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Discussion Starter #1
I'm going to change my cam. Motor is a 421ci Motown LS with 317 heads, Pac 1204X springs at 8.8:1 compression. I'm considering a set of 799 heads to raise the compression to 9.3:1. Current cam is 230/226 112+2 with .621 lift. Current cam was spec'd by a reputable engine builder, but seems like an odd spec to me. It will make 800whp without issue and cruises pretty well. This has been a street driver (15K miles in the past 2 years), but looking for a little more top end with less street miles per year, maybe 1000whp reliably (?).

What are your recommendations and thoughts of the current cam?
 

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Not a fan of reverse split duration cams but it is probably actually helping this particular setup if it's back pressure / turbine limited. The 96mm turbine will only take you so far but you may still see gains with new cam and larger A/R turbine housing, going from a T4 to a T6 or even changing the turbine to one of the 102mm/104mm options. There are several options but they are all centered around 421cuin on a S400 turbo. A bit more detailed info would help us a lot.
 

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Discussion Starter #4
The current turbo is a VS T6 S480 with billet wheel.Cam is a hydraulic roller, and limits the RPM's to 6500-6800. I'd like to keep this turbo for a bit, but do intend to upgrade it later. I should mention that I have no issues building boost with this. I can get to 8 psi easily on the 2 step by 3K, and that is too much on an unprepped surface. What other details you're looking for?

Please explain how the reverse split is helping with back pressure. The guy that spec'd this cam indicated a similar sentiment, but I don't understand how that could be. It has 4 deg of overlap at .050. Is that a number that is chased to help with with backpressure? I was considering something like a 232/236 on a 112/+6 or 110/+6 - thinking being that would add a 4-5 degrees of overlap to my current setup. But I'm guessing, hence the reason for the thread/question.

Thanks for the help. The next turbo will be less budget minded, I fully expect to be losing the journal bearing and thinking along the lines of an S484 or S485 from speaking with Jarrod at FI.
 

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You have your numbers all screwed up. You are confused or misunderstanding the difference in lobe separation and intake centerline. You want 114* - 117* LSA in most applications. When you see a value like 115 + 4 means the intake centerline is 115* with 4* advance ground into the cam due to most turbo applications running +4* advanced to help with torque to get up on the converter as well as helping spool up. The 115 + 4 installed with timing gear on straight up symbol would actually already be advanced 4*. This can also help with timing sets that have limited adjustment range so you are already 4* without wasting any adjustment. Depending on lobe family I would probably be a bit larger on the cam especially with that much displacement. Either 235*/241* or 237*/245* considering displacement and weak exhaust port especially on OEM cathedral heads. Hope this helps.
 

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Discussion Starter #6
Thanks for the reply. I don't read cam cards often enough to be able to interpret them quickly. I don't think I'm confused or confused LSA, ICL, advance or overlap, but what I think is often incorrect lol. If I have, then PLEASE set me straight. Here's the cam card.

From what I gather from looking at this card is I have an LSA of 112 degrees. My ICL is 110 and ECL is 114. My cam events result in 4 degrees of overlap at .050". I did degree this when it was installed with a 10" degree wheel and everything came out to be within 1/2 a degree of the card. I figured the 1/2 degree could be in my measurement system. I took it to be close enough and ran it.

Based on my interpretations and your description above, I think I'd be better served with more LSA and exhaust duration. Your duration recommendations look great to me, but where would you recommend the ICL/ECL to be?

If I've fubar'd with my thought process, then let me know - I like criticism ;)

Thanks greatly - Jim
 

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I don't think about or listen to people that talk about cams in absolutes. A degree here or there has very little impact on performance and it could just as easily help vs hurt. Without extensive dyno and track testing the odds of having the perfect cam are about as likely as winning the lottery. It is all about tradeoffs, nothing is free and you have to give something to get something. That's how engines are in general not just camshafts. I hope this helps.

As an example I would go:
IN: 235* @ .050"
EX: 241* @ .050"
ICL: 115* + 4*
LSA: 115*
*Note: This would put your actual ICL at 111 and ECL at 119* with the cam installed in the "straight up" position with the 4* of advance built into the cam geometry.
 

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I dont know about cams , but I know what works on my 383sbc , HR , 8.8:1 , S484 1.32/96

About 1350hp shifting at 6800

Just put the S491 with 1.32/104 on it

I think this cam has been in my engine for 7 to 8 years now


cam.jpg
 

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There can also be a pretty large effective duration difference between cams depending on the lobe family and how aggressive the intensity values are between potential lobes. I'm not and was not saying the numbers I posted would be my pick due to differences noted. I am not much of a believer on "Stage" cams. I prefer to spec all my cams as customs, explicitly for the particular engine components, chassis, intended use, driving style/experience etc. We did a lot of cam testing when I was at KUP so I know a bit about what it takes to have an optimized cam for a particular engine design. I hope to be able to do that level of testing again before the end of the year since I have the DTS engine dyno that we used at KUP. Working on building another 2400-2500sqft of shop space.
 

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There can also be a pretty large effective duration difference between cams depending on the lobe family and how aggressive the intensity values are between potential lobes. I'm not and was not saying the numbers I posted would be my pick due to differences noted. I am not much of a believer on "Stage" cams. I prefer to spec all my cams as customs, explicitly for the particular engine components, chassis, intended use, driving style/experience etc. We did a lot of cam testing when I was at KUP so I know a bit about what it takes to have an optimized cam for a particular engine design. I hope to be able to do that level of testing again before the end of the year since I have the DTS engine dyno that we used at KUP. Working on building another 2400-2500sqft of shop space.
Very nice!!
 
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