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post #1 of 18 (permalink) Old 02-04-2007, 01:22 PM Thread Starter
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Compression ratio

Suggest a compression ratio for me please.

-I am planning a forged block, compression ratio is unknown.
-I will use romeo PI heads and cams.
-I have a 3800 stall torque converter if that matters to you
-I want to run a roots blower rather than a centrifugal

To get the power up to higher PRMs, I was thinking of running lower boost and higher compression since blowers are positive displacement.

I'd like to hear some people's thoughs on this.
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post #2 of 18 (permalink) Old 02-04-2007, 05:56 PM
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What's your redline going to be? A whipple/bell screw type will perform better than an eaton roots. less heat, more possible boost.




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post #3 of 18 (permalink) Old 02-04-2007, 06:03 PM Thread Starter
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I'm considering getting an MMR foged shortblock, so probalby in the 6000-7000 range.. I'm not sure I could make very much usable power past 6000 though since I have to use the PI cams to afford this build.

I considered vortech, but I'm thinking it would be harder to find, and more expensive to setup. I don't have a PI intake manifold, so if I get a roots style blower, I'd be killing two birds with one stone.

I'm trying to keep the blower portion of things below $3000 if at all possible.

-Ryan
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post #4 of 18 (permalink) Old 02-04-2007, 06:08 PM Thread Starter
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Feel free to suggest other options or correct my thinking if you want too. I'm a newbie at superchargers. My only experiance with boost involves turbos, and I'm not going that route with this car. I'm just trying to make the most out of what I've got.
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post #5 of 18 (permalink) Old 02-04-2007, 08:47 PM
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10-ish to 1 compression is about as much as I'd go on anything supercharged forged will be able to take it just fine, I also would run about 6-7psi of boost, just me though, lots run much less and much more do what makes you comfortable

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post #6 of 18 (permalink) Old 02-04-2007, 08:59 PM
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I would go with around 9-1

Vortech superchargers are the are the least expensive you can go with, and they make nasty too.......

Last edited by Eric Z.; 02-04-2007 at 09:40 PM.
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post #7 of 18 (permalink) Old 02-04-2007, 09:52 PM
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with roots blower you can run lower comp and run high boost for good power. If your going forged might as well lower the comp to 8.5:1 and crank the boost up. You only want to keep the comp up if your going with centrifugal because they dont start making boost till higher revs

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post #8 of 18 (permalink) Old 02-04-2007, 11:54 PM
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You have to make up your mind what kind of boost you want to run.
If you want to make good power
- low or mid boost = high comp
-high boost= lower comp
You can ran high comp with high boost but you'll have to run racing gas.
If you get your short block built with low comp like 8.5:1 and run low boost you're just wasting your money and hp.My brother is running 10.8:1 with vortech blower without intercooler and it's running great so far.

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post #9 of 18 (permalink) Old 02-05-2007, 11:42 AM
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with a 3800rpm stall and only running PI cams and Vortech blower will work ALOT better then a roots type. at 3800rpm stall you will be making plenty of boost with a vortech off the line.

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post #10 of 18 (permalink) Old 02-05-2007, 09:36 PM Thread Starter
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Ok, so I was being stupid by wanting a roots blower. With a vortech, at 8 psi, what compression ratio would be best? 9.0:1?

Also, any suggestions on picking vortech kits?

Thanks,
-Ryan
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post #11 of 18 (permalink) Old 02-06-2007, 08:57 AM
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9.0:1 is fine for up to around 11-12psi on 91 octane with a good tune. I don't have much experiance with vortechs on 4.6L, mines on my 3.8L and with 9.2:1 compression I have no issues with 9psi boost.

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post #12 of 18 (permalink) Old 02-07-2007, 10:38 AM Thread Starter
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I'll go 9.0 to be on the safe side. I want this engine to last a longgg time.

Any suggestions on picking out a Vortech Kit? I.E. Things to look for? I've also heard something about a power pipe, and have no idea what it is
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post #13 of 18 (permalink) Old 02-07-2007, 11:02 AM
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This sounds alot like my build, i have a low compression forged motor built already, im just trying to decide on a blower kit.

Jim

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post #14 of 18 (permalink) Old 02-07-2007, 03:32 PM
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I wouldn't go over 9:1 in a V8.

I have a Dodge Stealth with 8.5:1 Ross forged pistons with twin TD04-15G turbos. With the 255lph Walbro and the 550cc injectors, I can run 19psi. Stock for 300 horsepower is 9psi/8:1... and that's in a 3.0 V6. I'm bored .040", custom true dual exhaust, port matched heads, open air intake, and an apexi s-afc.

