L28et powerband issue

[Nicksturboz2]

L28et not rev'ing past 4800 (like a wall) I have searched and can't find anything. I'm sure there's info on it though. I have a 71 240Z l28et megasquirt hx35 water meth 1.4bar low boost high boost is 2bar runs and drives great but only wants to rev to 4800. I recently put this engine together about 18,000 miles ago and it used to pull hard way past 5K (5500-5800 is where it would normally start to fall off at but I could push it to 6-6200) only thing that has changed is I've gone to sea level adjusted the tune accordingly 24 degrees of ignition timing 10.8 -11.2 afr (only thing I've changed is fuel). I've been going easy on it because I was driving it across the country and don't have a garage to work on it and was the first time Ive turned down the Boost from 2bar. Normally I don't rev it that high unless I'm racing or driving it hard (on track) and haven't really gotten on it really hard since before I drove it across the country... what I think is happening is my cam timing is advanced... while driving it across the country one morning I got up to start it to let it warm up and it backfired through the intake and idled backwards for a couple of seconds (sounded horrible). Quickly turned off the ignition checked everything and went to start it and it started and drove fine. That was about 2800 miles ago. Full Boost @ 3800 feels like it should be at 4500 or even higher. In order for me to check ignition timing on the crank I would have to put a dial indicator in cylinder 1 because there's no key way in the underdrive pulley. it's only been dialed in when the engine was first assembled for the offset to megasquirt. this is what makes my dilemma a little harder to check cam timing. I can't just pop up off the valve cover and check crank to cam timing. I may need to just go buy a dial indicator take off the valve cover and go from there and start turning the engine over. Anyway anybody else have this happened there engine... engine rotates backwards and the timing chain jumps on the cam? Ideas.. thoughts . Thank you for your time ahead of time and please go easy on me.

[Chickenman]

PM sent. Help is on the way. 

[Chickenman]

It would be fairly rare for a L-series to skip a Tooth. On the chain. Particularly on a fairly new engine with only 18K on the chain. I think there are other issues going on here. 

[TimZ]

On 6/3/2018 at 2:31 AM, Nicksturboz2 said:

 In order for me to check ignition timing on the crank I would have to put a dial indicator in cylinder 1 because there's no key way in the underdrive pulley. it's only been dialed in when the engine was first assembled for the offset to megasquirt. 

 

Wait - what?  Am I reading correctly that you have a crank pulley with no keyway?  Where are you getting your ignition timing from?

Edited June 9, 2018 by TimZ

[zeeboost]

You could also just do it the old fashioned way and find TDC with a piston stop. Just need some kind of pointer on your crank pulley, even if it's a makeshift one. And timing tape helps but isn't necessary. Then you'd be able to easily verify ignition timing and cam timing. 

[Nicksturboz]

 so I'm getting my ignition signal from the crank and that's how we set it up in the beginning. we use a piston stop marked top dead center on my reluctor ring 1/8 in in front of where the sensor is and that Mark is gone. That was before I drove it from New Mexico to New England. I've never had a problem with the car. I will say this I've had many turbo engines but they've all been hydraulic heads. I've done a valve adjustment on it and it seems to run fine... may e the valve adjustment could be causing these issues if it was adjusted too tight. My last engine I put over 50,000 miles on making over 350hp with no keyway in the crank with no issues banging it off rev limiter road racing time attack all kinds of things so I don't think that's an issue.  I really think it's a cam timing issue from the engine running backwards for a couple seconds or the valve adjustment is too tight. That's the only thing I can think of. I really thought this engine would be more rev happy than the hydraulic head. Here in the next day or so when I get a chance I'll do another valve adjustment just to check it. unfortunately I'm working in a parking lot while traveling and can't work on it in a garage.

[Nicksturboz2]

Just want to give an update... I've redone the crank pulley setup. There's now a keyway with an ATI underdrive pulley with a DIY trigger wheel.  I've also verified top dead center with a piston stop and it's really close... like within half a degree. I also put a  Schneider turbo cam 460 lift 280 duration 270 on the exhaust on a 114. But it really still doesn't want to rev above 6K. I don't have to run near as much boost to get the same power... right now it makes more power than it's ever made...  and I'm happy with the power. I just want it to Rev. Supposedly it should rev all the way out to 7400.  which I find really hard to believe and even if it would go that far... I probably wouldn't take it that far... maybe 6800.

