 
     |
| 250 WHP Supernatural 3.4 Build (Page 16/47) |
|
La fiera
|
DEC 05, 08:27 AM
|
|
| quote | Originally posted by unboundmo:
La Fiera --- talking back regarding that 2.8L.. and the cam.. how is your powerband with your config now.. 10.8:1 and lobe lift.. is the 3.4L have the same .512 lift?
|
|
The Supernatural is .533 lift int and ext Right now the engine pulls strong till the rev limiter kckls in at 6400rpm and it gets there pretty quick. I want to try it higher at the dyno so I can see where to set the limiter.
|
|
|
|
mender
|
DEC 05, 10:43 AM
|
|
| quote | Originally posted by unboundmo:
112 octane with this chart is way up there in compression.. just a little overkill?.. where does one even purchase the additive to make it that octane? ..... >---rocket fuel----->
Per the chart and your compression.. I don't see any less than 100 octane to be safe?.. no knocking.. not sure if 93 will be okay?
|
|
I built an iron head 4.3 with 9.9:1 compression and a stock cam (very mild) for my Astro that I ran on 87 octane all the time. It doesn't hurt that I'm at 3000 feet altitude but no problem down at sea level either.
It depends on the engine. With good prep and good combustion chamber design etc 11:1 is doable, whereas with a poor design (my old '54 Chev 235 for example) the max compression on 87 would be around 9:1.
It gets pretty involved when exploring the fringes and the consequences can be dire, so run a bit more octane than you think it needs until you've thoroughly tested your combo.[This message has been edited by mender (edited 12-05-2017).]
|
|
|
|
unboundmo
|
DEC 06, 02:38 AM
|
|
| quote | Originally posted by La fiera:
|
|
So quick question...---- I guess I've been the question guy lately😐.. Hey!-- bump to the top!
Anyway, what size primaries did you go with here?...... I thought I read somewhere that you were working on them at the time? Are these the new? For the other Y-section picture you posted, that was the old? I can't quite figure how that fits to this header?... long headers a ***** on the firewall side I bet?
and the 3to1 collector.. is that a 2-1/2" out?... after this section, did you route the same as stock for the rest of the pipe?...
any pictures ? ..... what muffler is that in the supernatural vid?.. might as well ask that one too... just get it out of the way --- hollowed out goodness to my ears..... I'm getting to think that mine is too mellow now.. but not like I'll atempt to make another system anytime soon.
|
|
|
|
La fiera
|
DEC 06, 09:55 PM
|
|
| quote | Originally posted by unboundmo:
So quick question...---- I guess I've been the question guy lately😐.. Hey!-- bump to the top!
Anyway, what size primaries did you go with here?...... I thought I read somewhere that you were working on them at the time? Are these the new? For the other Y-section picture you posted, that was the old? I can't quite figure how that fits to this header?... long headers a ***** on the firewall side I bet?
and the 3to1 collector.. is that a 2-1/2" out?... after this section, did you route the same as stock for the rest of the pipe?...
any pictures ? ..... what muffler is that in the supernatural vid?.. might as well ask that one too... just get it out of the way --- hollowed out goodness to my ears..... I'm getting to think that mine is too mellow now.. but not like I'll atempt to make another system anytime soon. |
|
Primaries are 1.5 inches, collectors are 2.24 inches go down to meet a 3 inch pipe, no muffler.
This shot is so you can see the Y pipe installed. Its pretty far from the distributor to avoid cooking the ICM. Also if you look at the header on the trunk side you'll see it covered by a shield, I have the same shield on the firewall and I still have plenty of space from the firewall.
It also gives me plenty of space to work around the trans cables and transmission. The clutch hydraulic cylinder is below it with plenty of clearance. I can take the cylinder very easy with the Y pipe in place
Here is the exit, a 3 inch pipe oval at the tip.
I never had any problems with it, my only complaint is that is a bit heavy because the gauge of the steel is thick.
I have the colletors that attach to the Y pipe on a bracket bolted to the transmission that way the headers don't hold the weight of the Y pipe.
The 3 inch pipe that serves as the final piece is also attached to the engine at the head, no exhaust part is held at the chassis. "If" the engine moves the entire exhaust system moves with it. The next Y pipe will be similar but it will be exiting on the drivers side made out of thin chromoly steel, so it'll be shorter and much lighter.
|
|
|
|
Daryl M
|
DEC 07, 07:23 PM
|
|
It is my understanding that changes in valve and ignition timing can allow for lower octane fuel to be used. It isn't just compression ratio that determines the octane requirements. Is this correct?
|
|
|
|
La fiera
|
DEC 07, 09:16 PM
|
|
| quote | Originally posted by Daryl M:
It is my understanding that changes in valve and ignition timing can allow for lower octane fuel to be used. It isn't just compression ratio that determines the octane requirements. Is this correct? |
|
You are right. With a motor that has a lot of compression you can install a large camshaft and it will bleed off a bunch of compression and at the same time you can retard the timing to run lower octane with a high compression motor. I use those compression vs octane charts just for reference.
|
|
|
|
Blacktree
|
DEC 07, 11:50 PM
|
|
| quote | Originally posted by Daryl M:
It is my understanding that changes in valve and ignition timing can allow for lower octane fuel to be used. It isn't just compression ratio that determines the octane requirements. Is this correct? |
|
Correct. To be more specific, the engine runs on dynamic compression. Dynamic compression is basically the static compression modified by the valve timing. So for example, a camshaft with lots of duration will reduce the dynamic compression significantly. This is why it's recommended to increase the static compression with a high-performance camshaft. Because you don't want the dynamic compression to get too low.
As a general rule, more dynamic compression requires a higher octane rating. And vice versa. Although cylinder head design can affect this, as well. For example, aluminum cylinder heads tend to run cooler than iron heads. So you can use a little more compression, or a lower octane rating, or a combination of the two.
[edit to replace the word "overlap" with "duration"][This message has been edited by Blacktree (edited 12-11-2017).]
|
|
|
|
Will
|
DEC 11, 04:20 PM
|
|
|
Well... it's actually a late intake valve closing event that modifies dynamic compression. That has nothing to do with overlap.
|
|
|
|
Blacktree
|
DEC 11, 08:42 PM
|
|
|
Either you misunderstood what I said, or you're trolling... not sure which.
|
|
|
|
pmbrunelle
|
DEC 11, 09:33 PM
|
|
| quote | Originally posted by Blacktree:
Either you misunderstood what I said, or you're trolling... not sure which. |
|
More like you misunderstood dynamic compression.
See the Atkinson cycle.
|
|
|
