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Old 11-02-2010, 12:40 PM   #1
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Default Airflow, Cams, and 6500RPM drop on Dyno

While reviewing several thread about camshafts another member noted that it wasn't valve size that restricted airflow but port size. So I started looking at Dyno charts and all that I saw have a power drop at around 6500 RPM.

So the question is; Is it the port size or the Cam? Maybe if we could post up some dyno sheets proving or disproving theorys.

1. Any dyno sheet that does not have the drop at 6500 with the cam and head info.

2. Any cam shaft swap that has had a dyno.

3. Any VVT or Adjustable Cam Gear dyno that has a different drop point.

4. Any ported or valve work that shows a different drop point.

Greg
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Old 11-02-2010, 12:48 PM   #2
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jtothewats dyno keeps building til he lets of at 7 or 7500 or something. cams, im, and I think some head work. He can chime in.

There are a few people here with im and cams that don't drop power after 6k. I think those 2 things are the more if not most important in not losing the top end.
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Old 11-02-2010, 12:59 PM   #3
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Yes, I have no power drop and a flat tq curve till redline, next year once I get the car tuned to 8,500 we'll really see the difference. I am going to guess it just flattens off though after 8k.

-I have a heavily ported and polished head
-Stock size aftermarket valves
-Kelford 272/272 10mm lift
-Stock cam gears
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Old 11-02-2010, 01:07 PM   #4
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Intake manifold tuning is an issue. The stock mani is designed for mid-range power. The stock cams are optimized similarly with regard to powerband. Shortening the runners and increasing the cam duration a little will increase the rev-range. Porting the head will be an additional bonus.
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Old 11-02-2010, 01:15 PM   #5
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IM Pwns j00



look at curve not numbers, this was done on a blown block.
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Old 11-02-2010, 01:16 PM   #6
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This is my last turbo set up on a stock intake manifold, I think it wasn't hold me back to much. I also had 264/264 cams on this set up (which are for sale) I think it helped out a lot.
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Old 11-02-2010, 01:17 PM   #7
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Quote:
This is my last turbo set up on a stock intake manifold, I think it wasn't hold me back to much.
your peak HP looks to be around 6K and your losing almost 50rwtq by redline. so yes it does look to be holding you back.

Here's a 1.6L with a greddy kit running a custom IM:

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Old 11-02-2010, 01:22 PM   #8
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before and after of an IM on Paul's 1.8L Absurdflow setup:



same boost: 14psi.
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Old 11-02-2010, 01:22 PM   #9
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Quote:
Originally Posted by Braineack View Post
your peak HP looks to be around 6K and your losing almost 50rwtq by redline. so yes it does look to be holding you back.
Peak power was around 6,500 but I wasn't loosing much power 10 +/- at redline, at the time. DID hold me back, not anymore.
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Old 11-02-2010, 01:23 PM   #10
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Quote:
Originally Posted by Braineack View Post
before and after of an IM on Paul's 1.8L Absurdflow setup:


same boost: 14psi.
Specs on intake manifold? Looks like it did a really good job.
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Old 11-02-2010, 01:26 PM   #11
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that was the old cast BEGi IM.
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Old 11-02-2010, 01:28 PM   #12
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Quote:
Originally Posted by jtothawhat View Post
Specs on intake manifold? Looks like it did a really good job.
Skunk2 did a good job, and then china did a good job copying it, and then someone did a good job making it fit on a BP.

All around a good job *hands out cigars*


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that was the old cast BEGi IM.
Nevermind...
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Old 11-02-2010, 01:30 PM   #13
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the skunk2 is a copy of the Intgera Type R manifold, the Blox is a copy of that...
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Old 11-02-2010, 01:31 PM   #14
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I do not think the Skunk2 is very good for FI. The gains not not really worth the cost to me, it seems looking at other charts. They're better Honda options out there for intake manifolds, but we, as Miata owners are too cheap I suppose to try them. lol
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Old 11-02-2010, 01:38 PM   #15
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that's why we buy the Blox version. see Levnubhin's last dynos.
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Old 11-02-2010, 06:13 PM   #16
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Quote:
Originally Posted by Braineack View Post
IM Pwns j00



look at curve not numbers, this was done on a blown block.
So this shows the advantage of VVT, Cams, intake?

