I have recently thought about a budget head build for my Bronco and question which of the mods have the best return. So what percent would the direct mount be, porting, three angle valve work, backcut, 1.5" exhaust valves and so on. Keeping in mind my limited experience I would think the direct mount is alot maybe 70% or so. The hole for the direct mount is about three times larger than stock and going from 200 cfm to 300 cfm or so has to have a large impact.
what each head mod is worth
- Thread starter bmbm40
- Start date
8) it is hard to say what each individual modification is worth, especially since each mod builds on the last. for instance, lets say you add a direct mount two barrel conversion, then port the head, then add headers. each mod individually might add a small amount of power, and two mods added together would add power in an additive effect, meaning if one mod added say 5hp, and the second mod would individually also add 5hp, both together would add about 10hp. but when you add the third mod, which by itself would add 5hp, combined with the other two mods may instead add 7-9hp, so instead of getting 15hp you may end up getting more like 19hp.
this is why i recommend doing modifications as a systems approach. define what you ultimately want, and the do the mods as you can afford them. and make sure each compliments the others.
this is why i recommend doing modifications as a systems approach. define what you ultimately want, and the do the mods as you can afford them. and make sure each compliments the others.
Howdy Bmbm40:
An interesting question. Adding a two barrel with a direct mount will immediately increase the CFM potential over a one barrel. Depending on how anemic the engine was with the OEM one barrel, a conversion to a direct mounted 300 cfm two barrel, properly tuned, on an other wise stock engine could amount to about a 10 to 15% increase in max HP. Say 100 hp to 110 or so. But, know that the other limiting factors of cam, exhaust and flow will limit potential gains. IF flow, cam, exhaust and compression are optimized the rpm curve would be raised and the potential power output from that same 300 cfm carb conversion would be significantly more-maybe as much as 25 -30%.
On the other hand, optimizing flow may not effect max power out put, but would have an effect on throttle response and efficiency. It could also make more efficient use of 200 cfm available from the one barrel, so some increase in HP would be very likely.
Keep in mind these are all guesstimates based on Dyno charts and my experiences, but guesses just the same.
In the real world, if one is going to the trouble and expense of purchasing or pulling a head to modify for a direct mount two barrel, it stands to economic reason that that is the time to do all that can be done while the head is off. A valve job gasket set is about $60.00 and the labor is labor. Which is why we have very little real world data to make the comparisons you pose. About the closest to real world would be a plan old fashioned valve job on a pretty worn out engine with burned and leaky valves. In the old days that would include a skim mill cut to true the head mating surface, recutting the valve seats with maybe a two angle cut and replacing valves, as needed and seating them. New seals were usually included. The difference to the driveability of that engine was significant. Smoother idle, better response and more power. So another issue is what you had when you started.
So, I guess, after all is said and done, given a choice of only one power adder- performance valve job or two barrel conversion, I'd have to agree with you. But, I'm too cheap and too lazy to only do one or the other.
Adios, David
An interesting question. Adding a two barrel with a direct mount will immediately increase the CFM potential over a one barrel. Depending on how anemic the engine was with the OEM one barrel, a conversion to a direct mounted 300 cfm two barrel, properly tuned, on an other wise stock engine could amount to about a 10 to 15% increase in max HP. Say 100 hp to 110 or so. But, know that the other limiting factors of cam, exhaust and flow will limit potential gains. IF flow, cam, exhaust and compression are optimized the rpm curve would be raised and the potential power output from that same 300 cfm carb conversion would be significantly more-maybe as much as 25 -30%.
On the other hand, optimizing flow may not effect max power out put, but would have an effect on throttle response and efficiency. It could also make more efficient use of 200 cfm available from the one barrel, so some increase in HP would be very likely.
Keep in mind these are all guesstimates based on Dyno charts and my experiences, but guesses just the same.
