Blower vs. Higher Compression/ Nitrous
Thread Starter
Melting Slicks
Joined: Sep 2004
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Blower vs. Higher Compression/ Nitrous
I have a 383 that I built to be a NA high compression motor, turns out the machine shop gave me a bad calculation and I ended up with about 9.4:1 compression.
I have been considering two options:
#1 Milling my heads, which should get me up to 10.4:1 and if I can using a .015 head gasket which should bring me up to 10.8:1. That's about as high as I can get it. Going with some higher ratio rockers, port matching the intake and shooting the engine with a 100-150 shot of nitrous.
#2 Using a thicker head gasket if I can which should bring me down to 8.5:1, ditching my Victor Jr. for a small roots supercharger, and leaving it at that (with an incorrect cam for boost) Profile: .520 in .540 ex 236 in 242 ex @.05 LSA 110. Or maybe running the charger with my compression as it is right now and using an MSD box to pull timing as I gain boost. Will this even work sufficiently?
If anyone cares to know, I have the 6" rods, all forged internals, AFR 195 heads, comp roller cam, and Mighty Demon 750 annular carb. Give me some opinions!
I have been considering two options:
#1 Milling my heads, which should get me up to 10.4:1 and if I can using a .015 head gasket which should bring me up to 10.8:1. That's about as high as I can get it. Going with some higher ratio rockers, port matching the intake and shooting the engine with a 100-150 shot of nitrous.
#2 Using a thicker head gasket if I can which should bring me down to 8.5:1, ditching my Victor Jr. for a small roots supercharger, and leaving it at that (with an incorrect cam for boost) Profile: .520 in .540 ex 236 in 242 ex @.05 LSA 110. Or maybe running the charger with my compression as it is right now and using an MSD box to pull timing as I gain boost. Will this even work sufficiently?
If anyone cares to know, I have the 6" rods, all forged internals, AFR 195 heads, comp roller cam, and Mighty Demon 750 annular carb. Give me some opinions!
Last edited by enkeivette; Nov 3, 2007 at 10:21 PM.
Safety Car
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From: Pettis Performance 565 with two stages of Nitrous Supply nitrous 1.082, 4.61 at 155, 7.17 at 192
I have a 383 that I built to be a NA high compression motor, turns out the machine shop gave me a bad calculation and I ended up with about 9.4:1 compression.
I have been considering two options:
#1 Milling my heads, which should get me up to 10.4:1 and if I can using a .015 head gasket which should bring me up to 10.8:1. That's about as high as I can get it. Going with some higher ratio rockers, port matching the intake and shooting the engine with a 100-150 shot of nitrous.
#2 Using a thicker head gasket if I can which should bring me down to 8.5:1, ditching my Victor Jr. for a small roots supercharger, and leaving it at that (with an incorrect cam for boost) Profile: .520 in .540 ex 236 in 242 ex @.05 LSA 110.
If anyone cares to know, I have the 6" rods, all forged internals, AFR 195 heads, comp roller cam, and Mighty Demon 750 annular carb. Give me some opinions!
I have been considering two options:
#1 Milling my heads, which should get me up to 10.4:1 and if I can using a .015 head gasket which should bring me up to 10.8:1. That's about as high as I can get it. Going with some higher ratio rockers, port matching the intake and shooting the engine with a 100-150 shot of nitrous.
#2 Using a thicker head gasket if I can which should bring me down to 8.5:1, ditching my Victor Jr. for a small roots supercharger, and leaving it at that (with an incorrect cam for boost) Profile: .520 in .540 ex 236 in 242 ex @.05 LSA 110.
If anyone cares to know, I have the 6" rods, all forged internals, AFR 195 heads, comp roller cam, and Mighty Demon 750 annular carb. Give me some opinions!
What are your goals and budget? Even with 8.5 to 1, you will not be able to run much boost with the blower (on pump gas), but they look cool. You can make more power a lot cheaper with nitrous.
