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Old 01-04-2006, 07:19 PM
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porting for a blower engine ?

i understand porting for a N/A engine. and i firmly believe that all the articals i have been studying are for N/A engines. i'm wanting to know what, if any, differences there would be for porting on a blower engine. i'm working on my vortec heads now. (man, the exhaust ports are pretty small). i'm thinking there are differences, but i don't know.

thanx

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Old 01-04-2006, 07:38 PM
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There are none. The better the head flows the less boost you'll need to make for the same power. As with any cylinder head the flow figures will determine the camshaft duration splits and lifts.
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Old 01-04-2006, 09:01 PM
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well. my thinking on this. the intake side doesn't need as much flow, because the blower is pushing the mixture in. but the exhaust side has only the piston pushing the gasses out, just the same as a N/A engine. and since the cyl has a lot more air/fuel in it because of the blower. the exhaust port would need all it could get.
am i not seeing something ?
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Old 01-04-2006, 09:53 PM
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Yes you are. You don't want the blower working any harder than it has to pushing the mixture in. Your correct that you also don't want the piston trying to push it out any harder than it has to either.

Flow is flow, the better you can make the cylinder head flow the more power it's going to make.

The harder you make it on the blower to make boost the more heat your going to make. The more heat you make the less power you make.
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Old 01-05-2006, 12:08 AM
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Ditto What Rick saud. This is a common mis-understanding. Boost is only part of making power. FLOW is the name of the game N/A or boosted. Boost is just back pressure in the intake manifold. Sure a blower will still make power with un-ported heads, but it can make even more power with better flowing heads. A lot of this will depend on how much power you are trying to make.

Royce
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Old 01-05-2006, 01:14 AM
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BUT, there is a period of time when the intake and exhaust valves are open (Overlap) In a normally aspirated motor, the intake charge actually helps scavenge the cylinder. sorta like blowing across the top of a bottle.
In a blown engine, you want to close the exhaust valve sooner to keep the boost from blowing out of the cylinder.
Because the blown engine is compressing the mixture into the cylinder, the "BANG" is bigger, and the exhaust is forced out faster initially and then the intake valve opens and forces more exhaust out.
So, the traditional ratio of Intake:exhaust valve sizes in NA engines is pretty close in blown engines.
I don't think that I would do much work on the Vortecs. What they don't have in valve size and runner cc's they make up for in effiecient design and high velocity. I had a pair of stock vortecs flowed and the numbers were amazing...how about 240 CFM on the intake at .5 lift, and 255 CFM @.6lift...
There is a discussion on another forum regarding superchargers; the premise is that heads that have been ported properly actually reduce boost read at the gauge...Un ported stock ports and chambers present more restriction, causing the boost gauge to read higher...I haven't bought cards in this game yet, but it is interesting.
I run a blower piston that is rated 8:1 with 64 cc chambers; I have 70 cc chambers, so I figure that my static compression ratio is down around 7:1.
I have a fairly long (236@.50) duration cam, aluminum heads, etc, so I feel that can run 10 pounds boost on 91 Octane. So far I have bumped it up to 7 or so pounds, but I have a new upper pulley coming, and I have a boost retard to install that will be activated by a 4 pound Hobbs switch. My blower service suggested that I not port and polish my heads for a street motor because I am not running much over 5000RPM..They want me to run a ton of boot down low and don't stress the rods by buzzing the engine..sounds reasonable to me.
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Old 01-05-2006, 11:00 AM
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Thadd,
I agree with the guys that say better flowing heads and intake will reduce the boost in the manifold to a point. For example if I took off my ported 215cc Dart heads and stuck on a set of camel humps, I will make more boost, but less power. There is a point where the engine/cylinders are just full and the boost is not going to change, unless the engine gets bigger. The trick is finding that point.

I am not sure what kind of boost retard you are looking at, but why would you want one that is switch activated? The one I run is boost activated and adjustable, you can pull X amount of timing out per pound of boost. I went with a Crane ignition (HI-6) and Crane boost retard.

Without knowing how your engine is set-up I don't see why you couldn't run 10lbs of boost on 91 octane. If you don't over spin that blower and keep the heat out, you should be fine. I know a few guys that did have issues with the smaller blowers trying to make big boost, but they were spinning way over 5000RPM.

