RamJet350 Header question

[73k5blazer]

Ok, so I"m putting together my last main parts order for my K5. I'll be getting a RamJet350 engine. I've been investigating headers for the engine. The RamJet manual states:

Headers:
A RAMJET 350 engine should be equipped with a header exhaust system for maximum performance in applications where a non-production exhaust system is legal. All of the calibration development work was done with a header exhaust system installed on our development engines. Installing production style exhaust manifold may increase backpressure and alter the performance of the system. The recommended
header configuration is 1-3/4" diameter primary pipes, 32 to 36 inches long, with 3" diameter collectors. Use 2-1/2" diameter tailpipes with a balance tube ("H" pipe) and low restriction mufflers.

The trouble is, headers for a SBC with 1-3/4" primaries seems far and few between, and the ones that are out there are very pricey are not particularly made for our trucks, so there may be clearance issues. Is it completely necessary to have the 1-3/4 primaries? I'm not an engine designer, but I wonder, what would the effects potentially be if I went with much more readily available 1-5/8" primaries?
Any recommendations? I do want a header with a good thermal coating, and I don't mind paying for it. I was leaning towards the Jet-hot coating, but some of the ceramics, so long as they hold up, might do good too.

 

[sweetk30]

basicly that is the ideal setup . and the nice way of telling you stock is crap for flow. thay are just telling you you will choke this thing with stock stuff.

i would get a good set that fits your truck and look at getting coated headers for the thermal heat stuff.

and possibly even a set of thorly tri-y headers.

 

[dyeager535]

I really think 1 5/8" would work ok, but if you can find what they recommend, I'd run them since they are the ones that built it.

I would expect the larger headers to help moreso at higher RPM's, so if you plan to spend some time wrapping the motor up, that might factor in.

 

[4X4HIGH]

A 1 3/4" header is for race car stuff and the ramjet350 isn't an engine designed for a truck. The 1 5/8" header will work.

 

[73k5blazer]

and the ramjet350 isn't an engine designed for a truck.

I humbly disagree. Check the dyno chart for it. It's got a high-flat torque curve, making in the upper 300's across the whole range. That's not far off the HT383 Crate, in fact the HT383 didn't make that until it was wound up a bit more, and the HT383 really had to be wound up to make any HP. I was thinking about the HT383, but I want EFI, and on top of the 383, would have exceeded the RamJet's price by quite a bit. The RamJet is not typically marketed for trucks, but, the specifications tell another story.

Yeah, the 1-3/4" primary headers seem much more geared toward racing. I was just wondering what I really might be losing and how it will affect the torque curve if I go with the 1-5/8" ones.

 

[dyeager535]

Interesting chart. I'd have to agree, that is pretty decent for a truck! Not often you see dyno charts start that low. Barely off of idle. But that's where it's important for those that don't mud so much.

 

[4X4HIGH]

I seen the dyno chart but if you knew what i was making you would think differently. Did i mention i build engines for a living??

 

[73k5blazer]

So, your compensating for something. OK, I get it now.

Sorry, but when your so blatant about it, I have no choice but to call you out. If you build engines for a living, then you might be able actually answer the question originally posed. What does one lose by going against the GM engineers recommendations of 1-3/4" primary's with slightly smaller ones.

 

[4X4HIGH]

So, your compensating for something. OK, I get it now.

Sorry, but when your so blatant about it, I have no choice but to call you out. If you build engines for a living, then you might be able actually answer the question originally posed. What does one lose by going against the GM engineers recommendations of 1-3/4" primary's with slightly smaller ones.

With a smart ass reply like that and you want my professional opinion now. I think it's time for you to go pound sand.

 

[73k5blazer]

Your the one coming in here, adding 0 value to the thread by saying the RamJet isn't a good engine choice, THEN continuing by following up after I politely disagree (and tell you why, and back it up with facts), with 'a my engines better than yours statement'. I think you should review your response skills first. One childish response illicit's another. I'm just sorry I got caught in it.
For that, let me be the first to apologize.


I asked a very pointed question, dyeager535 had value packed responses (as usual) with the statement about bigger primaries helping more so at higher RPM's. As always, more opinions are better. I'm wondering what effects slightly smaller primaries would have on it. So if anyone, including you 4x4high, has an opinion, I welcome it.

