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MPFI, SuperRam and Tuning Total Runner Length Hey guys. Let me give you all a distraction from the 334 post in favor of something a little more specific. As those who were following know, the 334 stroker in my car currently puts down 314rwhp and 363rwtq with a very flat and consistent powerband. However, I feel that it both peaks low (5200rpm) and tapers off earlier than it should. The cam is going to be the main culprit behind this (Not enough intake duration) however, until I have a new cam ground, let's set that aside and focus on the other half of the problem: The intake. Currently, I am running a siamesed SLP setup with the plenum matched. The base manifold is a lighted ported, flex honed and gasket matched superram base. The runner openings where they meet the head have been enlarged a bit to match the head openings. The throttlebody is a 58mm, also from an actual superram. I wanted to make it work with the SLP setup, but wasn't too fond of the idea of cutting and welding to access more of the divider wall. Hence, enter our current situation. I recently acquired a superram plenum and runner set after years of searching for the right price. In addition to easier access to the divider wall, there is no longer that full horseshoe shape to the runner and a more direct path for the air to travel down into the intake manifold and heads. I'm on the million dollar question though and that is tuning the runner length. According to common data that exists on the net, a typical SBC head runner length is anywhere from 5.5-6" in runner length. A MPFI base manifold, such as a TPI, Accel or FIRST, has a runner length of 8". Meanwhile, the Superram runners have a runner length of 7". Again, that is according to common data floating around. However, upon measuring the base manifold and runners myself, I discovered some discrepancies. The Superram runners are NOT 7" in length, Passing a somewhat piece of stiff wire through the ID of the runners (For ease of manipulation so that the wire could better hold its shape and follow the centerline of the port ID), I did the test twice and came up with a runner length of 5" both times. I then repeated the same test on a stock TPI base manifold. I came up with 7 1/8 the first time and 7 1/4 the second test. So, for the sake of worst case scenario, let's call it 7.25. I have begun porting the superram runners and already removed 1" of divided runner length from them. So going by the above data, assuming a head runner length of 6", manifold runner length of 7.25 and runner length of 4, we arrive at a total combined runner length of 17.25". This is a good 3" LESS total runner length than my current setup and I am strongly considering removing an additional inch from the runners over what I've already done before the final flex hone and hand sand treatment. What I'm after is a power peak in the high 5000s, say around 5800rpm IF NOT 6000 and a good, flat, average powerband all the way up to 6500rpm. Not only will this shift yield better torque and power, but it will also better match my converter and give me a broader powerband over what I have now. In my engine's current form, it's only putting out about 265ish rwhp by 6000rpm and starts declining sharply after that. By comparison, a Holley stealth ram which commonly likes to shine in the 6500-7000rpm range supposedly has a total combined runner length of 12.25" (6" head and 6.25" manifold runners). Please keep in mind that is NOT the powerband I am after. If it was, I would simply buy a stealthram. Like I stated already. There are other issues with the engine that need optimizing such as the cam and there are also other details I will be focusing on such as CSA but let's focus right now only on runner length vs optimal RPM so that it will already be taken care of and optimized for when everything else is done. So guys, thoughts? https://cimg2.ibsrv.net/gimg/www.thi...a41fb21491.jpg https://cimg5.ibsrv.net/gimg/www.thi...09c205e53e.jpg https://cimg5.ibsrv.net/gimg/www.thi...b50acc6bbf.jpg https://cimg6.ibsrv.net/gimg/www.thi...2667ba9339.jpg |
Re: MPFI, SuperRam and Tuning Total Runner Length The problem with all tpi setups is not at the runner. Its the base manifold. The problem in the flat port angle from the base manifold to the head. You can cut and max out the runners but it will have little effect on raising the powerband up close to 6k rpms. the base manifold even the tpis big mouth base needs the be reworked (welded up) and ported to get a better head angle shot for the air. This is why a mini ram and stealth ram raise the powerband closer to the 6k mark. Look at the intake angle into the head. |