I run 12lbs of boost on 91 octane with 8.47:1 compression (that is actual compression not an estimate). I have a large blower (10% underdriven), free flowing heads (aluminum), and a large port intake, so I don't have a problem with heat. I have no detonation issues, I even ran it for gently for a while with no boost retard (never beat on it until I had the retard in place).
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Old 01-05-2006, 06:49 PM
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ok guys, thanx

just a little on my engine. its(was) a stock 97 4.3, 9.2 compression. a vortec v2 sq blower kit, was said to be 8psi. i got about 10/11psi, with some minor pinging now&then. small headers and 3 1/2" single exhaust. i then put a powerstoke intercooler on it, about 2"x18ish"x30ish". yes, its pretty large. see pics for somewhat of an idea. i DID NOT change any pulley ratios, and i now see 15+psi with NO pinging at all. and no retard from the Hi6 ignition box. now i am doing the heads. porting as per the articals i see on the web, .500 cam, and better rockers. along with a better manifold and injectors.

yes, i understand what psi is. i figure mine will be going down, and thats ok.
yes, the vortec intake ports are very nice. but the exhaust ports are pretty small. this is where i am focusing my efforts.
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Old 01-05-2006, 06:59 PM
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Camaroman.
Once again I learned something bout blowers from ya. My thoughts was that with a blower why bother with the heads since it makes so much power anyway. But I guess I coulda ported out my Edelbrocks for more flow, but opted to leave em alone.
Oh well. Maybe next time. HG
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Old 01-05-2006, 09:24 PM
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Quote:
Originally Posted by THADD
I run a blower piston that is rated 8:1 with 64 cc chambers; I have 70 cc chambers, so I figure that my static compression ratio is down around 7:1.
I have a fairly long (236@.50) duration cam, aluminum heads, etc, so I feel that can run 10 pounds boost on 91 Octane. So far I have bumped it up to 7 or so pounds, but I have a new upper pulley coming, and I have a boost retard to install that will be activated by a 4 pound Hobbs switch. My blower service suggested that I not port and polish my heads for a street motor because I am not running much over 5000RPM..They want me to run a ton of boot down low and don't stress the rods by buzzing the engine..sounds reasonable to me
.
Why so low compression for such low boost ? If cooling is your issue then run a water or methonal injection (water is WAY cheaper). Even with the came setup and everything you should be seeing 20 + psi with a compression ration in the 7's and 8's.
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Old 01-05-2006, 11:40 PM
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Bob, there is no way you are going to see 20+ lbs of boost from a small roots blower. It just can't move that much air. I don't think you could get away with 20+ lbs even with a large roots blower on pump gas. Anything over 14 is really pushing it (IMO).

Hemmi, You will make more power than you know what to do with. Don;t sweat the heads. If at some point you are looking for maximum power out of the engine, them you might want a little port work. The difference is not as great with a blower as it is N/A. The blower does help cover up poor flowing heads and you already have decent heads, not to worry.
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Old 01-06-2006, 10:57 PM
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Quote:
Originally Posted by camaroman7d
Bob, there is no way you are going to see 20+ lbs of boost from a small roots blower. It just can't move that much air. I don't think you could get away with 20+ lbs even with a large roots blower on pump gas. Anything over 14 is really pushing it (IMO).

Hemmi, You will make more power than you know what to do with. Don;t sweat the heads. If at some point you are looking for maximum power out of the engine, them you might want a little port work. The difference is not as great with a blower as it is N/A. The blower does help cover up poor flowing heads and you already have decent heads, not to worry.

I'm just talking boosted motors in general,to me it's kinda useless to put that much money in something only to get such a small result. I know he's probably running some gynormous motor underneath it and everything. Just seems kinda pointless after a certain point but that just me.
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Old 01-06-2006, 11:02 PM
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Bob,
You need to do a little research. All boost is not created equal. Roots blowers make lots of torque down low. They are not high boost blowers (typically). You don't need to make a bunch of boost to make power. I understand your point, but I don;t think you understand the differences and how they work. Running big boost on pump gas with a roots blower is not easy.
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Old 01-06-2006, 11:05 PM
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Quote:
Originally Posted by camaroman7d
Bob,
You need to do a little research. All boost is not created equal. Roots blowers make lots of torque down low. They are not high boost blowers (typically). You don't need to make a bunch of boost to make power. I understand your point, but I don;t think you understand the differences and how they work. Running big boost on pump gas with a roots blower is not easy.
Believe me I understand plenty,

I'm simply saying personally I don't like my power limited. Yeah, roots do give it to you down low till what 5-5 1/2 then what ? Assuming this is a drag car then you're fine but about having power till say what 9-10K ? With a little nicer of a torque curve..owe how I love turbos .
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