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Thoughts on l28 build


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#1 ZHoob2004

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Posted 3 weeks ago

To start off, I already typed this once and lost it, so think of that if this seems at all incoherent.

I'm planning an l28 build for hot street/ very mild race. I'm currently running a stock n42/n47 and I want a bit more. I recently bought an f54/p79 and think it's a good base for my future plans.

Anyway, the plan:
F54 with flat tops. Probably keep the stock bottom end for now, unless there's a good reason to change something.
Lightweight flywheel
Decent clutch (stage2?)
P79 head, shaved .080-.100, shimmed cam towers, adjustable cam gear, performance valve springs, n47 valves, mild porting, and a stage2/stage3 cam.
I have a pair of flat-top su carbs or i might switch to megasquirt
280zx distributor

Questions: am I correct in understanding the main problem with shaving the head is not the valve timing, but the excess chain length? Will I have any problems running this combo on Arizona 91 octane? Will I need to do anything about piston-valve clearance? Is a stage3 cam too much, or am I being too cautious?

Sorry for so much at once, I've seen a lot of this information around the site but never all in one build with a conclusive yes/no

Edited by ZHoob2004, 3 weeks ago.


#2 Leon

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Posted 3 weeks ago

Well that was fun, I lost my entire reply as well...

 

Cam timing and chain length go hand-in-hand, milling the head retards the cam. Depending on your cam gear, you may be able to adjust the timing back to straight up (if that's what is desired).

 

Shaving the P79 more than .080" on flat tops and OEM head gasket will give >11:1 compression. Whether it'll run on 91 depends on the quality of your fuel and timing management, i.e. your components and tune. If you cam manage the fuel properly but have an old distributor, there will be problems and vice-versa.

 

Piston-to-valve clearance needs to be measured with your specific setup and cam timing. I have no idea what a "stage 3" cam is. I advise you to talk to a cam grinder about your specific build so that they can cut a cam for you, instead of picking something out of a catalog. I'm running a flat-top L28 with a 2mm shaved P90 and an Isky L6 grind (0.540" lift, 270deg). PTV clearances were measured to be >0.080" and deemed acceptable. I have more details on the build in this thread if you're interested: http://forums.hybrid...ons-other-260z/

 

Also, this engine will be screaming for a set of 45mm triples or ITBs!



#3 Chickenman

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Posted 3 weeks ago

Compression of an L28 with Flat Tops and stock P79 head is approx 8.8 to 1 .

 

9.0 to 9.5 is more than enough on Pump gas 91 Octane for the street IMHO. I'd shave the P79 no more than 020" to .040" and save yourself some aggravation.  No good having a high compression ratio if you have to take ignition timing out of curve to prevent detonation. 



#4 ZHoob2004

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Posted 3 weeks ago

Shaving the P79 more than .080" on flat tops and OEM head gasket will give >11:1 compression. Whether it'll run on 91 depends on the quality of your fuel and timing management, i.e. your components and tune. If you cam manage the fuel properly but have an old distributor, there will be problems and vice-versa.

 

Piston-to-valve clearance needs to be measured with your specific setup and cam timing. I have no idea what a "stage 3" cam is. I advise you to talk to a cam grinder about your specific build so that they can cut a cam for you, instead of picking something out of a catalog. I'm running a flat-top L28 with a 2mm shaved P90 and an Isky L6 grind (0.540" lift, 270deg). PTV clearances were measured to be >0.080" and deemed acceptable. I have more details on the build in this thread if you're interested: http://forums.hybrid...ons-other-260z/

 

When I say "Stage 3" I'd say it's about equal to or maybe a bit less intense than the cam you described. The plan of course involves speaking with a few grinders and picking out a profile. If I do go standalone (probably not happening for a bit, but we'll see), I'll most likely be going COP at the same time, so I should have timing under control. I'm trying to keep within a bit of a budget right now but am willing to stretch if that proves necessary. I'll read up on your engine build and see if anything there catches my eye.

 

Compression of an L28 with Flat Tops and stock P79 head is approx 8.8 to 1 .

 

9.0 to 9.5 is more than enough on Pump gas 91 Octane for the street IMHO. I'd shave the P79 no more than 020" to .040" and save yourself some aggravation.  No good having a high compression ratio if you have to take ignition timing out of curve to prevent detonation. 

 

So based on you and Leon, I think I might be better suited with a more conservative cut on the head (at least to start out with), shim the cam whatever I cut out to maintain valve timing, swap the cam and springs and see how that makes me feel. When I decide I want even more, I can up the compression again, add an adjustable cam gear and mess with the valve lengths as necessary.



