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Vortec heads and 283 cu in?? Confused on compatibility

 
ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/07/08 06:46 PM

Doing searches and reading up on the subject I have come across a lot of confusing and contradicting info. Hopefully, some here can help straighten this out for me.

I have a 283 that I would like to clean up and swap the heads and camshaft on. My first thought was the L31 vortecs because of a fairly cheap budget, and I like what they offer.

Now for my questions...  

1. Is the 1.94/1.5 going to be okay on my small bore?

2. What will the 64cc chambers do to my compression?

3. 305 vortec heads (such as the world products or EngineQuest versions) have been mentioned in my readings... they have 1.84/1.5 and  58 cc chambers I believe.  Is this the better option?


My goal for this 283 is to put it in my lightweight beater offroad truck (3400 lbs, 3.73 gears and deep geared tranny) that might get daily driven. So I would like to keep all the low end torque as possible (already have a cam picked out) yet if possible nudge the hp numbers into or above the 300 hp range.  

All suggestions and comments are welcomed and greatly appreciated.

- ForkHorn  

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GibTG
I mow my lawn and find Chevys
Posts: 1985
Joined: 10/03
Posted: 06/07/08 06:58 PM

1.94 and 1.5" valves would be fine in the small bore...

I can't really give an expected change in compression when I don't have an initial value to compare to. Obviously, it will lower compression over a 58 or 60cc chamber but that's all I can say.

The breathing capability of the 350 vortec heads would obviously be better. It's fairly common when using vortecs on smaller displacement engines to mill the heads to reduce the combustion chamber volume. This is a fairly good idea but it can end being very expensive to get the mounting surfaces and bolt holes correct again. If the engine is being "built-up" at the time the compression can be compensated with a slight dome on the piston.  
~Gibs

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ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/07/08 07:12 PM

Thanks, good advice can be hard to find sometimes and that is along the lines of what I was looking for. Glad to know that some cheap vortecs that are perfect for my purpose will bolt onto my 283 without any problems.

I know the compression question was vague, it was only asked because I had read the 64cc chambers would kill the compression putting it under 8.5 to 1. Which did not make sense to me, and I figured asking would be the safest bet. Sounds to me like it isnt a chronic problem in 283's with vortec heads like it was made out to be and isnt that big of a deal considering my purposes.

Does anyone happen to know the cc chamber of my stock heads? The casting numbers have it as a 1967.  

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GibTG
I mow my lawn and find Chevys
Posts: 1985
Joined: 10/03
Posted: 06/07/08 07:42 PM

The specific casting number may help as according to Mortec there was several different castings used on '67 283's...

Estimate your static compression with a calculator such as this...
http://www.mindspring.com/~steveflyer/compression.htm  
~Gibs

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ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/07/08 09:34 PM

The numbers were a little hard to read on the block but after double checking to see if it matched with a casting code on the internet this is what I assume it is.. 3896948.  Produced in 1967 estimated stock hp 195 estimated stock torque 195.  Hoping to bump those numbers up quite a bit with the heads and cam.

I'm gonna go see if I can discern what the numbers on the heads say. I might be able to match them.  

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wieder
My first time was in a Chevy
Posts: 214
Joined: 03/08
Posted: 06/08/08 08:46 AM

One area to consider with Vortecs is cam lift limits and press-in studs.TrickFlow and WorldProducts smallbore heads don't need to be upgraded the Trick heads have more current features,read up on these.   WIEDER  

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ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/08/08 03:36 PM

Alright after more reading I think I have a little better understanding of my situation and the technical aspect.  However this has brought up some new questions  Wink .


I believe that the stock heads are of a 60cc chamber design, which would mean the 1.94/1.5 64cc chamber vortecs would bring down my compression to the 8.3:1 range with flattops.  Will this kill my engines power?

A 58 cc head will bring the compression to around 9:1. Which brings the smaller 58cc 1.84/1.5 vortecs or the world products 58cc 1.94/1.5 heads back into play.   Out of the three choices which is my best option?

My last question I came across in my readings, it seems like a myth to me, but if there is some truth in it then this will affect my cam choice. This is quoted from another forum.

"In general, any description you read about a cam, carb, manifold, etc is for a 350. So, if the mfr says their 270 cam has a slight lope at idle, that means a cam that’s 1-2 sizes smaller will have a slight lope in a 283. And if the powerband is listed as 1500-5000 RPM, that probably means 2500-6000 RPM in a 283."


Thoughts?  Seems like some internet BS myth, and I would like to hear your opinions.