In the real world, if one is going to the trouble and expense of purchasing or pulling a head to modify for a direct mount two barrel, it stands to economic reason that that is the time to do all that can be done while the head is off. A valve job gasket set is about $60.00 and the labor is labor. Which is why we have very little real world data to make the comparisons you pose. About the closest to real world would be a plan old fashioned valve job on a pretty worn out engine with burned and leaky valves. In the old days that would include a skim mill cut to true the head mating surface, recutting the valve seats with maybe a two angle cut and replacing valves, as needed and seating them. New seals were usually included. The difference to the driveability of that engine was significant. Smoother idle, better response and more power. So another issue is what you had when you started.
So, I guess, after all is said and done, given a choice of only one power adder- performance valve job or two barrel conversion, I'd have to agree with you. But, I'm too cheap and too lazy to only do one or the other.
Adios, David
rbohm- I get what you are saying and appreciate your input.
CZLN6- Very detailed and well said.
I went from a 200 to a 250 in my Bronco a while back and am very pleased with it. 50 mores cubes makes a big difference and coupled with the 5 gears this Bronco feels very capable in all situations. I guess it is normal to look for a way to increase torque by just a little if not too expensive or time/labor intensive.
Reading the bucfan thread made me consider pulling the head for the direct mount conversion, mill the head and call it good. This is based on my experince with this used 250 which seems to be in great condition but when the head comes off there may be surprises and I do not want any down time for this vehicle. So I think I am going back to my original plan of finding another 250 with d7 or EO head and rebuild complete with mild cam, direct mount, performance valve job and some port and polish done by me. It will cost more but I will get more performance and peace of mind.
Thanks for your help.
CZLN6- Very detailed and well said.
I went from a 200 to a 250 in my Bronco a while back and am very pleased with it. 50 mores cubes makes a big difference and coupled with the 5 gears this Bronco feels very capable in all situations. I guess it is normal to look for a way to increase torque by just a little if not too expensive or time/labor intensive.
Reading the bucfan thread made me consider pulling the head for the direct mount conversion, mill the head and call it good. This is based on my experince with this used 250 which seems to be in great condition but when the head comes off there may be surprises and I do not want any down time for this vehicle. So I think I am going back to my original plan of finding another 250 with d7 or EO head and rebuild complete with mild cam, direct mount, performance valve job and some port and polish done by me. It will cost more but I will get more performance and peace of mind.
Thanks for your help.
Don't know if this info helps you though on my 250 was a very good running low mileage stocker that did not need to be fixed. Decided to do some work on the head to see if could improve performance some, budget port job (cost was materials used and my labor about 4 or 5 hours). Nothing much a clean up of a few areas in the intakes, mainly worked at blending in the valve bowls, polished the combustion chamber some, and also focused on porting out and polish of exhaust side. Next a 3 angle valve job with back cut, used all the stock valves, springs, etc. parts over again. Was quite pleased with the results. The only way to know what each mod did though is testing them all separately and than in combinations probably be costly in time and money. I will second that you should do them all together, would have liked to do the direct mount 2V carb and maybe rework the exhaust not sure I could get it to pass the Ca smog test’s visual part though.
Yah the pocket porting and valve job is good bang for the buck.bubba22349":3t1bupfu said:
But it's all part of a package. Camshafts are pretty good bang for the buck.
Along with the double-roller timing chain.
Even though I don't yet have a two bbl carb my engine has great power with the other mods.
bubba22349- Good info. So a three angle cut and some moderate port and polish gave a noticeable increase. Adding the direct mount 2v and a little milling could be a nice boost overall.
Jackfish- Sounds like you did this and had similar results. A cam would be a big increase with this.
Thanks for the replies.
Jackfish- Sounds like you did this and had similar results. A cam would be a big increase with this.
Thanks for the replies.
Airflow is really restricted in a log head. Port the heck out of the head while you have it off. Unless you do that, cams are of limited value.
The exhaust side of the head is REALLY bad. The area under the valve is so restricted that you can't even get your thumb in the port. The short and long side are full of bumps and lumps that need to be blended under the seat. Open up the bowls and the area under the seats, open the ports, and relieve the valve guide. Most exhaust gaskets are really wide, but I think the port should be made as tall as possible. Pretty much the same on the intakes.