Re: MPFI, SuperRam and Tuning Total Runner Length As Tealman said, the major issue with the stock based TPI systems are the runner to base and base to head transitions. You can offset port the runners and base to help that a little, but nothing can be done about the base to head angle without welding and porting that area. The FIRST is not based on the factory TPI design and has much better transition angles. As far as the runner length of a TPI intake is concerned, for any given combination, there is a point of diminishing returns when shortening the runner will give up more midrange (power under the curve) than you can make up on the top end. For most combinations I've found it appears to be about the halfway point of the runner. I'm glad you're embracing the power under the curve thinking and not trying to make a SuperRam act like a StealthRam (because it can't). That said, I sure wouldn't remove any more of the runner length on that SuperRam - there's been extrude honed SuperRam 383 cars run well in the 11s without removing any of the divider. Try what you have now and if you think you need to take another inch or so you can do that a lot easier than adding back length to the divider!! |
Re: MPFI, SuperRam and Tuning Total Runner Length I think I am going to agree with both of you. Take a look at the following thread and reshaping the head entry is exactly what they did. This was also on a 406 that didn't have to worry as much about torque under the curve. https://www.thirdgen.org/forums/alternative-port-efi-intakes/484073-super-ram-modifications.html I also think that I am comfortable with exactly how I've ported the runner after much debate. Like you said, it is much easier to remove than it is to weld, reshape and add back. I think 17" combined runner length will be ideal for my setup. Still open to suggestions. |
Re: MPFI, SuperRam and Tuning Total Runner Length FWIW, here are a couple pictures of work done to the base. I thought I had more highlighting the floor at the head transition and the minor work done to the walls inside, but I guess not. https://cimg1.ibsrv.net/gimg/www.thi...e829fcce15.jpghttps://cimg1.ibsrv.net/gimg/www.thi...5d9480a36e.jpg |
Re: MPFI, SuperRam and Tuning Total Runner Length I would shorten runners if you want to move the peak up to 5600+. cam is big enough imo but base and runner diameter is small. So shortening it up will help flow. can try port the base to help flow entry direction but the runner length is still long. 4700 rpm peak calls for 23.6 or 16.5 lengths for 2nd and 3rd harmonics. 13 for 4th 5200 rpm peak is 21.2 or 14.8 for 2nd and 3rd. 4th gets shorter at 11.6 5600 rpm peak is 19.6 or 13.7 for 2nd and 3rd. 4th is 10.8 i would help it out as much as possible by goin for the shorter length. 17 would help alot i think |
Re: MPFI, SuperRam and Tuning Total Runner Length
Originally Posted by Orr89RocZ
(Post 6243378)
I would shorten runners if you want to move the peak up to 5600+. cam is big enough imo but base and runner diameter is small. So shortening it up will help flow. can try port the base to help flow entry direction but the runner length is still long. 4700 rpm peak calls for 23.6 or 16.5 lengths for 2nd and 3rd harmonics. 13 for 4th 5200 rpm peak is 21.2 or 14.8 for 2nd and 3rd. 4th gets shorter at 11.6 5600 rpm peak is 19.6 or 13.7 for 2nd and 3rd. 4th is 10.8 i would help it out as much as possible by goin for the shorter length. 17 would help alot i think 17.25" is what I have measured my total runner length at right now with what you see in the above photos. I'm not entirely comfortable with removing anymore until I get the car on the dyno again and see how it has affected the powerband and torque from the above graphs. |
Re: MPFI, SuperRam and Tuning Total Runner Length Nevermind. Amazing what answers google has. https://en.wikipedia.org/wiki/Harmonic Interesting. I'll read more on this later. |
Re: MPFI, SuperRam and Tuning Total Runner Length Harmonics. Wave tuning. 2nd is stronger you can always remove more material later. Test it out |
Re: MPFI, SuperRam and Tuning Total Runner Length
Originally Posted by Orr89RocZ
(Post 6243389)
Harmonics. Wave tuning. 2nd is stronger you can always remove more material later. Test it out I run a 4 speed auto and was literally trying to wrap my head around how what gear the car is in affects the power peak. Looked like a lost dog. Lmao. |
Re: MPFI, SuperRam and Tuning Total Runner Length |
Re: MPFI, SuperRam and Tuning Total Runner Length Following |
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