I don't think it would make that much difference on a duke. Since, as your signature suggests, you have a cam upgrade and Holly TBI, which should let your engine run at higher RPM, you should make it stronger by using 88 crank and rods. I rebuilt my 88 duke with an Accelerated Motion cam and big block Chevy roller rockers. Before the rebuild, it would gasp for air at 4500 RPM. Now it still pulls at 5000 RPM. But it's still a duke, and isn't going to beat my V6 Fiero.
------------------ The more complex the mind, the greater the need for the simplicity of play.
I feel certain the intake valve is the bottle neck. Tried everything except the obvious. Larger intake valves. After this mod if the Duke doesn't feel as agile as my mom's Hyundai 4 door I will be looking to switch to MGs.
Actually, the whole air path in the head is more of a bottle neck than just the valve seat. I also put a later model head (91 or 92) on my 88 duke. I don't think you could do that on the 84.
With the FS performance cam yeah, the rpms can shoot up pretty well. Before it could not get air. THATS WHY I am thinking 30* valves..for low lift. This Duke thing is a puzzle...I mean it's got 2.5L displacement. Never hear of actual engine failure with these things only shinning reports of dependability. So it seems worth messing with.
There's room for 2" valves in this head by golly. That would require hawging out the chamber....better to go with earlier non swirl head for that. 1.875 would hardly require much alteration of the chamber and 30* valves... well, that's my thinking.
You should search this forum for turbo dukes. I'm sure you'll find a lot of engine failures. The weakest parts are the rods and crank, especially in the earlier dukes. The 88 rods have a wider beam, and the 88 crank is stronger by virtue of having the timing wheel added to the casting.
Thanks for the feedback Top. The Duke is pretty dependable obviously, so what are the changes required to squeeze more performance out of them? I see many a naturally aspirated Audi or Porsche and nowadays Hyandai and Honda with 2.5 engines or smaller in them that get over 150 HP. I gather it mostly has to do with air management and higher redlines. The cam was helpful to get it to breath better near open throttle which may be good for passing at highway speeds. What I am interested in is acceleration from 0-60. Do you think opening the passageways from manifold to the valve are important? Vizard in his book suggests the intake valve it's size and areas directly adjacent are the prime areas to address.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Thanks for the feedback Top. The Duke is pretty dependable obviously, so what are the changes required to squeeze more performance out of them? I see many a naturally aspirated Audi or Porsche and nowadays Hyandai and Honda with 2.5 engines or smaller in them that get over 150 HP. I gather it mostly has to do with air management and higher redlines. The cam was helpful to get it to breath better near open throttle which may be good for passing at highway speeds. What I am interested in is acceleration from 0-60. Do you think opening the passageways from manifold to the valve are important? Vizard in his book suggests the intake valve it's size and areas directly adjacent are the prime areas to address.
The modern engines making 200+ HP with 2.5L or less have a lot of advantages over the Duke.
DOHC, VVT, SIDI, a whole mess of sensors that cars in the 80s didn't have, and a much faster ECM to manage them.
The Duke was a nice reliable engine, but it's no Ecotec.
The Duke was a nice reliable engine, but it's no Ecotec.
Too true. They are good reliable engines, when you leave them mostly stock. If you want to still have a duke but make a bit more power, you may as well start with the best base line you can. The 84 works fine and runs nice, but I am not putting any money into mine to make more power.
The best duke you can start with were the ones out of the early 90's trucks. Roller cam, DIS, I believe a better computer, and a much better flowing head. The "swirl port" heads on the earlier engines are about useless if you want to make power from them.
Stock they made about 110hp or so. I am sure with a port, good coils, maybe a mild cam, and some time spent to properly tune it, you can make more than enough power to be comfortable on the highway.
Originally posted by KillerFrogg: Too true. They are good reliable engines, when you leave them mostly stock. If you want to still have a duke but make a bit more power, you may as well start with the best base line you can. The 84 works fine and runs nice, but I am not putting any money into mine to make more power.
The best duke you can start with were the ones out of the early 90's trucks. Roller cam, DIS, I believe a better computer, and a much better flowing head. The "swirl port" heads on the earlier engines are about useless if you want to make power from them.
Stock they made about 110hp or so. I am sure with a port, good coils, maybe a mild cam, and some time spent to properly tune it, you can make more than enough power to be comfortable on the highway.