 

[sweetk30]

aaa you might just want to hold off on scott (4x4high) and re read his first post here. he said the 1 5/8 headers will work fine. later he was basicly stating he has a new motor build he is doing and it will be vary cool thats all.

and he is a super short to the point reply person. if you dont understand that then dont ask for his help. he is a super motor man we all like here and value his info/input all the time.

and from my years here and reading his replys you sir are the one going off. and this will be a good quick death to you here at ck5 for replys like this.

as mods would say take it to the pm box and if you cant resolve it there talk to a mod.

 

[73k5blazer]

Look, I apologized for reacting that way. I've got a history here as well, helping many a brother out with much more than posts.

Let it die. Please.

He said they would work fine, yes, I recognize that. But I'd like to know why and what I might be losing with the smaller primaries.

 

[Greg72]

OK, I'll chime in with what's probably obvious to everyone.

The larger headers will flow better on the top-end, high RPM side and will produce more power there..... they will be soggier on the lower-end and will probably give up some torque to the smaller headers at low RPM. For a heavy truck, that's probably a poor tradeoff.

I've done quite a bit of reading on header and exhaust design, and it sure seems that the articles caution more about going too "big" on the primaries... a slightly small primary is a lot less detrimental than an overly large one.

Also, there is some really interesting reading on collector extensions. It's simply an 18" long section of exhaust that bolts to the collector and then gently tapers to the exhaust diameter at the opposite end (like a gentle, reverse-megaphone). So if you had say, a 3.5" collector....it tapers to maybe 2.5" on the opposite side to avoid any abrupt changes to diameter and flow.

Some of the dyno sheets I've seen show remarkable power gains (and smoothness) with the extensions added.... I'd argue that there's far MORE power available with careful tuning of the parts from the collector-back, than you'll get from only considering the header itself.

 

[4X4HIGH]

Your the one coming in here, adding 0 value to the thread by saying the RamJet isn't a good engine choice, THEN continuing by following up after I politely disagree (and tell you why, and back it up with facts), with 'a my engines better than yours statement'. I think you should review your response skills first. One childish response illicit's another. I'm just sorry I got caught in it.
For that, let me be the first to apologize.


I asked a very pointed question, dyeager535 had value packed responses (as usual) with the statement about bigger primaries helping more so at higher RPM's. As always, more opinions are better. I'm wondering what effects slightly smaller primaries would have on it. So if anyone, including you 4x4high, has an opinion, I welcome it.

I did not say the ramjet350 wasn't a good choice, i said "it wasn't designed for a truck".

I also never said my engine's better than yours, i said "if you knew what i was making you would think differently" (torque number that is).

If you really want to know what the difference between the 1 3/4" header versus the 1 5/8" header is then i suppose i should explain that the 1 3/4" header is a race car part which is for top end horsepower and honestly is too big for just about every SBC especially the one in question. The 1 5/8" header will help to produce more LOW end TORQUE (which is what you want for a truck) at the expense of TOP end HP.

 

[toomany]

I did not say the ramjet350 wasn't a good choice, i said "it wasn't designed for a truck".

I also never said my engine's better than yours, i said "if you knew what i was making you would think differently" (torque number that is).

If you really want to know what the difference between the 1 3/4" header versus the 1 5/8" header is then i suppose i should explain that the 1 3/4" header is a race car part which is for top end horsepower and honestly is too big for just about every SBC especially the one in question. The 1 5/8" header will help to produce more LOW end TORQUE (which is what you want for a truck) at the expense of TOP end HP.

Not to dispute you, but that's kind of a broad statement. I agree 100% that 1 3/4" is to big for most SBC truck applications...untill you start talking big inch small blocks. 383ci and up could make better use of a 1 3/4" header. Once you get above 420ci a 1 3/4" is on the small side.

But as far as the OP is concerned. The Ram Jet 350 is a great engine, and 1 5/8" headers will work just fine for you.

