View Full Version : DCR/SCR in relationship to motor "sluggishness"


ZexGX
01-13-2011, 01:10 PM
The '01 347 forged LS1 build I am doing is calculating out to these figures... I know that people say with a lower NA SCR (9.0ish:1), the motor becomes "unresponsive" down low and somewhat "sluggish". Is this true even if the DCR is "high"? The motor will be NA for about the first year so I am seeing if I should rethink my plan re: head choices. I was planning on going FI down the road and just switching heads to accomplish that, but unfortunately I only calculated the static compression ratios from changing the cylinder heads and did not factor in DCR. I am looking at two options right now (since I have both sets of heads)...

With 59cc heads:
10.23:1 SCR
9.435:1 DCR

With 67cc heads:
9.436:1 SCR
8.634:1 DCR

Which would you choose for NA and then FI later? Should I just go with the 67cc heads to begin with and ditch the 59cc heads? My plan was to use the 59cc heads for NA, then swap them out to the 67cc heads when I am ready to go FI. Any advice would be appreciated... My goal is 400RWHP NA, 600RWHP+ FI. Cam is similar to CheaTR v.3 but on a 115+2 LSA. Heads are both 241 casting (59cc is milled 0.045"). This will be in my DD so it will see a lot of miles on it.

$750 L98
01-13-2011, 01:28 PM
I had a cammed 6.0 with a torquer II and it was pretty sluggish. Still ran well, but it wasn't "snappy" you could certainly tell it was low on comp. I believe it was running about 8.5:1 SCR lol

ZexGX
01-15-2011, 06:56 PM
Bump...

Chente
01-16-2011, 01:21 AM
The '01 347 forged LS1 build I am doing is calculating out to these figures... I know that people say with a lower NA SCR (9.0ish:1), the motor becomes "unresponsive" down low and somewhat "sluggish". Is this true even if the DCR is "high"? The motor will be NA for about the first year so I am seeing if I should rethink my plan re: head choices. I was planning on going FI down the road and just switching heads to accomplish that, but unfortunately I only calculated the static compression ratios from changing the cylinder heads and did not factor in DCR. I am looking at two options right now (since I have both sets of heads)...

With 59cc heads:
10.23:1 SCR
9.435:1 DCR
With 67cc heads:
9.436:1 SCR
8.634:1 DCR
Which would you choose for NA and then FI later? Should I just go with the 67cc heads to begin with and ditch the 59cc heads? My plan was to use the 59cc heads for NA, then swap them out to the 67cc heads when I am ready to go FI. Any advice would be appreciated... My goal is 400RWHP NA, 600RWHP+ FI. Cam is similar to CheaTR v.3 but on a 115+2 LSA. Heads are both 241 casting (59cc is milled 0.045"). This will be in my DD so it will see a lot of miles on it.

I think your DCR is a bit high bro what are you using to get those numbers

ZexGX
01-16-2011, 07:35 PM
I think your DCR is a bit high bro what are you using to get those numbers

3 or 4 different DCR calculators. The numbers posted are the ones that matched the results from other calculators. These specifically are using the DCR calculator linked to in the sticky. I'm not asking if my DCR is the right amount. I alread know it is high. My friends cars are running fine at 10+:1 DCR on 91 octane with advanced spark timing over stock and still not detonating, so that is not something I am worried about any more. If you re-read the text above my SCR/DCR numbers you can see that I acknowledged that they were high.

Wicked94Z
01-18-2011, 09:14 PM
I think the 9.4:1 motor would be lazy as hell, especially with a camshaft like that.

Pray
01-22-2011, 12:58 PM
DCR is all that matters for the most part. That is all the motor sees and that is what determins how snappy it is. I am thinking that your DCR numbers are not calculated correctly either. How small is that cam? Most of the calculator numbers now want the ICP+15 at .005 lift. Unfortunately most cam cards are speced at .006 so the numbers get scewed. The most DCR I have ever gotten away with on 93 octane with the best designed heads around is 8.8 or so. That usually gives you a cranking compression of about 200-210 which is about the excepted limit of pump gas. Anything higher than that I have found you have to drastically reduce timing to get it to not detonate. Also, how are your buddies getting 10.0 DCR? What are the combos?

ZexGX
01-22-2011, 04:09 PM
DCR is all that matters for the most part. That is all the motor sees and that is what determins how snappy it is. I am thinking that your DCR numbers are not calculated correctly either. How small is that cam? Most of the calculator numbers now want the ICP+15 at .005 lift. Unfortunately most cam cards are speced at .006 so the numbers get scewed. The most DCR I have ever gotten away with on 93 octane with the best designed heads around is 8.8 or so. That usually gives you a cranking compression of about 200-210 which is about the excepted limit of pump gas. Anything higher than that I have found you have to drastically reduce timing to get it to not detonate. Also, how are your buddies getting 10.0 DCR? What are the combos?

