<puts on his flame retardent suit>
04-04-2002, 05:17 AM
#1
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<puts on his flame retardent suit>
Alrighty... I was thinking about a conversation I had with my sisters ex-bf a couple months ago about performance modifications that he can do in his shop...
One thing we talked about was converting the engine to a hemi (Or is the proper term hemi-head?)
I did a little bit of searching around, but at first glance, I couldn't find any *real* useful about hemi-heads except that they are a "good thing for sports and race cars"
I also searched on here, and found 4 references to the word "hemi", and none of which had any bearing on the Maxima...
So, what do you guys think of doing something like that?
<quickly pulls the hood up over his head and seals it up>
One thing we talked about was converting the engine to a hemi (Or is the proper term hemi-head?)
I did a little bit of searching around, but at first glance, I couldn't find any *real* useful about hemi-heads except that they are a "good thing for sports and race cars"
I also searched on here, and found 4 references to the word "hemi", and none of which had any bearing on the Maxima...
So, what do you guys think of doing something like that?
<quickly pulls the hood up over his head and seals it up>
04-04-2002, 05:41 AM
#3
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Originally posted by SEguy182
um.....no, waste of money imo, gas drinking heavy as hell front wheel drive waste of money, thats what you would have....
um.....no, waste of money imo, gas drinking heavy as hell front wheel drive waste of money, thats what you would have....
Hehe, in case it's not too obvious, I know little about it, so I'm also trying to gather information.
What exactly would it do for our engine? From what I understand, it changes the shape of the combustion chamber to exert more downward force on the piston...
And it wouldn't cost me too much to have it done, but since I'm trying to get the car fixed first, I haven't asked for a quote.
04-04-2002, 06:08 AM
#4
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Actually, back in the day it was a more efficient way to create horsepower. I have had a long term project on a 68 charger with a 426 hemi and it screams like no Maxima ever could, but (forgive me) putting a hemi in a Maxima sounds even more rediculous than putting in an RB26DETT, which in all honesty you would probably have an easier time with 
.
If you want a Hemi (and I don't blame you if you do) then you should buy an old muscle car. I recommend a Charger or the lighter Cuda, if you have the money for Cuda parts. If you live on the west coast or deep in the south that shouldn't be too much of a problem...
.If you want a Hemi (and I don't blame you if you do) then you should buy an old muscle car. I recommend a Charger or the lighter Cuda, if you have the money for Cuda parts. If you live on the west coast or deep in the south that shouldn't be too much of a problem...
04-04-2002, 06:29 AM
#5
he's not talking about an engine swap.. he's talking about pulling the heads off his current engine and having the combustion chambers reshaped to a hemi-style.
I would highly suggest talking to some good engine builders who know nissans before you undergo a project like this. you might end up buying yourself another set of heads if it doesn't work. If you're broke now, don't even think about pulling the engine apart and trying something crazy like that.. you might end up having to spend twice that much in the long run when you get to buy another engine.
I would highly suggest talking to some good engine builders who know nissans before you undergo a project like this. you might end up buying yourself another set of heads if it doesn't work. If you're broke now, don't even think about pulling the engine apart and trying something crazy like that.. you might end up having to spend twice that much in the long run when you get to buy another engine.
04-04-2002, 07:00 AM
#6
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Originally posted by Matt93SE
he's not talking about an engine swap.. he's talking about pulling the heads off his current engine and having the combustion chambers reshaped to a hemi-style.
I would highly suggest talking to some good engine builders who know nissans before you undergo a project like this. you might end up buying yourself another set of heads if it doesn't work. If you're broke now, don't even think about pulling the engine apart and trying something crazy like that.. you might end up having to spend twice that much in the long run when you get to buy another engine.
he's not talking about an engine swap.. he's talking about pulling the heads off his current engine and having the combustion chambers reshaped to a hemi-style.
I would highly suggest talking to some good engine builders who know nissans before you undergo a project like this. you might end up buying yourself another set of heads if it doesn't work. If you're broke now, don't even think about pulling the engine apart and trying something crazy like that.. you might end up having to spend twice that much in the long run when you get to buy another engine.
