What size valves

[d3c0y]

OK Guys, so i posted a thread before about building a forged L28 with FJ20 rods and 88mm pistons, reving to max 9000rpm - what sort of valve sizes should i be using with this beast?

 

What brand valves are reccomended?

[peter mc]

what head ?

[peter mc]

the valve is only a l28 stock  . the head is more inportant .it is very inportant to work the chamber around the valve if you make the valve any bigger it get shrouded by the bore and chamber

[peter mc]

ps you need one serious head and induction system and exhaust for it to work .it takes lots of work to get you engine to 9000rpm i did not get all right the first time . good luck

[d3c0y]

I have an E88 with some light work i just got off Dat2kman 40.9cc, mild port job and i have another N42 im looking at getting with some port work that looks like it has been shaved a bit.

 

When im saying stock valves i mean 42mm/38mm standard N42/P90 size valves - or should i hog them out and go bigger? I have also read in some places that just going bigger on the exhaust.

 

I do realise the above heads will need more work to make HP at those revs and i already have an appropriate cam shaft, valve springs and retainers.

 

Also i am starting to think there is some trickery involved in the valve guides too.

I plan on cutting them out of the ports because that seems to be a given for any large flowing head, but are there different types or thicknesses?

[NZeder]

Standard L28 aka N42/P90 intakes are 44mm and exhaust are 35mm I think you will find. Standard E88 are 42mm inlet and 33mm exhaust for the L24 E88 (L26 E88 - well there are 2 versions that I know of - one of the L26 E88 has the 35mm exhausts but the intake is the same as 42mm) then there is the E88 from the L24E ie EFI E88 used on the 80's skylines in Oz.

[peter mc]

from experience e88 wont support enough air . even with big valves as its cross section area is not big enough .it will fall over well before 7500rpm . even with monster cam. you will need a head that flows 225 cfm at 28in int and 160cfm ex to make good hp and this is only part of the story .it takes lots of work and $ at a good head shop good luck

[d3c0y]

Cross sectional area in terms of port size and volume? An E88 can be ported as far as any of the other L-series heads cant it?

 

So i take it from that message that if you were building such an engine you would run larger than 44mm/35mm valves?

[peter mc]

as i said no the e88 can not do it no mater wot valve .there is a post on this site that shows flow through all datsun heads you should have a look

[kolonelklink]

Are you refering to the old graph done by 1fastz years ago? I would like to see some repetition of those tests given as far as i know he only tested one example of each.

Also, I think the most recent part of the question made an allussion to port work: my understanding is that the castings between many of the n42 and e88 heads are interchangeable - I even have a late model stamped e88 with both n42 and e88 markings cast into the floor of the thermostat outlet. My suspicion is that the port castings are identical between e88 and n42 (but not the p90 as it has a shorter valve length.

so... just putting this out there as questions to consider -

1. how good condition is each head (if your starting from a blank slate to get work done on a head your outcome will depend very strongly on this... heads of EFI cars tend to suvive better in my experience, look for det marks in the chambers(5-6) and  corrosion ins the water jackets... signs of either should mean start with a different head)

2. What kind of port work are you considering and how does your exaust and intake complement this?

3. Do you need a quench pad? (compression??) or alternative (ceramic chambers?)

 

Having looked into extreme head work before unless you have a "lewd--i--crus" amount of money to throw at it you're better off buying something from japan that has already been ported and welded.

 

 

Hope this helps.

-pete

[nat0_240_chevZ]

plus the rod/stroke ratio will hinder anything over 7k,

as stroke is too large to maketorque that high witht that much reciprocating weight.....

 

try an l24 crank......ie destroke it, will rev higher easier, and the volumes you are after will be better supported with your intake and exhaust area limitations, amongst others......

a bottom end to hold together for long at that speed is 10-15k just in parts and yes i mean parts.....

nat0

[d3c0y]

First off i dont need the engine to rev to 9000rpm on the dot. Just a rough way of asking what size valves do you need for an L28 8000-9000rpm and hopfully over 200rwhp.

 

L28 crank / FJ rods (a/m h-beams)/ Custom forged pistons - will have a better rod/stroke ration and a stock L28 plus less reciprocating weight and what's the point of destroking it? It will make less HP and torque and that's the whole point, not to have a high redline for the sake of it. N/A engine rpm = power.

