My Datsun Spirit L28 Build.

[steve91tt]

I don't think you will have issues with detonation and you will still make lots of power if you control your AFR's and advance curve correctly. I have a L30 with an N42 head and 10.3:1 compression and it runs stong on 93 ocatane pump gas in Houston. Dave Rebello advised me to retard my advance curve until after 4500 rpm and keep my total advance around 31-33. I did this by playing with the springs on my Unilite distributor and the car pulls smooth and hard to redline. Your cam, porting, etc are likely different than mine but as you state above, I wouldn't worry about 10.5:1 CR on that motor if the engine builder says it will work.

[Zedyone_kenobi]

madkaw, I did not take any offense at all. You were just giving some very sound advice.

[Zed Head]

Did Eiji do port work on the head or is a stock N42 head?

Vicariously curious...

[LeonV]

So, with 10.5:1 calculated CR would you rather have a long duration or a short duration cam, to avoid detonation?

Longer.

You make the comment about a lot of squish; makes me think that's why Eli went with reworking your cam instead of messing with the pistons. He was looking for that ideal squish zone for these motors and the piston to quench pad was there to help with detonation, so he opted to increase clearance in other ways.

That does bring up a great point, however. How does such a mild cam manage to have valve-to-piston interference issues? I was very surprised when I saw this mentioned but refrained from posting. L-gatas have had much wilder cams put in (think .550" lift, over 300deg duration with 13-14:1 comp) without interference. That doesn't make sense to me, especially with relatively close lobe centers. I'm not saying he's wrong, but I would immediately think that the cam is timed incorrectly (too advanced) after having detected interference.

[madkaw]

Leon,

you see where I was going on that. That's a mild cam by any standards-it's also the cam I have in my car(at least close to it, Schneider 274). My head was shaved .12 and my block .005 and I have tons of room.

[Zedyone_kenobi]

I did some digging through Eiji's email. The cam was originally a .495 lift and 290 duration when it hit. He said the ROSS pistons were slightly different than the P79 pistons, an the .495 lift just barely touched.

also the cam was advanced 3 degrees on the cam sprocket (Nismo comp timing gear on cam) which leads some credence to LeonV's advanced statment, but I know as the cam sits in the car,

the IN is 105

the EX is 111

lobe separation is 108

Again, I am going to trust Eiji on this one.

[LeonV]

I did some digging through Eiji's email. The cam was originally a .495 lift and 290 duration when it hit. He said the ROSS pistons were slightly different than the P79 pistons, an the .495 lift just barely touched.

also the cam was advanced 3 degrees on the cam sprocket (Nismo comp timing gear on cam) which leads some credence to LeonV's advanced statment, but I know as the cam sits in the car,

the IN is 105

the EX is 111

lobe separation is 108

Again, I am going to trust Eiji on this one.

Aha, there's the problem! I wonder why he set it up advanced and not straight up. Besides that, if it was truly 3 degrees at the cam sprocket, then that's 6 degrees at the crank. Holy cow! Way too much cam advance (unless you want to kill top-end), of course the exhaust valve is going to hit.

Again, I'm not denying the builder's ability, just seems like a strange series of decisions. I would've set the cam straight-up, and then slowly advanced it to see where I run out of clearance. Then, when you dial in the cam, don't dial in more advance than it physically allows.

In the end, it probably doesn't make a huge difference to you and you'll enjoy the engine either way. I was just curious as that statement really threw me off.

[Zedyone_kenobi]

I can answer that

Eiji mentioned something about the cam alignment pin being slightly off but that he was able to compensate for it

[madkaw]

Well that cam was originally bigger then I thought. That's a lot of duration combined with .020 more piston height.

Why advance the cam?-maybe looking to get Stephen more torque down low, even though he has the pistons to handle the rpm---interesting

[Zedyone_kenobi]

Could be it. I was willing to sacrifice some top end for mid range punch. I told Eiji that many times. Peak HP numbers are not what I asked for but for a vintage road rally engine. He said these cams like to be advanced a little.

I am thinking madkaw is right. With this setup, I am getting exactly what I asked for. An engine making great mid range power.

[Travel'n Man]

Stephen -

Your build is very similar to mine and mine is perfect for me - If I wanted a high horsepower motor I would have built a stroker with a wild cam - much like you I really enjoy my powerband (I typically don't drive in the 6500 - 7500 rpm range). My cam powerband is 2500-5500 rpm's. I believe you will really enjoy the money spent once you get finalized and one the road. What oil are going to use in this engine? Are you going to use a different formula for break in - I believe I changed mine about 4 times in the first 1000 miles...........I have been using a custom blend that Dave Rebello recommended and has been working fine for me since my install.

[jonathanrussell]

Very nice. Ordered L24 and L28 kits. Thanks for the tip Guy.