Hey K Frog, I have my cylinder head off the 84, think I should hawg out the swirl spiral? I am thinking of making rubber casts of the port passage from manifold to valve just to see how awful it is. hmmmm... now if the passages were smoothed out (but not polished) the air might not stick to the sides = more volume in.... keep the chamber dimply......
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Keep in mind that duke heads, especially earlier ones, tend to crack. If you hog out an 84 head, you should have it checked thoroughly first. When I rebuilt my 88 duke, I found that my head had a small crack, which is why I wound up using a 91-92 head on it.
I agree with TopNotch. I don't know why, but these heads are prone to cracking, not always major, but it happens often. Not a lot of material there, and not the best quality iron either.
The later head is the way to go if it works on your block. It IS possible to remove the swirl in the intake, it wraps around the valve stem. It just takes more time than I care to put into an early head.
If you do go for any digging on the head, get it magna-fluxed now, and if there is anything questionable, set it aside for if something goes wrong so you still have a head you know drives, and find another head to play with.
And you do want some roughness on the intake path. I am not an expert by any means on air flow in engines, but from what I have read, you do want some roughness, as the turbulence helps with fuel atomisation. And unless you polish the entire intake path, the few inches up to the valve in the head are not going to show any improvment. Polishing is more important when you are trying to push air, as in a turbo application with some kind of multi port fuel injection or direction.
The one of the better and easier things you can do is a simple gasket based port match on the intake. Because the exhaust is welded steel tube, there is not really any area to safely remove anything on that side, but you could match the head to the manifold as best as possible.
Hey Thanks you guys, appreciated! The head I have is a reconditioned one. I tried some silly Singh Groove nonsense on the original and found a couple small cracks in the exhaust valve seats as well...so I traded it in. This one must be a later model. It is swirl port and all the gaskets and bolts line up (although 2 bolts seem to have been plugged and repositioned. Perhaps I am lucky as it seems like this one has been shaved at least 1/8th" inch off the bottom. Casting #10027767.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Had a search fest on the net and it looks like this head may be an 86 U code that has been plugged and tapped for R code fit. It also looks to have been shaved. Turns out GM cast the head with enough metal to be tapped for either U or R code cars. With that in mind it looks like this one came off an 86 GrandAm or Bonneville.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 07-21-2014).]
why would anyone, even refurb houses bother doing that? Not like there was ever a shortage of these parts. lol
$$$$ but I am not worried. It did take a few days longer than expected. Besides this one seems shaved....maybe someone thought "oh hey maybe this guy could make good use of that one" etc. Who knows.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Been reading Vizard's book "How to port and flow test cylinder heads", watching vids, and it seems there is a sort of accepted ideal ratio of intake to exhaust valve size in relation to bore and desired flow at what rpm. Honestly, the Duke seems way mangled in this area! It all seems to point to the Duke having undersized intake valves as well as the wrong angle valves in it. Seems the ideal would be 1.94 intake to 1.5 valves and they should be 30* intake and 45* exhaust. Simply keeping the 1.75 intake valves but giving them a 30* angle seat and valve would keep it high torque but more "punchy" as the chamber would fill sooner at higher velocity. A compromise like 1.875 valves with or without a 30* seem safe options.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
IIRC you start to open up a bolt hole for the thermostat housing or something when you take off that much material.
As far as the valves themselves, The only thing I ever found that was close to a drop-in was a mid-70s Buick or Olds 350 valve (can't remember which), with a 1.88" head. The issue is that 2.5 valves are much shorter than SBC valves, so you've got to look carefully for cheap replacements.
If you don't find yourself an older, 552 or 702 casting, pre-swirl, you're wasting your time. There's no performance in the 767 head no matter what you do; sorry.
Dobey, I do not know how much has been shaved, I only know that the heart shape seems shallower by eye. Is there a way to measure? Kurt, thanks man, I really dig that you found and share that the earlier heads have much more potential for serious porting and flow. I knew that (thanks to you) when I traded this one in. Had I gone to Summit pick a part I would have gone with your suggestion but as it happened I was given a gift card for AutoZone. We need to get that idea some flow tests! Tomorrow gonna try making that cheap flow test gizmo Vizard described. The one that just needs tubing, clay and a vacuum cleaner! But yeah, what d'ya think about the 30* intake idea? I heard back in th 50's it was pretty much standard for a reworked head.
