Inliners International Forums General Discussion Engines 292ex.manifold on a 230?

hello fellow inliners. back again with a few guestions. planned on lagdons headers, but budget will not allow it. i did come across a 292 ex.manifold with a 2 1/2,3 bolt flange at a good price. so i grabbed that puppy. the guestions are, what size exshaust pipe do i use? and how far do i run it back? this is on a 68 nova 230.HEI,500 edelbrock,offy intake, exshaust in the making. the cam and all will be next after this is done. thanks.

If you are not going to build it up that much or build a bigger engine, I would go with 2.5" all the way to the back.
Or if you are going to hod rod it & build a bigger engine I would go w/3" tubing.

If you dump it to the side before the rear wheel, it will be pretty loud.

MBHD

I would stick with the 2.5" from the flange all the way out the rear using a flowmaster muffler. Good torque and plenty of flow for a street driven 230.

allright, 2.5'' all the way it is. a far as using a muffler, which flowmaster do u guys reccommend? which series? what other mufflers can i use and still have good flow and sound. thanks for the good advice. as i always get it here from u guys, i appreciate everyone that helps out.

Whichever one you like.

It does't matter much with a stock engine as Hank points out.

I would guess at least 28" long etc.

Good luck.

The flowmaster 40 series has good flow and sound, there is also the Delta Series for around $10.00 more(Flowmaster says they out-flow the originals)If you want something a little more mellow then go with the 50 series.

check it out guys. i went to my local muffler shop and got a price on the exshaust to the muffler and everything included. the price is $175 BUCKS. sounds good to me. and yes its a flowmaster 40 muffler, hehe. but, the guy at the shop said i should run 2 1/4 all the way back. i told him that this web site, inliners.org recommends i should use 2 1/2. he says i will lose low end torque with 2 1/2. what u guys think about that statement? any further advice and comments would be helpful. thanks again.

He is kinda right. But also the longger you can keep the exhaust warm-semi hot The better it will flow Sooooooo???? I have heard( if the exhaust is made smaller as it goes back The warmer the exhaust stays)
But personaly to me it sounds as if your motor is still pretty much stock. So you don't need a 2 1/2 all the way back to start with.

this is the way i like to think of it. with a small block chevy around 400 ci, you would want at least 2 1/4 exhaust with duals. that is 200 cubes per side. if the motor is hotter, then go to 2 1/2. well a 230-250 is alot of cubes out one pipe. so i would tell you 2 1/4 minimum. 292's need more. on my motor , i have 3" w/ no muffler and when it is spooled up, the dust is really pushed by the force out of the pipe. almost like a leaf blower. tom

You can always put a smaller end piece on the tail pipe for more back pressure.

If you go with 2.5" you can install a smaller end piece.

But ,, if you go w/a 2.250 or smaller, you cannot just go a little bit bigger on your entire exhaust system, you would need to start all over again. = wasted money.

Just go w/a 2.5" system & like I said ,you can always go to a reduced size piece in the back/tip.

Another thing to consider is to go w/a mandrel bent system if you want the best flow.
Some muffler shops have premade up & over the rear end mandrel bent setup for V-8's but you can just use one side if you like.

Like for you,,,,, you could use a 2.5" mandrell up & over the rear end/tailpipe piece for a SBC 68-72 Nova, in stainless or mild steel

On my Syclone, my mandrel bent 3" up & over the rear end was for a Chevelle.

Just need to watch out for muffler shops the use the standard pipe bender & crush the pipes too much in the bends & in-turn will hurt the exhaust flow.

MBHD

Your exhaust guy is right, the smaller pipe should give you more torque. But at some point it starts restricting power on the top end, you mentioned that a cam is next??? With the 4 barrel, the offy, the HEI, and a little more cam I would think you would want the whole 2 1/2". On the other hand, if you don't plan on spinning it any faster than stock you may want the 2 1/4".

Stock pipe is 2".

One more half inch is not that much bigger,, especially if your muffler shop uses the standard tubing bender that crushes the pipes in the bends.