And it's not going to be something done lightly, I am going to do a lot of research on it before I decide either way, and when I learn more, I will post my findings on here, as well as several opinions. I just wanted to get a few ideas/opinions from you guys about it.
And if I do it, I'll buy a spare set of heads to work on, not use the ones I have in there... I'm naive, but not stupid
Now, my next question is, provided nothing is screwed up, and it's actually done correctly, what would be the pros and cons of doing this?
04-04-2002, 02:29 PM
#7
Hemispherical combustion chambers were super good design in the 60's. I think the the V8 dragsters still use the hemi head/blocks now.
Anyhoo. How exactly do you know that the Nissan dohc, 4 valve aluminum head designed on a CAD machine is not as or more efficent than a hemi design?
Anyhoo. How exactly do you know that the Nissan dohc, 4 valve aluminum head designed on a CAD machine is not as or more efficent than a hemi design?
04-04-2002, 04:46 PM
#9
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Join Date: Aug 2001
Posts: 2,941
[Lights up torch] 
I think this job is super-expensive if not outright impossible. You'd have to basically custom-design and fabricate from scratch a pair of cylinder heads. Also you'd have to design the valvetrain to work with the funky angles the valves sit at in a Hemi head. Forget about chopping a cylinder off a set of existing Hemi heads because the valvetrain is pushrod (OHV), not OHC, not to mention all the other incompatibilities. You'd need custom dome-shaped pistons too.
An interesting idea, but I think a turbo or built-up engine would be better time/money well spent.
I think this job is super-expensive if not outright impossible. You'd have to basically custom-design and fabricate from scratch a pair of cylinder heads. Also you'd have to design the valvetrain to work with the funky angles the valves sit at in a Hemi head. Forget about chopping a cylinder off a set of existing Hemi heads because the valvetrain is pushrod (OHV), not OHC, not to mention all the other incompatibilities. You'd need custom dome-shaped pistons too.
An interesting idea, but I think a turbo or built-up engine would be better time/money well spent.
04-05-2002, 04:28 AM
#10
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Jeff92SE - That's a good point, I hadn't thought of that, but, that is also the reason why I put this thread up, because there are a lot of things I still need to learn about it
Bman - Why would I need to fabricate a whole new head? From what I understand, it's a hemispherical combustion chamber, ergo you *should* be able to carve them out that way. As for the pistons, well, what I was thinking of doing is getting an extra set of everything, and practicing on them...
And as for using a different engine, or parts thereof, from all the "SEARCH, ******* you!" posts I've seen, I wouldn't even think of doing something like that
Bman - Why would I need to fabricate a whole new head? From what I understand, it's a hemispherical combustion chamber, ergo you *should* be able to carve them out that way. As for the pistons, well, what I was thinking of doing is getting an extra set of everything, and practicing on them...
And as for using a different engine, or parts thereof, from all the "SEARCH, ******* you!" posts I've seen, I wouldn't even think of doing something like that
04-05-2002, 09:58 AM
#11
Originally posted by Taegost
Jeff92SE - That's a good point, I hadn't thought of that, but, that is also the reason why I put this thread up, because there are a lot of things I still need to learn about it
Bman - Why would I need to fabricate a whole new head? From what I understand, it's a hemispherical combustion chamber, ergo you *should* be able to carve them out that way. As for the pistons, well, what I was thinking of doing is getting an extra set of everything, and practicing on them...
And as for using a different engine, or parts thereof, from all the "SEARCH, ******* you!" posts I've seen, I wouldn't even think of doing something like that
Jeff92SE - That's a good point, I hadn't thought of that, but, that is also the reason why I put this thread up, because there are a lot of things I still need to learn about it
Bman - Why would I need to fabricate a whole new head? From what I understand, it's a hemispherical combustion chamber, ergo you *should* be able to carve them out that way. As for the pistons, well, what I was thinking of doing is getting an extra set of everything, and practicing on them...
