head choices

[Flash13]

ok, its a 350, with the standard headman headers and an edelbrock performer rpm intake. Everything else is stock 1970, four bolt main, 350. oh yeah and it has a performer 750 carb.



The question is, do i go with the performer rpm heads with the matching cam to match the intake i already have, or do i go with the AFR 195 cc. heads with some other cam?



and what cam would make a fast street truck with maybe a weekend or two at the track. Its more important that it handle well on the street than the track though.

[rudedogg]

good head is best!!your motor is like your relationship,if you dont have good head it wont work to its fullest potential!now the heads you have listed work very well,afr has proven themself!cam choices are simple for what you are lookin to do,you need to be in the 218-228 duration at .050,112-114 lobe sep with 480-530 lift,just remember the head selection you have show 202 160 valves you would benifit more with 194 160 or 2.00 156 to keep the truck from being sluggish off the line look at the way the vortec heads work for the price they cant be beat! http://www.s10v8.com/images/smilies/icon_wink.gif

[Truckman91]

For this engine I would get the AFR 180s



And definatly find a different carb, 600-650 cfm max, 750 is WAY too big

[fastw23s]

Truckman!



What is with you and your small carb obsession???



A motor will only pull what it can use from a carb, as far as the throttle response thing if your motor is right, and your carb is tuned you still have plenty!



I ran a 750 on my 305.

[wild85]

hey fast

Too big of a carb apparently has siganl problems with fuel, I don\'t know the reason for it but alot of people say this. They aren\'t joe blow either.

[Truckman91]

a carb thats too big hurts throttle responce, as well a fuel mileage and all round drivablity.



People just go \"Oh its a 350, It needs a 750\" which isnt true. People take time to put the right cam in, why wouldnt they worry about getting the right sized carb? Just doesnt make sense to me.



I tell people what is good for their combination. Why would you generalize so much. 750 on a 305, Wow.... I understand you can make it work but why would you do that? There is very little difference in HP from a 650-750-850 on most street engines.



Carbs come in different sizes for a reason, or else they would all just be 750s...lol

[wild85]

I agree Truckman!!! Why not just put a 1050 dominator on it while your at it. reason, it is too damn big. I had a 750 model 3310 on my 350 at the beginning, my plugs were pure black with gas, now with the 670 the plugs look pretty good, maybe a little lean, but no detonation. Reason, the 750 was too big, so how did a 750 work on a 305. Must have been some 305. I know i have problems now, but the 670 made the engine run way better than the 750 did.

[knudsonm]

I\'m running a 3310 750 cfm on my 454 and it is perfect. People usually over carb their engines. a 600-650 vac sec carb is great for a street driven 350

[wild85]

YEP, solved. he has 100 cubes more and is only using a 750.

[BrandOmatic]

well to defend a 750\'s potential, David Vizard wrote in his book \"how to build max performance chevy small blocks on a budget\" that if you\'re unsure of what size carb to get, go with a 750 because it is as goof-proof as possible..



So in my personal opinion, to form a compromise between the two opinions, i think a 750 might be too big for your stock motor right now. However if/when you get better parts that flow and make power, that carb should be awesome.



And yeah, david says that the problem with carbs that are too big are that the booster signal is too low. There are things you can do to help booster signal though. He names a few, but this is definitely a subject of conflict and misunderstanding.



\"The most common racer mistake is to assume that bigger cfm numbers equate with bigger horsepower numbers. The next most common mistake is to assume that a carburetor can have too many cfm for the engine.\"

[wild85]

when plugs are black, it means it is too big, I have an engine with 100hp over stock and the 750 gave me black plugs also. 670 = good looking plugs. so a stock engine would do with a 570 or 600 vac sec.

[fastw23s]

You guys don\'t get ti.



A750 flows more air, than a 650. If you were rich it was because the 750 had jets that were out of range for your airflow, period.



A stock 650 flows mor fuel per cfm. YOU ARE BETTER WITH MORE AIR AVAILABLE AND TUNE IN YOUR FUEL CURVE!!



A low signal condition is normally due to the intake design, head, and cam combo, obviously the statement of a Dom on a stock motor is abit over stated, but I gaurantee I can make you a very responsive daily driver mild buildup run perfect on a 750.



Now if you don\'t have access to this then you are better to err on the conservative side.



BTW, I ended up running my 1100 on my motor and the sound and response totaly improved!!!!

[wild85]

So then why do the carb companies say, if your engine is running like crap, that it is likely that you have the wrong carb for the application, if you have these probs from the start. If every engine should run with a 750 for instance, everyone would piss around with the jets and other things, the carb companies would not make anything else.there would be only small parts to play with the 750.So it should be obvious that a 650 should work on a certain engine and a 750 on an engine with more power and more cubes. Not a stock engine or real mild one. I hope you guys understand what I am trying to say, evenif i am not going about it the correct way.