Is it a stick car ?? do you want to be able to drag race it?? Is the best et the goal ?
Thread Starter
Melting Slicks
Joined: Sep 2004
Posts: 2,412
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It's a 6 speed. It will see some track time, but never with slicks. The goal is the be a wicked street car, no specific numbers in mind I just want to be faster! 
I know that the nitrous will be cheaper, but I don't like the idea of having to fill the bottle up all of the time.
I know that the nitrous will be cheaper, but I don't like the idea of having to fill the bottle up all of the time.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Don't believe you should shoot for 10.8 compression at all with pump gas, believe you should scrap the idea of milling on your heads
maybe run a thinner gasket to get compression up some from
9.4. Your other option of a small charger
trying to drop compression from 9.4 down to 8.5 would take
one very thick gasket and if you end with 8.5 or more comp. to
start with that does not allow you to run much boost at all.
maybe run a thinner gasket to get compression up some from
9.4. Your other option of a small charger
trying to drop compression from 9.4 down to 8.5 would take
one very thick gasket and if you end with 8.5 or more comp. to
start with that does not allow you to run much boost at all.
Last edited by Little Mouse; Nov 4, 2007 at 01:01 AM.
Team Owner
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2024 C3 of the Year Finalist- Modified
What did you do, install some dished pistons?
My 11.2 compression 383 runs just fine on pump gas with my custom lobed 236/242 112 .620/.620 with 1.65 I and 1.6 E
Right now it has AFR 210 heads on it that were flat milled from 67cc down to 62 or 64 cc. I can't remember which. It has a .021 head gasket and pistons .020 down in the holes because of block surfacing.
My 11.2 compression 383 runs just fine on pump gas with my custom lobed 236/242 112 .620/.620 with 1.65 I and 1.6 E
Right now it has AFR 210 heads on it that were flat milled from 67cc down to 62 or 64 cc. I can't remember which. It has a .021 head gasket and pistons .020 down in the holes because of block surfacing.
Thread Starter
Melting Slicks
Joined: Sep 2004
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I would like to hit 11:1, or even a little higher. But that's not going to happen with this engine. I have the 74cc heads and -5cc flat top valve relief pistons. The heads can be taken down to 66cc and that's it, I found a .015 head gasket that I could use (hopefully) to replace my .041 head gasket which would yeild 10.8:1.
But right now I'm leaning towards the thicker head gasket/ supercharger option.
But right now I'm leaning towards the thicker head gasket/ supercharger option.
Le Mans Master
Joined: Apr 2000
Posts: 5,202
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From: cincinnati ohio
St. Jude Donor '09
8.5:1 will let you run about 6-8 psi to reach an effective compression ratio of 12:1 to 13:1.
For example dropping to 7.5:1 will alow you to run 10-12 lbs to reach about 12:5 to 13:5
On a primarily street driven car you'll have so much unusable torque either way it won't really matter....trust me
For example dropping to 7.5:1 will alow you to run 10-12 lbs to reach about 12:5 to 13:5
On a primarily street driven car you'll have so much unusable torque either way it won't really matter....trust me
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Instructor
Joined: Aug 2007
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From: Enterprise Ut
I have a 8.6 compression motor with a 144 supercharger. I got different pulleys to run 8-9 lbs boost and have had no problems. I love the setup, and the useable torque the motor produces. The only drawback is you will have to get a taller hood or cut a hole.
Thread Starter
Melting Slicks
Joined: Sep 2004
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Now here's something that I've been wondering about. Are these small blowers limited in hp potential or do they truly give your motor (however much hp you have already) a 25-40% boost?
I was reading info about some small roots blower last night and it said that it would support 500hp. If I'm already over the 400hp mark, with a minimum 25% gain I'd already be over 500hp. Right now I'm leaning towards a Weiand 144, does anyone know? Will this blower be sufficient for a motor that is already over the 400hp mark?
