Valve spring choice
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Valve spring choice I have an LQ9 with 243 heads and a Summit 8707 cam, I used their Sum-174004 Springs which have a seat pressure of 130 lbs and open pressure of 320 lbs. The cam description says it pulls strongly to 7000 rpm with as little as 150 lbs spring pressure. It doesn't seem to, it seems to drop off around 6400 and the manifold vacuum goes to 95 kPa.
I'm a little suspicious because their dual spring kits say in the description that it will pull strongly PAST 7500 rpm.
And to confirm I have a LFA, which is basically a fourth gen LQ9 with an aluminum block and 243 heads. It has a Summit 8706 cam with their SME-174003 dual springs and it pulls to 7500 rpm no problem, These two engines are built nearly identical. Same intake manifold, same air intake, same headers, same injectors, etc. The dual springs have 140 seat pressure and 380 open pressure.
Focusing on valve springs only, could the problem be the 174004 springs?
I'm a little suspicious because their dual spring kits say in the description that it will pull strongly PAST 7500 rpm.
And to confirm I have a LFA, which is basically a fourth gen LQ9 with an aluminum block and 243 heads. It has a Summit 8706 cam with their SME-174003 dual springs and it pulls to 7500 rpm no problem, These two engines are built nearly identical. Same intake manifold, same air intake, same headers, same injectors, etc. The dual springs have 140 seat pressure and 380 open pressure.
Focusing on valve springs only, could the problem be the 174004 springs?
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I think you answered your own question. The springs have 130lbs of seat pressure and the cam requires 150lbs of seat pressure. Chances are that it requires more open pressure than what the beehive is providing, too.
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Did I get this figured out?
Well as you can see here people can't comprehend a post. I said I built two engines nearly identical yet I still get questions about are they both the same. This is based on the other post where I asked the same question and it went way off topic. I deleted that one and this was a second attempt.
I called Summits tech support to ask why they say that one springs description says it will rev past 7500 rpm. Their response? What bottom end am I running because you don't want to run a stock bottom end at those rpm's.
Doesn't really answer the question about valve springs does it?
I called back and spoke to another person. Have you spoken to anyone at Summit recently?
Last edited by 4thGenCamaroZ28; Aug 2, 2024 at 01:02 PM.
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Since the OP decided to beat this dead horse some more, I think it deserves pointing out that MuhThugga gave a clear. concise answer to the original question. I have no idea why someone would need to solicit advice from internet forums and customer support to understand why a spring that is 20lbs under minimum spec is not letting the cam rev to what it is advertised.
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https://www.summitracing.com/parts/s...tcombocontents
See, read the "camshaft manufacturers description" The kit above say it pulls TO 7000 rpm
This kit https://www.summitracing.com/parts/sum-8707-1ds says it pulls PAST 7000 rpm.
Last edited by 4thGenCamaroZ28; Jul 20, 2024 at 05:57 PM.
The first link in your last post does indeed explain why you have a gripe with Summit. Surprised to see a "kit" put together with mismatched components. It also leaves out the spec about needing 150lbs of seat pressure in that description. The original links you put in the previous posts give the specs that show the mismatch, so I had no idea why you put those parts together. This makes more sense now.
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From: Franconia, PA
The first link in your last post does indeed explain why you have a gripe with Summit. Surprised to see a "kit" put together with mismatched components. It also leaves out the spec about needing 150lbs of seat pressure in that description. The original links you put in the previous posts give the specs that show the mismatch, so I had no idea why you put those parts together. This makes more sense now.
@Summitracing does the 8707 cam require 150lbs of seat pressure to rev out to 7k rpms? If one of your spring kits with the .600 lift springs with 130lbs of pressure were used, what should be the expected result?
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I've actually seen people ask @Summitracing about this on various platforms. I don't think I've seen a good answer though.
@Summitracing does the 8707 cam require 150lbs of seat pressure to rev out to 7k rpms? If one of your spring kits with the .600 lift springs with 130lbs of pressure were used, what should be the expected result?
