Is 9:1 compression ratio really that hard to tune on pump

[YanDsm]

Well my engine need a rebuild and i've read all the thread I could find in the last month and I still can't decide what compression ratio to go with. My plan is to run my td05h 20g at 20+ psi on pump (no e85 available here and no meth injection) looking for as close as possible to 400 crank hp. It's mostly a street car, all mods are in my profile. So is 9:1 compression ratio that hard to tune and prone to knock on pump vs 8.5:1 ? Please I want opinion of people who have personnal experience with setup like me.

 

[PrimerPLus]

Im also curious about this. Accept ill br using my current evo 3 16g.

So best to use 8.5 or 9.0? As far as running pump gas without meth inj. I plan on getting meth in the future but not any time soon.

 

[allthrottle]

I ran a similar setup for (9:1 Wiseco's, bastard 20g) for a couple of years on pump for a couple of years without a problem. I've recently tuned a couple of 9:1 pump engines; one with a ebay 20g on 22psi, one with a GT35 at 20psi. They usually require a little less timing.

 

[bastarddsm]

I would definatly use JE's or some piston that has a real quench area.

 

[jjw205]

I have tuned both on pump (93), 9:1 is a little more prone to knock than 8.5:1, believe it or not. You just have to run a little less timing, obviously. Don't look at other people's maps, every car is a little different.

I am running meth injection in my car with 9:1, and I can run a few degrees more timing now. And have the benefit of a little more power off-boost.

 

[PrimerPLus]

So if 400 hp is the goal with 90octane no meth the best choice would be to go with which one?

 

[jjw205]

So if 400 hp is the goal with 90octane no meth the best choice would be to go with which one?

Technically you can make a tad more power with a higher CR. But there's obviously plenty of 1G's (7.8:1) making as much power as 2G's and Evos.

IMO, the 9:1 just takes a little more patience to tune. That's all.

 

[WES_393]

For a 400hp 16g on 90 octane and no water/meth, you'll definitely want to use 8.5 compression. I had a hell of a time getting over 20psi with my 16g on 91 octane and 8.5 compression.

I would only suggest 9:1 on pump gas if you plan to run a more efficient turbo at low-mid boost levels. Turbos create a lot of heat when pushed hard, especially 16g sized ones. That's just my opinion though.

 

[YanDsm]

So, tune a 20g at 20+ psi with 9:1 on pump without meth is doable but you have to tune maybe a little richer and little less timing?

 

[1fastlaser]

All in the tune. My auto car made 604 on 30psi with 9.0:1 pistons on 92 octane.

 

[allthrottle]

So, tune a 20g at 20+ psi with 9:1 on pump without meth is doable but you have to tune maybe a little richer and little less timing?

Exactly. Remember; if you ever want more power, it's easier to change your tune than change your pistons. Go with the slightly higher compression pistons if you have the ability to get it retuned.

 

[WES_393]

All in the tune. My auto car made 604 on 30psi with 9.0:1 pistons on 92 octane.

Your also running a 70mm performance turbo in a 1.01+ A/R turbine housing. A tad more efficient than a 48mm factory turbo in a 7cm^2 housing.


What's the point of using a higher CR if you have to compensate with a weaker tune? That's the entire reason I switched to E85. I was tired of knocking at only 20psi and 5* timing with 91 dino-piss and 8.5 CR. With E85 I can safely run a much more aggressive tune, which of course significantly increased power.

So I agree that it's all in the tune. However, tuning programs can't change physics. And X octane fuel can only handle Y amount of heat before causing issues.

 

[Archer Fabrications]

Ive been doing just fine on my 9.2:1 on 94 octane, before that at lower boost on 92 in washington. No problems. Easy to tune. I'm on an hx40 though and she blows cold air.

 

[donniekak]

Your also running a 70mm performance turbo in a 1.01+ A/R turbine housing. A tad more efficient than a 48mm factory turbo in a 7cm^2 housing.


What's the point of using a higher CR if you have to compensate with a weaker tune? That's the entire reason I switched to E85. I was tired of knocking at only 20psi and 5* timing with 91 dino-piss and 8.5 CR. With E85 I can safely run a much more aggressive tune, which of course significantly increased power.

So I agree that it's all in the tune. However, tuning programs can't change physics. And X octane fuel can only handle Y amount of heat before causing issues.

It's not a weaker tune. The better a cylinder head, combustion chamber, and piston work together, less timing advance is needed to get maximum cylinder pressure at about 18* atdc, where you need it. The more timing advance you have to run, because of lower compression, poor head design, etc, the more degrees of crank rotation you are pushing a piston up against an already lit charge. This is one reason big v8's run 30+ degrees of advance. Their less efficient design requires it.

 

[1fastlaser]

Your also running a 70mm performance turbo in a 1.01+ A/R turbine housing. A tad more efficient than a 48mm factory turbo in a 7cm^2 housing.


What's the point of using a higher CR if you have to compensate with a weaker tune? That's the entire reason I switched to E85. I was tired of knocking at only 20psi and 5* timing with 91 dino-piss and 8.5 CR. With E85 I can safely run a much more aggressive tune, which of course significantly increased power.

So I agree that it's all in the tune. However, tuning programs can't change physics. And X octane fuel can only handle Y amount of heat before causing issues.

Yes. How about a 9.0:1 3065 galant 30psi 93 octane, 530hp.

Or a 9.5.1 60-1 with a p trim turbine on a bolt on bullseye housing (55 a/r) at 27psi 93 octane 11.4@125 on bald all seasons with a bad second.

I went to a gt42 on that setup and ran upwards of 35psi on straight pump gas, swapped everything into the auto car and started to hit the motor with a 50 shot on top of the pump gas. That was 8 years into that motor.

New setup just went 10.200@134 on straight 93 hitting the car with a 75 shot till 6k. My ricer math tells me if I put a 5spd in the car the car should make around 670 to the wheels on pump gas 93.


Again it's all in the tune

 

[WOTDSM]

Not hard at all to tune. My buddy has a 1G running a Borg Warner S256 and 9:1 compression. We flashed a 2G timing table to his car and eliminated all of his knock. He's only running 14 PSI though. I'm sure we'd have to pull some more timing once he cranks up his boost.

 

[rhamlinii]

Low compression helps because it's far easyer to tune. In my experience tunning various cars and setups. Intercoolers, injecters, total timing, cams, and turbo's have more to do with making power on pump then just static compression. I have a 10.5 to one motor sitting and waiting to go back inside my car. I like nitrous, so I prefer low compression motors.