8.5:1 or 7.8:1 which is better??

[AVC-R]

Ok I understand the concept behind compression ratios and all, but with the 8.5:1 in the 7bolt doesn't that make for less boost as compared to the 7.8:1 in the 6bolt? If so then why is it so popular to get the 1g block and put 2g pistons in it? just kinda lost and haven't found a good answer on here that i can understand, i may be an idiot though

 

[Slippi84]

Ok I understand the concept behind compression ratios and all, but with the 8.5:1 in the 7bolt doesn't that make for less boost as compared to the 7.8:1 in the 6bolt? If so then why is it so popular to get the 1g block and put 2g pistons in it? just kinda lost and haven't found a good answer on here that i can understand, i may be an idiot though

Because the higher compression makes for slightly faster spool and more power at the same psi level so it's kind of a toss up. If you have a big turbo I would go 7:8:1 as more boost puts you more in your turbo's ideal area of operation but with a 16g type turbo where you don't plan on running really crazy boost I would go with the 8:5:1 ratio.

 

[AVC-R]

i see that makes sence overall what i am trying to do is figure out what engine to but and right now i am really leaning toward the 6bolt cyclone engine cause that has 8.5:1 and it's a 6bolt(more reliable) cause i crankwalked my 7bolt and i don't just want to run out and buy a new engine. i would really like to find a laser RS engine with the yellow top 510cc injectors and the big 16g but the odd's of that are slim to none. i think no matter what i am gonna buy a 6 bolt though

 

[Slippi84]

i see that makes sence overall what i am trying to do is figure out what engine to but and right now i am really leaning toward the 6bolt cyclone engine cause that has 8.5:1 and it's a 6bolt(more reliable) cause i crankwalked my 7bolt and i don't just want to run out and buy a new engine. i would really like to find a laser RS engine with the yellow top 510cc injectors and the big 16g but the odd's of that are slim to none. i think no matter what i am gonna buy a 6 bolt though

Yeah don't waste yoru time with yellow top 16g combo besides 510's won't do jack if your trying to really move with a 16g. Get a plain 6bolt throw the 1g(90 becuiase they're big rods) rods on 2g pistons and get you a good 16g and your straight.

 

[AVC-R]

Sounds good thats what i will probably end up doing. but was i correct that the jdm 1g cyclone engine had 8.5:1 and not 7.8:1??

 

[EvolvingGST]

Simple fact that the 1G has better rods and 2G has better pistons. Now as far as I see it really doesn't make a terrible difference unless you are getting a HUGE turbo. I would say get 8.5 its better for daily driven applications for the fact of what compression does in the combustion cycle. As well as the fact unless you're gonna run over 30 PSI its not really a hinderence.

 

[Slippi84]

No i'm pretty sure they're still 7:8:1 why who told you they were 8:5:1?? As far as I knew they were just 6bolts with dual runniner intake manifolds and emissions stuff removed.

 

[Slippi84]

Simple fact that the 1G has better rods and 2G has better pistons. Now as far as I see it really doesn't make a terrible difference unless you are getting a HUGE turbo. I would say get 8.5 its better for daily driven applications for the fact of what compression does in the combustion cycle. As well as the fact unless you're gonna run over 30 PSI its not really a hinderence.

The 2g pistons aren't better just higher compression. They are only better persay if you plan on running less boost ir your trying to squeez every pis out of your engine before it starts to knock then the 7:8:1 is better.

 

[AVC-R]

so you can run more boost with the 8.5:1 than the 7.8:1? And i saw that they are (the cyclone engine) 8.5:1 in a thread about the cyclone.

 

[Slippi84]

so you can run more boost with the 8.5:1 than the 7.8:1? And i saw that they are (the cyclone engine) 8.5:1 in a thread about the cyclone.

No actualy you run more boost on the 7:8:1 compression. Think of it like this the lower your compression teh higher tolerance to knock. The higher your compression the faster your spool and slightl more hp at the sae psi level. In my opinion the 7:8:1 setup is fine and def easier to build.

 

[ChicksDigBoost]

You can run just as much boost with the 8.5:1 as the 7.8:1, its all about the tune.

 

[Slippi84]

You can run just as much boost with the 8.5:1 as the 7.8:1, its all about the tune.

Yeah of course you can add fuel or pul timing but I was referring to all things even. If you mess with the tune hell you coudl run the same amount of boost with 9:0:1 that doesn't make it the same thoug. Especialy since timing even more then a/f ratio will net you big gains.

 

[MonkRX]

I think the point is that you'll be changing engine internals before you have the chance to see how far the 1G/2G pistons go. I mean most people say the internals can take 400HP reliably. Most people here probably won't run either the 1G or 2G pistons past 26PSI, and both 1G/2G pistons should be able to handle that with a good tune.

Anything past that and you should really look into upgrading your internals anyway. So the most part, they both have the same HP potential, its just that the 8.5:1/2G pistons give you better low end power/response.

 

[MitsuBoost]

another factor would be your available octane gas, we have 91 octane here along with 100+ degrees during summer, then add hi boost levels to that and you're asking for it!! Im leaning toward the 7.8:1 pistons for my rebuild for those reasons

 

[AVC-R]

So your saying that when i would tune it then i tune it to the amount of boost i want to run, no matter what comp. ratio i have? and what all would i have to do to tune it? i don't have the money for the DSMlink right now so am i limited on what i can do to tune it?