 

 if you if you want a good laugh watch this video... it's my old crank trigger setup. it lasted about 14yrs and went through many many junkyard Motors and headgaskets. But surprisingly with the failure it didn't break anything.https://youtube.com/shorts/QXOTKOhxGMU

[Nicksturboz2]

 oh and ignition timing right now is 19° at 1.2 bar 11.8 afr. Water meth is 330cc injector 50/50 and comes on at 160kpa.  I think I'm going to add some ignition timing like 3 or 4.  maybe the water meth is putting the fire out?

[jonbill]

19° at what RPM? 

[NewZed]

2 hours ago, Nicksturboz2 said:

Just want to give an update... I've redone the crank pulley setup. There's now a keyway with an ATI underdrive pulley with a DIY trigger wheel.  I've also verified top dead center with a piston stop and it's really close... like within half a degree. I also put a  Schneider turbo cam 460 lift 280 duration 270 on the exhaust on a 114. But it really still doesn't want to rev above 6K. I don't have to run near as much boost to get the same power... right now it makes more power than it's ever made...  and I'm happy with the power. I just want it to Rev.

 

Cam timing generally determines where the torque power curve is, high or low on the RPM range.

 

Did you do all of this work yourself or have some help?  There's some odd things in the overall story.  No offense.

Edited November 22, 2020 by NewZed

[AydinZ71]

My L28et was mechanically stock, and my torque started falling off after 4800. It was obviously a breathing issue, but I never pushed it much with the stock internals. Aside from all the usual things I’m listing below, I think chief among them is the cam. To this day I still have not met anyone who has a full grasp or confident opinions on turbo cams for the L series. I often hear (what’s good for NA is good for turbo), but I’m suspicious. I even called Rebello about this, and they had only run a few L28et’s with Reground cams that they were impressed by. They could not quote me the cam they used over the phone and needed to do more research. I suppose I could call Datsun spirit next. 
 

The list to consider (in this order, although debatable) 

 

1) polish chamber and pay very close attention to eliminating any sharp edges. Think of anything you would anticipate would “glow” when hot. Deshroud valves. Straighten and widen (within limits) the intake and exhaust runners. Port Match to your desired manifold. Shave deck or add gasket material to adjust CR. 
 

2) cam and valve timing. I’m not an expert here so others can chime in.

 

3) stock exhaust manifold and down pipe are quite restrictive. Need to replace with Better flowing units.

 

4) 3” exhaust mandrel bent or 3.5-4” standard bending.

 

5) upgrade intake manifold and throttle body from stock. Obviously you will need an inter cooler, which should be 2.5” mandrel bent. 

 

I believe these improvements really matter after you get past the 250-300ft-lb range. this is just my opinion, and I do not have data to support this. Only my first hand experience which is anecdotal. 

 

 

[NewZed]

On 11/22/2020 at 9:31 AM, Nicksturboz2 said:

 I also put a  Schneider turbo cam 460 lift 280 duration 270 on the exhaust on a 114. But it really still doesn't want to rev above 6K. I don't have to run near as much boost to get the same power... right now it makes more power than it's ever made...  and I'm happy with the power. I just want it to Rev. Supposedly it should rev all the way out to 7400. 

 

You said you wanted it to rev higher.  Where is your cam timing?  Did you degree the cam to Schneider specs when you installed it?  You can move the powerband higher by changing cam timing.  Cam timing affects "breathing".

 

https://help.summitracing.com/app/answers/detail/a_id/4706/~/advancing-%2F-retarding-a-camshaft#:~:text=A Basic Overview of Cam,the camshaft and the crankshaft.&text=Advancing or retarding the cam,other of the crankshaft centerline.

 

https://www.jcmmachineandcoatings.com/understanding-combustion/degreeing-a-camshaft/#:~:text=Degreeing the Camshaft-,What is Meant by Degreeing the Camshaft%2C and Why is,that their rotation is synchronized.

 

http://schneidercams.com/284-70F-14_LET6.aspx