3998993 heads - Chevy Nova Forum
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Old 3rd-July-2007, 02:04 PM   #1
nogo69
 
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3998993 heads

Well the 350 i have has the 75cc heads on it with the small valves.
I want to build a mild 350 with 300hp to the crank.
Is this possible with these heads?
What do i need to do ? Will i need to put the big valves in them and port and polish with a 3 angle valve job ect.
Please dont say "just buy new heads" i already know that would be best but these are the heads im using for better or for worse.
Later Matt
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Old 3rd-July-2007, 02:12 PM   #2
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I wouldn't put much money in those heads if you have to use them. Definitely not porting and polishing since by the time you are done it would have been cheaper to buy new ones.
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Old 3rd-July-2007, 02:13 PM   #3
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If it takes $400 to put your heads back to good, useable condition (before the $500 to blend the bowls or >$1000 for an extensive porting), doesn't it make sense to keep your eyes open for a $400 set of vortec heads?

Kev
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Old 3rd-July-2007, 02:21 PM   #4
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My dad has a good friend that will work these heads for me next of nothing.
All i have to do is buy the parts like the bigger valves,springs and such.
I think these are the same heads GM uses are there 290hp crate engine.
Does anyone know for sure? I dont know if those heads have bigger valves in them.
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Old 3rd-July-2007, 02:31 PM   #5
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They should be 1.94/1.50 heads with the big chambers. They're a low performance truck head. They'll probably support the 300 you're looking for, but there's no opportunity for growth and I just don't think you're going to get as good a "deal" as you think. Buying those parts isn't exactly cheap and you're severely limiting yourself.

IF THERE IS ONE THING IN A NATURAL ASPIRATED ENGINE TO SPEND YOUR MONEY ON, IT IS THE CYLINDER HEADS.

Kev
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Old 3rd-July-2007, 03:51 PM   #6
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Why are you asking if you are going to do it anyway?

Why should we tell you the truth if you don't want to hear it?

I don't want to second guess your Dad or his friend but I'm gathering you aren't completely sure about the deal if you are asking us.

If a good deal sounds too good to be true it probably is.

We know all about "budget" engines having done a few on the site.
Here's what we've learned:
First of all take your engine budget and double it. More than likely it will cost even more depending on how many of these kind of good deals turn into do overs. Many dollars get wasted in a misguided effort to save money.

Make a plan and stick to it. Mid project changes waste time and money. Plan for the worst and hope for the best.
If the worst case budget is more than you can afford then don't proceed!
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Cubic inches is like Indiana Jones with a cheap pistol.
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Old 3rd-July-2007, 05:29 PM   #7
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The answer is yes you can get 300 rwhp out of these ! HOPEFULLY your machinist has more time than you do money! The heads will need 2.02 ,1.6 valves , screwin studs and guideplates ,bigger spring pockets,downcut guides ,it would be smart to open up the pushrod holes, and THEN THE 30HRS OF PORT AND BOWL WORK!!
Those heads were used with the target crate engines, and are one of the better (heavy weight) heads chevy made in the 75-76 cc range.

AS STATED ABOVE, the vortecs are good to go out of the box!! for 300 rwhp.
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Old 3rd-July-2007, 05:47 PM   #8
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Quote:
Originally Posted by jason snyder View Post
The answer is yes you can get 300 rwhp out of these ! HOPEFULLY your machinist has more time than you do money! The heads will need 2.02 ,1.6 valves , screwin studs and guideplates ,bigger spring pockets,downcut guides ,it would be smart to open up the pushrod holes, and THEN THE 30HRS OF PORT AND BOWL WORK!!
Those heads were used with the target crate engines, and are one of the better (heavy weight) heads chevy made in the 75-76 cc range.

AS STATED ABOVE, the vortecs are good to go out of the box!! for 300 rwhp.
You really don't need the 2.02 / 1.6 valves and the rest of the stuff you mentioned to build these heads up. You could use the S/S 1.94 / 1.5 valves
with a little back cut, port match the intake and exhaust and you could produce some low end torque and HP that will rock your world. These heads, along with the 997 heads, are the better of the late model bunch heads. I had a set of these on a mild 355 and they treated me quite well. And everyone has said that "go aftermarket" or other heads, its all depending on how deep your pockets are. What you could do is to put different pistions in the motor and that will help out..

