V6 manifold and exhaust design
V6 manifold and exhaust design
(OP)
Hi,
I'm in the process of transplanting a 3.0L V6 GM engine into an Opel Manta. I'm going to replace the cast headers with tubular manifolds, and build a full new exhaust system to suit. The main stumbling block is finding information specific to 6 cylinder engine manifold design. I've tried to adapt formula for 4 cylinder engines to formula for 3 and 6 cylinder engines, but I'm not that confident enough with it to actually start building the manifolds.
One idea I've been thinking about is pairing the primaries up with their opposite number so the pulses in that pair are 360 crank degrees apart, it'd be a plumbing nightmare, but unusually, I've loads of space in the engine bay, and would quote enjoy building it.
I'm not an automotive designer, just an enthusiastic amataur, so I don't have access to much information resource, so if anyone can point me in the right direction, I'd be very grateful. I've got A Graham Bells 4 stroke performance tuning, which is where I got the 4 cylinder equations from.
Thanks
Matt
I'm in the process of transplanting a 3.0L V6 GM engine into an Opel Manta. I'm going to replace the cast headers with tubular manifolds, and build a full new exhaust system to suit. The main stumbling block is finding information specific to 6 cylinder engine manifold design. I've tried to adapt formula for 4 cylinder engines to formula for 3 and 6 cylinder engines, but I'm not that confident enough with it to actually start building the manifolds.
One idea I've been thinking about is pairing the primaries up with their opposite number so the pulses in that pair are 360 crank degrees apart, it'd be a plumbing nightmare, but unusually, I've loads of space in the engine bay, and would quote enjoy building it.
I'm not an automotive designer, just an enthusiastic amataur, so I don't have access to much information resource, so if anyone can point me in the right direction, I'd be very grateful. I've got A Graham Bells 4 stroke performance tuning, which is where I got the 4 cylinder equations from.
Thanks
Matt





RE: V6 manifold and exhaust design
If you need to cross over primary pipes to the other side collector to achieve this, it might be prudent to try to keep the collectors merg point as close to the centre of the car as possible
If you want to keep it quiet with minimal restriction from a muffler, you should then merge the two tail pipes.
I have no idea of the appropriate primary or secondary pipe diameters and lengths
Regards
pat
RE: V6 manifold and exhaust design
6 - 2 - 1 sounds fine. I don't need to crossover (firing order is 1-2-3-4-5-6, banks are 1,3,5 and 2,4,6), so I can easily build manifolds in that configuration. I'm keen to keep the noise down to a level which'll let me run on most trackdays (98db ish).
I put together a spreadsheet with my guesstimated calculations on it, it's here http://www.valvers.com/v6/exhaustdesignv... . I built it so you enter your numbers on the first worksheet, and then play with one value per sheet.
The cylinder volume/valve area/chamber design etc is identical to a 4 cylinder GM engine (2.0L ecotec), so would it be valid to use tube sizes based on that engine?
Cheers
Matt
RE: V6 manifold and exhaust design
I guess the 4 is a 4 into 1 system. I would expect the intermediate pipes, between the two mergers, could be smallish vs the 4 (maybe 25% less cross sectional area), but the tail pipe after the second merge, would need 50% higher cross sectional area.
Regards
pat
RE: V6 manifold and exhaust design
Does anyone know if there are any published formula for 6 cylinder manifold design?
RE: V6 manifold and exhaust design
I once had (1970 something) a 3.3 litre inline 6 pushrod motor with about 250 HP for a daily driver. It had 3 Webbers with 42 mm chokes. I think the primaries were 1.75, I never measured the secondaries, but probably a bit over 2" and the tail pipe was 2.5"
Regards
pat
RE: V6 manifold and exhaust design
Cheers
Greg Locock
RE: V6 manifold and exhaust design
The firing order's great, it makes it hard to mess up when wiring the ECU in :)
Pat,
With regard to primary lengths, if I plug the numbers in for a 3 cylinder engine, it comes out with lengths of around 42". For a 6 cylinder, then it comes out as 24" (these are for maximum effect at 5500 rpm, 500cc/cyl, exhaust valve opening 65 deg after TDC (bit of a guess, that one, but probably not too far out).
The results make sense, but which one should I work to? I'm thinking that if I'm doing 6-2-1 then I should make the primaries 42" long as they'll effectively be working as a 3 cylinder engine, but then how long should the secondaries be, and how do I calculate the effect they'll have? I know some V6 exhaust designs use 2 systems and balancer tubes, so effectively the secondaries become the main system, and their length isn't too relevent. Should I just aim for a longish length (30"?), and see what happens on the dyno?
