Modifying the stock L28
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Registered User
Joined: Dec 2003
Posts: 56
From: Rockford, IL
Modifying the stock L28
Man, that stock motor doesn't really live up to it's power potential, so I decided to really give it some help. Here are some guidelines I thought up:
1. ABSOLUTELY needs to run on cat-**** octiane 87 gasoline. With 8.8:1 and aluminum heads, I don't think this is a problem.
2. No expensive machine work. No milling of the head or overbore or anything I can't do myself
3. Keep SOME low-end torque. I don't like full-blown motors that can't move around at low RPM.
I had the notion of a heavy port/polish on the intake, heads, and exhaust. This seems to be the cheapest way to do things. I was also contemplating possibly a cam with more duration to really get alot of fuel and air into the engine and really build up the pressure. I wouldn't think a header would be a major benefit on this motor due to its relatively small dispacement-- I might be able to get away with porting the stock exhaust manifold.
My question to you is, what is the obviouc restriction in this system? Is it just the ports are restrictive enough to not allow sufficient exhaust flow, or is there something else that keepd the poer numbers low?
I know plenty of engineers that say a well-massaged 6 cylinder can outperform an 8 cylinder simply because of its balance characteristics (crank doesn't absorb as much energy). Now I know there aren't any 2.8L V8s, but 200-220 HP in this engine shouldn't be too difficult, should it?
Thanks for any suggestions,
Brian
1. ABSOLUTELY needs to run on cat-**** octiane 87 gasoline. With 8.8:1 and aluminum heads, I don't think this is a problem.
2. No expensive machine work. No milling of the head or overbore or anything I can't do myself
3. Keep SOME low-end torque. I don't like full-blown motors that can't move around at low RPM.
I had the notion of a heavy port/polish on the intake, heads, and exhaust. This seems to be the cheapest way to do things. I was also contemplating possibly a cam with more duration to really get alot of fuel and air into the engine and really build up the pressure. I wouldn't think a header would be a major benefit on this motor due to its relatively small dispacement-- I might be able to get away with porting the stock exhaust manifold.
My question to you is, what is the obviouc restriction in this system? Is it just the ports are restrictive enough to not allow sufficient exhaust flow, or is there something else that keepd the poer numbers low?
I know plenty of engineers that say a well-massaged 6 cylinder can outperform an 8 cylinder simply because of its balance characteristics (crank doesn't absorb as much energy). Now I know there aren't any 2.8L V8s, but 200-220 HP in this engine shouldn't be too difficult, should it?
Thanks for any suggestions,
Brian
Registered User
Joined: Feb 2002
Posts: 2,906
From: Saskatoon, SK
im pretty sure the larger TB and larger AFM would do you good (my 2 mods im working on with some help obviously) and a nice exhaust i have a 2.5" OD i think or something like that with no cat and its straight trough loud but hey...
not sure what else tho to put it up to 200....its not taht easy
not sure what else tho to put it up to 200....its not taht easy
Guest
Posts: n/a
I don't think you can hit 200 hp very easily on a n/a L28 without switching to triple carbs. The fuel injection system in the ZX just won't allow you to pull a whole lot more power at high rpm's easily. Remember - you have to create a lot more torque to hit 200 hp at 5000 rpm than you do at 7000 rpm.
The Evil Twin
Joined: Mar 2001
Posts: 9,296
From: Seattle, WA
That's another good point. None of the 200hp L28s peak their hp at 5200 rpm like the stock motor does. They peak around 6500-7000rpm.
And, you'll never get to 200hp with the stock compression. No way, except with Nitrous.
But, you certainly can make it much more powerful than stock. Relatively speaking.
Mild cam. Dont' go overboard, especially on stock copression. 272 duration .450 lift. Call it good. That'll let your hp peak at about 5800-6000 rpm while maintaining all (or most) of your torque.
Port out the intake manifold (or make a manifold with larger runners) and port out the intake ports in the head. Leave the exhaust alone as well as the stock manifold. run 2.5" pipe off that manifold
And, you'll never get to 200hp with the stock compression. No way, except with Nitrous.
But, you certainly can make it much more powerful than stock. Relatively speaking.
Mild cam. Dont' go overboard, especially on stock copression. 272 duration .450 lift. Call it good. That'll let your hp peak at about 5800-6000 rpm while maintaining all (or most) of your torque.