#5 madkaw

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Posted 3 weeks ago

My approach will be a MN47 head on a 54 block. At 39cc stock, no shaving required. You could put larger seats on the intake and run your 47 valves - done . It might have too much pop and need MS to keep it under control.
Just another option
Steve,
9/71 240z. 2.4 -.40 over, balanced. E-88 Bigger SS valves, stage 2, 6x2 header, true dual exhaust. BW t-5 , STI LSD 3.90- triple Mikunis 40mm

#6 ZHoob2004

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Posted 3 weeks ago

My approach will be a MN47 head on a 54 block. At 39cc stock, no shaving required. You could put larger seats on the intake and run your 47 valves - done . It might have too much pop and need MS to keep it under control.
Just another option


I would love to go that route, but the mn47 is proving a bit hard to source. I stumbled across this motor on Craigslist for $400 so I figure I'll give it a shot.

#7 madkaw

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Posted 3 weeks ago

There easier to find than you think. Just look at sites selling used car parts . There's old Maxima's engines laying around. Usually cheaper than sourcing a z head .
Steve,
9/71 240z. 2.4 -.40 over, balanced. E-88 Bigger SS valves, stage 2, 6x2 header, true dual exhaust. BW t-5 , STI LSD 3.90- triple Mikunis 40mm

#8 ZHoob2004

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Posted 3 weeks ago

There easier to find than you think. Just look at sites selling used car parts . There's old Maxima's engines laying around. Usually cheaper than sourcing a z head .

 

I'll keep an eye out. I may end up taking my time to do the bottom end a little nicer than originally planned and I can find a maxima head, though I don't know how much that will save me versus just making the p79 maxima-like.



#9 marxjunk

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Posted 3 weeks ago

i have a spare MN47 head that came with a motor the dude was going to hot rod...i have no plans on using it..ive just held onto it for a bit..


Edited by marxjunk, 3 weeks ago.


#10 madkaw

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Posted 3 weeks ago

i have a spare MN47 head that came with a motor the dude was going to hot rod...i have no plans on using it..ive just held onto it for a bit..


I'd take it but I have too many now. Let me know if there's anything I could possibly trade for it:)
Steve,
9/71 240z. 2.4 -.40 over, balanced. E-88 Bigger SS valves, stage 2, 6x2 header, true dual exhaust. BW t-5 , STI LSD 3.90- triple Mikunis 40mm

#11 madkaw

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Posted 3 weeks ago

I'll keep an eye out. I may end up taking my time to do the bottom end a little nicer than originally planned and I can find a maxima head, though I don't know how much that will save me versus just making the p79 maxima-like.


It's about the same work, but your not taking .080 off the head so no chain issue . You have to swap out all valves on the 79 if you take .080 out, but the MN would just be intake seats and valves .
Steve,
9/71 240z. 2.4 -.40 over, balanced. E-88 Bigger SS valves, stage 2, 6x2 header, true dual exhaust. BW t-5 , STI LSD 3.90- triple Mikunis 40mm

#12 ZHoob2004

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Posted 3 weeks ago

It's about the same work, but your not taking .080 off the head so no chain issue . You have to swap out all valves on the 79 if you take .080 out, but the MN would just be intake seats and valves .


Is swapping the valves really necessary, or could that height difference be made up with really tall lash caps?

I think I want the p79/valve swap route anyway since that theoretically gives me another .080 of lift before coil bind and stem seals become an issue, correct?

#13 NewZed

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Posted 3 weeks ago

It seems that many engine builds are just taking the easy operations out of a list of operations for a very thorough, "complete" performance build.  Might be more effective to extract the things that have the most impact and focus on those, instead of the easy stuff.

 

For example, port work on the head is probably much more impactful than shaving the head.  The pros mill the head as part of the complete job, but would probably rather have a ported head than a faction of a point increase in CR.  



#14 madkaw

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Posted 3 weeks ago

Might want to read up on the whole p79 shave/swap - I think your skipping some steps or leaving out some stuff. I think you need to shim for that .080
Steve,
9/71 240z. 2.4 -.40 over, balanced. E-88 Bigger SS valves, stage 2, 6x2 header, true dual exhaust. BW t-5 , STI LSD 3.90- triple Mikunis 40mm

#15 BluDestiny

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Posted 3 weeks ago

I would start with a smaller combustion chamber. 

 

I had an F54 with +1mm pistons, e88 head with larger valves and an MSA "Stage 2 cam" kit. It was about a 9.8:1 CR. I also had a 40mm triple weber setup that I had rebuilt.

 

It would idle at about 1k and streetability sucked at taking off (partially the clutch/partially the webers), but after 3k it was glorious. I had a spec 6 puck (overkill) and a fidanza flywheel I used an MSD 6AL to help the 260z ignition. I also never broke 200whp. I had no head work done.

 

I would highly recommend you get head work done and either choose megasquirt or webers and build AROUND the EFI system first. If I had to do it again, first thing I would do is go megasquirt if the car came with EFI. 


