compression ratio

[slipkknotfan]

i was talking to a friend at work about turbo charging. he told me that he read (i think maximum boost) anyway, he said that when you turbo your motor that you should not mess with the compression ratio. is this true? and is it safe to do with a stock bottom end?

[jalmir]

Yes you can play with the CR (to drop it) and a stock engine is safe to a certain point.

Usually you shouldn't go above 10-12PSI unless you do some serious tuning.

[Keyan]

depending on the size of the turbo, and the amount of CFM it flows, you can run over 15psi on our stock, 10.1:1 CR.

people have used 1.8L pistons/rods or a decompression plate to lower the CR to around 8:1 but the car has no balls off boost.

Remember that the higher the CR, the more power you will make when on-boost.

I am on stock block @ 10psi on a little baby TD04 13g. Pulls good and no issues.

[ElantraEvo]

dk if this helps but like jalmir said, it is possible to run 10-12psi with stock compression but any higher than people usually lower compression. but a while back i was at a shop and the owner was telling me that with lower compression u also lower the hp per psi, so u can make the same power at stock compression with low boost than u can with low compression at high boost, only u wont spool as fast. so i am not really sure if its true that its bad to mess with it, but im thinkin its not really worth it unless ur goin for ridicules power

[BColeman]

I am of the opinion that you lower the compression when you are wanting to make some serious power.

It is true that lowering the compression, you lose horsepower, and you do lose balls when not in boost. However, if you do other things to the motor, in addition to lowering the compression, like installing cams, P&P the head, you can compensate a little for that lost power.

It also depends on the turbo you want to use, what your end goal for horsepower is, whether it's a street car, or track only, etc. We can get into a huge debate over it, and there's no real answer to the question until you decide on what turbo and power level you want to use/make.

I have personally witnessed the CVVT motors making 15 psi of boost and taking it like a champ. Same car, same turbo, overboosted to 22 psi and blew the number 3 cylinder piston rings. That being said, it depends on the turbo and power level you want to achieve.

[cclngthr]

I am of the opinion that you lower the compression when you are wanting to make some serious power.

It is true that lowering the compression, you lose horsepower, and you do lose balls when not in boost. However, if you do other things to the motor, in addition to lowering the compression, like installing cams, P&P the head, you can compensate a little for that lost power.

It also depends on the turbo you want to use, what your end goal for horsepower is, whether it's a street car, or track only, etc. We can get into a huge debate over it, and there's no real answer to the question until you decide on what turbo and power level you want to use/make.

I have personally witnessed the CVVT motors making 15 psi of boost and taking it like a champ. Same car, same turbo, overboosted to 22 psi and blew the number 3 cylinder piston rings. That being said, it depends on the turbo and power level you want to achieve.


I generally recommend using forged steel internals on the engine to prevent any damage and thus beefing up the engine so boosting is safe.

[BColeman]

^ I agree. Wiseco has a nice set of Forged OEM sized, OEM compression ratio pistons, for under $400. If you want to protect the internals, then this would be the ideal thing to do. And you can safely boost 15 psi or a little more, as long as you are tuned appropriately.

Do a little bit of work to the motor, like flowing the head, the intake manifold, and you could bump up the boost a little more, and see more power.

What's the old saying, oh yeah: "There's no replacement for displacement!"

[Cypher]

Yes there is, and its name is Boost.

[soccerfanatics3]

where could someone find those wiseco pistons for the xd

[Keyan]

probaby on the wiseco website :D

[optimoprime]

i really dont get why everyone wants to get forged this and forged that when the highest horse power betas are using 1.8L combo. it just plainly works so why use anything else....

[BColeman]

Actually, right there at SummitRacing.com (http://store.summitracing.com/egnsearch.asp?SearchType=Make&N=700+4294907302+4294907301+4294924641+4294925232+ 115+4294839001&NeXID=5).

And my bad, they are just over $500 for a set.

And yes Cypher, boost is a good replacement, but better if you don't lower the displacement, even better if you increase displacement and boost higher:D

i really dont get why everyone wants to get forged this and forged that when the highest horse power betas are using 1.8L combo. it just plainly works so why use anything else....

Would you really want to drive around town at 7.8:1 compression in traffic, under 3k RPM? I know I wouldn't.

[soccerfanatics3]

so with either of those two sets of wiesco pistons you would not have to have the head bored out?

[BColeman]

Actually, with the 83mm ones, I believe you do have to have it bored. But there are advantages to that.

It would clean up the cylinder walls, smooth them out better, and it would be like having a brand new engine to boost on.

If and when I get to that point, my choice would be for the 83mm, and I would not want to lower compression. But that's my personal choice, and one that some may not recommend. But my power level goal will be met safely, reliably this way.

[soccerfanatics3]

do i even want to ask how much boring out the head will be

[BColeman]

Probably not, but it isn't incredibly expensive either. If you are going to install new pistons in your block, you are going to want to take it to someone to get it "hot tanked", so it can be cleaned and free of carbon build-up, etc.

You are only talking .5mm of boring to do to each cylinder. I'm not well versed in it, but I'd imagine in the $400 range for hot tanking and boring. Maybe less, maybe more, I have no idea.

[soccerfanatics3]

well if its only 400 i will def do that then. i was thinkin about 1500 for some reason

[KeWLKaT]

400$ for boring out pistons? Do you bend over and take it too? It should be less than half the price.

[jalmir]

400$ for boring the block!!!! WTF???

I'll be boring mine and it's 125$ !!!!

[KeWLKaT]

There you go, lol, like I was saying ;)

[BColeman]

Like I said, I have no clue of the cost, I was just throwing a number out there.

Does that price also include hot tanking the block to clean it off? And if so, please tell me where to send my block for when I am ready.

[KeWLKaT]

Ok look.

You want to scrub the inside of your block, when you are already removing 1mm of material from the cylinder walls? There will be nothing but fresh metal to start with, the carbon build up will have been removed.

The only thing you will have to do is to ridge rim it, and that is pretty much standard with any piston installation.

I really fail to see a logic in washing a block before overboring it.

[Denisst99]

before sending out the block to be bored and hot tanked remove each pipe plugs,brush away the rust,retread each holes,remove (if present) the large amount of engine gunk inside the block
that way you'll get back a 90% clean engine block and you wil lonly have to do minor cleaning before final assembly