And as for using a different engine, or parts thereof, from all the "SEARCH, ******* you!" posts I've seen, I wouldn't even think of doing something like that
Your problem with reshaping the stock heads will be that the valve seats are already in place on that head.. let's say it's like putting a sticker on the outside of an apple... Now if you carve out a hemispherical chunk behind it, the sticker doesn't sit flush with the surface anymore.. i.e. your valves won't seal against the head... You'll have to either have custom valves made that seat at an angle (not a good idea), or shape the chambers in such a way that the valve seats flush still (completely messing up the hemi idea), or to completely re-design the head so that the valves all go into it at an angle so they'll seal properly against the domed top of the combustion chamber.
make sense?
04-05-2002, 10:23 AM
#12
You "could" actually weld in new material and then reshape the chamber. But as Matt said you would be limited to the pre-existing valve angle and entry point into the chamber. You would also must have this done on a cnc machine after the 1st is done to insure that the other FIVE combustion chambers are cut the same. Cost? Try anywhere from $5000+ I would assume.
THIS is AFTER you have determined that this semi-hemi head would do any better. This of course would have to be determined on some type of 3D CAD computor. Cost of this?? Probably another $5000-$10,000. Maybe if you have some ties into the Nascar mechanics or something.
Still sound like a good idea?
THIS is AFTER you have determined that this semi-hemi
head would do any better. This of course would have to be determined on some type of 3D CAD computor. Cost of this?? Probably another $5000-$10,000. Maybe if you have some ties into the Nascar mechanics or something. Still sound like a good idea?
Originally posted by Matt93SE
Your problem with reshaping the stock heads will be that the valve seats are already in place on that head.. let's say it's like putting a sticker on the outside of an apple... Now if you carve out a hemispherical chunk behind it, the sticker doesn't sit flush with the surface anymore.. i.e. your valves won't seal against the head... You'll have to either have custom valves made that seat at an angle (not a good idea), or shape the chambers in such a way that the valve seats flush still (completely messing up the hemi idea), or to completely re-design the head so that the valves all go into it at an angle so they'll seal properly against the domed top of the combustion chamber.
make sense?
Your problem with reshaping the stock heads will be that the valve seats are already in place on that head.. let's say it's like putting a sticker on the outside of an apple... Now if you carve out a hemispherical chunk behind it, the sticker doesn't sit flush with the surface anymore.. i.e. your valves won't seal against the head... You'll have to either have custom valves made that seat at an angle (not a good idea), or shape the chambers in such a way that the valve seats flush still (completely messing up the hemi idea), or to completely re-design the head so that the valves all go into it at an angle so they'll seal properly against the domed top of the combustion chamber.
make sense?
Makes custom turbo manifold sound easy ...
04-05-2002, 06:18 PM
#14
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Posts: 2,807
It would be difficult to reshape the chamber but it can be done. It can increase compression but not as much as higher compression pistons would. Besides a good street port that focuses on flow velocity would have better results. The power gain from 4500-7000rpm is almost more than what you get from 3000-6000rpm from a Y pipe.
04-08-2002, 04:27 AM
#15
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Originally posted by Jeff92se
You "could" actually weld in new material and then reshape the chamber. But as Matt said you would be limited to the pre-existing valve angle and entry point into the chamber. You would also must have this done on a cnc machine after the 1st is done to insure that the other FIVE combustion chambers are cut the same. Cost? Try anywhere from $5000+ I would assume.
THIS is AFTER you have determined that this semi-hemi head would do any better. This of course would have to be determined on some type of 3D CAD computor. Cost of this?? Probably another $5000-$10,000. Maybe if you have some ties into the Nascar mechanics or something.
Still sound like a good idea?
You "could" actually weld in new material and then reshape the chamber. But as Matt said you would be limited to the pre-existing valve angle and entry point into the chamber. You would also must have this done on a cnc machine after the 1st is done to insure that the other FIVE combustion chambers are cut the same. Cost? Try anywhere from $5000+ I would assume.
THIS is AFTER you have determined that this semi-hemi
head would do any better. This of course would have to be determined on some type of 3D CAD computor. Cost of this?? Probably another $5000-$10,000. Maybe if you have some ties into the Nascar mechanics or something. Still sound like a good idea?
Mebbe I'll just stick to my plan of making a turbo kit using duct tape, coat hangers, and bubble gum...
Thanx for the input everyone!
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