How important are ported heads for a FI setup?
Apr 17, 2007 | 11:15 PM
#31
Well I think......nevermind, I don't know what the hell you guys are talking about so I'm subscribing to read more.
Questions: I thought stock heads could only handle 14psi or so before lifting was a problem. If thats the case, saying "run stock heads and turn up the boost" isn't really an option if he can only turn it up to 14psi before hes risking a blown gasket. Yes/No?
He needs after market heads (thicker deck) and some ARP studs to keep them down. Yes/No?
Questions: I thought stock heads could only handle 14psi or so before lifting was a problem. If thats the case, saying "run stock heads and turn up the boost" isn't really an option if he can only turn it up to 14psi before hes risking a blown gasket. Yes/No?
He needs after market heads (thicker deck) and some ARP studs to keep them down. Yes/No?
Apr 17, 2007 | 11:24 PM
#32
I don't know about the 14psi part. I'd imagine it has more to do with internal combustion pressures than pounds of boost. An inefficient truck with restrictions like stock exhaust might show 18psi but flow less air (and make less power) than a fully modded truck that only makes 12psi.
Apr 18, 2007 | 06:51 AM
#33
I kinda feel like it is the cam. Here is the basic same Cammotion cam that I had and I liked it. Only difference really is mine was ground on a 114lsa.
https://www.performancetrucks.net/fo...d.php?t=390021
https://www.performancetrucks.net/fo...d.php?t=390021
Apr 18, 2007 | 06:53 AM
#34
How do I change this text
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From: Behind the TIG welder
Originally Posted by 1SlowHoe
Well I think......nevermind, I don't know what the hell you guys are talking about so I'm subscribing to read more.
Questions: I thought stock heads could only handle 14psi or so before lifting was a problem. If thats the case, saying "run stock heads and turn up the boost" isn't really an option if he can only turn it up to 14psi before hes risking a blown gasket. Yes/No?
He needs after market heads (thicker deck) and some ARP studs to keep them down. Yes/No?
Questions: I thought stock heads could only handle 14psi or so before lifting was a problem. If thats the case, saying "run stock heads and turn up the boost" isn't really an option if he can only turn it up to 14psi before hes risking a blown gasket. Yes/No?
He needs after market heads (thicker deck) and some ARP studs to keep them down. Yes/No?
One thing to keep in mind is cylinder pressures,
Just because the stock heads lift somewere in the 13-16psi range on a stock engine, doesn't mean they will lift on a very low compression 408 at the same psi..
Thunder, what boost pressure are you at now?
Apr 18, 2007 | 08:45 AM
#35
Couple of things:
1) the heads won't have a negative impact on performance with FI -- just like NA, bigger heads let more air charge into the cylinders, which means more power -- it just isn't as 'mandatory' as with NA because of the FI. There may be something to the flashing idea, but it seems like the less likely option to me.
2) the cam looks like it has some serious overlap -- my 'rule of thumb' estimation for getting to zero overlap says that cam needs about a 118.5 lsa to be at 0*. I've also found that my dual pattern cam (virtually the same specs except 1* less LSA and reversed durations as the reverse split I now run) ran rougher (more KR, more stutter, tougher to tune, etc.). I know folks are now saying the pattern of the cam doesn't matter, but my experience was that reverse pattern cams wtfpwn dual patterns...
3) If you are already having the KR trouble (which, as you say, you shouldn't be at 8psi and 9.4:1) I wouldn't up the compression just yet.
Also, your DCR needs to reflect your boost as I said about, and I found a good online calc for that: http://www.rbracing-rsr.com/comprAdvHD.htm
BTW: That cam Mark posted up looks pretty good, but would be kinda small on 408 cubes. It's also cheap
1) the heads won't have a negative impact on performance with FI -- just like NA, bigger heads let more air charge into the cylinders, which means more power -- it just isn't as 'mandatory' as with NA because of the FI. There may be something to the flashing idea, but it seems like the less likely option to me.
2) the cam looks like it has some serious overlap -- my 'rule of thumb' estimation for getting to zero overlap says that cam needs about a 118.5 lsa to be at 0*. I've also found that my dual pattern cam (virtually the same specs except 1* less LSA and reversed durations as the reverse split I now run) ran rougher (more KR, more stutter, tougher to tune, etc.). I know folks are now saying the pattern of the cam doesn't matter, but my experience was that reverse pattern cams wtfpwn dual patterns...
