Hi everybody,
this summer I'm thinking of doing some upgrades on the engine.
It's a crate engine, seems to me everything stock, bought the car used...
I was thinking of changing the exhaust using this kit from Corvette Central:

http://www.parts123.com/parts123/yb....ort~1~cadefibQ

For the Engine itself, I don't want to mess with the cam, I was just thinking of changing the heads with a Vortek kit SD:

https://sdparts.com/details/scoggin-...nter/sd8060kit

or

https://sdparts.com/details/scoggin-...ter/sd8060akit

I think "maybe" it is better to take the modified version, it should not make difference with everything else stock but if/when I will change the cam in the future I already have the right heads...

What do you think? how much gain I would expect from the stock?

thanks

 

can't answer your questions but can give you a bump to the top. Also interested in answers.

 

I like the second kit better that will accept more vavle lift. Seems like a good budget upgrade for heads.
Your not gonna see a huge improvement without getting a cam with better specs to match those heads though.
The heads allow more flow, but the cam may hold them back.
Any idea what cam is in there?

 

Unfortunatelly not... I can only tell you the cam seems very stock because I read a solid 23 psi vacuum...

 

I wouldn't pull the trigger on that kit until you can find out what you got now.
Things to find out are the cc of the pistons and how far down the hole they are. With this info you can start figuring out the CR of you engine with various head chamber sizes. The CR will be important to determine what cam can operate well.
You current cam must be af a short duration with 23" of vacuum. Too much CR and you'll run into detonation issues.
Once the heads and intake are off it's not much more to put in a new more suitable cam and lifters.
You'll need to check pushrods lengths in either case with different heads.

 

I thought 23 was a "stock" value for the manifold vacuum at idle... that is why I thought I can safely install vortex heads...

 

What is your goal by installing the Vortec heads?

If all you want is a 20-30 hp bump then that would be an expensive way to go about it.

If like most guys your looking for 50hp or more then more needs to be known about the current set up.
If what you have is a stock GM 260hp motor then you likely have 17cc dish pistons .025 down the hole and 76cc chambers with a .017"or greater thickness gasket.
But, maybe this engine has flat top 7 cc pistons with a zero deck. That puts the CR quite a bit higher.
Or maybe the pistons are .040" down the hole, that changes the CR again and now quench distance is increased to make a more detonation prone engine if you push the CR too high.
Being a crate motor of unknown origin it's hard to know.

Putting on a set of 64 cc heads will gain a little in performance with the vortecs, but not anywhere near their potential.

If you plan on putting in a different cam, now or later, then the CR of that engine will affect your available cam options.
So choosing the right heads now makes a difference on what CR you will have, and what options will be available to you later.

If you are going to put on different heads and your sure about that, then pull the old heads off and see what you have to work with. Then decide how to go about achieving your goal.
Also consider your budget. Vortec's are pretty cheap at summit racing.
http://www.summitracing.com/parts/su...Fcg7MgodrjcAPQ

 

You are right, I would like to have 50hp more and I thought changing exhaust, intake manifold and heads would have been enough... I'm coming from stock parts... am i wrong?

 

If you have the GM 260 HP crate motor then we have the same motor so I'm interested in hearing from our resident experts on this. I'd like to get closer to 100 HP more but doubt I could do that with current pistons.

 

Stock vacuum is around 19 to 21 inches. You have 23 inches. That's quite a lot. Were still just guessing on the cam specs though.

If you have a stock exhaust system now that is two into one through a catalytic inverter back to two, then changing to a true dual exhaust will gain you quite a bit.
If going from 2" dual to 2 1/2" dual with low back pressure mufflers then you will gain some. Headers with a 2 1/2 system, better yet. How much you gain is variable depending on what your changing from and how much back pressure would be present in the exhaust system with a given engine. Most try to reduce back pressure as much as possible to maximize the results.
With a stock low performance engine there is probably not much of a back pressure problem. Bump up the flow of the engine and now you may have a back pressure problem. So you're thinking along the right lines by increasing exhaust flow when you increase head flow to and from the engine.
How much power you can gain with just a Vortec head change I'm not sure I could answer that question. Usually head upgrades are done with cam upgrades to take advantage of the heads capability.
So the head can flow more, and will at lower rpms, but the cam will limit the capability of the head due to it's low performance capabilities. You'll probably get a gain in the lower rpms, but fall flat higher up.
In either case it will be better than an GM 882 head if that is what is on there now.
What I'm advocating is finding out what you have before you start purchasing components.
That information may or may not have a significant impact on what you replace the current heads with. At least you'll be dealing with a known instead of guessing.

 

After you pull the heads off you would be checking things like illustrated in this thread.
http://forums.corvetteforum.com/c3-t...er-size-2.html

Go to post #31.

 

Thanks many info!!! I think will start changing the exhaust.... this is something I have to do!

 

when I got my 77 one of the first things I did was change to side pipes with headers, it did make quite a difference in the way it performed.
Combine your exhaust change with a ignition re-curve and you'll be amazed how much that helps.
A q-jet rebuild (if this is what you have) or tune will help bunches too if you haven't looked into that yet.

 

Don't be intimidated by the distributor re-curve, it sounds technical, but it really isn't, it's super easy and cheap, and noticeable power and economy is your reward.

Scott

 

You are right, I have a qjet and I have already rebuilt it, tuned (with the help of Lars...), and also the distributor has been rebuilt and recurved, very fun! And the car thanked...

 

You might consider these ProMaxx heads, as I recall, they support up to .550 lift cams. They come complete for $925 and an online search will find a better price. Back about six months ago, Car Craft magazine did a head comparison and these produced the most power for under $1000. They even outflowed the comparable AFR heads. Patriot Performance has changed their brand name and now go by ProMaxx. Sorry, I forgot to post the link.
http://www.jegs.com/i/ProMaxx+Perfor.../2181/10002/-1

 

All, I'm resuming my thread because at the moment I did nothing (just a son...).
Any advice on this kit for the exhaust:

https://www.corvettecentral.com/c3-6...em-with-323189

Thanks!