The purpose of this thread is to continue a comment that I made about the benefits of modifying the original Datsun L28 exhaust setup and replacing it with headers and a bigger single system.

When I was much younger and first started playing around with cars, my mates owned a lot of Fords. They started with straight 6's and moved on to Cleveland and Windsor V8's. Whenever they bolted headers to their cars we could see/feel the difference, cause we were all naughty and raced each other on the street to see who had the quickest/fastest car.

"Last week Pete was slower than George but this week, since he's put those headers on....oh boy!"

The increases may not be there on 'other' vehicles that you've seen or worked on but with Fords there are significant performance gains.

Getting back to Datsuns, I modded my car at the same time and found exactly the same thing was happening. That sweet little L series (little compared to the Ford stuff) came alive with any sensible part upgrade but up until a few years ago, I could only talk about it and not prove it.

Then I got myself a stock Datsun with an unmodified L28 and thought, "I'm gonna document every change I make to this engine and dyno it every time to see what my butt dyno feels!"

So, I have a dyno sheet that shows the difference what headers and a nice exhaust make to the L series. The original exhaust manifold and 1.75 inch was replaced by a set of HM39 (Aussie brand) and a 2.5 inch exhaust with two mufflers.

I don't want to shoot my own argument down here by saying that the discussion only involves headers and not the rest of the exhaust but I kinda see it as a whole package really. If you didn't want to upgrade the whole pipe and muffler shebang your power gains probably won't be as much as mine. Still worthwhile?.......absolutely.

What you've just read is my last post in another mans thread. I posted a dyno graph of my results there too. It has three power pulls

Edited June 14, 201113 yr by ozconnection

Please show us dyno data for stock and modded exhaust to make this post complete.

I recall seeing graphs on zhome.com that showed ~ 4HP increase from stock.

I was in the middle of modifying my post, 60 minutes had come up and this is where I'm up to. I had to write to admin about it. I'll see what happens. Sorry for the hiccup people. You live, you learn.

Ah, I cut and paste.......

What you've just read is my last post in another mans thread. I posted a dyno graph of my results there too. It has three power pulls, two are obvious, the third is the less so, it's the curve that peaks at 65 kw on the power graph.

Ok, there is some expaining to do here. The baseline pull which peaks at 60 kw's was a stock L28S (single carburetor) engine mated to an L3N71B transmission and a H190 differential. Wheel size was 205/70/14. The pull was done in second gear, the transmission does not drop to 1st at all, even when at standstill! That's a very convenient feature.The distributor was also a 280zx unit where the original one was a single points unit.

The line that peaks at 65 kw's is a run that was done by replacing the standard Hitachi vac secondary two barrel (very similar to what is found on 510's) with a 4 barrel Holley 600 cfm vacuum secondary carburetor using two adapter plates to mate it (the carb) to the stock Y41 intake manifold.

Ah ha you all say, the bastard is lying to us and trying to fool us.....not so people. Look carefully. There was an improvement but its 5 kw's or 8.3% at the wheels. Not massive considering the relative size and flow capacities of the two carbs.

I interpret this result as a situation where the engine could perform better if it wasn't strangled by the small exhaust and stock exhaust manifold. I make this conclusion because as soon as the headers and 2.5 inch exhaust with two mufflers are bolted on, there's a jump to 80 rwkw's, up from the previous best of 65 rwkw's. That's over 20% people.

Cheers.

Edited June 14, 201113 yr by ozconnection

I love data! Especially data that correlates a butt dyno to a real dyno. Very cool. Keep it coming!

I read both of your posts and can't figure out the conditions for the three pulls. You mentioned a single carb, a four-barrel, a ZXT distributor and headers but didn't really identify the combinations used.

Could you describe the setup for each pull?

I wonder how/if this applies to an engine with dual SU's , or fuel injection. Still, a 20HP improvement at the rear wheels is... unexpected from just an exhaust system upgrade.

So here is data:

Stock exhaust and carbs: 60kw / 80hp

Stock exhaust and Holley carb: 65kw / 87hp

High flow exhaust and Holley carb: 80kw / 107hp

But most tuned L28's 280z stock put ~ 95kw / 125 hp?

Thanks, I re-read the post and extracted the same. I don't mean to wee in the punch bowl but, having some background in the scientific method, I have to wonder if it is the headers or the bigger exhaust. All that I have read implies that the stock cast steel exhaust manifold of the 280Z L28 flows very well. Still, the results support that the stock exhaust system of this unknown Datsun is restrictive. What kind and year of Datsun is it?

So here is data:

Stock exhaust and carbs: 60kw / 80hp

Stock exhaust and Holley carb: 65kw / 87hp

High flow exhaust and Holley carb: 80kw / 107hp

But most tuned L28's 280z stock put ~ 95kw / 125 hp?

At the wheels?

There could be a number of valid reasons why my dyno figures appear to be low compared to what you would expect from an L28. Perhaps the most important thing to realise is the relative changes to the power output since the actual figures are really not that important, but the changes as seen as percentage change is what I'm trying to demonstrate. ie the effect the modification had to the engine and how it responded to those changes.

Zedhead, the year model is 1978.

Yes, a stock tuned 280z is ~ 125-130HP at the rear wheels on a dyno.

Here is a good read: http://www.zcar.com/car_talk_forum/my_z_dyno_pics_836239.0.html

Interesting.

The engine bay plate from Nissan says that my L28 produces 139HP @5200 rpm SAE.

How can it possibly be expected to put 130HP to the wheels then?

The results I'm getting are all through an AUTO trans too btw.

Hmmmm.

Thanks, I re-read the post and extracted the same. I don't mean to wee in the punch bowl but, having some background in the scientific method, I have to wonder if it is the headers or the bigger exhaust. All that I have read implies that the stock cast steel exhaust manifold of the 280Z L28 flows very well. Still, the results support that the stock exhaust system of this unknown Datsun is restrictive. What kind and year of Datsun is it?

Have a look in my 'garage'

These old Datsuns (Nissan Cedric's) were once common sights all over the world except the USA. They were used as Taxi's in Japan and south east Asia including Australia and New Zealand.

Edited June 16, 201113 yr by ozconnection