Here's my motor specs:
'01 LS1 (not LS6)
3.905" bore
8.6cc dish pistons
6.125" lunati connecting rods
3.622" stroke crank (stock)
0.051" headgasket
3.910" gasket bore (?)
218/230 .605/.605 115+2 (113 ICL) 42* ABDC

Friends car with high DCR:
'00 LS1
3.898" bore
stock 0cc pistons
stock connecting rods
stock 3.622" crank
0.052" headgasket
3.910" gasket bore
228/228 .588/.588 112+2 (110 ICL)
stock 241 heads milled .042" (60cc?)

Grr
01-22-2011, 11:48 PM
for yours, assuming a 0 deck i get

10.159 SCR
8.558 DCR

Your friends with 60cc heads and 0 deck comes out to.

11.118 SCR
9.224 DCR

If hes using a stock shortblock I think they are usually .01 down in the hole or so? in which case it would be

10.844 SCR
9.001 DCR

ZexGX
01-24-2011, 03:56 PM
for yours, assuming a 0 deck i get

10.159 SCR
8.558 DCR

Your friends with 60cc heads and 0 deck comes out to.

11.118 SCR
9.224 DCR

If hes using a stock shortblock I think they are usually .01 down in the hole or so? in which case it would be

10.844 SCR
9.001 DCR

What did you use to calculate that? I figured the pistons will stick out 0.007" above the deck, since that is roughly what they are stock - not 0.010" below the deck. See quote below:
All the 6.125" rods and off the shelf 3.905" Diamond pistons I have used put the pistons above the deck pretty close to where the stock pistons are (which is ~.006-.007")
I am using said 3.905" Diamond pistons and 6.125" rods on a stock 3.622" crank - hence my calculations based off of the above info.

Pray
01-26-2011, 05:14 PM
I had a link to a great calculator that was on a website by AllanTrip I think. It is down now but if some one remembers it and knows where it went it was awesome. It had all of comps lobes in an index and a motor already set up. It used the .050 lobe duration numbers and the lift with lobe sep and advance. The easiest and most thought out one I have seen so far. I can't check your numbers since the link is down.

I also think you are right that the pistons are at least .005 out of the hole. I am pretty sure it is more. I haven't worked on a stock motor in a long time so don't quote me.

ZexGX
02-23-2011, 04:18 PM
So, I found out that if I switched to a set of 71.06cc heads, the compression ratio would be:
SCR: 9.04:1
DCR: 8.28:1

Now the DCR would be within acceptable limits, but the SCR is quite low... But, DCR is everything - so this combo would be what I want if my goal is optimal VE, low detonation probability, and a motor that performs well, right?

P.S. I am using the DCR calculator program from this site:
http://www.empirenet.com/pkelley2/DynamicCR.html

ZexGX
02-24-2011, 08:14 PM
Aw crap. I have been using the cam duration at 0.050.

No wonder. I needed to be using the cam duration at 0.006.

Now I get:
59cc:
SCR: 10.32:1
DCR: 8.07:1

66.67cc:
SCR: 9.46:1
DCR: 7.43:1

71.06cc:
SCR: 9.04:1
DCR: 7.11:1

'DOH!

http://picardfacepalm.com/picard-facepalm.jpg

KILLER-LS1
03-16-2011, 01:54 PM
Aw crap. I have been using the cam duration at 0.050.

No wonder. I needed to be using the cam duration at 0.006.

Now I get:
59cc:
SCR: 10.32:1
DCR: 8.07:1

66.67cc:
SCR: 9.46:1
DCR: 7.43:1

71.06cc:
SCR: 9.04:1
DCR: 7.11:1

'DOH!

http://picardfacepalm.com/picard-facepalm.jpg

there you go! i would look at the 66cc head. im right there with those ratios on the 66cc. if you go with the 71cc, youll have room for a lot of boost, but the lack of compression will make the car less powerful out of boost, and potentially spool the turbo slower. with the 59cc you will have more power out of boost, spool quickly, but you will not have as much capability for boost without detonation. If you wanted the fastest all around engine, id FI with the 59cc head and run race gas. if you want the highest peak HP engine, run the 71cc on pump gas with a lot of boost.

if you want best of both worlds, run the 66cc moderate boost with pump gas. you can always throw a splash of race gas or meth if you want to turn it up higher