Need some input - changed exhaust -awful sound
07-01-2005, 03:14 PM
#16
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John V-
The hardest part about installing 4V manifolds on a 2V car is that small section of pipe that needs to be fabricated to make the passenger side pipe hook up to the existing exhaust section. I don't know where to find one, don't know how to make one either, or I'd seriously think about replacing my cast-iron's with a set of later manifolds. Any chance you can make some sort of template for the part you produced?
N!
The hardest part about installing 4V manifolds on a 2V car is that small section of pipe that needs to be fabricated to make the passenger side pipe hook up to the existing exhaust section. I don't know where to find one, don't know how to make one either, or I'd seriously think about replacing my cast-iron's with a set of later manifolds. Any chance you can make some sort of template for the part you produced?
N!
07-01-2005, 03:24 PM
#17
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While I was looking for those tips online, I ran across this device...
http://www.ultrafitexhaust.com/products_turbolator.htm
It's similar to that idea that Porken was working on.
Similar to the exup valve on Yamaha motorcycles.
A way to get more backpressure at low rpm, to get more torque, but once the exhaust really
starts to flow, the valve opens up...
I wonder it a couple of those inline bullet versions, right after the cats, might work some magic?
http://www.ultrafitexhaust.com/products_turbolator.htm
It's similar to that idea that Porken was working on.
Similar to the exup valve on Yamaha motorcycles.
A way to get more backpressure at low rpm, to get more torque, but once the exhaust really
starts to flow, the valve opens up...
I wonder it a couple of those inline bullet versions, right after the cats, might work some magic?
07-01-2005, 04:37 PM
#19
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Normy,
I don't know how I could make a template... this almost has to be done on the car or on some sort of welding jig.
Just so everyones clear as to my "opinion", I'm not convinced this mod is worth while on an otherwise stock 4.5 L engine. Sorry, I really (really) wish it were... but I just don't see it at this point. Perhaps if there is some more displacement, some intake, head or cam work first,then there may be some benefit here. As it stands and with limited data and seat time, it seems to me that the pros and cons of this mod don't justify the time, effort and cost.
I will say that tonight I'm going to go back and make sure I didn't do anything stupid like reverse the distributer advance/retard lines or knock anything loose. I already checked and rechecked cam timing becuase of the resonance and the impression that the engine was missing. That was perfect but I was just reading the post about the vacuum porting to the distributer advance/retard and right now, I feel like a retard as I'm just not following the text. I'll be searching for a vacuum diagram tonight just to be sure.
T_Max,
I live in a state where they check presence of the cat even though my car is exempt from the rolling sniffer (hence the gutted cat).
I don't know how I could make a template... this almost has to be done on the car or on some sort of welding jig.
Just so everyones clear as to my "opinion", I'm not convinced this mod is worth while on an otherwise stock 4.5 L engine. Sorry, I really (really) wish it were... but I just don't see it at this point. Perhaps if there is some more displacement, some intake, head or cam work first,then there may be some benefit here. As it stands and with limited data and seat time, it seems to me that the pros and cons of this mod don't justify the time, effort and cost.
I will say that tonight I'm going to go back and make sure I didn't do anything stupid like reverse the distributer advance/retard lines or knock anything loose. I already checked and rechecked cam timing becuase of the resonance and the impression that the engine was missing. That was perfect but I was just reading the post about the vacuum porting to the distributer advance/retard and right now, I feel like a retard as I'm just not following the text. I'll be searching for a vacuum diagram tonight just to be sure.
T_Max,
I live in a state where they check presence of the cat even though my car is exempt from the rolling sniffer (hence the gutted cat).
07-01-2005, 05:05 PM
#21
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Popping noise in an L Jet fuel system during coast is the injectors continuing to squirt on deaccel. (fuel burning in the exaust) The idle switch may be misadjusted or not working. The switch controls fuel cut during deaccel. An emissions thing (also MPG) W/O a cat installed no harm done. With a cat converter install, then the cat would overheat and break up.
07-01-2005, 05:21 PM
#22
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The thing is, we always see those restrictive manifolds on the OBs, and assume that they would be much faster with headers. But maybe that is not the case. I think his exhaust is far from restrictive. It would be interesting to take a totally stock 4.5 ob, and put it on the dyno. Then bolt on a totally non-restrictive exhaust, and see what the numbers are. Like headers, no cats, and free-flow pipes... It almost always seems like you have to do all the things, for any real results. More fuel, more air, and free flowing exhaust. If you just do one of them, you don't see much results.
But I can say that I did notice a power increase on my euro when I added headers.
But maybe that was because the CIS is better at adjusting for increased flow...
Regardless, I would say that most external mods generally don't get you tremendous boosts in power.
Unless you do them all, or do something major, like a supercharger, it seems like a lot of these mods are
not really worth the $ and effort. I'd guess that a supercharger kit is a lot better bang for the buck,
once you add up the cost of all the other mods people do, like cams, heads, intake runners, RRFPR,
headers, x-pipe, exhaust, etc... I think if you just bolted a SC to a plain old 4.5, and that was all
you did, you would have more bang for the buck...
