New exhaust, need to retune?

[betts]

My stroker has been tuned my Alan Gibbs with his kalmaker software, and I have just put a new better flowing exhaust on. Do I need him to re-tune it to get the best out of the new setup?

Cheers

[Not_An_Abba_Fan]

Ideally yes, but it depends on what he did with the tune to start with, whether or not he allowed for future upgrades.

[spirto]

It's all about back-pressure, if you've upgraded from 2inch to 3 inch exhaust, then the TUNE, won't be effected.

[Not_An_Abba_Fan]

It's got **** all to do with back pressure. People and their obsession with back pressure.

If the tuner has tuned it to suit a better flowing exhaust, you won't get the full benefit of the tune until you put the better exhaust on. It's got more to do with AFR's and fuel delivery than back pressure.

[greenfoam]

It wont have changed the ratios much and I'm sure he added a bit of fuel for safety and future small changes anyway, So I'd say it will be fine

[betts]

I went from a twin 2.5 going into a single 2.5, to a single 3. The car has problems with pinging anyway so I might upgrade the fuel pump while I'm at it and then get it tuned to see if it fixes the problem.

[Not_An_Abba_Fan]

So you downgraded the exhaust then? A twin 2 1/2" will out flow a single 2 1/2" unless it had really restrictive mufflers.

[QldKev]

Reading it; I think he went from a
Twin 2.5 into Single 2.5 exhaust system
to a 3 inch system
So that would be about a 40% improvement in potential flow; allowing same style of mufflers etc. Not sure why with a stroker 355ci you would even go a single 3inch. Still waay too restrictive. Even the stock LS1 exhaust is 2 x 2.25inch


QldKev

[Not_An_Abba_Fan]

I read it wrong....

A 3" will outflow the original, but I would recommend a twin 2 1/2" on a stroker.

[spirto]

Each to their own re: Backpressure. As greenfoam said, they would have added a bit to the fuel mixture to enable future mods, if it's pinging then it sounds like a timing issue, it sounds like it will need a re-curve of the ignition. One of my car runs a 3 inch and doesn't ping, the other has twin 2.5 inch and pings, if I swapped exhausts would make no difference, on mine it's the ignition curve, as I upgraded the cam, now the computer isn't following it, making it lean top end, rich bottom end. Best of luck.

[greenfoam]

I don't believe in backpressure either, mostly because any and every stock 5 litre will 60 foot faster with the exhaust pull off at the cat. It's doesn't take any real loss in low end to make for a slower 60 foot time (I even lost 60 foot simply by putting pacemakers on) so that alone disproves it for me. Also a better flowing exhaust will keep chamber temps cooler and allow more timing and or less pings and twin systems are the only way. Also extending even just your collectors back to the gearbox mount on a typical stroker can be worth over 10 rwkw and the x pipe that again (at least)

[betts]

Reading it; I think he went from a
Twin 2.5 into Single 2.5 exhaust system
to a 3 inch system



QldKev

Yes that's correct sorry I didn't word it correctly. I went with the single 3" because a twin 2.5 would have been a little bit of a hassle with only one bumper cutout, and I wasn't particularly keen to dump one behind the bumper and have one exit out of the bumper. I also didn't have the money for 2 high flow cats. It's still quite an improvement over the previous one though. It feels like it has quite a bit more poke up in the higher revs, but down low I think it's lost a bit of power. Spirto, the timing has been checked and it still didn't fix the problem, at the moment it's running 10deg base timing and winding up to around a max of 18deg at about 3600rpm, and still pinging.

[chargedvx6]

I'd just get the tuner to log the car on a dyno or while taking it for a quick squirt up the street and he'd be able to tell you if a touch up tune is required or even beneficial.