For example, your are using 2.5" tubing, the muffler shop guy bends it for the up & over the rear end,,,(or other joggles) if he does not do a good job, the inside pipe diameter could end up 2.25 inches or smaller.
Well ,,,with that,,, it is really only flowing like a 2.25 inch tubing.

Now going to two,,, 2.5 pipes that would be a big difference.
Dual exhaust, w/headers

Another point,,,,, the exhaust manifold will give you plenty of back pressure (does not flow well)
So I would not worry about running a 2.5 inch exhaust system.

I agree with Hank, also I was looking in Leo's book, he say's if you "must" use a stock manifold, then use a HD-TD manifold on your STD-LD for street. He also mentions that not only does your manifold have provisions to run 2.5" pipe but it also has larger passages inside. I say you might as well take advantage of that extra flow, and (like earlier posts have mentioned) you can always go to smaller pipe at the exit if you need more backpressure.

Can anyone reference any article that states that exhaust backpressure is helpful to low end torque on a non-turbo engine? Primary tubing and collector sizes can be too large and hurt low end performance. However secondary exhaust pipe flow is mainly mass flow, with the lower the restriction the better. Now possibly too large an exhaust pipe may result in cooling of exhaust gases which increases resistant and backpressure, or that too low a flow rate through the exhaust pipe may actually increase flow resistance and therefore backpressure, which is not optimum. But I question that any increased exhaust backpressure from the secondary exhaust pipe is benefical. One of the main concerns (with the general public, not us) of a large exhaust pipe is the increased low frequency rumble exhaust noise.

Concerning exhaust pipe diameters and flow, the flow rate is related to the cross sectional area of the pipe, or pi x diameter x diameter. So small changes in diameter have larger changes in flow capacity. Going from a 2" to a 2 1/2" tube increases the capacity by 56%.

Diameter....Relative Flowrate Capacity
2" ...............1.0
2 1/4"..........1.26
2 1/2"..........1.56
2 3/4"..........1.89
3"................2.25

Winter, great point on diameter versus flow cap. I think heat has alot to do with scavenging and that may be how going smaller helps torque. (more exhaust velocity) In this case we have no primary tubes though. Isn't the premise of tuning a Super Trap muffler adding or subtracting back pressure??

I would think running 2.5in all the way back would even be a bit overkill. Ive always been a big fan of single exhaust. Even our 450+hp SBC's ran single 3in Exhaust w/ Flowmaster Super 40's.

I am planning on running a 292 manifold with a 2.5in to the turbo and then 3in back off the turbo.

If backpressure along helps low end torque, then a simple dyno test would prove this by adding a simple restriction to the end of a large diameter exhaust system.

The Supertrapp muffler is an appearly simple but sophisticated tuned engineered muffler system. Note that in the link below Supertrapp mentions that the disc are tapered, and that others had tried to copy their design without success. Revealing all their design principles would not be beneficial to Supertrapp.

http://www.supertrapp.com/resource/faqs.asp

I have used the Supertrapp muffler before on a SCCA sports road racing car, but due to the rules we were not allowed to tune the exhaust from the one provided.

Are they any articles with dyno tests of the Chevrolet straight sixes, like you see so many of the V-8's?

The Supertrapp design does create system back pressure.

I have seen dynos & 1/4 mile testing on V-8 cars w/gains by adding on their muffler instead of no muffler.
By adding supertrapp mufflers, they were able to fine tune thier cars. Improved low end torque ,driveability.
So I would think it will do the same for an inline engine.
I also have friends that put them on thier motorcycles, w/success.

Problem is sometimes you need to add so many disc's to get them to flow they tend to look a little funny.Plus,, the more disc's you add, the louder it gets.

The Supertrapp may be tuned to be beneficial to low end torque, but is it due to increasing backpressure? Is another tuning effect occurring ? What's the explaination of the effect at the the cylinders and valves. Among a number of factors more torque is due to more fuel burned. Are we preventing some fuel/air mixture from going out the exhaust? Is the header/collector and cam optimumly sized or are we overcoming a deficiency there? If backpressue is the tuning parameter, then we could weld a large gate valve on the end of the exhaust pipe and adjust to the best desired performance. If that works best then its fine by me.

