View Poll Results: what compression ratio are your running with boost?
8:1
8
2.92%
8.5:1
44
16.06%
9:1
55
20.07%
9.5:1
69
25.18%
10:1
66
24.09%
11:1
32
11.68%
Voters: 274. You may not vote on this poll
High static compression and forced induction
TECH Apprentice
iTrader: (3)
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From: Tinker till it blows, then back it off a notch, maybe!!
Originally Posted by cablebandit
i went higher static. lower dynamic. Every cam is different...do you not know the specs of your cam?
With Darts, my scr would be around 9.7, with afr 205's around 9.2.
Cam in car at present is an LG semi mystery cam G5X1 ...(bought car with it installed)
I do have a comp cam 224/228 .570/.578 114.....intake valve closes @ 67 btdc (.006") I got this cam several years ago, when this was going to be a maggie build.
Last edited by rjw; Sep 28, 2007 at 04:30 PM.
Trying to follow this thread. I've seen a few different answers to my question. I'm at 11.3:1 with afr 205's and 238/240 113 lsa cam. 9" rear 3.89 gears 18x10 wheels with 315's on them.
Not happy with my power level but satisfied I'm about all tapped out with a n/a 347 and my drivetrain.. Mcleod twin disk + 9inch rear + 18x10 aftermarket rims plus 4050 lbs with me in in.
Could I go with a s/c and meth kit and run how much boost to get how much more hp? Also engine was built for a 300 shot, is boost a different build?
Not happy with my power level but satisfied I'm about all tapped out with a n/a 347 and my drivetrain.. Mcleod twin disk + 9inch rear + 18x10 aftermarket rims plus 4050 lbs with me in in.
Could I go with a s/c and meth kit and run how much boost to get how much more hp? Also engine was built for a 300 shot, is boost a different build?
Thread Starter
Launching!
Joined: Mar 2005
Posts: 229
Likes: 0
From: cobourg ON
wow this thread went right where i wanted it to with the mention of static verses dynamic.... Im having a huge problem finding the 6 bolt heads I want... and well obviously now my build has gone way out of hand and i need to spend more time planning everything instead of just building...
New build will consist of
- 1982-1992 camaro body due to huge engine bay space on a track build.
- 427ci lsx build
- heads (yet to be determined)
- cam yet to be determined
- twin turboe charged
- intercooled
- methanol injected
- alcohol
drivterain is slowly coming together with a built 9"
4l80e transmission.
masive cage
and some TLC
if anyone has any news on 6 bolt heads please chime in and well with fuel being alcohol compression will stay hi and boost will be even higher haha approximately 20 psi if not more. call me crasy but I need a fast car for once.
New build will consist of
- 1982-1992 camaro body due to huge engine bay space on a track build.
- 427ci lsx build
- heads (yet to be determined)
- cam yet to be determined
- twin turboe charged
- intercooled
- methanol injected
- alcohol
drivterain is slowly coming together with a built 9"
4l80e transmission.
masive cage
and some TLC
if anyone has any news on 6 bolt heads please chime in and well with fuel being alcohol compression will stay hi and boost will be even higher haha approximately 20 psi if not more. call me crasy but I need a fast car for once.
Low compression = more boost/timing on pump gas before detonation
Higher compression = less boost/timing on pump gas before detonation
If you want to be able to run max safe boost on the streets w/ pump gas get lower compression. Then when you go to the track, turn the boost up and throw in some 104+ oct.
Higher compression = less boost/timing on pump gas before detonation
If you want to be able to run max safe boost on the streets w/ pump gas get lower compression. Then when you go to the track, turn the boost up and throw in some 104+ oct.
I am looking hard at doing E85, kind of the best of both worlds, but you have to pony up on the fuel system.