[BrickTop]

if you think about this issue simply in terms of airflow it may be a little simpler to understand. a 350 cid engine will at very best only attempt to \"pull\" a given amount of air through the cylinder heads at a given rpm. every 2 revolutions it will attempt to draw 350 cubic inches of air through the carburetor or throttle body. it takes 2 revolutions for every cylinder to go through its entire 4 stroke cycle. now, if the 350 has stock heads on it, it will not be able to draw 350 cid of air through the engine every 2 revolutions. what if it has pro stock heads on it? it may be able to come a lot closer to filling the cylinders within the complete cycle. the way an engine makes power is to mix fuel with air and then compress it and then ignite it and use the energy from those rapidly expanding gases to push the piston down, to rotate the crankshaft, and so on down the drivetrain. SO, the more air and fuel that we can pack into that engine, the more rapidly expanding gases we can create, the harder we can push on the pistons, and so on and so forth. so, theoretically, if there is less restriction to the airflow to the cylinders, the engine will make more power. unfortunately, the carb is not the first restriction to the airflow? the cylinder heads are. thats why a better flowing cylinder head will make more power. but, if you put a large carburetor on an engine that can\'t pull any air through the heads, it may not make more power necessarily than a smaller carb. this is not generally the case however, generally, the heads will flow enough air that the carburetor is the main restriction. i have a very good example that i hope will shed some light on this concept. i went to a school in houston, texas where i learned a lot about engines, after my first year there, i took the engine out of my s10 and we dynoed it. with a 750 holley, and an msd 6al, it made 312 hp, 330 ft/lbs-and we tuned the carb so that the plugs were not black. with my 600 cfm holley, and my hei dist, it made only 302 hp and 320 ft/lb. it only lost 10 hp between the 750 and the 600. the heads i had on it were junk, stock chevy heads, and the carb was a restriction, i think the motor pulled about 1.5 inches of vac* on the 600 at 5500 rpm. meaning that the air could not entirely get through the carburetor fast enough to equalize the pressure inside the intake manifold and above the carburetor. atmospheric pressure at sea level is 14.7 pounds per square inch, at an idle, the pressure inside the intake manifold is less than this, because the engine is rotating, and the pistons are going up and down, and trying to pull air through the heads, but the carburetor throttle blades are shut, so air cannot flow past them, therefore, there is a \"vac*\" inside the intake manifold, meaning that the pressure there is less than atmospheric. when you open the throttle blades all the way, the air outside will try to rush in and fill the voids that the pistons are making every time they go down on the intake stroke, but if the carburetor is too small, enough air won\'t be able to get through the carburetor to completely fulfill all the air needs that the engine is demanding, so, there will still be a \"vac*\" in the intake manifold, because the outside pressure cannot equalize between the outside air and the air inside the intake manifold. with the 750 carb on that engine, it pulled little or no \"vac*\" at 5500 rpm, which was where the engine made peak power. anyway, i rebuilt the motor, and put much better heads on it, fully ported and polished, they flowed 280 cfm on the intake ports as opposed to the old stockers that only flowed 205 cfm. i also added a solid roller cam and better intake manifold, more compression, etc. when we redynoed the motor, it made 527 hp at 6500 rpm. we dynoed it with an 800 cfm holley, and at that point, the carb was a restriction to the motor, it was pulling about 1 inch of vac* at high rpms, meaning that the carb was a restriction. just think if i would have tried it with the 600 holley! IT would have REALLY been a restriction. the engine changed only about 6 cubic inches, but the airflow capability changed dramatically because of the cylinder heads. the better cylinder heads also allowed me to turn it more rpms. at higher rpms, the engine is making those 2 complete revolutions a lot more often, therefore needing even more air to get through the carb and fill the cylinders. so, if a given engine has good cylinder heads, and turns more rpms, it can make use of a bigger carb even though its the same cubes as the stock headed, low rpm turd. so, heads, intake manifold, and rpm range all have to do with carburetor selction, not just cubic inch displacement. throttle response from an idle has to do with these concepts, but depends mostly on air speed through the carb venturi\'s, so you want relatively small intake ports/carb for off-idle throttle response. but, if you want good off-idle throttle response, you may have to sacrifice a little high rpm hp. in the instance where one wants the best of both worlds, a vac* sec. carb is best, because the secondaries won\'t open til they are needed, and you will get good airspeed therefore good throttle response because off-idle you will only be pulling air through the primary throttle blades. there\'s much more to it than all that, but, i hope that helps, and doesn\'t piss anyone off. thx.

[Truckman91]

Thats the longest paragraph ive seen in my life!!! HAHA http://www.s10v8.com/images/smilies/icon_biggrin.gif

[knudsonm]

better yet put a quardrajet on it

[fastw23s]

Yeah, What Bricktop Said!!!!!!



As I said, airflow is critical, fuel can be adjusted.

[Flash13]

Way to hyjack a thread guys. I used a 750 because that is what edelbrock recomends with there performer rpm heads and matching cam. I have had second thoughts about the performer rpm package so thats y im asking which heads would be better.

[Truckman91]

Your dont like all this great discussion?? This is how people learn new things. Hyjacked or not this is a good thread. We arent arguing, were discussing and throwing in very good points.



And youve got a vote for AFRs, Vortecs, and no votes for Edelbrock.



I still say AFR 180s would be great with a little 220-230 dur cam. Your 750 will match your combination much better IMO when your get a bigger cam and better set of heads.



Heads should be the most expencive piece in your engine. They are what make or break power potential. Do it once, and do it right... It is impossible to wrong at this point with AFRs.



\"You can have the best cam in the world, and bad set of heads and your engine will not make good power. But if a good set of heads and and average cam, your engine will make good power\"



Look ar AFRs website at the dynos they have done, they all make a ton of power with a lot smaller cams than their competition uses to make the same power.



The choice is obvious(if you can afford them, get them) http://www.s10v8.com/images/smilies/icon_biggrin.gif