A converstion about how much compression is too much for pump gas

[30 Ounce]

My piston's had eyebrows...Dave cut them slightly deeper after checking clearance.

[mdec]

Not so sure abot those earlier comments regarding octane boost. I do believe the Industry gets a bad rap & a lot of it is self inflicted, but do your research pick a reputable brand that has been 'independently' tested to raise octaine ~ 2.0 units & used on the right Engine (ie L28 10:1 CR !) the improvements can be profound.

My engine is running 10:1 CR & I has suffered from a pinging issue from day1. The 'pinging' is marginal though & I only ever hear it under heavy load. Right now I'm not looking to do anything radical with the Motor (replacing heads etc). I'm hoping that a succession of incremental improvements (cooler plugs, octane boost etc) will keep me in a SOA.

I'm hearing a lot of talk about the need to keep the engine cool - was wondering wehther the waterless cooling systems may help here ? Evans the Manufacturer claim detonation issues can be reduced as the mix with a 180C BP is better at reduces 'hot spot' in the engine..

[Zedyone_kenobi]

I'm with Carl, your numbers seem weird. I remember reading about your build and thought it curious that the builder had to reduce the cam lift to increase clearance. Reading countless threads of other builder's( Braap, 1fastZ, and others on Hybridz), the guys that do many of these motors, piston height above deck is usually positive in stock configuration. I believe Braap said he measured and almost all motors were .019 +. That's more then what your forged pistons gave you. So what HG thickness are you running? Trying to figure your head to piston distance.

My point being is the squish distance is very important on these motors to fight detonation. Getting outside this distance makes these motors more prone to detonation. Now from what I have read you want to stay less then .035 . Some run as close as .022. Their claim is it makes a profound difference in power in achieving MBT.

Also head cooling is a issue with these motors the more power you extract from them. This is most prevelant in track conditions or hard driving. Maybe you should go with a cooler thermostat.

I will get the exact numbers for you guys since curiosity has been shown. NO worries

I know my cam was advanced by a large amount. Remeber that. Eiji told me when my cam came in it had a weird pin location so he had to degree it 6 degrees advanced. Gives great low end, but will probably petter out on the top end a tad. I wanted a midrange engine, so we both agreed to move forward.

The huge initial advance was probably the cause for the low clearance piston to valve. Still, I could recam, but that may involve new lashpads and all that as well.

I just want to reiterate. My car drives wonderfully, and the power is just great, but I wanted an open talk about sets ups and cam duration and compression, etc.

And as usual you guys have answered the mail!

[Zedyone_kenobi]

I'm with Carl, your numbers seem weird. I remember reading about your build and thought it curious that the builder had to reduce the cam lift to increase clearance. Reading countless threads of other builder's( Braap, 1fastZ, and others on Hybridz), the guys that do many of these motors, piston height above deck is usually positive in stock configuration. I believe Braap said he measured and almost all motors were .019 +. That's more then what your forged pistons gave you. So what HG thickness are you running? Trying to figure your head to piston distance.

My point being is the squish distance is very important on these motors to fight detonation. Getting outside this distance makes these motors more prone to detonation. Now from what I have read you want to stay less then .035 . Some run as close as .022. Their claim is it makes a profound difference in power in achieving MBT.

Also head cooling is a issue with these motors the more power you extract from them. This is most prevelant in track conditions or hard driving. Maybe you should go with a cooler thermostat.

I will get the exact numbers for you guys since curiosity has been shown. NO worries

I know my cam was advanced by a large amount. Remeber that. Eiji told me when my cam came in it had a weird pin location so he had to degree it 6 degrees advanced. Gives great low end, but will probably petter out on the top end a tad. I wanted a midrange engine, so we both agreed to move forward.

The huge initial advance was probably the cause for the low clearance piston to valve. Still, I could recam, but that may involve new lashpads and all that as well.

I just want to reiterate. My car drives wonderfully, and the power is just great, but I wanted an open talk about sets ups and cam duration and compression, etc.

And as usual you guys have answered the mail!

[madkaw]

Don't doubt your engine runs great. I am a little surprised that more dyno testing is not done by the members on here. I'm talking mostly the guys that have substantial money invested in a motor and that can probably afford the 100$ it takes to confirm your butt dyno.

The dyno in your case would let you know if your HP is limited by detonation.

We are not talking bragging rights, but maybe verification the big $$ you spent on your Rebello or whatever is putting out reasonable power.

I'm trying to get to the dyno next week to see what gains I really got from my Mikunis. It feels great on the butt dyno, but I don't trust that and the direct comparison to the SUs would be great.

As far as the advanced cam, I thought retarding the cam got you closer to valve bashing the advancing - but I might be backwards on that.

I run my cam slightly advanced to get the Intake valve closing number correct.

[Zedyone_kenobi]

Okay, I pulled my build sheet. Carl, this is for you.

the L28 stock bore is 86mm, and mine is 86.5mm, not 87mm (Sorry about that, he listed OEM, first then actual, and I cut and past the OEM bore, not actual)

I went and looked at the actual Excel sheet Eiji made me with the bore measurements on it, so I am sure about it.

