Originally Posted by Steven6282

I'm not looking for anything amazing, 300 rwhp would be nice. Just a nice sporty street engine build. But as I said I don't want to upgrade at the cost of losing the sound of the engine as it is now.

Why would .440 lift be part of the problem? I'm no expert on cams but I thought more lift was supposed to be more power generally. I know .440 isn't a huge amount of lift, but I didn't think it was small either?

Originally Posted by Orr89RocZ

What are the specs of the cam you have? Do you know?

What intake manifold and carb are on it? Is it carbed?

Even if the cam is fairly mild a good set of heads will make alot more power than those smoggers... if you are at 220ish whp now well tuned, a set of good heads should be an easy 30-50 hp gain by itself. Cam sounds fairly good sized so it should make some hp with good heads.

Originally Posted by strrtwinkle

I know I'm under the wrong topic but needing a quick answer concerning an IAC replacement and when replaced do I need to do a relearn

Originally Posted by Steven6282

For the Carb, I can't say why it was recommended to me, I was just told it was a good street carb. The Street Avenger I have is a double pumper. And all the CFM calculators I've used all point to me needing nothing larger than a 520 CFM. That is the only reason I ordered the 570 CFM over the 670 CFM. Everything I read said that having a carb with to much CFM would cause just as many problems as a carb with to little CFM. I do not have any bogging on take off, and no choking at max RPMs. My AFR on it stays at 12.7 to 13.4. I can say with some certainty that I do not want a carb with mechanical secondaries on it for a street car. This is one thing I did research somewhat extensively when I was ordering this carb. There is nothing mechanical secondaries offers over vacuum secondaries on a properly tuned street car that I need.

Originally Posted by Steven6282

Anyway, to respond to a couple things from above:

1) I'd like for it to have a little bit of pep to it, but I only am in love with the way it sounds right now.

2) There is nothing mechanical secondaries offers over vacuum secondaries on a properly tuned street car that I need.

3) I did mention my intake above, it's an Edelbrock Performer RPM.

4) I'm almost wondering if it would be easier for me to just buy another block and build something from scratch...

Originally Posted by JaBoT

I don't know how the carb calculators say you only need 520 cfm that's just not right or you did not enter the correct info. Just for reference even holleys carb selector on their website recommends a 650 for a 355 that revs to 5800 (the max rpm of the cam you have).
Also I don't know where you get the impression a double pumper is bad or not a good choice for street car. I think you have been reading a lot of bad info.

Originally Posted by Steven6282

Well, one place is Summitracing's CFM Calc (where I ordered the carb).

http://www.summitracing.com/popup/ca...cfm-calculator

I put in 5500 max RPM (since that is the number I had from the engine builders) and 350 cubic inches, it says 473 for a street carb 612 for a racing carb. The 570 seemed good because I'm not intending it as a race set up lol. If I put in 5800 RPM it's 499 / 646. The holley carb selector on their website gives me a list of multiple carbs including a 570 CFM and a 670 CFM among various others. It didn't tell me any specific recommendation anywhere that I saw.

The "street" carb sizing thing is bull do not buy a carb going by that ever. And anyone else on here who knows what they are doing will tell you the same thing as stated in the previous post to yours. If you put a 475 cfm carb on a 350 that revs to 5500 rpm not only will it not make any power up top it might not even want to rev to 5500 anymore!

This is the one used there:
http://www.holley.com/applications/C...bSelection.asp

From additional reading I see most sites (including Holley's) saying a smaller CFM will work fine and give better low RPM response, where as a bigger CFM will delivery high rpm power. So if that holds true, yeah maybe the 570 CFM will lower my peak hp some, but it should give me a better start? I don't know, if I ever get the engine up in HP I'll try swapping between the 750 CFM quadrajet and the 570 CFM street avenger and see what the HP number are between the two.

No it will not give you a better start. You will not notice any diference in throttle response as long as both carbs are correctly tuned.

As for double pumper, I didn't say that it was bad. Assuming you meant mechanical secondaries there, or maybe you actually meant double pumper I don't know. I always assumed a double pumper was simply a carb with two fuel inlets / squirters. The carb I have has dual fuel inlets and squirters for the back and front, but it is a vacuum secondary. I'm probably just mixing that term up for something else entirely.