Just a thought or II.....
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Old 3rd-July-2007, 06:31 PM   #9
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SORRY I DONT HAVE 10 GRAND TO BUILD MY MOTOR!!!!!!!
NEVERMIND SORRY I ASKED!!
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Old 3rd-July-2007, 07:11 PM   #10
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Quote:
Originally Posted by nogo69 View Post
SORRY I DONT HAVE 10 GRAND TO BUILD MY MOTOR!!!!!!!
NEVERMIND SORRY I ASKED!!
I think you're pissed about not getting the answer you wanted to hear. If you can run the heads with no cash outlay and can deal with low compression, by all means use them. Everyone here, by their experience, knows you will be back at some later point complaining about the lack of performance and I can guaranty you will be reminded that you were warned.

Ask Paul, it takes some people a few years for the actual listening and understanding to kick in.
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Old 3rd-July-2007, 07:17 PM   #11
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Originally Posted by nogo69 View Post
SORRY I DONT HAVE 10 GRAND TO BUILD MY MOTOR!!!!!!!
NEVERMIND SORRY I ASKED!!
Dude ,read your first post! Then read mine ! I gave you an honest answer ! And it wasn't sarcastic.JUST the truth. In no way did i dog you ,or the heads.
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Old 3rd-July-2007, 08:57 PM   #12
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Look i just wanted to know if it were possible for the heads to support 300hp to the CRANK thats it ,not the rear wheels.If they wont well then they wont ...Im still going to use them for now.
Im not building a dragster here, hell i'll be happy if it runs low 9's(1/8th).
Im building a mild 350 for now and later im going to build a bigblock when i have more funds available.
To all that were helpful, thankyou for the info.
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Old 3rd-July-2007, 11:35 PM   #13
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you dont need 300 hp to go low 9s in the 1/8th. You can go low 9s with gearing but 250 to 275 will get you there with ease. My 63 is making proablay 250 at the rear wheels with 3.08 gears and is capable of going in the mid 8s.
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Old 3rd-July-2007, 11:55 PM   #14
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Probably the single most important component of any engine are the heads. You can dump a fortune into the rest of the engine and if you have low-perf heads, you'll end-up with a low-perf engine. On the other hand, you can have a budget bottom end with nice heads and it will be a runner!

You can get a pair of awesome used heads like a pair of Sportsman IIs or Dart IIs on eBay for $500 or less. Money well spent. I wouldn't waste my time with the heads you're considering using unless I were building a driver for basic transportation from point A to point B.

That's just my opinion.

Now can you get 300 HP out of the 993 heads? Maybe, but if you bolt-on a pair of stock Sportsmans, you can easily make 350 HP without even trying.

If you want to spend even less, there are plenty of better stock heads to choose from too that you can get for even less.
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Old 4th-July-2007, 12:31 PM   #15
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The 3998993 has 1.94/1.5" valves and they were used on the base '72 Corvette among other models. In stock trim the Corvette produced 175 hp.
The head #330545 is identical to the 993 head but has 2.02/1.6 valves. It was used on the 73 Corvette 350/250 Hp and Camaro Z28 350/245 hp.

So obviously if you modify the heads to 330545 spec your engine can make 250 Hp. Your still short 50 hp of your goal. With bowl porting, a good seat, headers, intake and the right cam you should be able to make 300 hp, if everything is done correctly.

Is that what you wanted to hear?
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Originally Posted by Paul Wright
Building a small, high rpm engine
with the perfect bore, stroke and rod ratio is very impressive...
like a highly skilled Morrocan sword fighter with a Damascus Steel Scimitar.

Cubic inches is like Indiana Jones with a cheap pistol.
.

Last edited by Paul Wright; 4th-July-2007 at 12:35 PM.
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