Relationship of Comp ratio to HP

[FastWoman]

Oh master, Zedyone...

Great post! I enjoyed reading it. You obviously know a LOT more about engine design than I do. However, one thing you omit is that Nissan was under pressure from US regulations on auto manufacturers to bring emissions down, so they had to detune their engines, including by lowering the compression ratio. (Pretty sure that's right...) So they were obviously forced away from what they would have considered an ideal engine design. This begs the question of how the Nissan engineers would have designed an ideal street engine if emissions were no longer a huge issue. Of course their going to fuel injection in '75 certainly changed the equation, but weren't they also using fuel injection in other markets for the 240's?

From what you know of these engines, how would the 280 engines have been done if not for US emissions concerns? (Interested in your perspective!)

Thanks,

Sarah

[sblake01]

Post deleted

Edited December 2, 2009 by sblake01

[jmortensen]

I think stock compression on an L28 is 8.3:1. L24 was 9:1. I wouldn't go over about 9.5:1 on a street motor. Someone mentioned backing off the timing to prevent pinging, and I agree with him and Paul Ruschman. I'd rather lose a full point in compression and be able to run the optimal timing then have to back the timing off to prevent pinging. There is a good deal of power to be lost in those last couple degrees of timing, and it's a real bummer to have to back it off.

Edited December 2, 2009 by jmortensen

[Zedyone_kenobi]

Oh master, Zedyone...

Great post! I enjoyed reading it. You obviously know a LOT more about engine design than I do. However, one thing you omit is that Nissan was under pressure from US regulations on auto manufacturers to bring emissions down, so they had to detune their engines, including by lowering the compression ratio. (Pretty sure that's right...) So they were obviously forced away from what they would have considered an ideal engine design. This begs the question of how the Nissan engineers would have designed an ideal street engine if emissions were no longer a huge issue. Of course their going to fuel injection in '75 certainly changed the equation, but weren't they also using fuel injection in other markets for the 240's?

From what you know of these engines, how would the 280 engines have been done if not for US emissions concerns? (Interested in your perspective!)

Thanks,

Sarah

I hear ya, but all manufacturers had to fight that battle. The small block chevy is a classic example. It was choked down to 135 HP in some forms in the 70's if I recall my history. But the bones are still there. When you look at what they designed starting form the early 4 cylinder L series engines, they had it right from early on. Look at the L20 with that sweet DOHC setup you see in some pictures with the exhaust and intake on opposite sides of the head as God intended. I think you do not need to look further than that to see what Datsun engineers would have done. Just my 0.02 cents.

How would the L28 have been done if not for emissions is tough. I mean its hard to play what if, as SO many variables were in play at that time. Datsun would not have made a race engine for the street, even though they certainly could have. They still had to make it a street car. I think honestly, they would have changed very little.

I would wager that it still would have had fuel injection, as that increased driveability at the time. I think you would have seen more compression, and perhaps a more aggressive timing curve. Perhaps a more free flowing head. I do not think that the cam would have changed much, but perhaps a little higher lift cam along with a freer flowing exhaust. Again, I think that if left unregulated and restricted by emission laws, Datsun would have put out a 280Z with around 190-195 HP at the crank. I know that is only ~20 HP more than the 170 gross HP it was rated at from the factory, but I think it would have had more torque. They still had to run on pump gas, and still had to get somewhat decent mileage while be civil enough to idle in traffic for hours if it had to.

I think the L28 is a wonderful engine to build up and one day I plan on trying my hand at a strong, yet reliable street engine, that I am hoping to make 210 to 225 HP and still be livable on a daily basis. Of course, i will need another Z car to put it in, as I am never butchering my silver arrow.

[tlorber]

Great posts guys. Thanks inline6er for the formula. Just out of curiosity, does the 14.7 have something to do with the stoichiometric ratio or is it just coincidence?

[jmortensen]

Great posts guys. Thanks inline6er for the formula. Just out of curiosity, does the 14.7 have something to do with the stoichiometric ratio or is it just coincidence?

14.7 psi is the air pressure at sea level.

[Lazeum]

I think we all forget about money when Nissan did the engine. Money is the first think people are looking at.

Does it match customer expectations at that time? Was it good vs. competitors? yes/no? How much it cost to make it ok? where can we save something?

I was designing suspensions some years ago, I was coming with super nice hollow aluminum parts, forged aluminum stuffs. Money was always the problem, most of those came in production in cast iron which is cheaper. Same goes for engine.

Regarding my build, I've decided to go with custom head and I've chosen exactly the route Zedyone_kenobi has described. Sure, it is bad to have spend $xxxx for a head that is not going to give me 300ish crank hp but I should have a very fat torque curve to provide all the fun I need, I've chosen Paul since he knows what is doing and I'm sure I'll forget about the bill as soon as I will drive the car the first time. I drive my z on twisty French forest roads, I've tried to match the need.

Regarding webers, there are 40 DCOE and I will see what I can get out of them (I might go with 45DCOE in the future with small chokes since webers could be quite cheap here in Europe).

I have never driven my setup with SU, I'm not able to compare then. However, I know the sound they make, they are not so hard to tune as long as you have the right tools (wideband sensor). I don't look back!

I've also heard good stuffs about SU & high hp. I don't know thou if there are so easy to tune over the entire rpm range.

Edited December 3, 2009 by Lazeum

[Zedyone_kenobi]

Just to clarify, I do not think its bad to spend big bucks on parts, as long as all the other parts in the engine can support it. You have a high flow head but you have matched it with a nice set of triples and probably a good exhaust. It sounds like you know what you got yourself into and did not just buy a big name part for the sake of having it. I would LOVE to hear your Z run after your engine build, as it sounds like you have chosen to build what I would call a 'fast street' beast! Good luck!

[Lazeum]

I was not referring to $$$ because of your comments thank you btw for your comments.

I'll definitely post some stuffs on youtube when it will be done.

I've spent a lot of time reading, tuning the engine by myself (so I know the tunability limits). I also drove other Z with good / well build setups

Paul has been the first one to ask what I had already and provided me a lot of advices about what to get. Cam, size of the port, valves size, etc... hae been done to match my needs / combo. I have to say, Paul has been awesome regarding communication and support

It's in French but you can check pictures at the following link

Edited December 3, 2009 by Lazeum

[Zedyone_kenobi]

That head work looks spot on. Looks like you are going to be set for a long time to come. Very nice looking build up.

[Lazeum]

Hopefully it would work as good as it looks!

[kensval]

I've got a 1976 280Z. N42 block, N42 head, stock cam, stock FI setup, 160 deg thermostat. The head was recently done as part of a rebuild and got shaved 10 thou. The dished pistons were replaced with flat-tops, pushing the comp ratio up 9.99:1. I think the timing is right around the original factory setting as well. I've been running 94 octane fuel with 10% ethanol in it and not having any problems. I'm planning a road trip from home (Saskatoon, Canada) to Los Angeles for a japanese car show. Is 91 octane premium gonna cut it, or am I going to have to retard the timing and carry octane booster with me? Are there any stations with higher octane fuel in L.A.? I understand the lower altitude is also going to negatively impact my octane needs.