All Big Six Help with budget head build please

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Mydogisshaggy

Well-known member
I have an 86' carb head that's been ported and I need new valve springs at the minimum. The block is a 93 efi. The labor is more of a concern than cost but also not looking to spend too much, just a balanced rebuild. I was thinking better push rods and springs than oem and 1.7 scorpion rockers but no camshaft change or valve change so I don't have to have the seats done or anything else I can't do easily/myself. I was going to buy a spring compressor and do that part myself since I hammered the old ones off since it was my first time and no tool, just wanted to port. Last issue, I plan to run strictly ethanol free 90 octane, I have no fuel injectors right now so wondering if a similiar flowing 4 hole swap or even a 19# would be worth it to keep duty lower but messing with pressure and wrapping my manifolds and hoping the 90octane won't vapor lock at slightly lower pressure especially with the 4 hole(if that matters) and egr removed. Running off stock eec-iv and hoping an adjustable fuel regulator and wideband can help get me in the ballpark with timing the distributor and monitor the computer while it tries to adjust, Any thoughts/input would be great thanks.
 

pmuller9

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The 1986 carb head has larger combustion chambers than the 1987 and later EFI heads and will drop the compression ratio form 8.8 to 8.25.
The second problem is the 1986 head doesn't have the heart shaped fast burn chamber design of the later EFI heads and requires a lot more ignition timing.

You should get new valve springs and replace the rotating style exhaust retainers.
Use Comp 903-12 springs and Goodson valve retainers.

The pushrods will need to be longer.

Everything you need to know including the things I just mentioned is in this thread.
 

THE FRENCHTOWN FLYER

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I winced a little when I read that you hammered the old valves off. It is not difficult to bend a valve stem doing that. Or crack a guide. Do you have a way to check for valve straightness? If not just lightly chamfer the tip and install each valve in the snuggest guide you can find. Spin each valve to see if they offer any sort of drag as you spin it. If so, discard and replace it. I like to use a brass hammer around valves to reduce the possibility of damaging anything.

For a budget rebuild if you are not going to grind the valves / seats just get some lapping compound and lap them in. It will expose the pits and / or warped / burnt faces.

I am not averse to "budget build" anything. Heck, I worked for years with the crudest of tools and methods, until I could work my way up to better procedures and equipment. But if I had to choose between pricey bolt-on stuff like injectors and rocker arms or doing sound machining on a cylinder head rebuild I would invest in the best possible rebuild - head resurfacing, valve guides, valve job, stem seals, etc.
Bolt on stuff can always be added later. You can't add on new valve seats without completely disassembling the upper engine later.
Headaches.
If you are reusing the EFI valve cover on the carbed head open up the holes to fit the early 5/16" bolts.
Good luck on your project build up.
 
Last edited:

BigBlue94

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Listen to these two guys ^^^ they know these engines inside and out and upside down in the dark. They've been there, done that.

i picked up a valve spring compressor at an estate sale for about 5 bucks.
 

Mydogisshaggy

Well-known member
I winced a little when I read that you hammered the old valves off. It is not difficult to bend a valve stem doing that. Or crack a guide. Do you have a way to check for valve straightness? If not just lightly chamfer the tip and install each valve in the snuggest guide you can find. Spin each valve to see if they offer any sort of drag as you spin it. If so, discard and replace it. I like to use a brass hammer around valves to reduce the possibility of damaging anything.

For a budget rebuild if you are not going to grind the valves / seats just get some lapping compound and lap them in. It will expose the pits and / or warped / burnt faces.

I am not averse to "budget build" anything. Heck, I worked for years with the crudest of tools and methods, until I could work my way up to better procedures and equipment. But if I had to choose between pricey bolt-on stuff like injectors and rocker arms or doing sound machining on a cylinder head rebuild I would invest in the best possible rebuild - head resurfacing, valve guides, valve job, stem seals, etc.
Bolt on stuff can always be added later. You can't add on new valve seats without completely disassembling the upper engine later.
Headaches.
If you are reusing the EFI valve cover on the carbed head open up the holes to fit the early 5/16" bolts.
Good luck on your project build up.
Thanks hopefully It wasn't as bad as you imagined, it was a rubber mallet and I wacked the springs one good time to pop them out, not exactly the valves, just what I read to do in a pinch... Injectors will probably come from a junkyard or be cheaper ones than the stock that need replacing , I noticed the OEM are around $60 while others like the sable 4 hole being half the cost new.
 

Mydogisshaggy

Well-known member
The 1986 carb head has larger combustion chambers than the 1987 and later EFI heads and will drop the compression ratio form 8.8 to 8.25.
The second problem is the 1986 head doesn't have the heart shaped fast burn chamber design of the later EFI heads and requires a lot more ignition timing.