I know that if all areas are addressed (porting, cams, intake) then the engine will make more power but which area offer the best bang for the buck? Would intake and porting offer 90% of the gains? Or just a camshaft?

for example the red line for my VVT with Hydra is electronicly limited to 7450. My factory camshafts and valvetrain was limited to 7200 but if power is dropping off at 6500 then I am not even using all the RPM my valvetrain will allow, with that being said would a intake solve it or could it be cam profile.

I hope that with enough info provided about a dyno sheet we would be able to tell that one mod may or may not be worth the expense.
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Old 11-02-2010, 06:24 PM   #17
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Quote:
Originally Posted by jtothawhat View Post
I do not think the Skunk2 is very good for FI. The gains not not really worth the cost to me, it seems looking at other charts. They're better Honda options out there for intake manifolds, but we, as Miata owners are too cheap I suppose to try them. lol
Which other manifolds are you thinking of? The Edelbrock performer would probably work well given the RPM range it is tuned for. Victor-X no one revs their miata to 9-10K.
Golden eagle? Beyond that you are looking a pretty expensive welded sheet metal manifolds like Magnus, Endyne or others and they get pretty expensive 1-3K. That's a lot of scratch for a couple more horsepower in your typical under 400hp Miata.
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Old 11-02-2010, 06:32 PM   #18
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Quote:
Originally Posted by jtothawhat View Post


This is my last turbo set up on a stock intake manifold, I think it wasn't hold me back to much. I also had 264/264 cams on this set up (which are for sale) I think it helped out a lot.
So this is just cams? No porting or oversize valves? You didn't say but the stock TB I am sure on the IM?

Also do you have one in RPM scale to compare? Without a RPM scale on yours it is hard to tell but it looks like there is still a point that the power falls away.

Compare this to the Absurdflow dyno posted by Braineack. The IM seems to add a bunch of power down low and some above the 6500 rpm line sort of smoothing the hump. Much better than before but it still has a change at 6500. What manifold was used?
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Old 11-02-2010, 06:50 PM   #19
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What got me thinking about this is this revived thread.

https://www.miataturbo.net/showthrea...t=16885&page=2

The thread is about how to increase RPM but after reading Post 22 and 23 what would be the point if power falls off after 6500. Then looking at the S2000 dyno it is flat to 8200. Yes it is a S2000 but we are not even getting our 7200 rpm Mazda sold us in a way.

Then on post 27 there is a reference to valve float..... ????
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Old 11-02-2010, 08:01 PM   #20
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Quote:
Originally Posted by DOHCPanther View Post
I know that if all areas are addressed (porting, cams, intake) then the engine will make more power but which area offer the best bang for the buck? Would intake and porting offer 90% of the gains? Or just a camshaft?
Porting and headwork produces small gains across the entire powerband, but it is hugely expensive. I'm making fairly big power numbers through a completely stock VVT head - IMO under 400whp the money is best spent elsewhere. Change the valve seals and leave the rest alone.

Cams (at least the current crop of high-duration high-lift cams) appear to produce big top-end gains, but gives up equal amounts down low. There are a couple of Kelford 272 cars producing huge numbers at low boost now, but neither of them make anything that resembles low-end power, and even the mid-range power is lackluster. At this point there's no cam set that offers a solid power bump and an extended torque curve without sacrificing a (IMO) significant amount of low-end torque.

Intake manifolds are proven to produce big top-end gains with no effect on midrange, or solid but small overall gains, depending on whose manifold you use. IMs are also extremely cheap considering the no-downsides power they produce.

Today, with currently available parts, I would do an intake manifold and nothing else. Low cost, big gains, and pretty much no downside. If you have money to burn, spend it on headwork. I wouldn't put any of the current high-duration crop of cams in a turbo car.
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