If you can, also relieve the chambers to move the walls away from the valves. The chamber wall is nearly vertical on most versions of the head so even increased lift nets little additional flow. You'll have to mill the head to get compression back. Zero decking the block to get decent quench helps too, but is hard to accomplish on a 250 because of 1. the piston height, and 2. the compression ratio.
But one thing to consider; unless you can do most of this yourself, you come out better by buying an alloy head. The cost of having someone else do your porting and machining can be prohibitive.
The exhaust side of the head is REALLY bad. The area under the valve is so restricted that you can't even get your thumb in the port. The short and long side are full of bumps and lumps that need to be blended under the seat. Open up the bowls and the area under the seats, open the ports, and relieve the valve guide. Most exhaust gaskets are really wide, but I think the port should be made as tall as possible. Pretty much the same on the intakes.
If you can, also relieve the chambers to move the walls away from the valves. The chamber wall is nearly vertical on most versions of the head so even increased lift nets little additional flow. You'll have to mill the head to get compression back. Zero decking the block to get decent quench helps too, but is hard to accomplish on a 250 because of 1. the piston height, and 2. the compression ratio.
But one thing to consider; unless you can do most of this yourself, you come out better by buying an alloy head. The cost of having someone else do your porting and machining can be prohibitive.
MustangSix":3lne61df said:
+1
I wanted a dependable head, and the large log 78 head I got was the ticket, by the time I was done price point came out to ~1150 on just the head,
, I wish I just went alum, but glad I didn't as I would've added more just to control the carb. (or TBI) maybe if i win the lotto I'll finish the car the way I want it.you can get more power by probably adding a 2bbl (or 3x1bbl) TBI kit, it will regulate to precise amounts and keep your power at it's max, plus the best economy without worry'n bout jets and re-tuning @ different elevations.
I like the port, bigger valves, the 2bbl direct mount, double roller timing chain, cam, milling, 3 angle valve cuts... these are where your money is best spent
you don't "need" valve seats, valve guides, the port divider, ARP studs, polishing... these don't really "add" enough or any power to make a difference but just add strength/equality to the engine.
More solid info
MustangSix- Much appreciated sounds like a detailed plan for success on the head. The plan was to do most of it myself except the direct mount for a low budget build. If I could get the head done for a bit less than $500 including the carb I would be happy. As far as zero decking I planned to get it close as possible. For a lower rpm Bronco application don't have to get that last 20%, the most expensive gains as you know-going for the low hanging fruit so to speak.
MPGmustang- I like the idea of TBI basically an electronic carb as I understand. I have limited info on a TBi setup off a Astro van on a 250 in a Bronco- the guy was pretty pleased with it. Most of the stuff was from picnpul so not too expensive but required a lot of fab work. I have not seen anyone on this site with TBI from junkyard unless I missed it somehow in EFI section. Cold starting ease and immunity to elevation change are great benefits. Plus modern injection setups seem to be practically trouble free and the wrecking yards are full of vehicles with these parts.
Thanks for the replies.
MustangSix- Much appreciated sounds like a detailed plan for success on the head. The plan was to do most of it myself except the direct mount for a low budget build. If I could get the head done for a bit less than $500 including the carb I would be happy. As far as zero decking I planned to get it close as possible. For a lower rpm Bronco application don't have to get that last 20%, the most expensive gains as you know-going for the low hanging fruit so to speak.
MPGmustang- I like the idea of TBI basically an electronic carb as I understand. I have limited info on a TBi setup off a Astro van on a 250 in a Bronco- the guy was pretty pleased with it. Most of the stuff was from picnpul so not too expensive but required a lot of fab work. I have not seen anyone on this site with TBI from junkyard unless I missed it somehow in EFI section. Cold starting ease and immunity to elevation change are great benefits. Plus modern injection setups seem to be practically trouble free and the wrecking yards are full of vehicles with these parts.
Thanks for the replies.