Yes I think you are a little confused. Double pumper and mechanical secondaries are the same thing. It means the secondaries are opened directly with the throttle. All mechanical secondary carbs also have a second accelerator pump and squiter on the secondaries to avoid a lean spot upon opening the secondaries. That is where double pumper comes from. It has to accelerator pumps.

And the reason I don't want mechanical secondaries is because all they do is force the secondaries to open at a specific amount of gas pedal travel. That's the primary reason I don't want one. This makes them less gas efficient, if you aren't accelerating hard enough to drop your vacuum down, then they open anyway. Also on a smaller engine, if the engine is already running a little rich for whatever reason (weather, height, humidity, etc), mechanical secondaries are just going to make it worse as it dumps even more gas in. Vacuum secondaries would not open if the engine didn't need it. Do a search for mechanical secondary vs vacuum secondary. Nearly every article you find will recommend vacuum for street and mechanical for race builds. Noting that vacuum is more drivable on the street, and a lot easier to tune / more forgiving on smaller engines.

First telling the people who are trying to teach you something and actually know what they are talking about to do a search on it is not a good idea!!
The fuel mileage between both carbs is exactly the same. If you tune tune the primaries to cruise at 14.7 on the highway and have the same pump cam and squirters then both carbs will have the same milage. The only difference is when kicking in the secondaries it will squirt a very small amount of fuel from the rear accelerator pump. So unless you dive like a maniac the difference is not even noticeable. Yes a vs carb is more forgiving, but only if the wrong carb size is chosen. All these things you read about vs versus ms are old school stuff from 50 years ago that just keeps getting repeated over and over.

Just to note there are also quite a few sites that specifically point out the old misconception of mechanical for anything "performance". A properly tuned vacuum will produce the same amount of power as an equivalent mechanical. The mechanical will simply respond to the gas pedal, where the vacuum responds to when the engine needs it. This means a vacuum can have a slight delay where as the mechanical is already feeding it to the engine. If you've got a big engine that can swallow the extra gas down even if it might not exactly need it, then sure, throw a mechanical on there and have at it. But for a small street build, vacuums are universally the recommended choice.

Another misconception, First a ms carb does not run richer or give more gas than an engine can swallow. Yes a properly tunned vs can make around the same power as ms but not the same low end torque. I have actually used vs carbs on race cars that had traction issues off the line.

And one final further point on it. I'm also reading multiple places that mechanicals should never be considered for street applications or even most race applications if the full car weight is heavier 3000 lbs. Even Holley's site says this (except it says 3100 lbs). Considering the curb weight of my car is like 3400 lbs. Add in me, the fuel, and everything else in it, it's probably closer to 3800 lbs if not more, I don't really know how much 10ish gallons of fuel weighs .

Originally Posted by JaBoT

They say that so they get less calls on my carb isnt performing right because from there perspective the vs will be more forgiving if things aren't right with the setup and or carb size. They also have been saying things like power valve size should be 1/2 of idle vacuum for like 50 years and now are finally updating the tech stuff to say it should be a couple inches below cruise on a street car. Meanwhile we have know this for years.

Now I'm not saying to not use a vs carb. It will work just fine. I am saying there are a lot of misconceptions about ms carbs and you hit almost every one of them!

Originally Posted by DeltaElite121

1) I get it, but you'll always have a turd if you jump for sound before performance. Besides - having a car that "lumps" and drives like a Honda civic makes you look like a big idiot with no knowledge, and certainly all bark with no bite. Lame factor x 1,000.

Originally Posted by Steven6282

And this is the problem with the internet

You say I hit the misconceptions, and yet those misconceptions are based on other sites (also written by people that have experience) saying that the counterpoints you make are the misconceptions.

For reference when you read all the threads saying to use a vs carb notice that there are always a bunch of people who run a vs carb saying you should too because that's what they were told and that's what they used and have never used a ms carb. Then there is always a few people who chime in and say... I have no idea what you people are talking about. I have been running ms carbs for 20 years and they work great on the street. Or I have tried both and there are no adverse effects of the ms carb. Yet people who never used them or are not capable of a couple adjustments insist they are wrong because that is what they were told.

Telling you to search is not meant as an offense, it's just to point out that your suggestions on the mechanical secondary is actually the minority. With so much information and so many varying opinions one such as myself without direct experience and solid numbers to review, can only assume the majority are the majority for a reason. I am appreciative for all suggestions and advice given, I just wish the advice given was more consistent from various sources that all claim to be experienced. In the end I still usually have to end up guessing and spending money on something to figure out for myself.