You should get new valve springs and replace the rotating style exhaust retainers.
Use Comp 903-12 springs and Goodson valve retainers.

The pushrods will need to be longer.

Everything you need to know including the things I just mentioned is in this thread.
The 1986 carb head has larger combustion chambers than the 1987 and later EFI heads and will drop the compression ratio form 8.8 to 8.25.
The second problem is the 1986 head doesn't have the heart shaped fast burn chamber design of the later EFI heads and requires a lot more ignition timing.

You should get new valve springs and replace the rotating style exhaust retainers.
Use Comp 903-12 springs and Goodson valve retainers.

The pushrods will need to be longer.

Everything you need to know including the things I just mentioned is in this thread.
Thanks I will go over that thread again. How much could I shave the 86' head or should I if I wanted to bring compression back up? Any thoughts on naturally aspirated C/R recommendations for max power with a stock block/cam etc. and the mentioned springs and recommended injector size, fuel psi, and timing for 90 octane with no ethanol. Long-term plan is boost but will use a efi head for that(just because it's my other spare) I know the 84 pushrods are longer, would those work?(nvm will check thread)
 
Last edited:

pmuller9

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If you are going to do boost later it requires a lower compression ratio so the 86' head would be better for that application.
The EFI head would be better for the naturally aspirated build.
You can't or shouldn't shave enough off the 86' head to bring the compression ratio up one point.

Naturally aspirated compression ratio with the stock cam and 90 octane fuel can be as high as 9.2 if the pistons are close to zero deck clearance for good quench.

Are you going to freshen up the bottom end using new pistons?
 
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Mydogisshaggy

Well-known member

If you are going to do boost later it requires a lower compression ratio so the 86' head would be better for that application.
The EFI head would be better for the naturally aspirated build.
You can't or shouldn't shave enough off the 86' head to bring the compression ratio up one point.

Naturally aspirated compression ratio with the stock cam and 90 octane fuel can be as high as 9.2 if the pistons are close to zero deck clearance for good quench.

Are you going to freshen up the bottom end using new pistons?
Going to worry about pistons/valves etc and c/r with the boost build down the road. For now just getting the daily efi running better, the exhaust and intake needs to come off for a 96 exhaust manifold swap, need to fix or remove a cracked EGR pipe and replace injectors...

I want to put on this 86 head I ported while I'm at it, but it needs the new comp springs you recommended... then the 1.7 rockers and pushrods.... I'm basically just collecting parts but putting them to use now as I collect them because who knows when the rest will finally occur. Just trying to figure out the details, I'm either moving the stock o2 sensor in the y pipe to the 96 manifold and putting a wideband gauge in stock location or vice versa, undecided but having computer read the manifold and wideband at the y pipe spot seems to just make more sense 🤔. After the head swap I'm just trying to get a grasp for fuel and timing. Everyone says how restrictive the heads are (I didn't port match or blow it out, just smoothed the exhaust and bowls etc.) I want to test my head out guys that's about all this is about 🙂. Still waiting for the trac lok I installed myself to blow up (500+ miles ). Not really worried about the motor going too, I can always walk to work, just motivates me to fix it faster but I'm confident with the proper precautions and research I can prevent that and maybe even put out 150+horses Thanks again

Edit: forgot to mention engine management in the future and just totally undecided from maf conversion to piggyback to moates or Holley or Fitch. But willing to test the waters until I hit problems, then probably just wideband and self adjust as much as I can and then piggyback/standalone it when need be.
 
Last edited:

Mydogisshaggy

Well-known member
I winced a little when I read that you hammered the old valves off. It is not difficult to bend a valve stem doing that. Or crack a guide. Do you have a way to check for valve straightness? If not just lightly chamfer the tip and install each valve in the snuggest guide you can find. Spin each valve to see if they offer any sort of drag as you spin it. If so, discard and replace it. I like to use a brass hammer around valves to reduce the possibility of damaging anything.

For a budget rebuild if you are not going to grind the valves / seats just get some lapping compound and lap them in. It will expose the pits and / or warped / burnt faces.

I am not averse to "budget build" anything. Heck, I worked for years with the crudest of tools and methods, until I could work my way up to better procedures and equipment. But if I had to choose between pricey bolt-on stuff like injectors and rocker arms or doing sound machining on a cylinder head rebuild I would invest in the best possible rebuild - head resurfacing, valve guides, valve job, stem seals, etc.
Bolt on stuff can always be added later. You can't add on new valve seats without completely disassembling the upper engine later.
Headaches.
If you are reusing the EFI valve cover on the carbed head open up the holes to fit the early 5/16" bolts.
Good luck on your project build up.
Never planned to reuse these valves anyway, have a bunch of stock ones laying around now anyway...
 
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