Is it bad raising cam duration without raising compression ratio?
03-28-2006, 07:02 PM
#21
Originally Posted by s346k
if that cam is on a 108 icl, it HAS to have 4* of duration ground into it. that is where you get 112 lsa...
one reason people might keep compression down in a ground up build is to maintain the use of pump gas. not everyone wants to run cam 2 race fuel..
one reason people might keep compression down in a ground up build is to maintain the use of pump gas. not everyone wants to run cam 2 race fuel..
03-28-2006, 07:19 PM
#22
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Originally Posted by JakeFusion
No, you leave some on the table with the larger cams for sure, but they are an economical way to increase power on an otherwise untouched motor. But a lot of times, people wonder why they don't make the power they want with their cam-only setups and that's why. That's also why a 224 cam with a tight LSA makes equivalent numbers to a 234 cam with a longer LSA--the DCR is so low on the 234, it doesn't matter that lots of air is getting into the engine that it doesn't produce nearly as an effecient setup in an otherwise stock engine.
With a fully built engine, it's stupid to keep compression down near stock, because the camshafts are much larger and the discplacement is a lot bigger thereby pushing the DCR way down below an acceptable level.
With a fully built engine, it's stupid to keep compression down near stock, because the camshafts are much larger and the discplacement is a lot bigger thereby pushing the DCR way down below an acceptable level.
Thanks!
03-28-2006, 07:49 PM
#23
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Jake what is your opinion on this... I am running 12.5:1 CR on my 408. The my cam is a Comp XE-r 244/248 112 +4. Is that a good choice for my setup or would something else be better or worth while to swap it out??? My new heads are coming this week and are ETP 225's.. Thanks
03-28-2006, 08:19 PM
#24
Originally Posted by 2001 Pewter WS6
Jake what is your opinion on this... I am running 12.5:1 CR on my 408. The my cam is a Comp XE-r 244/248 112 +4. Is that a good choice for my setup or would something else be better or worth while to swap it out??? My new heads are coming this week and are ETP 225's.. Thanks
03-29-2006, 02:01 AM
#25
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Originally Posted by JakeFusion
No, you leave some on the table with the larger cams for sure, but they are an economical way to increase power on an otherwise untouched motor. But a lot of times, people wonder why they don't make the power they want with their cam-only setups and that's why. That's also why a 224 cam with a tight LSA makes equivalent numbers to a 234 cam with a longer LSA--the DCR is so low on the 234, it doesn't matter that lots of air is getting into the engine that it doesn't produce nearly as an effecient setup in an otherwise stock engine.
With a fully built engine, it's stupid to keep compression down near stock, because the camshafts are much larger and the discplacement is a lot bigger thereby pushing the DCR way down below an acceptable level.
With a fully built engine, it's stupid to keep compression down near stock, because the camshafts are much larger and the discplacement is a lot bigger thereby pushing the DCR way down below an acceptable level.
03-29-2006, 08:17 AM
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Originally Posted by JakeFusion
That's a lot of DCR, around 9.2:1. I bet it peaks around 5700-5800, also. I actually like the 244/248 XE-R, but I prefer to run a wider LSA and not much advance, because the compression helps out, so you can move the powerband up to a 6300-6400 peak and get a little more out of it without sacrificing too much in the midrange (low end doesn't matter in a stalled auto). But if you are running it now and your cooling system and current quench fight off detonation, I'd keep on running it. However, if you are not running this yet, I would definitely go with a 244/248 114+1 to make more peak power and give a smoother idle on the A4. The higher ICL will also take better advantage of the heads. Of course, if you have the cam sitting there, just retard it 3-5 degrees and let her rip.
