Disappointing L28 Dyno Results

[jenks]

Hey guys,

 

I just got my car back from the dyno and I was a bit underwhelmed with the results - 156hp and 161ft/lb at the wheels (curves with AFR attached).  The long block was assembled by a pretty reputable builder with the following specs:

 

Bored out L28 to 2.95L

F54 block with a N47 head

11.3:1 CR

290° cam with 0.490" lift

 

Then I came along and messed something up with the following:

 

MSA 6-1 header into 2.5" exhaust

MSD 6AL-2 programmable ignition box triggered by a 280zx dizzy

Cannon intake manifold

Weber DCOE40s

36mm chokes

160 main

160 air correction

F2 emulsion tube

3.5 A/V

55F9 idle

 

The timing curve was initially dialed in by the tuner to eliminate knock with the 94 octane that I delivered the car with.  The dizzy is locked out at 35°BTDC and the timing map they arrived at is attached.  After the 1st round of results, I asked them to run some higher octane to get in all the timing that I thought was left on the table to control the knock.  With 108 octane the car didn't pick up any power from advancing the curve that was developed with the 94.  I found that a bit odd, but not sure how you argue with the data.

 

The dyno was an eddy brake Land and Sea Dynomite axle hub set up.

 

Let me know what your thought are on where I could look next, or if you think something is really bottlenecking the output. From all the searching I've done, it seems like all the hardware should support 200+whp, but we're not even close.

 

Thanks!

L28 dyno.pdf

[Roberto260Z]

Has the head been ported? 40mm Webers with 36mm chokes will restrict top end hp on this motor.

[jenks]

I don't believe too much was done in the way of significant port work.  More just cleaning it up and smoothing things out as opposed to a lot of material being removed.

 

You're definitely not the first person that has mentioned that the carbs are too small, but I didn't think they choke things up that much.  Seen a few guys with SUs making a decent amount more. I suspect the 40s would outflow the SU set up although I haven't actually seen the data to validate that assumption.

[grannyknot]

I only dabbled with triples for a year or so but isn't your air corrector jet way too small in relation to the main? By the general rules of sizing your ACJ should be 215-220

[jenks]

Normally I would agree, but I think at the end of the day the AFR curve should trump whatever I think the jets should be.  If they were in fact too small, wouldn't the curve be way too fat on the top end?  I'll pop one out tomorrow and have a look.  Maybe the tuner was mistaken on which ones ended up in there.

 

So did you give up on the triples and go FI?

Edited September 3, 2016 by jenks

[Nismospek]

Everything I have always heard is that the money is in the head work when it comes to unlocking HP in L Series engines. There are 300 hp race engines still on 2.8 liters. 

Edited September 3, 2016 by Nismospek

[NewZed]

Not an expert but the shape of your torque curve shows a steep drop at 5800 RPM.  Seems like it might be a sign of just not enough air flowing in to the cylinders.  Choked off somewhere in the path.  Probably obvious, but I thought I'd go ahead and state it.

 

If I read your timing curve right it shows 6 degrees pulled, from 35, so 29 degrees total advance at 6500 RPM.  26 total at 5000, and 25 at 4000.  Most L series tuned for power are set to max advance are 34 at 2500 and above, thereabouts, from what I've seen.  So timing seems retarded, overall.

 

Might just need a few tweaks and some more tuning.  You only gave two numbers on the cam profile, bit didn't indicate if it was degree'd properly or maybe it was just put on a timing chain sprocket notch number.  Just another small detail.

 

Seems like the cam profile should push much higher.  A comparable Schneider cam shows a 3500 - 7500 working range (however they figure that). http://schneidercams.com/dastsunL6_NA.aspx

[jenks]

Yep, you're reading the timing curve right.  I was thinking the same thing you were, so I had asked them to run some 108 octane and put the timing curve back in that the car that it was delivered with (33° all in by 3000). That timing curve only made 149ft/lb. 

 

This is the only L-series I've seen that needs only 26° to make peak torque.  Seems a bit odd...

 

I'll double check the cam and make sure it's installed straight up as per the builders recommendation.  I didn't actually check this before sending it off to the dyno as it was set by the builder.  Maybe I shouldn't have assumed, but I'll check it.

 

I'm with you guys on the 'not enough air' theory based on how the torque falls off a cliff at 5000.  Having said that, I think the carbs should be good for a bit better than 156hp, but given my lack of experience with these engines, what I 'think' doesn't exactly carry a lot of weight.  I'll go do some more searching and see how people have been doing with the N47 head as well.

 

Thanks for your comments guys.

[NewZed]

I would check all of your timing associated items.  Make sure you really know where TDC is, degree the cam, don't use a hole in a sprocket, verify that the MSD program is actually creating those advance numbers (the curve you showed is what's supposed to happen, but might not be what is), that kind of stuff.  There have been a couple of posts recently from people who got cams that din't match the profile cards.  Not sure where they ended up.  You might not even have the cam profile you think you have.  Don't trust - verify.