But I can say that I did notice a power increase on my euro when I added headers.
But maybe that was because the CIS is better at adjusting for increased flow...
Regardless, I would say that most external mods generally don't get you tremendous boosts in power.
Unless you do them all, or do something major, like a supercharger, it seems like a lot of these mods are
not really worth the $ and effort. I'd guess that a supercharger kit is a lot better bang for the buck,
once you add up the cost of all the other mods people do, like cams, heads, intake runners, RRFPR,
headers, x-pipe, exhaust, etc... I think if you just bolted a SC to a plain old 4.5, and that was all
you did, you would have more bang for the buck...
07-02-2005, 01:06 AM
#23
Race Car
Originally Posted by bcdavis
http://www.jcwhitney.com/autoparts/P...001736/c-10101
http://froogle.google.com/froogle?q=...iw=1062&tab=wf
I think these are an excellent addition to any 928 exhaust system.
Even if you still have to change something with the cats, or have to add a bigger intermediate muffler,
I still think having one of these tips really helps to smooth out the raspyness, pops, etc...
Also, I had headers on mine, and did not hear any heavy tinnyness or resonance.
So I think if you are hearing something like that, it's probably from your gutted cats...
I did the same thing, trying many configurations, many mufflers, etc, until I found something that sounds good.
If you want it loud, but not that insane loud, I would really recommend dropping a flowmaster muffler where
your intermediate lives, and run a Monza tip. I thought it was the perfect blend between too quiet, and too loud...
http://froogle.google.com/froogle?q=...iw=1062&tab=wf
I think these are an excellent addition to any 928 exhaust system.
Even if you still have to change something with the cats, or have to add a bigger intermediate muffler,
I still think having one of these tips really helps to smooth out the raspyness, pops, etc...
Also, I had headers on mine, and did not hear any heavy tinnyness or resonance.
So I think if you are hearing something like that, it's probably from your gutted cats...
I did the same thing, trying many configurations, many mufflers, etc, until I found something that sounds good.
If you want it loud, but not that insane loud, I would really recommend dropping a flowmaster muffler where
your intermediate lives, and run a Monza tip. I thought it was the perfect blend between too quiet, and too loud...
07-02-2005, 02:02 AM
#24
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I toasted all of the factory exhaust, installed 2-1/2 duals all the way behind a magnaflow x-muffler. Real loud above 2500 rpm. I have set off every car alarm in Prince George this summer. Every time I drive downtown, I set off car alarms from the rumble. I quite enjoy it 
but have decided to install a couple of resonators in the interest of civility.
but have decided to install a couple of resonators in the interest of civility.
07-02-2005, 05:56 AM
#25
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my car has a 3" stainless system, custom made for a PO. It consists of a Y into 3 straight through resonators, basically. I was told the rear can was added later to make it less noisy.
http://www.svendsen-eksos.no/images/...33_PORSCHE.jpg
I experience an awfull miss-like sound in the 1200-2000 rpm range, "chugga-chugga" like an old boat or a run down seventies US v8.
I've considered deleting the front resonator, and pulling the Y back in it's place. Like the powerbroker avenger. This involves fabricating a new powerbroker-style Y.
Will this address my miss-sound issue?
What causes this low rpm miss sund thing that several of you experience? Too little back pressure?
The funny yhing is that it is almost not present when the engine is cold (running richer?) and gets really bad at fully saturated opperating temperature.
mm
http://www.svendsen-eksos.no/images/...33_PORSCHE.jpg
I experience an awfull miss-like sound in the 1200-2000 rpm range, "chugga-chugga" like an old boat or a run down seventies US v8.
I've considered deleting the front resonator, and pulling the Y back in it's place. Like the powerbroker avenger. This involves fabricating a new powerbroker-style Y.
Will this address my miss-sound issue?
What causes this low rpm miss sund thing that several of you experience? Too little back pressure?
The funny yhing is that it is almost not present when the engine is cold (running richer?) and gets really bad at fully saturated opperating temperature.
mm
Last edited by gruffalo; 07-02-2005 at 07:04 AM.
07-02-2005, 11:01 AM
#26
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Update:
Last night I double checked the distributer plumbing, all was well. I did add some timing (went to 30 BTDC @ 3000 RPM from 23). Took it for a ride and I can confirm a couple of things. My resonance exists from around 1400-2500 RPM. Its popping a little less (perhaps the injectors are sealing better after running a while (the car sat for a few weeks while I messed with this mod and all the seal work).
Lastly, I am noticing a more pronounced difference in high RPM performance. Before this mod, my engine would climb to 5400-5500 fairly quickly. After that, the rate of climb slowed and you sensed that it wasn't as willing to rev. That point has moved up, substantially. I got on it last night and I was 6600 RPM and it was still climbing. I don't like reving that high so I backed out of it but this is definitely new. I would bet this would show up on the dyno as horsepower. I'm going on vacation this week but if all goes well, I hope to dyno this thing this month.
