FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: Grbmaverickmo on February 28, 2014, 04:33:55 PM
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Could somebody help me out with the part number of the blue thunder intake with a single carb to use with my c8 390 heads? Also will this intake fit my 63 406 heads when I finish the 406 and wanna swap it in place of my 390. Thanks guys
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I don t think blue thunder makes more than the one single 4 v intake , and it s standard c j intake runner s size so you use c j intake gaskets and probably do some port matching ., Bud
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BT makes both a low riser/CJ version and a medium riser version. Same intake, just has ports machined differently.
If you are planning on switching to 63 heads I would buy the LR/CJ version. Yes there will be a port mismatch with your C8 heads, but it will work much better when you do put the 63 heads on.
LR/CJ version : #IM-428CJ-4V
MR version: #IM-427MR-4V
On that note, what 63 heads do you have?
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Ok Thanks thats what I needed. I have the c3ae-6090c heads, actually I have the whole motor minus the intake
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They are all the same basic casting as far as ports are concerned. I normally recommend the medium riser version and port matching to the heads you desire. Lots easier to remove the metal than it is to reinstall it.
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For what its worth, I've done some pretty extensive dyno testing on a few different intakes, including the factory Cobra Jet and the Blue Thunder intake, to compare the low riser and medium riser port configurations on different cylinder heads. At least up to 500 horsepower, the port configuration doesn't matter. What this means is that you can put the Blue Thunder intake with the low riser ports on the medium riser style heads, or use the Blue Thunder intake with the medium riser ports, and you will not see any significant difference in performance. Similarly, you can use either port version of the Blue Thunder intake on a factory low riser set of heads, and you will also not see any significant difference in performance. The engine just doesn't care too much about this.
Here's an example, from data in the appendix of my book. On my 390 stroker engine, which used Edelbrock heads with the normal medium riser port configuration, dyno results with the two different versions of the Blue Thunder intake were as follows:
Blue Thunder intake with medium riser ports:
Peak torque 504.6
Peak HP 497.0
Average torque 479.5
Average HP 409.3
Blue Thunder intake with low riser (Cobra Jet) ports:
Peak torque 508.7
Peak HP 497.1
Average torque 482.0
Average HP 411.5
In this case, the manifold/head combination with the mismatch at the port made more torque and horsepower! Of course, it is also worth noting that accuracy of the dyno is probably around one percent, which means that these two sets of measurements are within the measurement error range of the dyno equipment. So, there is effectively no difference between the two intake manifolds in torque and horsepower production.
This is counter to long standing beliefs that many people have about the need to port match, but I have quite a bit more data to back up this statement. The port mismatch between low riser and medium riser version is at the floor of the port, and it just doesn't make much of a difference on these engines.
I haven't run tests like this on higher horsepower engines, but there I would expect the differences to be a little more pronounced. However, for most FE engines, there just isn't much to be gained by matching a medium riser intake to a low riser port, or vice versa.
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Very Interesting Jay
And having the data to back it up pretty much sums it up doesnt it. Not digging in that deep I would have never thought this to be the case...................Good stuff!
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The MR ports are my preference when porting, even though I can get the CJ style port to flow a little more air on the flow bench. But every time I port a set of MR style heads and get the flow into decent territory, they loose flow when I lower the entry to match a CJ style intake manifold, and if I flow the head with the intake, there is a small loss of combined flow. It is not much, maybe 3-5cfm, but that is close to 10 hp when running on the engine. I would just buy the BT MR intake, and bolt it on if you cannot port the heads and intake, or afford to. JMO, Joe-JDC.
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MY bad on the the two different intakes , my parts book shows only the one ? now i wonder ? ..Bud