Some motorcycles have electric motors controlling valves in there exhaust systems that let more exhaust out or less depending on RPM.
So yes , to a point a gate valve will work.Is it practical????
Now these engines are making 160 -170 HP per liter.
What other thing could be going on here when adding or subtracting there disc's?
Back pressure???? More ,less? Magic??

Don't forget, you still need some type of muffler, & that is what Supertrapps do also sound deadning.

sorry i took long to reply. l would like to thank eveyone for their thoughts and opinions. i do appreaciate all of you in your input and advice. yes, i plan on using comp cam 260h. and i believe i will run 2 1/2 all the way out. it makes more sense to me. and if i do need more back pressure, ill just add a 2 1/4 pipe after the muffler. the shop guy charges the same price for either pipe size. figures right, hehe. any further advice, comments, and opinions are more then welcome. thanks.

just remembered something. i need to purchase the 2 studs that go on top of the exhaust manifold,what size do i need, if anyone knows?

The motorcycles with the controlling valves in the exhaust such as the Honda HVIX & (HTEV™) system and Yamaha EXUP system vary collector performance (right after the headers) to minimize exhaust backpressure at different rpm's for a broader power band, 1nvolving pressure waves.

The other exhaust sytem valve by Honda (CB1300 Super Four) mounted at the end of the muffler is for sound purposes.

Pressure waves, the effects of Bernoulli's principle, Helmholtz resonantors, surge suppressors, and other gas/fluid flow characteristic are like magic sometimes.

I see I got you looking at & reading up on motorcylcle stuff now.
My GSXR 1000 (Suzuki) had a simular type of valve.

MBHD

Yep Hank, you sure did. I even purchased a paper on line from SAE (Society of Automotive Engineers) that looked promising on exhaust tuning tests for a Honda 600 cc engine. Interesting article by some engineering students, but not exactly applicable to our discussion. I have the often referred to book "Scientific Design of Intake and Exhaust Systems" written by Philips back in the early 1960's. It's fine for what it is, but I wouldn't necessarily recommend others purchasing it. I don't know of any great books on exhaust systems.

Winter,,,,

I believe if you can talk to Burns stainless tech dept. They might know some more info.
http://www.burnsstainless.com/

Gentlemen, you've got my attention!! If there is one thing I know, it is motorcycles,(been riding and racing them for 30+ years). A So-Cal company called FMF markets a "power bomb" exhaust system for 4-stroke m/cycles. Looking at it reminds you of a snake that swollowed a rat. At about 12" after the pipe begins, a larger diameter section about 4-6" long happens, then it goes back to the original pipe size all the way back to the muffler. I have no idea how this technecaly works, but FMF pipes do create some serious power. It only seems logical that a similar setup would work on an I-6 using a single pipe exhaust system. Do any of you technical/engineer types have any thoughts on this line of thinking??

The aircraft guys have also been into tuning and scavanging for years. One of my friends in the EEA told me about this link.
CAFE Foundation

I have not digested all (very little of it, actually) of the information, but they appear to have conducted lots of experiments with exhaust system designs. Since most aircraft engines run at relatively low RPM, their results may not be directly applicable.

Hoyt, II# 922

Most aircraft also run at a steady speed too.

Hot Rod exhaust are made for high RPM/rapid speed increase(s)etc

Truck/commercial systems are larger to keep the engine cool as it/they run for long periods at varying speeds/loads which create more heat.