[Andreas]

Mine made 180hp/235nm to the wheels on a hub dyno. Runs great but i havent had a proper tune done to it so there should be some more power to be had.

Cr around 10:0

L28 bored +1mm

Flattops.

Triple 45s

Msd 6025 and zx dizzy

Msa stage 3 cam

No port job/head work done exept some cleaning, shave and bigger valves ( head is the late E88 head )

Timing shows 18-19 at idle and 36 at max.

Mine is built in a garage by a friend.

 

Your engine should be making more power than mine so I guess you should check the timing and related parts firsthand then look into the jetting of the carbs.

40s should be able to provide enough.

[grannyknot]

Normally I would agree, but I think at the end of the day the AFR curve should trump whatever I think the jets should be.  If they were in fact too small, wouldn't the curve be way too fat on the top end?  I'll pop one out tomorrow and have a look.  Maybe the tuner was mistaken on which ones ended up in there.

 

So did you give up on the triples and go FI?

I started with a .040" over L28, flat top pistons, 9.5:1 comp., N42 head heavily ported,polished and matched, mild cam, Pertronix in the distributor, single ign. coil. With ZTherapy SU's, 32 degrees all in at 2600 rpm, it pulled 188hp at the rubber of the rear wheels, then I went with SK/OER triples, DCOE 40's,36 chokes, there was a definite power increase but after a year an half of tweeking up and down the anal retentive side of me wanted a tune that didn't change with the temperature so now I'm trying to figure out FI and megasquirt.

You are missing 30hp somewhere, as mentioned above verify your timing, your cam profile and your ACJ's.

[SHADY280]

From what I have experienced the n47 head is a junker head with horrible chamber design. I had horrible detonation with mine and I swapped out to a shaved down p79 and the detonation went away and I was able to up the timing quite a bit. With your current compression and large cam mixed with a poor chambered head your not getting any potential out of your parts. With that head the 40's are fine. Get a better head and bigger carbs and you will be happy.

[JMortensen]

With the compression that high I'm guessing he's using the Maxima N47. Good combustion chamber shape, but smaller valves and I think the ports are smaller too, can't remember for sure. I think this engine would benefit from a whole lot of porting and polishing and some bigger valves.

 

Re: carb size, zredbaron made 270ish whp with his stroker on 40s if I recall. I would go 44s or 45s too, but you can't argue with results. It is at least possible to do a lot better than you're doing with the smaller carbs.

[jenks]

I only had a few minutes in the garage today, but I did check the mains and air correctors and they are in fact both 160 and 160.  Maybe because the engine is so anemic on the top end, the air correctors just don't have that much of an impact on the AFR.  Just speculating here.

 

I also popped off the valve cover and confirmed that the adjustable cam sprocket is still at the same setting that it was when it was assembled by the builder - supposed to be straight up.  I know, I know - I will verify (not trust) that it was set up properly from the get go.  Just didn't have time to get a degree wheel on it.  I will chase down and verify the cam and ignition timing as you guys suggested.

 

Jon,

 

By all indications, the head is indeed a N47 and not the MN47.  The build sheet has my combustion chambers at 37cc from the stock 44.6cc.

Edited September 3, 2016 by jenks

[NewZed]

Does the head have a threaded CHTS boss, between #5 and #6 (approximately)?  That's the simple indicator for MN47, the 280Z N47 doesn't have it.  Don't know if you can get to 37 from 44 without welding.  The MN47 is about 38-39, from past posts I've seen (from jmortensen and others), so 37 is about a shaved MN47.

[jenks]

I don't see any threaded boss between #5 and 6.  The cam towers are shimmed, so it appears that the combustion chamber volume was achieved through milling the head. Not sure on the details around how this played out with the valve train geometry, but the wipe pattern on the rocker arm pad and valve tip all seem to be ok.

 

In other news, I decided to check the cylinder leak down last night as I there seemed to be a lot of blow by (decent amount of smoke and oil coming from the valve cover vent).  Found that cylinder #3 was gurgling the rad pretty good.  .  I guess I'll be checking the items noted above after I get a new head gasket in there.  This new engine is turning into a good learning experience if nothing else.

[skirkland1980]

Since you're pulling the head make sure the roof of the head intake port is not lower than the roof of the intake manifold runner. If so it makes for a terrible running engine.

[SHADY280]

Check the cam tower shim thickness. Will give you a slight indication of how much was shaved off the head. That and look at a picture of a stock n47 stamp and look at yours. Kind of a visual cue to see if it's got a ton taken off to get that low cc. If your going to pull the head maybe take advantage of the situation and grab a different casting number head like a p series and shave it down .080" and do some intake runner work. Put the longer valves from the n47 into it and grab some shims from Derek.