 

To answer your question about supporting mods i already have mikuni 44s with 40mm chokes and i know that isnt optimal but we'll see how we go there. I can always run it without chokes too for an extra 4mm of bore size. Headers will be long primary 6 into 1s, and really exhaust isnt that hard compared to building the engine.

 

I dont see how you could spend $15k on that bottom end on parts alone.

A preped block and crank for sure - put good money in there. Rods and pisons are new already, timing gear modifications - even if you go for kamieri stuff its $700.

Balance the set up $1000, and we are at what $5k - $6k, and i've already started including labour. Also im not going to be droping the car off to a shop and say phone me when you are done, that takes the fun out of building datsuns.

 

I was under teh same impression about the castings, there maybe minor differences but if you going to machine everything out anyway will it matter? As i stated i dont plan on doing this with a stock head with some bigger valves in it. I have already purchased a supporting valve train for this project (minus valves obviously lol) and am aware of the costs involved. As i have also stated that i have begun buying heads with work already done to them as i know this will save a tone of money

 

Since pistons are custom compression can be set to be optimum for the head i end up going with so not really a big deal.

[nat0_240_chevZ]

i could make you a head from billet ally........big penny's bit.

bottom end $$$ to get a 'stable' 9k spinner

titanium rodbolts

titanium rods with mating endcaps(machined sawtooth face to hold together)

Need i describe the price of this stub suitable for the above apps, then there is cold cutting, machining, boring, finish boring etc etc, not exactly stuff a mate could do at work if you get my drift.

Crank, is not just a nitride, linish & balance either trust me on this one

pistons arent too expensive, i agree.

 

Sorry my bad, thought you said a 9k spinner, not 'able to support' ie bolt ons.

only L series ive had to 9k was an l24 and it loved it.....sort of, untill a rod bolt let go, after too many bounces off the top of the tacho. luckilly no leg outa'bed, but was a fair few years ago.

yes RPM is the key to good power, not so much torque, but if youre only in that rev range for a second, or two, then money is best spent getting you up there ie torque below,

 

the rod stok ratio only changes if youre changeing rod length which ill doubt you will be changing it much at all,

if you want the key to big stable revs, open up any jap motorbike engine, you will see immediately what I am talking about, skinny rods and big ends, small crank and biggish pistons fwiw.

 

nat0

 

[d3c0y]

We're getting a bit off top here guys, back on the valve band wagon - the only sizes over stock i've read about so far on hybridz is 45mm/41mm which seems like a massive step up on the exhaust. So, you guys with big HP L28s what size valves do you run?

 

I already know i need to build a decent bottom end but i already have a fair idea of what i need to do there. To add to your post:

 

I do understand what you are saying about big bore and short stroke for sure and if there was an easy way to maintain a capacity close to 3.0L with a shorter crank then i would do that. Unfortunately having to stick to an 88mm bore (was talked out of 89mm in another thread), de-stroking the motor will remove too much capacity.  An L24 crank based motor and an L28 crank based motor (longest applicable rods, 88mm overbore) and the same prep, bolts-ons etc you know which one is going to make the most power at the end of the day.

 

Titanium everything is nice but not necessary, most modern forged rods are rated to 10,000rpm with the right ARP fasteners. Did you your 9K L24 have titanium internals? What sort of rod bolts were you using in it?

 

It's a 7.5% (9.7mm) gain in rod length so ill get what i can take, its going to be better than running a standard L28 rod.

 

[NZeder]

Never seen 41 exhaust used before.

 

The stock L28 intake at 44 is large enough for most performance applications. I would start with a N42 for the following reasons.

 

1. Already has 44mm intake valve. The stock nissan valve are well made.

2. They are form a later car = newer head = less likely to have been over heated/lower number of heat cycles = not as soft.

 

Find someone who know how to get good numbers from the L6 head and invest in their time to work on your selected head (you might need a few so the can select the hardest one to start with). If you an old soft one put it in the bandsaw so you can cut it up and learn more about the ports/water jackets locations etc.

 

Good number can come from 37mm exhaust valve (ie purchase 38 and turn down).

 

My old 240z had 250rwph with stock intake valves 36mm exhausts. 

[peter mc]

yes the ex valve needs to be bigger in 88 42 heads as they are not as good as p90 with standard valve .i have made the ex flow more with standard valve 90a than both 88 42 with big valves .the port and chamber is more efficient  with small valve if you flow if on 87.5 bore  and 88mm

[d3c0y]

Thanks Peter and Mike they are the answers i was after.