Why top mount?

[Tony the Tiger]

It's way too difficult to generalize all types of manifolds... This discussion has been beaten to death, but we are at the point that so many brand and makes are piecing together the same type of manifold. A log manifold is simply, a log.. Picture a log with 4 tubes mashed together. Runners 1-2 and 3-4 are firing against eash other. These are the ones you commonly see that are fabricated with pipe "tees". They are downright the shit of all shits. Inline Pro, HKS/GReddy, and quite a few others are not log or tubular manifolds. If you are clueless on general designs of manifolds, your best bet is to do more research on popular setups similar to your goals. Anyone with good basic knowledge on manifolds will know how to define what is a good or bad manifold despite the common "categorization". A ramhorn tubular manifold that uses a stamped box collector is going to be less efficient versus a mini-ram with a full length merge collector. Same deal with a ramhorn style manifold with full merge collector vs a top-mount long length manifold with a shitty box collector. Either type of manifold can outperform each other, which kind of makes this entire discussion pointless from the start. How do we figure out which type of 'header' works better, imagine if we were shopping for headers for an all motor setup? Don't all the NA headers have long length runners, proper cylinder pairing or whatnot? The power gains come from quality collectors, R&D on runner lengths, and all of this design is based on the power level, compression, cams, displacement, etc... Turbo manifolds are no different... When we decide on manifolds, we can't look at the manifold itself. You have to choose it by the turbo you are running, the cams you choose, and the type of performance you are expecting to get out of it. You don't choose a top-mount that has long length runners on a motor with B16A cams, and running a GT28RS. You don't choose a "log" manifold for a GT42R and running huge cams on there. You don't try to make 450WHP on pump gas on a box collector. Just like for the all motor guys, we don't put big tube all motor drag headers on a stock B16A hoping for more midrange torque. Same deal with turbo, we don't put long length top-mount turbo manifolds onto 300 WHP setups hoping for more midrange on GT42R. I know folks always used to say "build a manifold that has the straightest path, best wastegate placement, etc etc... We are way beyond that these days, because our engines are efficient, turbos are efficient, etc.. We can have turbo motors that run at high power levels with minimal back pressures and exhaust reversion. When there is minimal back pressures, the engine now behaves similar to an NA motor. It needs better breathing cams and heads, it wants longer runners, it wants a manifold that can scavenge. You see the pattern here now, and turbo manifolds isn't a one size fits all thing anymore. No single "classification" of manifolds are better than another, just rather different designs for different purposes.

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[Schister66]

^Very well written. This thread is stickied in the Forced Induction FAQ so that this question can be avoided in the future. Thanks Tony for your input

[SPCBoyles]

So, if I was trying to achieve a fairly modest goal of about 350whp on pump gas, would the manifold I would need to source change between a B16A to a B16B because of different cams and compression? Or is 10.4:1 and 10.8:1 and B16A cams and B16B cams too close to matter? Or is 350whp on pump gas too low to really make a difference between, say an SLS mini ram and a Full-Race ram horn with a GT28RS on any motor?

Also, when dealing with manifolds that are top quality, assuming their collectors and runners are well designed for your specific application, does it make a difference then between ram horn and top mount? There still hasn't really been an outright answer to this question. I understand that there are all kinds of variables and different applications, but is there ever an instance where a top mount would actually be preferred over a ram horn performance wise, assuming all variables were the same?

I appreciate all the info in this thread. I feel like I'm actually learning something (from the few people who sound like they ACTUALLY know what they're talking about).

[Schister66]

I personally think the mini ram would be the better manifold for your goals if you want a quick spooling setup that has great midrange; however, if you wanted that GT28rs to have a little more pull towards redline (and lose a little low-mid range) the ramhorn would be your pick.

Tony runs that turbo with an HKS log and it has a great all around powerband. The turbo whips up to speed in a hell of a hurry and pulls through redline without issue.

[mike@synapse motorsport]

Here is the graph of our top mount vs our ramhorn manifolds. the temperatures were very different, november vs june here in ny figure around 85 degrees and 40 degrees. both at 26psi. the top mount is the solid line, as you can see it spooled faster and made more power. i think they would have been a little closer if there wasnt a huge temp difference.

[Schister66]

wow...the torque hits a wall right before 6k

[mike@synapse motorsport]

Originally Posted by Schister66

wow...the torque hits a wall right before 6k

lol that would be the WG opening up. The setup has a bit more in it, we just ran out of fuel. car was still making good power per lb of boost.

[Schister66]

What turbo was that? It seemed like it was finally starting to come to life and you cut it off...

[mike@synapse motorsport]

Originally Posted by Schister66

What turbo was that? It seemed like it was finally starting to come to life and you cut it off...

gt35r .82 a/r

such is life, i wanted to push it farther, but not willing to risk my motor on a 100 dollar walbro 255

[SPCBoyles]

Wow...am I reading that right? 420ft/lbs at around 5800rpm with the top mount at 26psi? That's pretty impressive.