Port out the intake manifold (or make a manifold with larger runners) and port out the intake ports in the head. Leave the exhaust alone as well as the stock manifold. run 2.5" pipe off that manifold
Guest
Posts: n/a
I recall reading somewhere yesterday that with a very little bit of modification, the P79's exhaust ports can outflow the P90's unlinered ports.
Something to do with reworking the bowl in the combustion chamber so the gases can enter the port without having to slow down... I suppose I'd better go find that page again..
I'll edit when I've got the info.
EDIT: The following is taken from http://www.geocities.com/row4navy/head2.html
"So what is he saying? He is saying that because the heads with liners have a larger radius coming out of the cylinder, and a larger area at the turn, the air has an easier time making that 90 degree turn to exit the head. Some minor work needs to be done to the bowl area to see the full benefit of the exhaust liner heads. The bowl area is immediately above the valve, and appears, well, like a bowl! It is where the air has to turn to make the entry into or out of the cylinder. The idea is to enlarge that area so the air can slow down, and has an eaiser time making that turn. When I get a chance, I will scan an excellent diagram from a book about porting chevy heads. It clearly illustrates what we are trying to say. Again, here is Paul:
We are familiar with fluid flow, and it takes the path of least resistance. If it must change direction dramatically, it slows down and loses energy. Now in a stock vs stock configuration, the square ports flow better. But with some minor bowl work on the liner heads, they really shine. When I port Datsun heads this is the main thing I do: I unshroud the valves by bringing the chamber wall out to the gasket and under cutting the chamber walls immediately around the valves to aid in air flow. Any work in the ports themselves will yield no performance benefits as the ports themselves already out flow the region in the chamber around the valves usually by 2 fold, depending on the head of course. "
He's talking about N47 Maxima heads, but they've got pretty much the same chamber design as P-series heads, so I figure it should all match up reasonably well. I can't say for sure if this sticks within the "no expensive machine shop work" guideline, but it's a thought.
Something to do with reworking the bowl in the combustion chamber so the gases can enter the port without having to slow down... I suppose I'd better go find that page again..
I'll edit when I've got the info.
EDIT: The following is taken from http://www.geocities.com/row4navy/head2.html
"So what is he saying? He is saying that because the heads with liners have a larger radius coming out of the cylinder, and a larger area at the turn, the air has an easier time making that 90 degree turn to exit the head. Some minor work needs to be done to the bowl area to see the full benefit of the exhaust liner heads. The bowl area is immediately above the valve, and appears, well, like a bowl! It is where the air has to turn to make the entry into or out of the cylinder. The idea is to enlarge that area so the air can slow down, and has an eaiser time making that turn. When I get a chance, I will scan an excellent diagram from a book about porting chevy heads. It clearly illustrates what we are trying to say. Again, here is Paul:
We are familiar with fluid flow, and it takes the path of least resistance. If it must change direction dramatically, it slows down and loses energy. Now in a stock vs stock configuration, the square ports flow better. But with some minor bowl work on the liner heads, they really shine. When I port Datsun heads this is the main thing I do: I unshroud the valves by bringing the chamber wall out to the gasket and under cutting the chamber walls immediately around the valves to aid in air flow. Any work in the ports themselves will yield no performance benefits as the ports themselves already out flow the region in the chamber around the valves usually by 2 fold, depending on the head of course. "
He's talking about N47 Maxima heads, but they've got pretty much the same chamber design as P-series heads, so I figure it should all match up reasonably well. I can't say for sure if this sticks within the "no expensive machine shop work" guideline, but it's a thought.
Last edited by mikado; Apr 23, 2004 at 10:20 AM.
Registered User
Joined: Mar 2002
Posts: 646
Are we talking at the wheels or crank HP ?? You can get 200 HP using oversized SU's. The head work is where all the power is hidden , also the low 8.3 - 8.8 to one compression isn't much help either. Most of the modern engines making over 200 HP are running more compression with a better electronics system.
An E Production 240 Z using a small cam and a limit of 12.5 to 1 compression
and SU's cam make around 240+ HP... And they are limited to .500 lift cam.
Mike
An E Production 240 Z using a small cam and a limit of 12.5 to 1 compression
and SU's cam make around 240+ HP... And they are limited to .500 lift cam.
Mike
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