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#16 turbogrill

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Posted 2 weeks ago

1.

You could save your self some trouble and go with the N47 head on the F54 block with flat tops. It's the ghetto way of doing it but several people seem to be alright with it.

 

2. 

I have partially done a megasquirt fuel only and it's not that hard if you know a little about computers and electronics. I got the already assembled Microsquirt and their generic harness. 

If you do it make sure to add a 1k resistor between Negative- and Opto+, otherwise you can fry your MS. 

 

Doing timing with MS is a little more complicated because you need to fab stuff for the hal or source a 280zxt dizzy.

 

3. 

Some people go with the 300zx NA springs instead of the Isky or Schneider springs for hot street/mild race. There is a debate if the Isky springs are to stiff or not for the typical hot street cam.

(I asked Isky but they are very unhelpful, so no luck there. I gave my money to someone else).

 

4.

Cam selection is a jungle, here are some thoughts:

- Stay with a < 460 duration if you want to keep things simple and stay with stock drive train. Isky and/or Rebellos has cams for this. Not going to be a hot street.

- Over 7000 RPM and stock pistons might be of a concern

- Make sure to check both adv. and @0.050". Just adv duration is misleading for colt cams vs isky/schneider

- Most people seem to recommend doing a regrind (cheaper to)

- Check the dyno threads, sometimes they list what cam they used. It's good to get an understanding for what power curve you get. 

- 290F or Isky L-490 would be my pick for a hot street and still something you can drive. (I ended up with something less brutal due to my racing regulations).

 

5.

No headers?

They are only $300 or so, so might as well.

 

6.

I went with this clutch, http://www.advancedclutch.com/nx1-hdg6



#17 marxjunk

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Posted 2 weeks ago

i was offering the head to ZHoob..i have a good set of headers too...reasonable...shipping sucks probably


Edited by marxjunk, 2 weeks ago.


#18 ZHoob2004

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Posted 2 weeks ago

1.
You could save your self some trouble and go with the N47 head on the F54 block with flat tops. It's the ghetto way of doing it but several people seem to be alright with it.

2.
I have partially done a megasquirt fuel only and it's not that hard if you know a little about computers and electronics. I got the already assembled Microsquirt and their generic harness.
If you do it make sure to add a 1k resistor between Negative- and Opto+, otherwise you can fry your MS.

Doing timing with MS is a little more complicated because you need to fab stuff for the hal or source a 280zxt dizzy.

3.
Some people go with the 300zx NA springs instead of the Isky or Schneider springs for hot street/mild race. There is a debate if the Isky springs are to stiff or not for the typical hot street cam.
(I asked Isky but they are very unhelpful, so no luck there. I gave my money to someone else).

4.
Cam selection is a jungle, here are some thoughts:
- Stay with a < 460 duration if you want to keep things simple and stay with stock drive train. Isky and/or Rebellos has cams for this. Not going to be a hot street.
- Over 7000 RPM and stock pistons might be of a concern
- Make sure to check both adv. and @0.050". Just adv duration is misleading for colt cams vs isky/schneider
- Most people seem to recommend doing a regrind (cheaper to)
- Check the dyno threads, sometimes they list what cam they used. It's good to get an understanding for what power curve you get.
- 290F or Isky L-490 would be my pick for a hot street and still something you can drive. (I ended up with something less brutal due to my racing regulations).

5.
No headers?
They are only $300 or so, so might as well.

6.
I went with this clutch, http://www.advancedclutch.com/nx1-hdg6


1. I've considered the idea, but heard it's quite detonation prone so I'd rather go with the better chamber design for not much more effort.

2. Programmable fuel would be nice, programmable ignition even nicer. I hope to have both eventually, but we'll see what comes first.

3. The springs sound like a good idea to look into. I'm not planning to shim the springs, so I'll have to ask around and see how that will affect the spring pressure.

4. I'm planning to rev to ~7000 so not too crazy for the stock bottom end. Can selection is a whole topic in its own right but that isky .540 is looking pretty good at the moment. I have a few cams I can send to be reground so that should save me a bit.

5. I do have a set of headers on the car right now, just forgot to mention them. I believe they're msa 6-1 from pictures I've seen online.

6. Based on a few other builds I think I can get away with a stock clutch or just slightly stronger, so that's what I'll start with.

i was offering the head to ZHoob..i have a good set of headers too...reasonable...shipping sucks probably


I appreciate the offer, but shipping will be the killer on either of those. I think running the p79 is the way to go for me.

Way I see it
P79 needs shave, shims and maybe valve swap (can be done with lash pads)

MN47 needs valve seats replaced, valves swapped.

When changing cams, both will need a valve job, rockers, lash pads and springs

It's not different enough one way or the other to justify not using the parts I already have.




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