 

[73k5blazer]

Well thanks Scott, really, I appreciate it. Also thanks to Greg, I didn't know anything about collector extensions. The header-back system was next on list to research before placing my last order. The is the type of information I was hoping to illicit. I do really like to know the cause and effect of the things, and was just really hesitant to go against GM engineers recommendations.
Perhaps this is what I like to call a Three's Company moment, that being, I mis-interpreted your response to be talkin' smack about my engine choice. My apologies.
Just so you know, there is a reason I choose the RamJet. I know I could get more HP and torque for the money. But I want EFI because, I'm horrible at engine tuning and I know it, so a nice packaged system, especially by GM where you know it was tested in all adverse conditions they can think of. I really want reliability and drivability in all conditions. That is, extreme cold weather, off-kilter trail riding, highway driving, throttle response, hot weather, humid weather. Here in Michigan, it's a big concern. The weather changes on a dime from humid to cold to hot. I cannot stand starting an engine when it's cold out or really humid only to find that the engine is running different today, or is idling lower, or running richer..or whatever, and I've found I can dial in for any particular situation, I cannot seem to dial in for all conditions, which is what the pre-packaged EFI system is buying me. That is what the myriad of vacuum lines and goofy thermal vacuum switches and goofy little air and exhaust diverter valves and all the other silly little tricks the OEM's used to use to try and make an engine work in most conditions. Those things were on pre-efi vehciles from the factory for drivablity reasons, and are near impossible to emulate on newly built or carbureted crate engines. Which is why I really want a pre-dialed in EFI system, one I know will work well.

I just didn't want to change the torque or HP curve for the worse by going against the GM engineers recommendations.

From the responses here, I think if I can find the 1-3/4" headers GM recommends, I can at least ensure the torque and HP output curve as giving by GM, which I still think is pretty darn good for a SB in a truck.

Since time is on my side, (meaning I don't need them tomorrow), I could probably order some and experiment with them to see if they fit and send them back if I didn't nick them up to bad during test fit, if not, I can order up some ones which will fit with the 1-5/8" primaries and from the sounds of it, I may actually improve my torque curve, but in all likelihood, I won't affect much if at all negatively.

 

[Greg72]

Get online and search for an article called "Exhaust Science Demystified" by David Vizard....

Probably more than you'll even want to know about exhaust design, but not an overly complex read. Really interesting stuff on calculating correct tubing size, and even calculating muffler "flow"....the topic of resonators as a way to give a well-muffled system the same exact performance as an unmuffled, open header system was a real eye-opener as well.

 

[4X4HIGH]

No problem. I haven't looked into the Ramjet EFI at all so i don't know the system but keep in mind that unless it is a self learn system you will still need to do some "tuning" once it's in a heavy rig. The weight of a vehicle will change the tune required for an engine as will gearing, and tire size. Maybe you've already researched this part but if you haven't i might suggest you do so BEFORE you buy this engine and become quickly unhappy with the fact that it was "more than you bargained for".

I fully agree with wanting the EFI for the reasons you stated, i used to be a carb guy but ever since i bought my first EFI vehicle i can't see EVER going back to a carb unless it's an old muscle car.

 

[fishinnutt]

As long as the RamJet in question has a MEFI4 computer, it will be closed loop and adjust with feedback from an O2 sensor in the header collector.

 

[73k5blazer]

All of them sold now are the MEFI4 controller. Yes, you have to put the 02 sensor in. Which is good with me, the MEFI3 controllers didn't have that and there were complaints from certain installations that it wasn't running right in certain situations. I think the O2 sensor is almost a must have for any EFI system, I think it's the most important input the controller can have.

The downside is, the system is completely closed to tuning. There is only 1 company that has figured out how to change it (actually I don't think they change it, they swap it for one of their controllers IIRC), and they want big bucks to do so. I think the people that do it have heavily modified the engine from it's sold form, thus requiring a change in the programming tune. I don't plan on swapping out major engine components. I think if your going to want to heavily modify the motor, and still want EFI, you have to go with one of the aftermarket EFI systems that comes with software for your laptop and is completely tunable. But the RamJet system generally gets really good reviews from magizines to garage installers. Hopefully, I'll have the same good fortune.

There's a few people here with the Ramjet350 motor, and they've had nothing but good things to say about it.
My truck is full fiberglass, but I had to also add a full cage to frame and heavy Kurt bumpers, so I don't think in the end I'll be saving much weight. I did fiberglass for rust reasons mostly.