RB Designs Carb Mod for EC300 - Anyone had it done?

[noobi]

I was able to finish bolting up my rb-designs mod'd head and carb yesterday and get out for a little rip. As I mentioned before the man's work just looks top-notch. The first thing I did was another compression test. It was 148psi when I sent the head out and it now tests at 150psi. I told him to set it up for pump gas, but I expected we'd be up a bit higher than that compared to other readings I've read about. I've got an inexpensive compression tester I picked up at Autozone, which I assume is consistent if nothing else. Whatever, I emailed Ron to let him know what it tests at now and he said it was fine, more about getting the squish correct. I just wonder if there is something more to be safely had out of it. What do you guys think?

The thing with compression testers is that the variance between testers is huge, they are good to measure changes, but cheaper ones are not always that accurate. We borrowed a compression tester from a friend with a sprint car shop and tested the engines at around 200psi. Borrowed another friends cheap tester and it measured 150psi on the same engines on the same day.

Point being, if your tester measures low, then the change from 148 to 150 seems like a waste of time, but it is more likely that the tester isn't accurate in the first place.

 

[mrkartoom]

The thing with compression testers is that the variance between testers is huge, they are good to measure changes, but cheaper ones are not always that accurate. We borrowed a compression tester from a friend with a sprint car shop and tested the engines at around 200psi. Borrowed another friends cheap tester and it measured 150psi on the same engines on the same day.

Point being, if your tester measures low, then the change from 148 to 150 seems like a waste of time, but it is more likely that the tester isn't accurate in the first place.

I assumed mine would at least be consistent if not accurate, but that may not be the case. I need to get my hands on a good one and get another test for comparison. Thanks

 

[GMP]

Also keep in mind that 300s have a compression bleed hole over the exhaust port for easier starting.

 

[pscook]

There is a difference between compression ratio and cylinder compression. One is the volume of the combustion chamber, the other is the ability of the rings to seal. Just changing the volume does not change the ability of your rings to seal.

Also, did you hold the throttle wide open when testing? How many kicks did you give it before you took your measurement?

 

[Jakobi]

There is a difference between compression ratio and cylinder compression. One is the volume of the combustion chamber, the other is the ability of the rings to seal. Just changing the volume does not change the ability of your rings to seal.

Also, did you hold the throttle wide open when testing? How many kicks did you give it before you took your measurement?

Good points.. But you'd also expect a fresh engine with a higher compression ratio to have higher cylinder compression too.

 

[mrkartoom]

There is a difference between compression ratio and cylinder compression. One is the volume of the combustion chamber, the other is the ability of the rings to seal. Just changing the volume does not change the ability of your rings to seal.

Also, did you hold the throttle wide open when testing? How many kicks did you give it before you took your measurement?

The test I did before shipping the head off was with the carb off, so just the reed cage in place. I pulled the carb before I remembered to get a test. The test after I put the modded head back on was with the carb on, WOT. Each test I did several kicks until the gauge would absolutely go no higher.

 

[pscook]

Good points.. But you'd also expect a fresh engine with a higher compression ratio to have higher cylinder compression too.

I didn't read it was a fresh engine, I understood it to be a simple head swap and carb install. If, However, new rings were involved I would expect higher numbers after it was broken in.

The test I did before shipping the head off was with the carb off, so just the reed cage in place. I pulled the carb before I remembered to get a test. The test after I put the modded head back on was with the carb on, WOT. Each test I did several kicks until the gauge would absolutely go no higher.

Sounds like you got it right. If you didn't put new rings in then your numbers are a correction factor off, i.e.: right on the money. If you did put new rings in, you need to break the engine in and allow the new rings to seat before you test their sealing capabilities.

 

[mrkartoom]

I didn't read it was a fresh engine, I understood it to be a simple head swap and carb install. If, However, new rings were involved I would expect higher numbers after it was broken in.



Sounds like you got it right. If you didn't put new rings in then your numbers are a correction factor off, i.e.: right on the money. If you did put new rings in, you need to break the engine in and allow the new rings to seat before you test their sealing capabilities.

The engine only has about 16 hours on it. I was only able to ride enough last season to break it in really.