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Spoke to my tuner today about my motor. I told him I believe my motor is 11:1 compression, I don't know why, but It seems like my motor is roughly 10:5 compression, with the specs below, and both the head and block were decked/resurfaced. I don't know how much.
As far as I know, flat top pistons in my block would yield roughly the same compression as a GSR long block, probably a tad bit higher compression.
My block :
81mm bore
89mm stroke
137mm rod length
flat top piston (wiseco 6542m81)
So a b18c1 is 10:1 compression with flat top pistons (my pistons are flat top)
Lets say I take out the gsr crank, rods, and install ls crank, and rods, and kept the flat top pistons. How much would the compression be bumped up from the longer stroke of the ls crank?
I know gsr rods are longer than ls rods, so that lowers the potential of higher compression compare to the shorter ls rods, but I don't know how to calculate the amount of compression added with the longer stroke.
yes, I researched for hours, yes, I used calculators, which all give me different readings, so I gave up on them.
Reason why I am concerned is because my tuner said flat out he won't tune my motor if its 11:1 compression. he told me I need to find out exactly what my pistons my motor are for (I'm sure to find out what stroke the crank is to determine compression)
See that tab on the block with the circle in side? between the head studs on the number one cylinder. That's the tab you measure to find out how much has been shaved. Once tat circle gets touched the block cant be shaved anymore. Same with the head.
Now you would need a depth gauge and reference a stock block to know how much its been shaved
It looks like RTV or Hondabond to stop that pesky oil seepage from the drain backs B18s are known for.
Travis - If you fill out the zeal werks compression calculator completely and accurately then that is an accurate compression ratio.
Asking the same question here is only going to get an answer that is generated from the same calculator.
And here it is:
The 6542m81 are -2.4cc, correct? And the picture looks like a B18B1?
Im getting 10.33:1 compression with an estimated .006" head + deck milling.
Even with .010" combined milling I get 10.43:1
You're no where close to 11:1. Tell your tuner hes a coward.
How about Nichtskönnerfotze? That's one word. I mean, in German it is. Translate it to English and it becomes two words, but we didn't specify language!
notaracist - i thought so too... thats why I went with the pistons to begin with, to have high comp..
@turbohatch, yup, I'm aware. I don't know what a non decked blocked looks like though, height wise, so I'm not sure how to tell how much has been shaved off.
@muckman
-2.4cc? I am unsure. I actually messaged wiseco earlier when I made this post. As far as I know, that is what I find on google. zealworks cal is showing 10:77 compression
(b18a/b block, b18a/b crank, b18c1 head, I just chose p72 pistons to match my piston, b18a/b rods, oem gasket)
Hes one of the most popular tuners in the seattle area... hes probably tuned everything you can imagine. I was real surprised he said he won't tune it if it was 11:1, I even MENTIONED YOU muckman, and your high comp build.
oh I see, you can change the dome height, well, aren't p72 pistons flat top? Well, the piston I purchase is also flat top, so how come this calculator is saying a p72 piston is -.60cc and websites are saying 6542m81 is -2.4cc?
The valve reliefs are bigger on the Weisco piston compared to those on the OE P72 piston. There are many other dimensions that can affect the compression, so assuming that all "Flat Top" pistons are essentially the same would be like saying all '92-95 civics are "EG"s... not technically true, but you are getting general information that puts you in the ball-park... you get the idea.
Since you cannot prove the amount that has been shaved from both the block and cylinder head, you can only estimate your compression within a few tenths of a point +/-, and using the Zeal calculator would suggest that you are likely between 10.2 and 10.5:1 based on the information you have given us.
A competent tuner should have no problem tuning a car with 11:1 compression, assuming that your goals are reasonable. So maybe there is something else that the tuner is concerned with that you have not shared here. For example, if a customer came to me with an 11:1 rod/piston "B" series engine with a quality turbo kit installed asking me to give him 300 WHP, I would say no problem. However, if the same customer told me he wanted to run 25 psi of boost on pump gas on this same set up, I would attempt strongly to discourage him in his quest and steer him toward a more sensible target so that the engine has a better chance of long term survivability... and if that didn't change his mind, I would likely turn him away as well. No tuner wants to get blamed/flamed for an engine failure on the dyno.
The valve reliefs are bigger on the Weisco piston compared to those on the OE P72 piston. There are many other dimensions that can affect the compression, so assuming that all "Flat Top" pistons are essentially the same would be like saying all '92-95 civics are "EG"s... not technically true, but you are getting general information that puts you in the ball-park... you get the idea.