Last night I double checked the distributer plumbing, all was well. I did add some timing (went to 30 BTDC @ 3000 RPM from 23). Took it for a ride and I can confirm a couple of things. My resonance exists from around 1400-2500 RPM. Its popping a little less (perhaps the injectors are sealing better after running a while (the car sat for a few weeks while I messed with this mod and all the seal work).
Lastly, I am noticing a more pronounced difference in high RPM performance. Before this mod, my engine would climb to 5400-5500 fairly quickly. After that, the rate of climb slowed and you sensed that it wasn't as willing to rev. That point has moved up, substantially. I got on it last night and I was 6600 RPM and it was still climbing. I don't like reving that high so I backed out of it but this is definitely new. I would bet this would show up on the dyno as horsepower. I'm going on vacation this week but if all goes well, I hope to dyno this thing this month.
07-02-2005, 02:52 PM
#27
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"Joel, do you notice anything different about the stereo? A preponderance of bass, perhaps?".
That low-mid rpm resonance is resistant to mitigatation.
This sound is heard a few days after putting in a new big-bore exhaust (sans cat'verter). At first you are full throttle all the time, 'cuz it's so cool, but when you eventually go back to normal driving, it sounds nasty.
I cut and rewelded my exhaust many times before I got the 'right' sound. As it turns out, it's about the same sound as my stock '80, but with the bass turned up a few notches.
The US '80-82 cams are designed for low exhaust and sound emission, and are oblivious to passive modification of the engine or exhaust. The L-Jet barndoor (AFM) does a good job adjusting for air flow changes, though, so most changes don't require any fuel pressure tweaks.
The only way I got higher horsepower on the dyno, however, was to raise the fuel pressure up to 43PSI using a AFPR, along with a basically straight pipe exhaust (stock exhaust manifolds). This was good for 10HP - psha. The higher fuel pressure made for rougher running at low speeds (41PSI was the max I could run and still have the O2 sensor loop operate), so it was cool for a while, but just wasn't worth it for me.
That low-mid rpm resonance is resistant to mitigatation.
This sound is heard a few days after putting in a new big-bore exhaust (sans cat'verter). At first you are full throttle all the time, 'cuz it's so cool, but when you eventually go back to normal driving, it sounds nasty.
I cut and rewelded my exhaust many times before I got the 'right' sound. As it turns out, it's about the same sound as my stock '80, but with the bass turned up a few notches.
The US '80-82 cams are designed for low exhaust and sound emission, and are oblivious to passive modification of the engine or exhaust. The L-Jet barndoor (AFM) does a good job adjusting for air flow changes, though, so most changes don't require any fuel pressure tweaks.
The only way I got higher horsepower on the dyno, however, was to raise the fuel pressure up to 43PSI using a AFPR, along with a basically straight pipe exhaust (stock exhaust manifolds). This was good for 10HP - psha. The higher fuel pressure made for rougher running at low speeds (41PSI was the max I could run and still have the O2 sensor loop operate), so it was cool for a while, but just wasn't worth it for me.
07-02-2005, 03:04 PM
#28
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I'd verify that the fuel deliivery system is callibrated correctly. Mine stopped popping when I replaced my MAF (I know you don't have a MAF). But there may have been an existing error condition that did not manifest itsellf untiil you changed the acoustics. YMMV.
07-02-2005, 03:25 PM
#29
"Performance is not something you can measure on these cars without a dyno, so get thee to a dyno."
Save the dyno money and go to a racetrack.
Dyno numbers are great and all, but they can very widely from dyno to dyno, and nothing beats actual timeslips for verifying what works and what doesn't.
As for exhaust, i have a 928 specialists test pipe(which also replaces the stock Y pipe) feeding into a 3" borla XR-1 offroad racing muffler(with a 2 1/2- 3 step up), followed by mandrel bent 3" straight pipe, no rear resonator or muffler.
It sounds like a winston cup car. People often ask me how i fit a big block chevy into a Porsche, lol. When i tell them it's the original V-8 engine i often get, "I didn't know a porsche could sound like that".
Hollowing out your cat will normally create a very tinny and raspy exhaust note. That's probably the majority of your problem.
Save the dyno money and go to a racetrack.
Dyno numbers are great and all, but they can very widely from dyno to dyno, and nothing beats actual timeslips for verifying what works and what doesn't.
As for exhaust, i have a 928 specialists test pipe(which also replaces the stock Y pipe) feeding into a 3" borla XR-1 offroad racing muffler(with a 2 1/2- 3 step up), followed by mandrel bent 3" straight pipe, no rear resonator or muffler.
It sounds like a winston cup car. People often ask me how i fit a big block chevy into a Porsche, lol. When i tell them it's the original V-8 engine i often get, "I didn't know a porsche could sound like that".
Hollowing out your cat will normally create a very tinny and raspy exhaust note. That's probably the majority of your problem.
