Pricing and sources for 32v valve job/porting
03-20-2013, 09:53 PM
#16
Former Sponsor
I can tell you that in Houston, a set of 1R heads were rebuilt by a local shop that has been around forever, and does a lot of Porsche work, for just over $700. New valve guides, 3 angle grind, not sure about milling. No performance work, just a standard rebuild. I have these rebuilt heads for sale for $900 and they were NOT blasted when cleaned (inside joke).
I'm not sure I buy all the mystery around a standard head rebuild. 4 valve aluminum heads are supper common these days, and most machine shops have rebuilt many 1000's of them. Maybe there's something special I'm not aware of, and happy to hear that I'm totally wrong and it does take a specialist to rebuild them.
I'm not sure I buy all the mystery around a standard head rebuild. 4 valve aluminum heads are supper common these days, and most machine shops have rebuilt many 1000's of them. Maybe there's something special I'm not aware of, and happy to hear that I'm totally wrong and it does take a specialist to rebuild them.
03-20-2013, 10:11 PM
#17
Former Sponsor
Head development is an art. Greg is giving good advise as he has probably done more of them than anyone else. Development come from hours of trying things.
I knew a guy that worked at Chaparral on the Trans Am Cameros. At that time Chevy/G.M. used Chaparral for their "unoffical" factory race team.
He told me that Chevy sent down a whole pallet of head castings so they could try anything. Instructions were- we don't care if you ruin most of them, sooner or later you'll find something.
If it meant grinding into a water passage- no problem, just epoxy it for flow test purposes.
When they finally got the heads the way they wanted them- they shipped them back to Chevy & they re did the casting core to allow for enough material. Took hours & hours & lots of scrap heads before they got it.
Someone that only does a set every once in a while is at a big disadvantage.
I knew a guy that worked at Chaparral on the Trans Am Cameros. At that time Chevy/G.M. used Chaparral for their "unoffical" factory race team.
He told me that Chevy sent down a whole pallet of head castings so they could try anything. Instructions were- we don't care if you ruin most of them, sooner or later you'll find something.
If it meant grinding into a water passage- no problem, just epoxy it for flow test purposes.
When they finally got the heads the way they wanted them- they shipped them back to Chevy & they re did the casting core to allow for enough material. Took hours & hours & lots of scrap heads before they got it.
Someone that only does a set every once in a while is at a big disadvantage.
Try and find a picture of one of my ports.....
That will give you an idea of how much work it was to make airflow and not kill the velocity. I've "ground" more than one "sample" head into scrap metal, trying to make this happen. And I'm not goiing to show anyone what it takes.
03-20-2013, 10:41 PM
#18
I agree with Greg that good port work takes trial and error..... there are some huge differences between wet flow and dry flow..... flow is nice but velocity is king.... especially with fuel in the mix. I had some head work done by a local shop that does both wet flow and dry flow before and after. They mentioned that the 928 heads have better numbers using both methods than many aftermarket domestic performance companies.... but they were able to improve them with 968 valves and their own custom guides.. the factory 928 valve guides wreck the flow in these heads....
03-20-2013, 11:45 PM
#20
Former Sponsor
I agree with Greg that good port work takes trial and error..... there are some huge differences between wet flow and dry flow..... flow is nice but velocity is king.... especially with fuel in the mix. I had some head work done by a local shop that does both wet flow and dry flow before and after. They mentioned that the 928 heads have better numbers using both methods than many aftermarket domestic performance companies.... but they were able to improve them with 968 valves and their own custom guides.. the factory 928 valve guides wreck the flow in these heads....
I'm not going to give exact numbers....those are proprietary.
However.....
Let's say that the stock heads flow enough air to support 450hp.
And let's say that 968 valves "hurt" this by 10%, in almost everyone's heads.
That means the "new" heads are only going to flow enough air to support 410hp, once they are done.
Not very many people, building a naturally aspirated 928 engine (unless they are building a stroker), are going to make 410hp. Actually, the total amount of people that are going to do this is zero.
Net result: Person with 968 valves spent money, supported the economy, and still has enough airflow to make the amount of power he wants, even though the airflow went down.
03-20-2013, 11:56 PM
#21
Rennlist Member
03-21-2013, 11:14 AM
#22
Nordschleife Master
I am trying to make sure that I understand what you're saying before jumping in.
03-21-2013, 11:29 AM
#23
How much is it per hour to put an engine on the dyno?
03-21-2013, 07:21 PM
#24
Rennlist Member
Not very many people, building a naturally aspirated 928 engine (unless they are building a stroker), are going to make 410hp. Actually, the total amount of people that are going to do this is zero.
Net result: Person with 968 valves spent money, supported the economy, and still has enough airflow to make the amount of power he wants, even though the airflow went down.
Are you telling me I could have made more???
P.S. The 928 heads can be rebuild to factory spec by any good shop. Agree on your words about porting being best left to those who actually know...
03-21-2013, 08:46 PM
#25
You could have made more with ethanol with that 12:1 because you would not have had to reduce timing as much for the 99ron.
03-22-2013, 04:43 AM
#26
Nordschleife Master
Anybody thinking porting 4V heads on the 928 is low hanging fruit, easy hp for the money, needs to erase that thought. Get your standard valve job and look at headers, X pipes, cams, etc. More can be gotten out of the heads, but its not going to be cheap hp.
Having the wrong place do head work has to be the universal money down a rat hole hot rod story.
Having the wrong place do head work has to be the universal money down a rat hole hot rod story.
03-22-2013, 06:54 AM
#27
Rennlist Member
I guess I could have made even more if I went with methanol or race fuel - we do actually have BP 102RON available at the pumps in Europe. Or I could have run it on Sunoco's go-go juice at $30/gal and had the ultimate dyno queen...
As it stands, it is a race car, which still has number plates attached to it and theoretically can be driven on the public road - mind the fully rose-jointed suspension though
It idles like a stock 928 and it also passes European Union emissions tests for a 1990MY 928GT. It also has to last races which could be up to 4hrs long... The point of my original post was that there are other people out there who also know what they are doing. Dismissing them out of hand gets a bit tiresome after a while, you know...
03-22-2013, 11:08 AM
#28