Also, A OEM Nissan L28 headgasket was used, as were OEM L28 rods.

I am hoping this friday I can get my colder plugs in and if I can find a cooler thermostat.

[AlexS13]

I too have been dealing with some pinging issues with my engine. Its a F54 L28 with a P79 head shaved .080

I cannot seem to run more than about 10 degrees (set at 1000rpm idle) without getting pinging with 94octane. I tried NGK bp7's but I didn't really notice much improvement. I may in the future change to a thicker headgasket to get me closer to about 9.5:1 because this pinging issue is driving me crazy. I have backed off the timing a few degrees to the point where it does not ping at all. I hate the feeling of driving and knowing that your right on the edge of pinging, I just cannot enjoy driving my car that way. I recently have installed a knock sensor to monitor knock via a LED light. The knock sensor I mounted in the factory location on the P79 and wired up the module and LED light that comes in the kit. The reason I did this is because I have aftermarket McKinney motor mounts and the cabin noise gets quite loud so it makes it almost impossible to hear ping happening, it's more for piece of mind than anything. The unit is programmable so you have to set the threshold for the LED light.

This might be something you guys can look into.

Engine knock detection and indication for all vehicles

Edited August 13, 2013 by AlexS13

[madkaw]

Stephen

What about your timing curve? I'm assuming the pinging you hear in 3rd and 4th is in 3000 rpm range?

This is the range I hear pinging on my motor. I attribute mine to a timing curve that isn't that great- comes in too early- and my triples that seem to go lean in this transitional rpm range.

OEM HG is 1.25 correct? That puts your squish around .040 - this is not optimum from what I read.

When the head was redone I am assuming the fine details were done like removing or smoothing excess spark plug threads to eliminate hit spots?

All these things add up from what I have researched . Combine that with the L series motors that are prone to detonation compared to other aluminum head motors, then you have little margin for errors on a high CR motor

[Zedyone_kenobi]

I was going to play with the springs in my Mallory to make the timing come as late as possible, but even with the heaviest springs, the curves are not that different. But it is in the direction of goodness, so it cannot hurt.

My goal is to make the carbs, the head, the cam and the timing all working together to achieve the same goal. In my case that is a huge midrange torque hump with a fall off all the way to 7000 rpm. Everything I have done up to this point is to maximize mid range power. The smaller carbs, the high initial advance on the cam, the selection of a mild cam, etc.

It is all about parts working together. It seems this pining issue means I have exceeded a boundary somewhere, but I can fix that with timing, or fuel, or plugs, or even a head gasket change.

This is all part of the fun of building the engine and it also adds to the appreciation of how hard it is to build an OEM engine that must be used by an entire country with different fuels, climates, elevations, etc. and still be robust and fun.

The more you modify an engine, the more you appreciate how good stock is.

[Zedyone_kenobi]

I was going to play with the springs in my Mallory to make the timing come as late as possible, but even with the heaviest springs, the curves are not that different. But it is in the direction of goodness, so it cannot hurt.

My goal is to make the carbs, the head, the cam and the timing all working together to achieve the same goal. In my case that is a huge midrange torque hump with a fall off all the way to 7000 rpm. Everything I have done up to this point is to maximize mid range power. The smaller carbs, the high initial advance on the cam, the selection of a mild cam, etc.

It is all about parts working together. It seems this pining issue means I have exceeded a boundary somewhere, but I can fix that with timing, or fuel, or plugs, or even a head gasket change.

This is all part of the fun of building the engine and it also adds to the appreciation of how hard it is to build an OEM engine that must be used by an entire country with different fuels, climates, elevations, etc. and still be robust and fun.

The more you modify an engine, the more you appreciate how good stock is.

[Diseazd]

"Holy horsepower Bat Boy".....don't ever say that! I run the .080 inch cut P79 head which is 10 to 1 CR just like yours. The P79 head is a more modern head, but shouldn't make that much difference. Z Doctor has told me that that set up won't have detonation because of the higher duration and lift of the Isky Stage II and Stage III cams that I run (don't know if that's true or not, but I believe what Doc tells me). Stage II is 280 degrees and .480 lift while the Stage III is 290 degrees and .490 lift. At 17 degrees timing at 1000 rpm, I can't make either engine ping, under any load. Seeing as your engine is close to my engine in just about every aspect, what is the lift and duration of your camshaft? Maybe that could be the difference, or maybe the increased deck height of your pistons are putting you closer to 11:1. If the engine runs good on an additive, so be it. It's your cheapest alternative. We can buy 100 octane race gas in Richmond, but it's $7.00 per gallon, which still makes the additive your best bet.

[Zedyone_kenobi]

My lift is around .480 Guy, with a 274 duration. Maybe more duration would help. Still like I said before, with additives I am fine. I have heard the P79 head is more resistant to detenation... I am enjoying this thing very mucy, and I would buy another Engine from Eiji if I wanted another. But I still have plans to overhaul my stock engine in some way. Maybe I will make it into a screamer...