L98 Head Porting
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,861
Likes: 4
From: Houston TX
L98 Head Porting
Anyone tried porting their L98 heads or have ported L98 heads with flow numbers?
If so, could you port here? I knew the L98 casting was really crappy, but I didn't think it would be possible to find 30 cfm on the exhaust side in 30 minutes and still have more material to go.
If so, could you port here? I knew the L98 casting was really crappy, but I didn't think it would be possible to find 30 cfm on the exhaust side in 30 minutes and still have more material to go.
Racer
Joined: Apr 2002
Posts: 415
Likes: 0
From: loughborough Leics ENGLAND
Re: L98 Head Porting (CorvetteZ51Racer)
I ported my 113's using David Visards book Modifying small block chevy heads as a guide. ( excellent )
It took me about a day per head going steady plus machining time for seats, new guides and valves total cost was $560
I fitted these heads with a zz4 cam and picked up 5mph over my previous average mph while still using the standard ex manifolds which were a lot smaller than the exhaust port.
I have now fitted 1.5/8 headers and expect to see another 1.5 to 2 mph on top to give me 110mph traps
I have no flow numbers but the book has a good description of what and were to remove metal.
I am happy with the results but if you are worried about doing it, add the cost of machining and parts ( $560 for me ) plus the $450 you could get for your heads and you are within a hairs breath of getting some afr's which are a better casting anyway with more potentail
:cheers:
It took me about a day per head going steady plus machining time for seats, new guides and valves total cost was $560
I fitted these heads with a zz4 cam and picked up 5mph over my previous average mph while still using the standard ex manifolds which were a lot smaller than the exhaust port.
I have now fitted 1.5/8 headers and expect to see another 1.5 to 2 mph on top to give me 110mph traps
I have no flow numbers but the book has a good description of what and were to remove metal.
I am happy with the results but if you are worried about doing it, add the cost of machining and parts ( $560 for me ) plus the $450 you could get for your heads and you are within a hairs breath of getting some afr's which are a better casting anyway with more potentail
:cheers:
Drifting
Joined: Mar 2001
Posts: 1,636
Likes: 3
From: Lafayette IN
Re: L98 Head Porting (CorvetteZ51Racer)
A good article on the D-ports can be found at crossfire...you might have to register to view it.
http://www.crossfire.homeip.net:81/c...ID=18&CAT_ID=1
Good luck, -Matt-
http://www.crossfire.homeip.net:81/c...ID=18&CAT_ID=1
Good luck, -Matt-
Racer
Joined: Apr 2002
Posts: 415
Likes: 0
From: loughborough Leics ENGLAND
Re: L98 Head Porting (HighHopes85)
That is a nice artical :yesnod: pictures are great
More or less what i did but there are suttle refinements in the book which i also did to mine like bronse guides new under cut valves etc.
:cheers:
More or less what i did but there are suttle refinements in the book which i also did to mine like bronse guides new under cut valves etc.
:cheers:
Racer
Joined: Oct 2000
Posts: 476
Likes: 0
From: Socorro New Mexico
Re: L98 Head Porting (CorvetteZ51Racer)
If you are talking about the standard L98 aluminum heads, be carfull. You can do more harm than good.
Check out David Vizards book "How to Build & Modify Chevrolet Small-Block Cylinder Heads". He slapped a three angle valve job on a stock set of heads and hurt the air flow on the intake. He then pocket ported and still did not get back to the original flow numbers. Next he slapped on a full port job and exceeded the original flow numbers, mainly at higher lifts. Next he installed larger valves and got some good flow numbers.
By the time all that work was done, a set of aftermarket heads that flow better out of the box is the cheaper way to go. You could even buy a set of the aluminum fast burn heads and the SD manifold for that kind of money.
Check out David Vizards book "How to Build & Modify Chevrolet Small-Block Cylinder Heads". He slapped a three angle valve job on a stock set of heads and hurt the air flow on the intake. He then pocket ported and still did not get back to the original flow numbers. Next he slapped on a full port job and exceeded the original flow numbers, mainly at higher lifts. Next he installed larger valves and got some good flow numbers.
By the time all that work was done, a set of aftermarket heads that flow better out of the box is the cheaper way to go. You could even buy a set of the aluminum fast burn heads and the SD manifold for that kind of money.
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,861
Likes: 4
From: Houston TX
Re: L98 Head Porting (Rynda)
Well, I don't know how in the world it took him a full port job to increase flow (well, it is easy to hurt flow in a lot of heads)...I unshrouded the valves in the chamber, smoothed the flashing from the casting and blended it in (especially on the short side) and I have picked up flow at all lifts. I haven't yet smoothed the walls or even touched the bowl past blending.
It is very easily possible to lose flow by simply doing a valve job on the head, as you're cutting the seat down further into the head. If you don't clean up the edges of the chamber around the seat when you do the valve job, you have shrouded the valve more which will cancel out the benefit of keeping the air from separating from the surface with the valve job.
