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Old 09-29-2005, 08:53 AM
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Help! How do I get 400hp out of 355 with 305 heads?

Someone please help. I need to get 400hp out of a Chevy .030 over 350 with ported 305 58cc heads and flat top pistons with static ratio of 10.8:1 and Comp Cams hydraulic XE268, RPM air gap intake with Demon 650 vac secondary and no nitrous. Running in a class all my own, well I think there is one other car on this forum that has this combo. Can it be done???

Thanks
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Old 09-29-2005, 09:06 AM
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Flow is power, unless you can get the head ports in decent enough shape to flow well enough to provide that kind of power, then I`d say your gonna come up a bit short. Also to reach that goal your cams a bit short also.
Stock 305 castings don`t flow very well.
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Old 09-29-2005, 09:13 AM
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Quote:
Originally Posted by Fultron
Someone please help. I need to get 400hp out of a Chevy .030 over 350 with ported 305 58cc heads and flat top pistons with static ratio of 10.8:1 and Comp Cams hydraulic XE268, RPM air gap intake with Demon 650 vac secondary and no nitrous. Running in a class all my own, well I think there is one other car on this forum that has this combo. Can it be done???

Thanks
*********
Sounds like a circle track hobby stock engine/ which would make a pretty snappy street engine.

I don't know much about those 305 heads or your particular set's valves, porting/ actual airflow.

You are requesting 1.14 horsepower per cubic inch.

Based on the numbers from other combos: You will need a 180 cc intake port volume and 230 cfm intake flow, a 750 cfm carb, and 6200 rpm, and maybe the 274 cam.

You are going to have to shoot for more than 400 calculated horsepower if you actually expect to see 400 REAL hp on the engine dyno. Theory is only theory. The proof is on the dyno.

Last edited by xntrik; 09-29-2005 at 09:22 AM.
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Old 09-29-2005, 03:22 PM
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Would a 4 hole or open carb spacer make a difference

OK then. So your saying that it would probably not be possible with the combination of parts listed to make 400hp at the flywheel? Tell me what it would take to get there with as little changes as possible.
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Old 09-29-2005, 03:58 PM
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It is going to be really hard, but it might be possible with the right porting and enough cam. Here is a company that seems to know what they are doing porting 305 heads. http://www.castheads.com/factory_chevy_305.php they are expensive, but trying to get this kind of hp out of parts that arent made to get you big hp will not be cheap. I would look in to a solid roller cam. I think the XR268R (230 236 @.050 .552 .564 ) cam from comp might work well. It has a little more lift that I think you need, but it is the smallest dual pattern solid roller that they offer, you could also look into a custom grind somewhere closer to .500-.525 lift. Depending on how well your heads are ported, the cam swap amy get you close, but I would not bet on it.

Adam

Last edited by firestone; 09-29-2005 at 05:57 PM.
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Old 09-29-2005, 04:05 PM
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Thread from another topic

Quote:
Originally Posted by Mad Maggot
The engine was already in my car and I had a 4 hole spacer on it with my 650 DP Holley. I had to shave a bit of the webbing back on the hood but it clears fine now, so no worries there. Seeing as how I will be helping the upper end HP with the upgrades to the motor, I thought I should see if the 4 hole should stay or if I should change it to an open spacer. The upgrades over the last engine configuration are just the heads, carb, bigger headers/exhaust and new accessories, so there should be no dimensional changes to the engine. The only thing I will notice is a better pull from 5000 to 6000 over the old configuration with the ported 305 heads and 650 Holley - even the 58cc chambers are the same. (Those 305 heads actually worked quite well... sad to see them sit now)

I never realized the annular boosters like single plane intakes, I will certainly use the open spacer for that reason. Will a spacer really cause a HP loss? I would have thought that increasing the plenum size helps increase HP. Perhaps you could enlighten me on this.
Quote:
Originally Posted by Mad Maggot
I don't think I will have a problem getting 450HP with these parts. The motor that is being upgraded already had 400HP, and I am going to much better flowing heads (comparable to AFR 180 with the porting, I have the flow numbers), bigger headers and a bigger carb, plus I am eliminating my flex fan and going to electric and adding an underdrive pulley. Not to mention switching to Royal Purple oil to reduce friction. I may also upgrade to 1.6 rockers as well.

Considering I am using a vacuum secondary carb with decent gears and stall, would I still notice a reduced throttle response with the open spacer?
Quote:
Originally Posted by Mad Maggot
You just don't get it, do you?