It is pretty difficult to find alternate valves for the Duke. Not gonna sweat it for this project and instead just do a classic DIY port and polish and have the seats and valves ground to 30* at the machine shop. With luck the flow test gizmo will work and offer relative although crude quantification. I'll be sure to post pictures. It will take a few weeks as I only will be doing this on Sunday evenings.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Originally posted by White 84 SE: Dobey, I do not know how much has been shaved, I only know that the heart shape seems shallower by eye. Is there a way to measure?
If you have another totally stock head of the same casting you could measure the difference easily/closely enough with a straight and a dial caliper.
If you have the equipment, you could measure the head chamber volume and if you have the stock numbers anywhere, you could use the difference in those values to calculate how much the head has been shaved. I don't know the exact formula for that, but I know it's going to be complex, due to the shape of the chamber not being a cylinder.
If you have another totally stock head of the same casting you could measure the difference easily/closely enough with a straight and a dial caliper.
If you have the equipment, you could measure the head chamber volume and if you have the stock numbers anywhere, you could use the difference in those values to calculate how much the head has been shaved. I don't know the exact formula for that, but I know it's going to be complex, due to the shape of the chamber not being a cylinder.
I guess a simple but messy way is to fill the chamber in the head with plaster and level off accurately then drop the dried plaster into some water and note the displacement. I think in the 50's that was a common way but I have no idea how pros would do it these days. They got quart sized boxes of Plaster of Paris at the hardware stores or art stores for sure. If the chamber is oiled well prior i see no potential for harm.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
I guess a simple but messy way is to fill the chamber in the head with plaster and level off accurately then drop the dried plaster into some water and note the displacement. I think in the 50's that was a common way but I have no idea how pros would do it these days. They got quart sized boxes of Plaster of Paris at the hardware stores or art stores for sure. If the chamber is oiled well prior i see no potential for harm.
I always thought 3 angle valve seats were the way to go (60,45,30) along with back-cut intake valves.
Air will travel in a straight line if it can so says Vizard in his book, "How To Port and Flow Test Cylinder Heads" and I believe him. A straight line for a Duke cylinder head is along the top of the port to the far end of the valve expanding into the piston chamber. A 30* opening at the far end of the valve seat/valve is closer to being in this horizontal line from manifold to piston chamber than a 45 would be. In a way the 30* at the long side of the port allows the air to travel more as it wants.
Oh yeah! That would be much easier! Just need some plexiglass scrap and some Vaseline! Totally awesome Dobey! Thanks!! P.S. I am still gonna use plaster just cause it's so retro but filling it will be way more accurate with the plexiglass seal!!
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 07-22-2014).]
Remember that a duke has dished pistons, so you'd also have to do the piston (fill the top of that with the green alcohol) and add that measurement to the head chamber measurement to get the total compressed volume.
Remember that a duke has dished pistons, so you'd also have to do the piston (fill the top of that with the green alcohol) and add that measurement to the head chamber measurement to get the total compressed volume.
Right. But the piston doesn't tell you how much metal was taken off of the head, which is what was being questioned here. Knowing the volume of the shaved head, and the volume of the stock head, one can calculate how much metal was taken off. But I don't want to be the one doing the math work for the non-cylindrical volume difference.
Right. But the piston doesn't tell you how much metal was taken off of the head, which is what was being questioned here. Knowing the volume of the shaved head, and the volume of the stock head, one can calculate how much metal was taken off. But I don't want to be the one doing the math work for the non-cylindrical volume difference.
Just gonna drop the plaster in some water and see how much is displaced. But where can we find the spec volume?
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Just gonna drop the plaster in some water and see how much is displaced. But where can we find the spec volume?
Well, if you had a stock head as well, you could measure it. But that will still only give you part of the answer. You'd then have the volume difference of two complex shapes, and would still need to calculate the height difference. If the pieces of plaster were perfectly flat on the deck side, you could of course just measure the difference between them. But it would be even easier to just use a straight edge and a dial caliper to measure the difference in height from the exact same spot in the chamber on both heads.
Unless you really need to know how much metal was taken off (if any), I'd just check the piston to valve clearance and if it's good, throw the head on and run with it. And if you get any ping/knock, adjust the timing and/or bump up the fuel octane you're using.