Thanks - ForkHorn  

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GibTG
I mow my lawn and find Chevys
Posts: 1985
Joined: 10/03
Posted: 06/08/08 05:40 PM

Using the formula for Otto cycle efficiency you could assume a drop in power of about 3.5%, of course this is a pretty theoretical value and probably best applies to peak torque, peak horsepower, and between.

The other advantages of added compression such as turbulence, exhaust gas velocity, and low-speed power gains are probably what's more important, and depending of the size of the cam the low speed loss could be much more significant than the formula would suggest.

I would imagine the World heads would be best but I have very little knowledge on the 305 vortecs, but I find it hard to believe that they would perform better than an aftermarket head with a larger valve, albeit only slightly larger.

The internet "story" you posted has some truth but it's not very clear. I don't really know what 1 or 2 cam "sizes" are and I think the manufacturers' power "bands" are nearly worthless. 2500-6000? There is no way an engine can make peak torque at 2500 and peak horsepower at 6000, and for a drag car the only range that matters is peak torque, peak horsepower, between, and possibly slightly higher. So what does that 2500 number mean?

That being said, it is true that a larger engine can tolerate more valve overlap (indirect way of saying duration) with a slightly better 'manners' than a smaller engine.

I'm a believer in the Vizard (or maybe more accurately put the "Cam Master") way of determining duration in that you determine a lobe separation angle and overlap first and lash point duration is derived from those two starting values.
"Be the Camshaft Expert" - David Vizard

2[(1/2 × overlap°) + lobe separation angle°]  
~Gibs

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ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/08/08 08:24 PM

Very good information. Looks like I have some more reading to do.  I agree on the compression, turbulence, and exhaust velocity. That all made a lot of sense to me.    

I believe that the 2500 - 6000 numbers were for where it would pull and make its best hp and torque numbers. I guess its "curve" is what its referring to.  The 2500 rpm mark dictates that it wouldnt have much low end, and power wouldnt really kick in until that mark.

I think the myth meant that a relatively milder cam in a 350 would be a lot wilder in a smaller cubed engine such as the 283?


Personally Im looking for something making all of its power from idle or just above idle to about 5500 rpms.  This is the cam I had picked out:
comp 4x4 cam  210/218 duration and .447/.462 lift LSA 111
Supposed to pull from 1000 to 5200 rpms.  I feel that is the right range for me as this will probably end up as a daily driver/ weekend offroad warrior.  

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ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/08/08 09:25 PM

Made an error calculating the compression ratio with the 64 cc chambers. It would come out to be about 8.5:1  compared to the 58cc chambers which would be about 9.1:1.  The stock 60 cc heads gave the engine something like an 8.9:1  I believe.

So basically its the 64cc chambers with an 8.5:1 ratio vs the 58cc chambers with a 9.1:1 ratio.

I'm unsure of how the difference in the compression ratios would affect my engine and its power combined with what I want in a cam.  

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ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/10/08 10:21 PM

After contemplating my options Im leaning pretty heavily toward the 58cc heads and the slightly higher 9.1:1 compression ratio over the 64cc heads and a lower 8.5:1 compression ratio.

Which leaves only a few head options such as the enginequest 305 vortec heads or the world products 305 torquer heads.  Which ones do you like more?  I believe that the world products heads do flow better. I dont know anything about the combustion chamber designs though.

I would love to use the 64cc vortec heads but I have a feeling that large drop in compression would kill my power.

All opinions and input greatly appreciated and welcomed  

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ForkHorn
I love my Chevy Chevette!
Posts: 10
Joined: 06/08
Posted: 06/11/08 01:19 PM

Just throwing ideas around...


What about using the 64cc vortecs and a thinner intake gasket to get the compression that I want?  Thoughts on this?  Any problems I may run into, or reasons for not doing this?  

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d-faria1
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Posts: 24
Joined: 06/08
Posted: 06/15/08 04:22 PM

you can also mill your block to zero deck and bring your comp higher.Use a .040 thick head gasket and your quench will be great making more power without detonation.Then choose your head chamber size.just a sugestion  

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stempak
V-6 Camaros rule!
Posts: 47
Joined: 11/08
Posted: 11/13/08 06:46 PM

Depending on your budget, ??? The World heads are probably a bit better of a head plus then your not limited on intakes and valve covers. Either head should give you great performance. Vortec heads are going to be at least a 20hp gain and more with porting. Either way you should be able to make some power. I think for sure your going to want the small chambered heads unless your trying to make a lot of power out of that engine because to big of head on that engine might hurt performance.  

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GibTG
I mow my lawn and find Chevys
Posts: 1985
Joined: 10/03
Posted: 11/13/08 10:41 PM

Too big of a head may hurt performance? Do you mean a chamber or a port that is too big?  
~Gibs

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