ArcticZ28

iTrader: (14)

I had my 317's ported and finally got it all back together and up to the shop for the dyno. With the new heads at about 70cc and a .040 cometic gasket I'm at about 11.6:1 SCR and 8.1:1 DCR. On the dyno pulls, my tq peaks at 430 at about 3100 and holds flat through 5k and then starts to fall off. My HP is peaking at 6000 which is also a bit low, but that's due to the cam being advanced 4 degrees. My main concern is why in the hell am I getting KR from 3k-5k? My tuner thinks it's because of the high cylinder pressure - did a compression test and all cylinders are reading about 225 psi. I'm going to retard the cam back 4 degrees to straight up but was wondering what else might be causing this. I'm running 93 gas with no ethanol so that shouldn't be an issue. Any ideas?

Patrick G

iTrader: (14)

225psi is good, but not too much to justify backing your cam up. FWIW, my cranking psi is 245-250 and my DCR is 8.7+:1. No knock on 93 octane. Timing is 26 degrees around peak torque and 30 degrees at peak hp.

Could you be getting false knock?

ArcticZ28

iTrader: (14)

I'm not sure where I'd be getting false knock from though

And for reference I've attached the cam sheet.

Nickn20

peaking at 3100? rediculous knock? make sure that cam isnt off a tooth, what it sounds like to me, 4 degrees advance in a cam will not do this.

Zick

iTrader: (18)

Dang How did you manage 30* at peak hp? I can only muster about 25-26* and I'm at about 8.6 DCR on 93 octane.

Oh sorry about the H/J. Btw, what is your timing?

Patrick G

iTrader: (14)

Tight quench. My quench is around .032". This allows me to run higher dynamic compression without knocking. I run around 27 degrees from 2800-4400, then 26 degrees from 4800 to 5600. From 5600rpm, I begin ramping up to 30 degrees which I reach by peak hp. [/hijack]

ArcticZ28

iTrader: (14)

My quench is .032 as well, but I don't see me getting that much timing from this thing and it's not as hot here as it is in Texas I'm sure.

The cam is not a tooth off, it was installed 4 degrees advanced b/c I was running the stock 317's before and wanted the powerband lower for the heads to utilize it. I'm retarding the cam back to straight up now to see how that helps. Other than that, I have no clues on what's going on.

Zick

iTrader: (18)

My quench is also .032", using Cometic .040" gaskets. Anything over 26* and I ping like a bitch.

ArcticZ28, have you tried running 100+ octane to see if maybe its false KR?

ArcticZ28

iTrader: (14)

Thought of that and may have to do it, but if it is false KR I'm certainly not gonna fill up with race gas or put octane booster in every damn time I fill up. This thing is a daily driver, so I'm hoping it's not something I have to do.

xaon

iTrader: (12)

If it is false knock, then you work from there to figure out what is causing the false knock and/or desensitize knock sensors to make it go away.

I'd run it close to empty, throw 3-4 gallons of unleaded race gas in it and see if you still get the knock retard.

GrannySShifting

iTrader: (10)

big bore warmer running motor like Iron block i dont push as hard compression wise

Dont know what gas Patrick runs but its better than most guys get!

GrannySShifting

iTrader: (10)

It doesnt "peak" at 3100 but at 3100 its making 423 ft lbs, and peak its making 431 at 4800 rpm. Very heavy torque on the low end (Mustang dyno, 6 speed, LS6 intake, cat y pipe)

JakeFusion

iTrader: (7)

Have you upgraded your cooling system? All that cylinder pressure makes heat. You can't raise the DCR without improving the cooling system.

The other thing is that Patrick is running an AFR head, which can take more compression + timing, because it has a double quench area. Stock heads only have the single quench pad, so they are not as resistent to detonation. However, at 8.1:1 DCR, you should still be okay with 93 on a stock head.

ArcticZ28

iTrader: (14)

What is there to upgrade on the cooling system? I've got a 160 stat with the fans programmed for it which should be plenty enough b/c like you said I'm not running crazy DCR. There is nothing crazy about this setup at all at 11.6:1 SCR, which befuddles me.

Patrick G

iTrader: (14)

Do you have a graph you can post or hp/tq numbers in rpm increments? That might shed some light on the subject. The shape of the curve tells a lot.

ArcticZ28

iTrader: (14)

The tq curve is supposedly flat as a pancake. I'll see if Jeff (GrannySShifting) can post it up for you all.

GrannySShifting

iTrader: (10)

Ill see if I can get it on here. Trying to get the damned clutch to bleed so I can redyno it

ArcticZ28

iTrader: (14)

Well hurry it up, son. I want my car back.

And post the dyno graph!

verbs

graph!

ArcticZ28

iTrader: (14)

Alright, I haven't seen the graph, but based on what Jeff has told me I've attached a very accurate representation of what it looks like. You can clearly see how low the torque peaks.