First rule is exhaust pipe must be able to flow at least as much air out as it is taking in, then you have to allow for expansion due to heat, then any automobile exhaust is a comprise as to where you want what to happen. Then a different cam grind will respond to the same exhaust system in a different manner. Years ago they discovered that the over all length of pipe caused a different response from the engine. Then you get involved in the effect of reverberation of sound which also has an effect on flow. This is why so many different designs have been used for so many years. Those of us old enough to remember when Headman made 1 5/8 tube headers for 283 cu in chevys then everybody started making large tube headers for the larger small blocks and many guys went to the large tubes only to discover that they slowed down. All the math and all the designs in the world won't give you a fool proof answer on exhaust systems because it all depends on who, what, when, where, and how the vehicle is made and operated. We can site many examples of what will work here or there but that doesn't mean it will have a positive effect on what we are doing. As was mention earlier many engines are designed to operate in a small operating range under fairly constant conditions but our cars aren't one of them. So that leaves us with two options. Use a design that is generally accepted and be happy or spend the bucks for dyno time and several different systems to find what works best for us. Then change tire size or cams or anything else and discover that if we want the ultimate power we get to start all over again designing an exhaust system. In top fuel, nascar, indy cars where 5 hp makes a difference this is critical but in our street driven cars I don't beleive it is. My advice would be pick a system that looks and sounds the way you want and put it on your car.
Big Bill

An interesting article on mufflers and exhausts:

http://www.pontiacstreetperformance.com/psp/exhaust.html

hi all, just wondering what is the stock size diameter exhaust pipe on any 292 truck? hmmmmmmmm? thanks.

It depends which manifold it came with.

The light trucks had/came with the 250 manifold which had the smaller 2" header pipe and the heavy duty ones with the larger manifold & the 2.5" pipe.

The logic being that the heavy ones hauled more cargo/weight and needed the heat release etc.

This guy has a passenger car engine (in a car) so it doesn't matter.

Good luck.

Hello all! New here...

Noticed the thread was getting a little off topic.
I have a 66 Nova with a 250 inline engine. I too have added an HEI, mild Comp cam, have an Offenhauser 4 bbl intake, and a Holley 390cfm carb. I was planning on getting the bigger 3 bolt 292 exhaust manifold and using that on my 250.
However, I called Stovebolt co. this morning and they tell me that the 292 exhaust manifold will only work if using the stock intake manifold?? Anyone knows what kind of clearance issues there are or if the 292 manifold can be modified to work? I'm curious as to how the 68 Nova Guys project is coming along, or if he encountered any problems with his setup??

I went on a wild goose chase for one of those HD 292 manifolds. Guy told me he had a few at a yard about an hour from me. Me and dad drove up there and what he had was the 3 bolt exhaust but it still came out on an angle like the car manifold. We eventually found one on a mid 70's School Bus but the guy said "oh I dont wanna part that motor out that bus ran when we brought it in here" funny thing was that bus was sitting behind 3 rows of junk cars so I doubt its ever going anywhere. ugh oh well the hunt continues.

Try Tom's Truck Parts. The # is: (918) 542-3871

Mine angles back too. There 'fater' with a larger outlet (3 bolt) is what helps.

Good luck.

i have a extra if needed. give me a PM. tom

im back with with some results. but first thing first. i did have some clearance issues on the HD 292 ex. manifold and the intake. i did have to do some grinding on both. from the top of the ex.manifold on the left side, and the bottom of the intake on the left side. and i had to use 2 of them gaskets between the intake and exshaust. and then it finally fit flushed between them both. i used 2 gaskets just to keep me from grinding any further. but it did work just fine. if i knew i had to go thru all of this, i would have just saved my money and got them stovebolt headers instead. but here is the results,,,,. this is with 2 1/2 pipes and flowmaster 40 series all the way out back behind the driver side wheel. it sounds awesome!!!!!!!! runs great! power all the way across the board. simply love it. it pretty much helped from low to high on the power band. i can really feel it pull much much stronger. any questions or comments? just ask. ill do my best to explain. ty.

68 nova dude Quote:" runs great! power all the way across the board"
another quote:::" "it pretty much helped from low to high on the power band. i can really feel it pull much much stronger"

I figured it would work fine, not sure why people here were scared to go with the 2.5" pipe? :rolleyes:
You made a wise choice.

MBHD

68NovaDude,

Thanks for the reply. I should be getting my HD 292 manifold this week. I had heard from someone else there was a slight clearance issue between the two manifolds. If this manifold works out, it will be cheaper than the cast iron headers.
Someone told me their 3 bolt 292 manifold only had a 2 inch outlet? I guess I'll find out when mine arrives.