I don't post fairy tale numbers from a wannabe bench racing program - when I say 400 HP it is because my as-measured 3464 lb 85 Trans Am with a maxed out suspension (every part upgraded) and subframe connectors, and only 3.27 gears with 26.2" diameter 265/50R16 tires runs consistently high 12's with a G-Tech sensor (which is proven accurate), and has put out 343 HP on a chassis dyno - using your magic formula that equates to approximately 400 HP. All this at an altitude of about 3500 feet. I also know some guys at a reputable machine shop who will let me use their dyno and once the engine is complete I will personally email you a photo of the results they give me so you can see for yourself that my claims are not bogus. Have you stopped to consider all the factors of my engine before you automatically dismiss the numbers as not plausible? Probably not. Hopefully for your sake the little number "22" beside my name did not attribute to your attitude toward this. I know that bigger isn't always better and that all parts must match each other to work properly, and that is in fact what has been meticulously researched in this engine build. If you want every single specific part I put into this engine so you can make an "informed assumption" I will be happy to provide it.

Anyhow, if you feel you must get into a pissing match about this, use the handy PM feature of this website, otherwise this thread will likely get dumped.


Now, for the back on topic stuff...

Tech @ BG, I will use the 4-hole spacer I currently have in light of your advice, however the holes in the spacer are just a shade bigger than the bottom of the throttle bores. They match up to the bigger 1-3/4" bores on an 850 Demon, but the 750 I believe only has 1-11/16". Should I get one that matches to the 750 throttle bore size to eliminate the small step here and reduce turbulence, or will this be insignificant? I already plan to radius the bottom half of the spacer where it meets the intake plenum to further reduce turbulence, because the 1/2" cut-out of the plenum divider in this manifold would have more cross flow from the other side in the high RPM if it has a radius to move over rather than the square edge.
I just dont see it, somebody help me to see the light!
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Old 09-29-2005, 04:28 PM
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just give it the juice. 305 heads are crap, so to make up for having bad parts just you NOs, yea its a poor excuse of a fix, but hey, its relatively cheap and it works.
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Old 09-29-2005, 05:28 PM
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HEADERS and elc water pump will help, are you drag racing, good gears
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Old 09-29-2005, 05:35 PM
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Whats with the requirement of using only 305 heads?
Is this some sort of circle track class or what?


Have you ever considered using a set of 283 power pack heads as a starting point instead of 305?

How about giving up some compression and running 350 heads?
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Old 09-29-2005, 06:11 PM
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It's entirely too easy to find heads with larger valves and ports for very little money. Unless you're racing in a particular class that requires these specific heads, just stack 'em in the corner. You can get rebuilt heads from Aerohead for $359 that have stainless steel 2.02/1.60 valves, screw in studs and three angle seats. There's no core charge either.

305 heads make good boat anchors.

Larry
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Old 09-29-2005, 06:47 PM
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I agree, 305 heads will max around 375 hp or so with a very nice port job and 2.02/1.6 undercut valves...at least from my experience on pump gas/street compression using a Performer RPM cam.
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Old 09-29-2005, 07:24 PM
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Can't everyone see that this entire thread has been nothing more than Fultron getting everyone to gang up on me because of a disagreement we had in a totally different thread? I already admitted to him that I was misled on the information I received from numerous sources, but the only thing that seems to interest him at this point is getting everyone to side with him to prove his point. I can't believe that any decent person would go through this kind of trouble to discredit someone, it's as though he has some personal grudge against me even though I have never met the guy or know how I could have touched a nerve so badly by saying my motor produces 400 HP when I was only asking about a carburetor spacer. Unbelievable. He even went so far as to insult me because of my nationality.

Fultron if you are reading this, what the hell is up, man? You have only 20 posts so far on this forum, can we expect you are going to act this way to every other member of the forum you have a disagreement with?

This site is a great resource for hotrodders, especially us young ones, but I really don't need to deal with this. Life offers enough challenges as it is.
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Old 09-29-2005, 07:40 PM
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I honestly thought he was just asking a question about heads. As for your car aand engine, you have a dyno sheet and time slips to prove what your engine was capable of.

Larry

Last edited by coldknock; 09-29-2005 at 07:54 PM.
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Old 09-29-2005, 07:51 PM
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Wow, I just blew over most of that stuff he quoted but now that Ive gone back and read it you werent kidding. Thats pretty low.
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Old 09-29-2005, 09:14 PM
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No, Coldknock, unfortunately I don't have a dyno test for my engine because spending over $800 for nothing tangible didn't seem like a wise investment for me when I had the engine built - I had already overspent my budget. I bought one of those G-Tech sensors that measures 1/4 mile times, acceleration, etc. and got my HP figures from this. Also, the car club I belong to set up a chassis dyno at their yard and members got a free run on it. My car put out 343 rwhp which I thought was enough to compute to 400HP at the flywheel but a number of factors could have altered my results. Seeing as how this was all I had to work with, I was simply putting the two figures together and feeling confident that my motor was producing 400HP.

The thing is, that wasn't even the subject of the other thread, it was about selecting a carburetor spacer. The thread is called "4 hole or open spacer for carburetor", and if you read it you'll see that Fultron did not even address my question he just attacked my credibility and never let up. I could understand if he had a disagreement with me but he didn't need to be so mean spirited about it. That is what PM's are for. Then he goes and creates this thread on top of it.

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