@Summitracing does the 8707 cam require 150lbs of seat pressure to rev out to 7k rpms? If one of your spring kits with the .600 lift springs with 130lbs of pressure were used, what should be the expected result?
In early 2020 I talked several times to the guy who was the engineer for the pro LS line of cams. One of these was a conference call with a guy I think named Mike from Trick Flow. Apparently the double springs are made by Trick Flow, he said they will rev past 8500, said I'll never float valves with those. I'm only saying this because I'm not the type of person to just jump to one conclusion and go off on their tech support. And I don't feel comfortable calling this guy now because the reason I talked to him is because he emailed me and offered his number for the problem I had back then.
Yea, I know this is the internet and this will be questioned. I don't have the phone transcripts so you either believe me or don't post on here questioning me about it. @Summitracing WILL NOT either reply, or provide any useful information. I will put money on that.
Last edited by 4thGenCamaroZ28; Aug 2, 2024 at 04:30 PM.
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I just ordered the same cam kit. 8707 with the recommended springs. Wondering now if I should return the single springs and get the double? @Summitracing
At the risk of sounding like Mr. Obvious, Summit certainly needs to change the nomenclature if they've been misrepresenting this kit, and for years, as good to 7,000+ rpm. The open pressure may (or may not) be OK, but the seat pressure, per their own specs, is not. Muh Thugga gave good info, and Che70velle brought up some good points. IMHO, people tend to focus more on max lift pressure than seat pressure. Seat pressure is just as important, maybe even more so. You could probably, hypothetically, design a spring that would have 100lbs of seat pressure, but have 500lbs of open pressure. It would still suck. I understand your frustration, trust me. I have a total cluster going myself. There are some smart people on here, in this very thread, that can help you. But insulting them will get you nowhere. I wish you well. If I were you, I'd be calling someone at Summit, perhaps a department manager, and point out the discrepancy in specs you have discovered. If you do get thru to someone who can actually help, if you must vent, do it constructively. If you accuse them of being too stupid to "comprehend" you, a hangup is sure to follow. Best of luck to you, my friend.
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Hey folks,
We've reached out to our internal team that developed these cams for clarification. As soon as we have an update we'll be sure to let you know.
We've reached out to our internal team that developed these cams for clarification. As soon as we have an update we'll be sure to let you know.
I have an LQ9 with 243 heads and a Summit 8707 cam, I used their Sum-174004 Springs which have a seat pressure of 130 lbs and open pressure of 320 lbs. The cam description says it pulls strongly to 7000 rpm with as little as 150 lbs spring pressure. It doesn't seem to, it seems to drop off around 6400 and the manifold vacuum goes to 95 kPa.
I'm a little suspicious because their dual spring kits say in the description that it will pull strongly PAST 7500 rpm.
And to confirm I have a LFA, which is basically a fourth gen LQ9 with an aluminum block and 243 heads. It has a Summit 8706 cam with their SME-174003 dual springs and it pulls to 7500 rpm no problem, These two engines are built nearly identical. Same intake manifold, same air intake, same headers, same injectors, etc. The dual springs have 140 seat pressure and 380 open pressure.
Focusing on valve springs only, could the problem be the 174004 springs?
I'm a little suspicious because their dual spring kits say in the description that it will pull strongly PAST 7500 rpm.
And to confirm I have a LFA, which is basically a fourth gen LQ9 with an aluminum block and 243 heads. It has a Summit 8706 cam with their SME-174003 dual springs and it pulls to 7500 rpm no problem, These two engines are built nearly identical. Same intake manifold, same air intake, same headers, same injectors, etc. The dual springs have 140 seat pressure and 380 open pressure.
Focusing on valve springs only, could the problem be the 174004 springs?
Thread Starter
Teching In
Joined: Mar 2023
Posts: 38
Likes: 19
From: USA