[mike@synapse motorsport]

Originally Posted by SPCBoyles

Wow...am I reading that right? 420ft/lbs at around 5800rpm with the top mount at 26psi? That's pretty impressive.

yeah 416ftlbs at roughly 5800rpms, my gt3076r made 420ftlbs at 5500rpm. as expected torque dropped of a little quicker after 7500 though so peak power was less.

we were using a front mount turbo manifold on the gt3076r though.

[gogunkergorilla]

Originally Posted by mike@synapse motorsport

Here is the graph of our top mount vs our ramhorn manifolds. the temperatures were very different, november vs june here in ny figure around 85 degrees and 40 degrees. both at 26psi. the top mount is the solid line, as you can see it spooled faster and made more power. i think they would have been a little closer if there wasnt a huge temp difference.

Interesting results. The temp difference obviously accounts for the difference in power. But what is more interesting is that the shape of the powerband is relatively the same, showing furthur proof that manifold design is not a factor here. The turbine a/r and valve overlap control are what will make the most difference in the shape of the powerband. I'd love to see an overlay of a mini-ram manifold with the same setup. Theoretically if there was not significant valve overlap, the shape would be retained and spoolup would be even faster.

[mike@synapse motorsport]

Here are the overlays of my front mount 30r vs top mount 35r. as you can see from the graph below the change in turbo and manifold didnt affect the shape of the curve either. the engine is breathing similar in all 3 manifolds/turbo combinations. i dont have a shorty for testing though.

[SPCBoyles]

It seems like at that level of power I'd go with what I'm assuming is the 30R, with much quicker spool, thus, getting power sooner and not sacrificing all that much on the top end. Once again, a very impressive dyno chart I'd say.

[Schister66]

30r vs 35r....if that's the power graph, i dont understand why people buy 35r's. I'm sure everything isn't equal in those two setups, but i love the quick spool of the 30r.

Hey Mike, have you gotten that S258 test unit yet? I'm curious to see what kind of power that thing makes in comparison to a GT30r

[mike@synapse motorsport]

Originally Posted by Schister66

30r vs 35r....if that's the power graph, i dont understand why people buy 35r's. I'm sure everything isn't equal in those two setups, but i love the quick spool of the 30r.

Hey Mike, have you gotten that S258 test unit yet? I'm curious to see what kind of power that thing makes in comparison to a GT30r

well my 30r is at or near its limits right now, the 35r definately has a bit more in it. im happy i didnt lose much top end power switching to the 30r, and gained huge midrange. I'd like to get a 5 bar see what the 30r can do on my motor, but im running out of fuel again, and im not sure if my clutch will hold at that level.

We did get the S256, weve been very busy, the test will be done shortly, we just have to finish up a few things here at the shop.

[Schister66]

Originally Posted by mike@synapse motorsport

We did get the S256, weve been very busy, the test will be done shortly, we just have to finish up a few things here at the shop.

Good to hear...and as with every other successful company in the industry, you dont always have a lot of free time to do side projects. We all understand business comes first...i just cant wait to see the results side by side.

[gogunkergorilla]

I figured there was something upstream that was causing it to lose VE but I don't eve know what the rest of your setup is. It could be something as simple as switching to a higher flowing intake, bigger throttle body or porting the head. I'd say change the cams, but Its difficult without knowing what you have. You are pushing those turbos to a range of very high manifold pressures which increases the systems sensitivity to the amount of valve overlap. What cams?

[mike@synapse motorsport]

Originally Posted by gogunkergorilla

I figured there was something upstream that was causing it to lose VE but I don't eve know what the rest of your setup is. It could be something as simple as switching to a higher flowing intake, bigger throttle body or porting the head. I'd say change the cams, but Its difficult without knowing what you have. You are pushing those turbos to a range of very high manifold pressures which increases the systems sensitivity to the amount of valve overlap. What cams?

35r setup was using GSR cams, 30r is using ITR cams, the head is ported with reshaped chambers, 1mm oversized valves, im using a victor x intake manifold and 70mm throttle body. on my 35r setup power was still increasing at 9500rpm at 26psi. the 30r is being pushed a little harder so you can see the turbo is starting to run out juice.

no matter how well a motor flows when you push a turbo towards its limits torque will drop like you see here. VE has an affect but its is unavoidable.

[gogunkergorilla]

It looks as if your head is built for a much bigger turbo that will be running at a lower PR and less manifold pressure. Hopefully the valves aren't too big as it will be easier for reversion to set in. I would put the ITR cams on the 35r setup. Of course there is nothing you can do about the 30r, your already outside the choke line.

[mike@synapse motorsport]

Originally Posted by gogunkergorilla

It looks as if your head is built for a much bigger turbo that will be running at a lower PR and less manifold pressure. Hopefully the valves aren't too big as it will be easier for reversion to set in. I would put the ITR cams on the 35r setup. Of course there is nothing you can do about the 30r, your already outside the choke line.

i really dont get how you come to any of those conclusions. care to explain a bit more?