[Darren_L]

if it was me I'd give Alan a call and ask. Alan is the man who did the tune, and is the Delco/Kalmaker guru.
He's a no BS sort of person, he won't suggest bringing it back for a tweak unless he believes it would be beneficial

[betts]

Yea I think I will give him a call and ask, no harm in doing so. Can anybody tell me the best replacement in tank fuel pump to feed a 355, for a vs ute? That's next on the list to try and eliminate my problem with detonation.

[Not_An_Abba_Fan]

What fuel are you using?

[betts]

At the moment I'm using BP ultimate, it seems to be the best fuel available.

[Darren_L]

Yea I think I will give him a call and ask, no harm in doing so. Can anybody tell me the best replacement in tank fuel pump to feed a 355, for a vs ute? That's next on the list to try and eliminate my problem with detonation.

the Walbro in tank pumps are supposed to be good
usually can find them on ebay

talk to Alan about the detination as well, it shouldn't detonate if Alan has set up the tune correctly. Unless of course you are running some big compression
Sounds like Alan may need to take another look at the tune.

[betts]

Ok cheers I'll have a look on ebay. Alan was unsure about how to fix the detonation problem. He suggested that I upgrade the ignition system, so I have gone and got an MSD coil, new leads and a 6-al2 but it hasn't fixed the problem. I have spoken with my engine builder and he is confident the cam is degreed properly and that the compression is between 9.5 and 10:1. So the only other thing I can think of is not enough fuel supply. On the dyno the afr's seemed to be ok though. Where other strokers are getting around 28-30 degrees of timing around 3800rpm, mine only has 18 degrees at the most before detonation starts. It's by no means a slouch though, and is making decent power compared with other strokers with the same specs, so I'm starting to think that maybe it's not that big an issue.

[Darren_L]

hmm... never a good thing when you get detonation. At the very least it can lead to broken rings, worst case scenario a hole in a piston. Really need to figure it out.
Compression isn't over the top, mine runs around 10:1 with no probs. It used to get some pinging on my 304 before I got a proper tune, but the tuner managed to get rid of it all.

You said AFR's are good, but they don't always tell the entire story. Have you thrown a fuel pressure gauge on it on full revs ? Might be worth a look
I know the standard pump was beyond it's limit on mine - tuner noticed fuel pressure nosing over at 5000+rpm on the first attempt at a tune. I ended up fitting an external Bosch 044, 42lb injectors and took it back for another go. Fuel pressure issues were sorted

[betts]

Ok I'll look into this fuel issue a bit more then. Can I use a fuel pressure gauge while I'm driving the car, or will it need to be strapped to a dyno? I may even just be best off buying a new in tank pump anyway, they are pretty cheap and if it fixes the problem then it's a win anyway. I presume I will need a retune after putting a new pump in?
Thanks for all the help folks.

[Darren_L]

Ok I'll look into this fuel issue a bit more then. Can I use a fuel pressure gauge while I'm driving the car, or will it need to be strapped to a dyno? I may even just be best off buying a new in tank pump anyway, they are pretty cheap and if it fixes the problem then it's a win anyway. I presume I will need a retune after putting a new pump in?
Thanks for all the help folks.

I temporarily hooked a fuel pressure gauge up, ran a hose from the fuel supply line under the bonnet. I removed one of the air vent covers on the bonnet (VH) and stuck the gauge through it,under the wiper arm facing the windscreen and took it for a road test - watching fuel pressure. A bit unorthodox but it gave me the info I needed

[betts]

Ok righto, I'll get myself a pressure gauge and see what sort of reading I get. What sort of psi should I expect?

[nate-vy]

walbro pumps are pretty good ey i had one in my blown ecotec and ive got one in my blown ls1 only issue is they can tend to whine a little bit ... other than that a bosch 044 or 040 ..
cheers
if and when i do it again though i going the full fuel system

[betts]

Ah that's ok about the noise they make, I have a gilmer belt whining away anyway so I probably won't notice the fuel pump. Will I need to retune after I get the fuel pump? Because I'll probably get one next week and put it in, just want to know whether or not I can drive it afterwards.