I do know how to port heads, and have gotten gains as high as 48 cfm on heads like the Brodix 11...I just hadn't realized that the L98 castings could be opened up so much so quickly.
It is very easily possible to lose flow by simply doing a valve job on the head, as you're cutting the seat down further into the head. If you don't clean up the edges of the chamber around the seat when you do the valve job, you have shrouded the valve more which will cancel out the benefit of keeping the air from separating from the surface with the valve job.
I do know how to port heads, and have gotten gains as high as 48 cfm on heads like the Brodix 11...I just hadn't realized that the L98 castings could be opened up so much so quickly.
Racer
Joined: Apr 2002
Posts: 415
Likes: 0
From: loughborough Leics ENGLAND
Re: L98 Head Porting (CorvetteZ51Racer)
His testing was done with standard valves which do did not work as well with a 3/a valve job as they do with the std valve job ( that was his opinion ).
Also bear in mind this was testing the head step by step which hi lighted were we should start work when we get to do ours.
From what i remember with new valves and recut seats he got 225 cfm ( up from 180 cfm ) inlet and 175 cfm ( up from 145 cfm )exhaust
He claimed this was good for 450 hp :D
Also bear in mind this was testing the head step by step which hi lighted were we should start work when we get to do ours.
From what i remember with new valves and recut seats he got 225 cfm ( up from 180 cfm ) inlet and 175 cfm ( up from 145 cfm )exhaust
He claimed this was good for 450 hp :D
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,861
Likes: 4
From: Houston TX
Re: L98 Head Porting (BLUE ONE)
Hmmm....his new valves and recut seats still had less than what I started with on my heads, and I have more now...I have about 240 cfm intake and I can't remember the number on the exhaust, and this is with the stock straight cut valves and seats.....
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Melting Slicks
Joined: May 1999
Posts: 2,037
Likes: 0
From: Sarasota FL
Re: L98 Head Porting (CorvetteZ51Racer)
Check out this thread so I don't have to retype my results. Relative numbers, not CFM.
http://forums.corvetteforum.com/zerothread?id=461648
http://forums.corvetteforum.com/zerothread?id=461648
Racer
Joined: Apr 2002
Posts: 415
Likes: 0
From: loughborough Leics ENGLAND
Re: L98 Head Porting (CorvetteZ51Racer)
They can be worked to flow 250cfm, but it takes a lot of skill and you need to do it on a flow bench to get those numbers some have even got up to 275 cfm but why bother :crazy: Afr's get up there if you pick the right head for your application from the start.
:cheers:
:cheers:
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,861
Likes: 4
From: Houston TX
Re: L98 Head Porting (Aaron's 87)
In my last post I mentioned some numbers that were wrong...I was tired when I posted that and remembering the numbers from the first stage of the port job, not stock.
I haven't had a chance to polish the ports or chambers yet (we're out of sanding rolls here at the shop), but I'm currently looking at ~230 cfm intake and ~140 exhaust. I don't have the flow numbers in front of me for the entire lift range, but I'm seeing significant gains over the entire lift range with what I would consider to be minimal work (~1-1/2 hours per cylinder for the chamber, intake, exhaust, and flowbench)
Also, even though I will use calipers to ensure that my ports are the same all the way across when I go in for the final clean up, right now the ports (both intake and exhaust) are all flowing to within 1-2% of each other copying them by eye and feel.
I have a lot more material I can take out in key areas if I want to, but I don't know if I do right now. I haven't flowed the intake and don't know what the stock TPI runners will flow...I don't want to make the head flow a lot better than the intake, but rather to try to match them.
I haven't had a chance to polish the ports or chambers yet (we're out of sanding rolls here at the shop), but I'm currently looking at ~230 cfm intake and ~140 exhaust. I don't have the flow numbers in front of me for the entire lift range, but I'm seeing significant gains over the entire lift range with what I would consider to be minimal work (~1-1/2 hours per cylinder for the chamber, intake, exhaust, and flowbench)
Also, even though I will use calipers to ensure that my ports are the same all the way across when I go in for the final clean up, right now the ports (both intake and exhaust) are all flowing to within 1-2% of each other copying them by eye and feel.
I have a lot more material I can take out in key areas if I want to, but I don't know if I do right now. I haven't flowed the intake and don't know what the stock TPI runners will flow...I don't want to make the head flow a lot better than the intake, but rather to try to match them.
Thread Starter
Drifting
Joined: Dec 2002
Posts: 1,861
Likes: 4
From: Houston TX
Re: L98 Head Porting (CorvetteZ51Racer)
I do have a flowbench that I'm using extensively.
And the reason I'm porting these instead of buying a set of AFR's is that we have all of the burrs, grinders, a flowbench, etc so the porting isn't costing me anything...a set of AFR's cost $$
And the reason I'm porting these instead of buying a set of AFR's is that we have all of the burrs, grinders, a flowbench, etc so the porting isn't costing me anything...a set of AFR's cost $$