Thanks
Matt
RE: V6 manifold and exhaust design
I expect, that if the secondaries are long and the tailpipe is big, the engine will behave as two seperate 3 cylinder engines. This will be even more so if you run the secondaries into a two in one out muffler, as all pulsations and wave motions will tend to smooth out in the muffler. Is this a road car?
I must say, that I agree with Greg on the fireing order, but as I didn't know I took your word. I'm still astonished and a little doubtfull.
To test valve opening point, get a degree wheel, or if you don't want to buy one, get access to the ring gear.
Put a dial indicator on the exhaust valve or the spring retainer or rocker arm or pushrod, whatever is convenient, mark TDC on the compression stroke, then turn the engine by hand until the dial indicator starts to move. measure the # of degrees from TDC with the degree wheel, or count the teeth on the ring gear, vs the total # of teeth, then do the sums to work out the degrees per tooth.
Regards
pat
RE: V6 manifold and exhaust design
Thanks for the methodology for working out exhaust valve opening degrees, I'll figure out a way of doing that tonight, it'll be slightly different as the engine isn't 100% built up yet, but I can easily figure it out from the cam teeth, and then translate that into crank degrees.
It's going to be used for sprints and hillclimbs, and I'm wanting it to stay road legal. I don't think it'll do that many road miles, but it'd be good for sorting out any reliability issues, and for testing/mapping.
Could a 2 in 1 out muffler be effectively the 2 pipes entering a chamber, which then tapers into a conventional 'straight through' silencer? If so, that's something I could make relatively easily. Alternatively, would it be enough to merge the secondaries immediately before they enter the first silencer?
Thanks very much for your help, Pat.
Cheers
Matt
RE: V6 manifold and exhaust design
Cheers
Greg Locock
RE: V6 manifold and exhaust design
Out of curiosity, why do you think it is wrong?
RE: V6 manifold and exhaust design
Cheers
Greg Locock
RE: V6 manifold and exhaust design
The concecutively fired cylinders are separated by a minimum 70 cm (roughly) of intake tract at low rpm, this changes at 3.5k rpm.
The cranks a weird thing, the journals for the opposite cylinders are slightly offset relative to each other. I'll see if I can find a photo of it, as the explanation of it leaves a lot to be desired. The big ends are quite big relative to the 4 cylinder varient (54mm vs 49mm)
RE: V6 manifold and exhaust design
I believe you about the fireing order.
One thing I forgot, if it's a hydraulic cam, is that you need to consider how to avoid errors from the followers bleeding down as you test.
If you have the inlet manifold off, simply put the dial indicator on the edge of the follower where it does not move to adjust itself
Re mufflers
It depends on how quitet, or noisy you can accept, and I am guessing, but you could carry the 2.5" pipes right through as twins, with no merge of the 2 into 1. Then use a hotdog on each. This will be simple and effective, but noisy.
If you can blend all the pulses together, you can get a quieter result for less backpressure and weight, but it usually takes a few experiments and some dyno time to get it right.
My purely speculative idea of the two in one out muffler was more for a road car with the two in at either side and running pretty well full length internally with a series of holes and baffels allowing the gas a relativly free, but indirect route with various path lengths into a central chamber. The tail pipe would come from near the front of this central chamber. I expect this could confuse any waves travelling in the exhaustand kill of a lot of sound.
I'm sure it is not a new principal and is certainly how some oem mufflers are made, I just havn't seen many 2 in 1 out with a larger outlet
Regards
pat
RE: V6 manifold and exhaust design
3800 Series II and Series III 3.8L V-6 (L26/L36)
Firing order: 1 - 6 - 5 - 4 - 3
No, I didn't leave anything out- but methinks they did!
Jay Maechtlen
RE: V6 manifold and exhaust design
Anyway, I've not had a chance to get near the exhaust cam, lifters and head to measure the degrees when the exhaust valve opens.
I did have a thought about modeling the secondaries though. I could treat the secondaries as a 2 cylinder engine running at 3 times the rpm of the engine. I put the numbers in, and the tube sizes look about right.....
What would be more effective, tuning the primaries to where I want peak torque to be, and the secondaries to peak power, or the other way round? Am I right in assuming that the primaries would provide more of a usable effect than the secondaries?
Thanks for the help with this, Pat. I know you class what you've told me as speculative, but it makes sense, and has helped me immensely.
RE: V6 manifold and exhaust design
RE: V6 manifold and exhaust design
Cheers
Greg Locock