I got flamed on another site for giving horsepower estimates, so I'll let you guys judge for yourself here. Check near the very bottom of the page under the 1/4 Mile Track Performance. One guy has mods like mine.

In a V8 with 9:1 @ 9 - 10psi, you'd be making some very good power from a supercharger. I know compression isn't ALL that there is to factor into the power, but remember, boost IS compression... it's making compression.

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post #15 of 18 (permalink) Old 02-10-2007, 12:08 AM
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Quote:
Originally Posted by Silenced
Ok, so I was being stupid by wanting a roots blower. With a vortech, at 8 psi, what compression ratio would be best? 9.0:1?

Also, any suggestions on picking vortech kits?

Thanks,
-Ryan
Not stupid, you'll just get more horsepower for your dollar out of the Vortech than you will say a Roots or a Twin Screw set up. For someone wanting a ton of low end grunt, 100% stock drivability, and has the money to spend on it, the Positive Displacement blowers on a heavy car like ours is that cat's meow. But since you're pinching pennies and it sounds more like you're building a street/strip brawler, the Vortech might be a better choice. For what it would cost you for an intercooled KB 9psi unit and the custom fabrication work you would need to do to install it, you could pay for the Vortech, a full PI swap and a nice Throttle Body/Plenum combination. That'll put you way ahead as far as power is concerned.

Since you're going forged internals, feel free to keep the compression in the 8.5 to 9.0:1 range and pulley it for a lot more boost than what the Vortech is equipped to deliver in stock trim. Going from a standard 3.60" pulley to say a 3.33"-3.25" will not only raise you peak airflow levels, but it will spool the blower up much faster and pick things up on the bottom end quite a bit as well. Combine that with your 3,800-stall converter (and I'll assume at least a 3.73:1 rear gear ratio) and you'll be hard pressed to find a Roots or Twin screw blower guy with the same amount of money into his set up that will pull on you from a stop light. Once you get past that first 60ft, you'll be in the meat of you power band and its all S-Trim, all the time.

Sounds like a fun project. Just be prepared to dish out the money need in order to make it happen. Although it will be cheaper to put together than a Twin Screw car, you should still plan on plunking down about $10,000-$12,000 minimum to do it right.

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post #16 of 18 (permalink) Old 03-01-2007, 10:55 AM Thread Starter
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Well guys, It looks like I've moved forward on this plan.

http://forums.tccoa.com/showthread.php?t=96617

I think I'll probably go with 8.5:1 compression ratio with this blower. I want as little chance of predetination as possible. Its a little on the low side I think, but lemme put it this way -- I'd like my kids to be able to feel this motor pull someday, and I'm not even dating at the moment. I'd rather have it last than make a crazy amount of power.

Assuming I can't get someone to build me a motor for around $4k before I'm ready to get started, I've been looking at the MMR 600 shortblock. I'm not quite sure how built up I'd need this sucker as I havn't had a blower before. Are there any trouble spots that I need to beef up? Here's a link: http://www.modularmustangracing.com/...hortblocks.htm

They have other options listed, and I'm not sure if I actually NEED them or not to have a reliable motor:
Coated Pistons (ceramic dome/teflon skirt) $399.99
Brand New Current production Aluminum Block +$399.99
Upgrade to forged crankshaft +249.99
ARP Mainstuds (recommended for 600+HP) +169.99
MMR Street/Racing Oil Pump (highly recommended) + $199.99
ARP Headstuds and MMR/Felpro Extreme Duty Headgaskets + $369.99
MMR windage tray and hardware kit (+15HP) + 129.99

The Windage tray I can and will get elsewhere. I know I don't need the forged crank. What I don't know about is the ARP stuff and the coated pistons. What are your thoughts on those?

Also, concerning Oiling -- Does anyone have any thoughts on HO Oil pumps and deep sump pans? Typically the HO pumps are only suggested for 4v applications, but the vortech might change that.
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post #17 of 18 (permalink) Old 03-01-2007, 11:40 AM
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Just to give a reference Timb used the FRPP roots with a stock PI motor (around 9.5-1) for many many miles.
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post #18 of 18 (permalink) Old 03-02-2007, 09:10 AM Thread Starter
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Bump for shortblock advice! (sorry, this section doens't get as much traffic, and maybee someone will see it on the list)
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