Add some better fuel and turn the boost up........
well guys I have a local shop buddy running well into the 9's localy and was wondering how safe it is to actually run high compression and boost. I know the general rule is to lower compression and add more boost but hes running 10.5:1 compression N/A and running about 9 lbs of boost through his 426. its running low 9's now and looks as if it has more. yes hes running race fuel i believe 110 but nuthign out of the norm that we cant get at any track around here. I was just wondering if there are any high compression engine out there ont eh street running boost at all? and maybe if you guy can post up your compression ratios that would give me a resonable answer.
Procharger - minimum of 9.5-1 up to 10.5-1 on pump -boost varies by combo.
Our shop car runs 11-1+ compression with 26lbs of boost from a Procharger. And people wonder how our Stangs keep winning championships
Remember,boost levels mean nothing.It's the power output you are looking for. I'd rather get 700rwhp with 4lbs of boost rather than 16lbs of boost.This is where DCR comes in.
[QUOTE=Carnutz;8084523]Thats what I am thinking, With HIGH SCR, you have to detune the snot out of it to make it live on the poorer fuel. I would rather be safe,(lower SCR) on the street and then turn up the boost at the track.....
I am looking hard at doing E85, kind of the best of both worlds, but you have to pony up on the fuel system.
i'v been ruuing 11.4:1 for about year at 8-9 pounds with no issueson on 91 octane, but want more so i switched to E-85 a month ago so i can up the boost. i just need alot more fuel system it's running real lean,(14:1) from 5500-6700
I am looking hard at doing E85, kind of the best of both worlds, but you have to pony up on the fuel system.
i'v been ruuing 11.4:1 for about year at 8-9 pounds with no issueson on 91 octane, but want more so i switched to E-85 a month ago so i can up the boost. i just need alot more fuel system it's running real lean,(14:1) from 5500-6700
like slowhawk said.... if your a race car you want to make the most horsepower with the least boost... all it does is heat up the air... the really fast guys only run about 5# of boost on BIG motors (600+ CI)... its volume not pressure that makes a big difference...
im taking my car from 8.0CR to atleast 10.5CR this winter with a baby blower (d1sc) and try and capture a 6.00 1/8th mile pass...
im taking my car from 8.0CR to atleast 10.5CR this winter with a baby blower (d1sc) and try and capture a 6.00 1/8th mile pass...
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when you can supply enough octane to keep it from detonating. Especally with a blower, the added boost pressure takes added HP to drive.....
Last edited by Carnutz; Nov 9, 2007 at 02:42 PM.
Teching In
Joined: Nov 2007
Posts: 1
Likes: 0
From: Midwest
Someone may have already covered this but I thought I would throw in my two cents about compression ratio. Determine which fuel you want to run and then how much boost you intend to run, and then back into a compression ratio. Intercooling has an impact as well.
When we did the ProCharger pump gas Nova we ran 30psi on 91 Octane. In order to get there we ran looooow (about 7:1) compression. The engine still made more than 1hp/ci naturally aspirated too..
-Chris
When we did the ProCharger pump gas Nova we ran 30psi on 91 Octane. In order to get there we ran looooow (about 7:1) compression. The engine still made more than 1hp/ci naturally aspirated too..
-Chris
Thread Starter
Launching!
Joined: Mar 2005
Posts: 229
Likes: 0
From: cobourg ON
ook guys none of this really matter untill we start talking about camshafts. really the main question was to peak intrest and see who was using what as a base number . I know you can run a 10:1 compression static then it turns out to be 8:1 dynamic with the simple implementation of a camshaft. Valve overlap and durations and advance all have to deal with the dynamic compression side of things that make it possible to run street fuels that your using. my goal is to keep it in street fuel about 94 cause that i swhat we get around here so. anyways i guess it always comes down to that little drum stick to make power
This is a very good thread. I'm having a motor put together right now and am trying to decide on a lot of things. I've pretty much narrowed it down to a lsx 408 with some etp heads. Now I'm trying to decide on the compression I want. I'm using my d1-sc and intercooler set-up that I had on my stock 346. It made 682rwhp with 317 heads, an F14 cam and 13psi. I was very happy with that set-up so I was going to try to set it up simular just bigger and stronger. For that reason I'm thinking I want 10-1 compression, a pretty large cam and low boost. I only plan to run race gas so this set-up should work good with more power potential than say a 9-1 with more boost, right? Higher compresion will net you more power, you just need better fuel or am I missing something?