If I were some rich millionaire I'd by identical carbs one being mechanical and one being vacuum and run them on the same engine with a proper tune and get some solid numbers to go by. Unfortunately, I'm not rich, and especially not a millionaire

I have on many occasions. I tune cars for a living.

And it's the same thing with the carb size. Although a lot of people scoff at the size if I tell them in person, I know the majority of them to not really know what they are talking about and to just go with the common interpretation that bigger is better. These are the same people that would throw a 750 cfm carb on a 305 that red lines at 4500 rpm. A lot of the "experts" I have consulted about it say that the 570 is not to small. So how the heck am I supposed to know who to believe! Trust me after I first got the carb, I thought at first it was to small because I was having a problem with the carb choking and such. So I talked with numerous techs (including summit's technical staff that are all supposed to be expert mechanics..bah), called chevy and talked to some of their mechanics, talked to a few different mechanics around town, talked to a couple different performance shops, the majority of them said the carb was plenty for my configuration. Even with so many people telling me it's plenty I still don't know if it's to small or not (as expressed in my post above) because I don't have any direct experience myself and the "popular" online opinion is that it should be in the mid 600s. And just to note, all the issues I had with the carb were solved when I bought a wideband afr gauge and learned how to tune the carb.

For your setup the way it is now the carb is fine. With the head upgrade I would recommend the 650 upgrade also.
A wideband is a very helpful and highly recommended tool for carb tuning.
For idle don't use the afr. Just adjust it for best vacuum and or highest rpm. With your setup it will probably wind up in the low 14's maybe high 13's for afr. Then for cruise tune for 14.7 - like 15.5. As high as you can go without it lean bucking on light accell or cruise. (note: hooking up a vacuum can on the distributor will alloy you to cruise leaner). Now when you adjust the cruise to be lean like that you are going to need to change you powervalve to something that is about 2 inches below your highway cruise vacuum. In alot cases on street cars it is above 12.5 and since no one makes a pv over 10.5 anything from 12.5 on should use a 10.5 pv. For wot shoot for around 12.8. When you go on the dyno you can find out exactly the afr that makes the most power for you. Also you can just follow the holley tuning sticky in the carb section.


Bottom line is, I'm not really looking to do a huge internal change on my engine right now. If people think just swapping the heads can get me a descent performance boost, then I may do that for now and worry about the rest later. So far only one person has suggested swapping just the heads could give me a boost. Everyone else has just expanded talking about replacing the cam and other components as well.

Swapping the heads alone will absolutely give you a big performance boost. Even if the compression is low do to deck height and other stuff. Just going from a 72cc to a 64cc head you will still be almost a point higher than wherever you are now.

Oh and I meant to respond to this earlier:

I'm perfectly fine with looking "like a big idiot with no knowledge" if it makes my car sound how I want it to sound. This is all about how I want the car, not how other people think it should be. If I were building this car to sale, or to try and impress other people, then I might care more about what others thought, but I have no intentions of doing either.

I want it to sound like it does now. If I can do that and get a little more hp out of it without having to replace the cam, or if I can replace the cam with one that sounds nearly identical, then that is all I really want to do right now. If I can't then I'll probably leave it as is for now. At least as it is now it's making more hp than a stock third gen did... not much more and definitely not enough to warrant the amount I've spent on the engine but it's something. And it's definitely an improvement over the 135 rwhp worn out 305 that was in the car when I first got it

Here is a vid of the lunati cam idling for reference
http://www.youtube.com/watch?v=4EjN-MjiLEg

Originally Posted by Orr89RocZ

Jegs and profiler are the same castings. Jegs sells them under their own name.



Really depends on how aggressive the roller is but most likely yes you will have to change springs later on. A stock type roller may work ok with flat tappet springs but a decent lobe performance grind you would be looking into will need abit more pressure, mainly open pressure loads. Typical flat tappets seem to be 110-130 lbs seat 250-330-ish lbs open. Hyd roller milder cams need 120-130 lbs 350 ish open. More aggressive hyd rollers need abit more like 140-150 seat 350-380 lbs open. Really aggressive stuff esp with heavier valves need 160-180 seat 400-450+ open

That last spring would flatten a flat tappet cam