too much compression!!

[shadow88]

I know we in the turbo community never deal with very high compression ratios, but I hope someone here has done a little high output n/a stuff.

Background, 95 sohc neon, 11:1 pistons r/t head shaved .035. cranking compression broke a 250 psi gague. (not kidding)!!!Pings like a mother.....

I've searched comp cams' site and crane cams' site and found little help. Basically, we need to lower compression on this engine through a longer duration camshaft. Any suggestions for advertised durations to look for? I was thinking 268ish, but that was honestly a shot in the dark.
thanks.

[Clay]

duration combined with overlap. The more overlap, typically the lower the dynamic compression

[turbovanman²]

Time for C16, ouch,

[tryingbe]

You're running 91 octane already?

[turbovanman²]

You're running 91 octane already?

91 is too low for that, he needs at least 94 octane, or some Diesel fuel,

[shadow88]

Already has 94 sunoco, although it sounds like a diesel, we double checked we pulled up to the 94 pump. This is planned to be a daily driver. It's an all motor neon that has run 14.6's last year.

I'd like to hear any guesses regarding the duration and overlap suggested to lower the static compression (and dynamic compression) to a reasonable level where this car can see daily driver duties without race fuel.

Expected power band from 4000 rpm to it's 7200 rpm fuel shut off.

[jre97]

Is it timed right? sounds to me like cam timing and the valves aren't opening and closing at the right time causing the compression to spike. 11.1 should be fine on high octane pump gas. you might have to pull a little igniton timing. I would go with something in the 270's for duration considering the rpms you want to spin.

[bn880]

Also maybe shimming the head may help a little... ? 250+... holy cr..

[The S is Silent]

I'd shoot this question over to neons.org or Turbododge.com. I have a friend at neons that has run high compression in a neon without a problem, and the guy that goes by allmotor in td.com knows his stuff when it comes to n/a stuff.

[shadow88]

thanks for the inputs.

He has no plans of changing the pistons to lower the c.r., nor does he plan on layering the center sections of head gaskets. He's a member of neons.org and neon canada.

We're treating this as 1/2 a v8, so if you had a v8 with 250 psi cranking compression and it's too high, what cam specs should be used to lower the compression? I understand there's a few people with 11:1 engines on pump gas, but they must have longer duration cams to help bleed of some compression.

the cam timing is correct and ignition timing is not adjustable, uses a mopar performance controller, and he's had that for a few years without issues.

The post that said " somewhere in the 270's' " Was the kind of response I was after. Question has been re-asked in t.d.com. Thanks for any more inputs.

[jre97]

I would look for a 108 to 110 degree lobe center. And maybe read up on some split duration cams. They are usually a good way to bleed compression. If you have desktop dyno you can play with your cam profiles and it's good for giving you a ballpark to look for. i downloaded mine free from a p2p server.

[WVRampage]

I was running 10.5 on a 2002 neon on pump gas,mostly sunoco 94 or exxon93.

[shadow88]

I know it's been done with high compression pistons and pump gas on neons. What cam did you use? Had you ever done a compression test? results?

Was it jre97? could you post a link for the calculator you used?

This car should be a terror when it works but this is too much compression to drive it at this point.

Please keep 'em coming. god I love this site.

[Una]

Replace the spark plugs with diesel injectors. Get the diesel pump off a rabbit..

[gkcooper]

Head on over to http://www.mpgresearch.com and do some reading! There are people running high compression on 87 Octane getting very good fuel economy. There are also a lot of TD's there.

Greg K. Cooper
Huntsville, Alabama

[TurbododgePirate]

I know we in the turbo community never deal with very high compression ratios, but I hope someone here has done a little high output n/a stuff.

Background, 95 sohc neon, 11:1 pistons r/t head shaved .035. cranking compression broke a 250 psi gague. (not kidding)!!!Pings like a mother.....

I've searched comp cams' site and crane cams' site and found little help. Basically, we need to lower compression on this engine through a longer duration camshaft. Any suggestions for advertised durations to look for? I was thinking 268ish, but that was honestly a shot in the dark.
thanks.

Quick question, is it a SOHC or a DOHC? I read the above post and it says SOHC, but a neon R/T head could ONLY be a DOHC. Just wondering. ~~H

[mock_glh]

With that much compression you could probably run about 300 degrees of duration and get away with it (no kidding). 108 lobe separation would work ok with this. Get the cranking compression down around 200 and it should work pretty good. I used to run small block Chevys like this and they ran great on pump gas (93 octane in California back then). The Neon's chamber design is much better than the "wedge" chamber that many V8's have.

[Captain Chaos]

If you have pistons that are designed to give you 11.1:1 with a SOHC head and your using a DOHC head that will raise compression even more, almost a point IIRC, and add to that you milled the head and there is more compression.

[shadow88]

i'll get to that link that was posted soon enough. thank you.

It's a 2002 neon r/t head so it is a sohc, normally refered to as the "magnum" head.

300? wow, that seems pretty wild. I'll pass the info along to him.

As of when I left the shop, he was swapping out his cam for a crane #14 that he had at his house. I think it's advertised at 262/268 duration and .350/.330 lift. I'll let you know how it goes after we do some "testing" tuesday night. Thanks again.

[jre97]

I know it's been done with high compression pistons and pump gas on neons. What cam did you use? Had you ever done a compression test? results?

Was it jre97? could you post a link for the calculator you used?

This car should be a terror when it works but this is too much compression to drive it at this point.

Please keep 'em coming. god I love this site.

It's actually the desktop dyno 2000 program that i downloaded a long time ago from kazaa. I wouldn't say it's gospel but it's good for giving you ideas. I've used it on couple of 350's with the basic program but you need to know head specs, cam specs, etc... to the number to get it accurate. It will create airflow files and cam charts and stuff if you know all of your specs.