Since you cannot prove the amount that has been shaved from both the block and cylinder head, you can only estimate your compression within a few tenths of a point +/-, and using the Zeal calculator would suggest that you are likely between 10.2 and 10.5:1 based on the information you have given us.
A competent tuner should have no problem tuning a car with 11:1 compression, assuming that your goals are reasonable. So maybe there is something else that the tuner is concerned with that you have not shared here. For example, if a customer came to me with an 11:1 rod/piston "B" series engine with a quality turbo kit installed asking me to give him 300 WHP, I would say no problem. However, if the same customer told me he wanted to run 25 psi of boost on pump gas on this same set up, I would attempt strongly to discourage him in his quest and steer him toward a more sensible target so that the engine has a better chance of long term survivability... and if that didn't change his mind, I would likely turn him away as well. No tuner wants to get blamed/flamed for an engine failure on the dyno.
thank you for your reply.
I am sharing all the information I can with you guys. I guessed my c/r to be around 11:1, and it sounds like I'm wrong. I have a hx35 7 blade turbo (60lbs/min) and I told him I want to run as much boost as possible, safely on 92 octane.
I assumed all flat top pistons were the same, so shame on me.
So heres a question for yall. There is a gas station that sells e85 locally, about 25 miles away. Do you guys think I should get a tune with both fuels? He said I could run 25-30 psi if I wanted to, but at that point, my 1000cc injectors and fuel pump would be my limiting factor.
In the end, I want 500whp, which I think I would get very very close to, or actually hit with 92 octane, but honestly, even i'm just shy of 500, I'd be happy. I'm just excited to run this holset and see how my setup will perform.
Not...really a Google translatable word, so I feel like that went over people's heads. "Incompitent c**t".
Originally Posted by TravisBiggie
So heres a question for yall. There is a gas station that sells e85 locally, about 25 miles away. Do you guys think I should get a tune with both fuels? He said I could run 25-30 psi if I wanted to, but at that point, my 1000cc injectors and fuel pump would be my limiting factor.
On E85, you're realistically going to need 1200cc+ to see 500 BHP. What sleeves do you have?
Originally Posted by turbohatch96y7
i wouldnt go that high on pump gas. The tune has to be spot on and if you get a bad tank of gas then there goes all this time and money.
I would also look into an aem ems and run a flex fuel sensor. That way you have one tune and never worry about switching maps.
The car runs better on aem too. I can get my motor to idle at 15-16 afr on my old cheap rc1000 high impedance injectors.
Flex fuel is great and all, but if his "tuner" can't/won't do 11:1 CRs, do you think he'll be capable of doing flex fuel properly? I kinda doubt it.
Unless you've played with deck height, combustion chamber volume, excess decking, etc an 81mm b series with flat top pistons falls between 10:1-11:1 typically no more no less
Not...really a Google translatable word, so I feel like that went over people's heads. "Incompitent c**t".
On E85, you're realistically going to need 1200cc+ to see 500 BHP. What sleeves do you have?
benson/darton
Flex fuel is great and all, but if his "tuner" can't/won't do 11:1 CRs, do you think he'll be capable of doing flex fuel properly? I kinda doubt it.
I think I'm going to go to a different tuner.
benson/darton sleeves
Originally Posted by wantboost
Unless you've played with deck height, combustion chamber volume, excess decking, etc an 81mm b series with flat top pistons falls between 10:1-11:1 typically no more no less
If your in the Seattle area, why would you not just go to Speedfactory for your tune? Yea, its probably a little more expensive than what you current tuner will charge. But I highly doubt they will turn you away because of your compression. Plus there reputation speaks for itself. Just my opinion.
If your in the Seattle area, why would you not just go to Speedfactory for your tune? Yea, its probably a little more expensive than what you current tuner will charge. But I highly doubt they will turn you away because of your compression. Plus there reputation speaks for itself. Just my opinion.
I plan to.
Originally Posted by sleepencivic
Did you compression test the motor? what numbers did you see?
No I haven't but this wouldn't tell me anything about my static compression, would it?
No I haven't but this wouldn't tell me anything about my static compression, would it?
It doesn't give a precise static compression "number", but it can create a better correlation between what you believe is your static compression is, and a relative idea as to where you actually are in your static compression.
02-20-2015, 04:58 PM
Compression ratio, flat top