Teching In
Joined: Jan 2007
Posts: 20
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ok so i just bought a 408 turn key motor. it has 10.8-11.1 compression not sure. but can i run my magnacharger with it at 4-6 lbs of boost with 93 octane? i am going to change my cam to a blower cam but is it possible to do this on pump gas and not really fear anything?
ok so i just bought a 408 turn key motor. it has 10.8-11.1 compression not sure. but can i run my magnacharger with it at 4-6 lbs of boost with 93 octane? i am going to change my cam to a blower cam but is it possible to do this on pump gas and not really fear anything?
http://www.exoticperformanceplus.com...Car.php?car=39 Bob
Why wouldn't it makes sense for a street car?
If we're talking about the same power output, the lower boost (lower intake temp) would be better for pump gas. The higher compression would also enhance gas mileage and drivability. ProCharging the LS2/3 follows this same principle.
Why wouldn't it makes sense for a street car?
If we're talking about the same power output, the lower boost (lower intake temp) would be better for pump gas. The higher compression would also enhance gas mileage and drivability. ProCharging the LS2/3 follows this same principle.
If we're talking about the same power output, the lower boost (lower intake temp) would be better for pump gas. The higher compression would also enhance gas mileage and drivability. ProCharging the LS2/3 follows this same principle.
By the way, I think that I would be content with a stock LS2/3 procharged with low boost. Would make a wicked ride
TECH Resident
Joined: Jan 2007
Posts: 751
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From: Texas
10.1:1 CR with 9-10psi. Pump 93/32oz Torco/Meth/11.4afr/14*@6k, spinning to 6800 then shift 
4k miles beatin on it, so far so good 
Safe tune with lots of insurance (Torco & Meth)....My weekend driver every 2-3 weeks, maybe 
4k miles beatin on it, so far so good Safe tune with lots of insurance (Torco & Meth)....My weekend driver every 2-3 weeks, maybe 
That is what I'm doing!
My goal is 900RWP on the corn with the set up in my sig.
At least there is some benefit to live in the midwest!
You could run a little more compression depending on your goals.
My last setup was a Procharged all iron SBC at 10:1 compression
and 12psi and ~650hp at the motor.
I built the new engine at 9:0 as a middle ground.
If the availability of the E85 diminishes and I have to run 93 octane,
I can set up two tunes for the car and program accordingly.
The tune on the corn will want LOTS of low speed timing, a little more through the curve, and about the same at peak torque.
For fuel, set up the desired AFR at about 8.75-1 and go from there.
E85 is very forgiving on the tune, you could probably take a good gas tune
and add 40% to the entire fuel map to get you started, then trim the
low speed/steady state cells as needed.
Nice build up by the way!
My goal is 900RWP on the corn with the set up in my sig.
At least there is some benefit to live in the midwest!
You could run a little more compression depending on your goals.
My last setup was a Procharged all iron SBC at 10:1 compression
and 12psi and ~650hp at the motor.
I built the new engine at 9:0 as a middle ground.
If the availability of the E85 diminishes and I have to run 93 octane,
I can set up two tunes for the car and program accordingly.
The tune on the corn will want LOTS of low speed timing, a little more through the curve, and about the same at peak torque.
For fuel, set up the desired AFR at about 8.75-1 and go from there.
E85 is very forgiving on the tune, you could probably take a good gas tune
and add 40% to the entire fuel map to get you started, then trim the
low speed/steady state cells as needed.
Nice build up by the way!