You know I may have the perfect part for you to squeeze power out of that duke, the Holley TBI is nice and all but I have a intake manifold for a two barrel carburetor that fits the 84 head your in chicago I'm sure you don't live too far if you want it you can come get it for free
You know I may have the perfect part for you to squeeze power out of that duke, the Holley TBI is nice and all but I have a intake manifold for a two barrel carburetor that fits the 84 head your in chicago I'm sure you don't live too far if you want it you can come get it for free
Wow that's pretty Awesome Fade! Honestly all this electrical claptrap seems like some sort of failed experiment for the Duke. I'd love to stop by but it won't be till this one is running well. With luck a month or so. September October perhaps? Anyway what car did it come off of for future reference for anyone who might want to swap out the EFI?
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Well, if you had a stock head as well, you could measure it. But that will still only give you part of the answer. You'd then have the volume difference of two complex shapes, and would still need to calculate the height difference. If the pieces of plaster were perfectly flat on the deck side, you could of course just measure the difference between them. But it would be even easier to just use a straight edge and a dial caliper to measure the difference in height from the exact same spot in the chamber on both heads.
Unless you really need to know how much metal was taken off (if any), I'd just check the piston to valve clearance and if it's good, throw the head on and run with it. And if you get any ping/knock, adjust the timing and/or bump up the fuel octane you're using.
Dobey, looks like TopNotch is right on target. I have on original 84 shop manual showing piston location at TDC. There appears no appreciable gap between the top of the piston and the top of the block...SOoo it may be that just the volume of dish + chamber would for practical purposes give the actual volume. Then there's actual volume at BDC.. "oh my head, Rock On!" -Led Zeppelin III But right, there may not actually be ANY metal taken off and it could very well be that they simply tweaked the shape a little in 86. Nothing to loose cause if it shows signs of high compression that just means more fun with de-shrouding next spring. This does bring up an interesting opportunity with the plaster mould. One can then examine the chamber shape in greater depth to aid in de-shrouding the valve seats. The plexi-seal seems like dead on accurate stuff, thanks! ------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
[This message has been edited by White 84 SE (edited 07-22-2014).]
I've done the research and a month is fine I work on a boat so I won't be home for a month I leave in two days. It came off of a 78 cj6 jeep wrangler the distributor you have to use for the duke is from a 82 Chevrolet citation that had an iron duke can get it at a parts store for about 100$ and a in line fuel pressure regular at about 4 psi now you may need to just find a carb andiet make a adapter plate but you can order all of the mounting gaskets from auto zone. The Gasket For Manifold To Head Is Identical. You can order a direct fit carb as well but it's about 600$ and no duke is worth that. Honestly it's a sweet upgrade if you are dedicated to the duke
I've done the research and a month is fine I work on a boat so I won't be home for a month I leave in two days. It came off of a 78 cj6 jeep wrangler the distributor you have to use for the duke is from a 82 Chevrolet citation that had an iron duke can get it at a parts store for about 100$ and a in line fuel pressure regular at about 4 psi now you may need to just find a carb andiet make a adapter plate but you can order all of the mounting gaskets from auto zone. The Gasket For Manifold To Head Is Identical. You can order a direct fit carb as well but it's about 600$ and no duke is worth that. Honestly it's a sweet upgrade if you are dedicated to the duke
That's good info Fade thanks!
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Fade, that extra work involved does not seem worthwhile with the Holley EFI in place already but thanks that is great stuff. Couple that with an early non swirl head up the compression, larger valves and stuff. Good info for someone doing a rebuild.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
Doing more research on the 30* valve thing. One thing that comes up is that they are not optimum for heat transfer. Also they tend not to seal as well. These are probably the reasons why they are not in as widespread use as they were in the 50's. Although everyone seems to agree that a 30* back cut on the intake valves results in increased flow and HP. Also often covered in the same articles is that a skinnier valve makes for better flow when the air is coming more in a horizontal direction. Some experts recommend 30* valves for heads with horizontal ports like the Duke head and 45* valve seats for heads with diagonally oriented ports like the SD4 head. Hey Dukesters I still think 30* valves are the way to go. The 60* V6 not so much.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
oooooo... I just realized something. Correct me if I am wrong but ya cant just grind 30* seats into the head because the valves will then sit deeper in the head. This would mess with a lot of stuff. Ya gotta go larger valves. That kinda scraps my plans. So larger valves are a must if you want to get significantly more air in the Duke. Larger it is but not THIS summer anyway.
------------------ 84 Duke, Holley TBI, Manual Trans 4.10, CompuCam, White
