walls...
Tom
QUOTE(Tom Perso @ Apr 23 2006, 10:38 AM)
QUOTE(Aaron Cox @ Apr 23 2006, 01:35 PM)
it is one of 3 things due to all the fuel being dumped in the cylinder.....
1 ) rings
2 ) guides
3 ) or glazed cylinder walls....
Ooohohohoh... I pick 3. That's the easiest to try and fix.
Yeah, just go give it the Italian tuneup and see what happens. Worst case? You glaze the other 3 walls...
Tom
yep. that would be fin with me too
this is all do to the cold start enrichment circuit dumping mass amounts of fuel.......tom- yep - i have a mallory ignition, dizzy, cdi, coil......
BTW2 - your friend grant rocks. what a nice guy.
AA
if you are going to drive this on the street 10.1 is a good CR depending on your intake and fuel set up ie 2x45mm bodys with 26lb injector's and a good efi setup 10.1-11.0 CR will not be a problem if you have the OEM set up 9.0 CR is as high as i would go
bug man nrg
www.emeraldperformance.com
bug man nrg
www.emeraldperformance.com
QUOTE(bug man nrg @ Apr 23 2006, 10:51 AM)
if you are going to drive this on the street 10.1 is a good CR depending on your intake and fuel set up ie 2x45mm bodys with 26lb injector's and a good efi setup 10.1-11.0 CR will not be a problem if you have the OEM set up 9.0 CR is as high as i would go
bug man nrg
www.emeraldperformance.com
2 x 44IDF carbs
don't forget to check for valve stem taper. couple that with worn guides, and there goes the money (good thing you appear to have tons of it these days;) ). i don't know what all you did 3 years ago. stock valves?
k
k
QUOTE(rhodyguy @ Apr 23 2006, 11:03 AM)
don't forget to check for valve stem taper. couple that with worn guides, and there goes the money (good thing you appear to have tons of it these days;) ). i don't know what all you did 3 years ago. stock valves?
k
new stock valves by PO (in a box when we got the car - everything in boxes)
It's all in the combo!
I just got back from a 400 mile trip with 9.9:1 on pump gas...
My routine CR is 9.1-9.6:1
I have ran up to 11.3:1 on pump gas with a single spark plug. The camshaft is your friend- nothing is as important to a TIV than the cam! It either opens doors or locks them!
Static CR is only part of my calculation for finding a combinations dynamic CR, and even altitude impacts dynamic CR.
Compression is your friend, it's the lifeblood of efficiency!
Okay, I'm outta here again- just figured I'd pop in!
I just got back from a 400 mile trip with 9.9:1 on pump gas...
My routine CR is 9.1-9.6:1
I have ran up to 11.3:1 on pump gas with a single spark plug. The camshaft is your friend- nothing is as important to a TIV than the cam! It either opens doors or locks them!
Static CR is only part of my calculation for finding a combinations dynamic CR, and even altitude impacts dynamic CR.
Compression is your friend, it's the lifeblood of efficiency!
Okay, I'm outta here again- just figured I'd pop in!
Hey you, come back here!
What would you run for the max on an otherwise dead stock D-Jet 914 2.0?
What would you run for the max on an otherwise dead stock D-Jet 914 2.0?
QUOTE(914-8 @ Apr 23 2006, 02:51 PM)
Hey you, come back here!
What would you run for the max on an otherwise dead stock D-Jet 914 2.0?
With a stock cam 8 to 1.
I am running 9 to 1 witha Raby cam and it nice a cool too.
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