Also, would the Weiand 144 flow well enough for my power band? Or is this blower made for engines that don't breathe as high in the rpm range. (You might be able to tell from these questions, I know very little about superchargers.)
I'm trying to make some chicken soup with chicken sh*t. These are my options.
I was reading info about some small roots blower last night and it said that it would support 500hp. If I'm already over the 400hp mark, with a minimum 25% gain I'd already be over 500hp. Right now I'm leaning towards a Weiand 144, does anyone know? Will this blower be sufficient for a motor that is already over the 400hp mark?
Also, would the Weiand 144 flow well enough for my power band? Or is this blower made for engines that don't breathe as high in the rpm range. (You might be able to tell from these questions, I know very little about superchargers.)
I'm trying to make some chicken soup with chicken sh*t. These are my options.
Last edited by enkeivette; Nov 4, 2007 at 03:10 PM.
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Thread Starter
Melting Slicks
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Racer
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From: Tampa by way of MIAMI! FL
The AFR's are aluminum right? You should mill them and run 92 octane and you won't have probs tune it right you'll be fine. Don't kill yourself with the gaskets just buy good ones MLS's are the deal. Like they said 1/4 point isn't going to make too much of a difference. Iron heads and you gotta worry about your compression alot more.
Race Director
Joined: Nov 1999
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From: Foxfield CO 1970 Convertible
Now here's something that I've been wondering about. Are these small blowers limited in hp potential or do they truly give your motor (however much hp you have already) a 25-40% boost?
I was reading info about some small roots blower last night and it said that it would support 500hp. If I'm already over the 400hp mark, with a minimum 25% gain I'd already be over 500hp. Right now I'm leaning towards a Weiand 144, does anyone know? Will this blower be sufficient for a motor that is already over the 400hp mark?
I was reading info about some small roots blower last night and it said that it would support 500hp. If I'm already over the 400hp mark, with a minimum 25% gain I'd already be over 500hp. Right now I'm leaning towards a Weiand 144, does anyone know? Will this blower be sufficient for a motor that is already over the 400hp mark?
When a blower is sized properly, you can mathematically expect a 50% increase in hp if you get to 1 atm of pressure regardless of where you start. In real life, it's somewhat less. I don't know about the 144 but you should be able to do the math by looking at your engines flow rate and the s/c rated flow rate.
I went with a twin screw because they are much more efficient than the roots type. Like yellow72 said, once you reach 600-700hp on the street, it hardly matters...
Team Owner
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From: Reno Nevada
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There used to be this Oregon vette man. He had the 144 weiand and it never made much boost even on his 355 ci motor driven to near it's max rpm. He went with the 177 and custom manifold and it was still low boost.
That is why they give that 500 hp rating. You have to get on the blower sites and the Whipple is one of the best. The belt driven centrificles can be done with custom mounts to clear the a-arms
That is why they give that 500 hp rating. You have to get on the blower sites and the Whipple is one of the best. The belt driven centrificles can be done with custom mounts to clear the a-arms
Racer
Joined: Apr 2005
Posts: 259
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From: Columbus Mn
Go with the blower. I had a 400 internally balanced with Keitgh Black KB126030 pistons AFR 190cc heads, and a Comp Cam CL12-560-4 268/280 Duration, 477/490 Lift and 1.6 rockers. My compression was 8.7, and I ran the smallest pulley available on my B&M 144 blower. 7-9 psi boost. It made 502 HP and 551 Trq with Hooker 1 3/4" Super Comps. This was on 92 Octane Premium. It never missed a beat. I ran that motor in my 75 K1500 (5030 lbs) and got 14 mpg on the highway, and 12 city. Lifted 35" tall tires 4.56 gears. Even with all the tire spin it ran 14 flat at 100mph, and 0-60 in 6.02 seconds. I would think it would be a excellent combination in a corvette. I ran nitrous on the street first, but got sick and tired of filling the bottle. Why wouldn't you want the power there all the time??? I went blown, and it was the best thing I ever did.