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

[Davey G]

No go on my 280Z yet either. I do expect to do the test drive sometime this week. There will be some fine tuning and last items after that, but she'll be coming home soon, and I'll have to put her through the paces.

[Davey G]

I took the '78 280Z on a 75mi test drive on Saturday. Everything was fine, but I kept it 3000 rpm and less during this break-in period. With the low-rpm-only driving I'm not sure if I have any detonation, but I did run 93 octane Shell premium for the test. The higher compression, cam, headers and 2.5" exhaust will not be utilized much until revving past 3000. More tweaking of timing, fuel pressure, etc. this week, as well as a/c. I may have her back home by this weekend. :laugh:

[Zedyone_kenobi]

congrats on the maiden voyage... keep her rolling!

[Davey G]

congrats on the maiden voyage... keep her rolling!

I'm to pick up my 280 Thursday or Friday of this week. At <3000 rpm there have been no signs of detonation. I'll see if that holds true above that, as the 485/270 cam will let the engine easily rev to 6500 rpm now.

I may need to come to League City to let you have a look at her.

[Zedyone_kenobi]

That is fantastic! Good Luck

[Davey G]

Zedy

Are you running conventional oil or synthetic in your '71's new engine? Why?

Davey G

[Zedyone_kenobi]

I run Brad Penn oil exclusively now. It has a high zinc content.

10W30 Semi Synthetic Racing Oil by Brad Penn The Green Oil 1Case on eBay!

I run 10w-30 in winter and 10w-40 in summer

[conedodger]

I run 10W50 all the time... Good stuff. I get it from Summit Racing right down the street from work.

But what about that dyno?

[Zedyone_kenobi]

I tell you what happened. My 5 year old started kindergarten. Every day I am swamped explaining why you cannot talk without raising your hand or why the teacher cannot call on you every time... Lets just say my boy is very bright, but conduct is going to be an issue.... he is 'enthusiastic'...

[conedodger]

I just had a conversation with a teacher about bright boys and girls. Boys can be 'enthusiastic' and this is a little hard for teachers to handle sometimes. I suspect this is a reason why the diagnosis ADHD has managed to multiply so dramatically in recent years.

Childhood is not a mental illness. Let's leave the pills in the bottle!

Now about those dyno results...

[bajcsi]

I would definitely like to see the dyno results as well, Zedyone... My engine build is a little silly in that I'm at about 12.5:1 compression according to the calculations but it might be a little less. They look something like below (when using the calculator posted above). Unfortunately, I also have DCOE 40's which most say will be fairly limiting with my motor. I'd actually prefer to run ITB's but that's not really in the budget just now. Anyhow, I have yet to get it on a dyno as I'm just finishing the break in process also. I run 93 oct + the NOS Octane Booster in every tank.

As for timing, I'm running around 15 @ 1100 and 33 @ 3k. I had to dial it back a little bit because of pinging but right now the engine seems pretty content with that - at least from the perspective of detonation. I've ordered a Knocksense so that I can get a better handle on it as well.

Block Height= 207.87 mm

Deck Height= 0.63 mm

Chamber Volume= 42.4 cc

Cylinder Volume= 516.35 cc

Gasket Volume= 6.5 cc

Dish Volume= 0 cc

Deck Volume= -3.92 cc

Uncompressed Volume= 565.26 cc

Compressed Volume= 44.98 cc

Compression ratio= 12.57:1

Total displacement= 3098.13 cc

[Lazeum]

Your timing seems not appropriate to me.

I'm running a much more conservative setup with CR at 9.5:1, quite aggressive cam from Rebello for the street with some overlap (don't have numbers, Rebello doesn't share data, you have to measure if you want to know), L28 with F54 & ported P79.

You're not saying which head you're running, since combustion chamber has a major impact on detonation & max timing to get max output, it's important to know.

Anyway, I'm running 20° at idle (with no load, obviously) whereas your setup is much more aggressive so you should be in that range too.

32-36° is the range where max hp is reached so you should be good there.

Regarding knock, it usually happens at high load, mid rpm range (where max torque is). You're likely running classic distributor and I believe this is why you run such timing at idle. You should check what timing you need at idle and get your dizzy recurved. Running such low timing at idle means also you're running very low timing at cruize, fuel consumption is probably very bad and you're not getting the torque the engine is capable of.

To check knock, you can also build your own detcan with some noise cancellation helmet at $7 from hardware stores, some fuel hoses and a copper pipe. Total cost should be $20 max.

Once more, with proper timing management, you could most likely run your engine at proper timing at WOT & manage to reduce timing only where it needs to be reduced to avoid knock.

At cruize, you're running between 11 & 33° (most likely around 20° at 2000rpm) whereas I'm running 50° with my setup. It makes a huge difference. I've switched from dizzy to distributorless system with engine load input last winter, I cannot be happier.

Edited September 13, 2013 by Lazeum