Just put a shaved head on 08 M8

[dmkhnr]

I have an 08 nightfire M8 with SLP single pipe, that runs really good.
I had a stock head that SLP shaved when they did their porting package on another M8 I have, and decided to install this head on my stocker.

I did a compression check before I pulled the head and had 125 psi at 4500 elev. Did the head swap and am now seeing 155 psi.

My ported motor with RKT 14.5:1 head pushes 130 psi on the same gauge/same elev.

I ride at 7-10k elev so I'll have less compression when I unload and start to climb.

What do you guys think, is 155 psi flirting with danger? Sled is piped, and has a boondocker box.

[m8magic]

should be fine at 7-10k..a couple gallons race fuel per tank if your worried..maybe a little thicker base gasket ..??..pm hobb-z on here..he will give you an idea

[HOBB-Z]

The best way to up the comp is to cut the heads face and then cut the squish back in, I would really consider doubling up on the base gasket with the cut head. The higher port heights, higher comp and a +2 key would really wake it up.

You need to measure the squish on the head and see what they did, if all they did was take 10-15 thousand off the face it will be close to det if run lean at all.

I'm not a big fan of just shaving a head, SLP does it all the time, if you're not running a timing key and you always get good fuel and never run it lean you will probably be ok.......A little more octane will also take care of it

I forgot to add, its not about the compression ratio thats the problem, its all about the squish band and dome design. 155 is just fine if it has enough squish



.

[backcountryislife]

This isn't apples to apples, but we've seen horrible results with cut heads on 1000's around here, where we're riding 10k+, det like crazy & **** performance. Never done an M8, so not sure if that compares to the 1000's or not.

Seen MUCH better results with Kelsey's head.

[dmkhnr]

I use 91 octane, and have the lucas octane boost which shows +36 points so I should over 94 octane.
I'm going to run it today to see how it reacts. I've got an extra base gasket, and I wish I would have thought of that while I had it apart.
I have an RKT port/head sled, and an SLP port/RKT head sled. The SLP sled runs good, but not quite as strong as the RKT sled. The RKT sled, and RKT head doesn't have a big compression jump, like this cut head and I wonder if this SLP head should be run with the SLP cyls.
The only reason I put this cut head on the stocker is because I had it laying around for a year and wanted to see if it made any difference.

[HOBB-Z]

I didn't do a very good job explaining the head and compression thing, when you do a comp check the reading on the gauge really means very little.

To get an accurate compression ratio you have to CC the head, I'll bet Kelseys head has a higher compression ratio than the cut head, the gauge reading higher is just a result of how the head was cut.

I know it doesn't make sense that the higher PSI head would have a lower comp ratio than Kelseys but we see it all the time on cut heads.

[dmkhnr]

Well the cut head gave a noticable difference in the low end and mid range as it pulls harder. The top wasn't effected as much, I might see 40 more R's but this could have been snow conditions. I know it didn't do anything negative to the top. No det, no 21 code and the sled ran strong.

[HOBB-Z]

Originally Posted by dmkhnr

Well the cut head gave a noticable difference in the low end and mid range as it pulls harder. The top wasn't effected as much, I might see 40 more R's but this could have been snow conditions. I know it didn't do anything negative to the top. No det, no 21 code and the sled ran strong.

Thats exactly what a cut head is supposed to do, make it snappy and pull a little harder. It won't do much on the topend and if its not causing det I'd run it on whatever you want.

Kelseys head will actually increase your RPM by about 200-300 if its tuned good.
I didn't mean to come across as if the heads a pile, I run cut heads on everything I have, I just cut them to be a little safer than the way SLP does it.

Sounds like you are going to have fun with it...Be safe, have a great season..

[dmkhnr]

Thanks Hobbz, and everbody else.
We need to get this forum moving, so post up your questions/comments whether you already know the answers or are just learning.

By the way, I did use 94 octane, and in my ported motor, I use 93 octane as I can set the det code off pretty easy when on 91.