3) If you are already having the KR trouble (which, as you say, you shouldn't be at 8psi and 9.4:1) I wouldn't up the compression just yet.
Also, your DCR needs to reflect your boost as I said about, and I found a good online calc for that: http://www.rbracing-rsr.com/comprAdvHD.htm
BTW: That cam Mark posted up looks pretty good, but would be kinda small on 408 cubes. It's also cheap
Apr 18, 2007 | 05:28 PM
#36
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Camshaft, Rod Length, Boost and Altitude Correction to Compression
Your engine summary is as follows: Bore 4.03 inches, stroke 4.00 inches, rod c-c length 6.125 inches, with a static compression ratio of 9.4 :1. Your camshaft specifications call for an inlet valve closing of 46.5 degrees ABDC (after bottom dead center).
Your chamber volume is 99.54 cc's. With this camshaft your dynamic, or effective stroke is 3.55 inches. Your dynamic compression ratio is 8.21 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 164.40 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 8 PSI is 12.68 :1.
Knowledge is power.
Your engine summary is as follows: Bore 4.03 inches, stroke 4.00 inches, rod c-c length 6.125 inches, with a static compression ratio of 9.4 :1. Your camshaft specifications call for an inlet valve closing of 46.5 degrees ABDC (after bottom dead center).
Your chamber volume is 99.54 cc's. With this camshaft your dynamic, or effective stroke is 3.55 inches. Your dynamic compression ratio is 8.21 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 164.40 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 8 PSI is 12.68 :1.
Knowledge is power.
Camshaft, Rod Length, Boost and Altitude Correction to Compression
Your engine summary is as follows: Bore 4.03 inches, stroke 4.00 inches, rod c-c length 6.125 inches, with a static compression ratio of 9.4 :1. Your camshaft specifications call for an inlet valve closing of 39.5 degrees ABDC (after bottom dead center).
Your chamber volume is 99.54 cc's. With this camshaft your dynamic, or effective stroke is 3.68 inches. Your dynamic compression ratio is 8.49 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 171.68 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 8 PSI is 13.11 :1.
Knowledge is power.
Your engine summary is as follows: Bore 4.03 inches, stroke 4.00 inches, rod c-c length 6.125 inches, with a static compression ratio of 9.4 :1. Your camshaft specifications call for an inlet valve closing of 39.5 degrees ABDC (after bottom dead center).
Your chamber volume is 99.54 cc's. With this camshaft your dynamic, or effective stroke is 3.68 inches. Your dynamic compression ratio is 8.49 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 171.68 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 8 PSI is 13.11 :1.
Knowledge is power.
Camshaft, Rod Length, Boost and Altitude Correction to Compression
Your engine summary is as follows: Bore 4.03 inches, stroke 4.00 inches, rod c-c length 6.125 inches, with a static compression ratio of 9.4 :1. Your camshaft specifications call for an inlet valve closing of 42.5 degrees ABDC (after bottom dead center).
Your chamber volume is 99.54 cc's. With this camshaft your dynamic, or effective stroke is 3.63 inches. Your dynamic compression ratio is 8.38 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 168.81 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 8 PSI is 12.94 :1.
Knowledge is power.
Your engine summary is as follows: Bore 4.03 inches, stroke 4.00 inches, rod c-c length 6.125 inches, with a static compression ratio of 9.4 :1. Your camshaft specifications call for an inlet valve closing of 42.5 degrees ABDC (after bottom dead center).
Your chamber volume is 99.54 cc's. With this camshaft your dynamic, or effective stroke is 3.63 inches. Your dynamic compression ratio is 8.38 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 168.81 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 8 PSI is 12.94 :1.
Knowledge is power.
Those are very different numbers than the DCR calculator that I have installed on my PC gives me. The difference is the numbers I put in. Do I use the seat timing or .05" timing duration numbers? The website tells me to use .05", but the software tells me to use advertised duration, which I understood to mean either seat or .006" numbers.
Apr 18, 2007 | 11:41 PM
#38
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I'm using the one that you can download from this site
http://www.empirenet.com/pkelley2/DynamicCR.html
Not sure if it's the same one.
http://www.empirenet.com/pkelley2/DynamicCR.html
Not sure if it's the same one.
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