Exhaust ideas with an enforced diameter reduction
Discussion
One of the last things I have to do in the LS7 engine swap (from a Small Block Chevrolet 383) is to re-do the exhaust system. Unfortunately this isn't an 'ideal' exhaust solution as I've serious constraints with en enforced reduction in tube size in the system.
The cost of getting custom-made headers was crazy money, but I found a set of off-the-shelf up-and-forward headers designed for a turbo installation that will fit. So, constraint number 1 is these exit (forward, at the front of the block) in a 3" v-band fitting and expect 3" pipework.
Constraint number 2 is the silencers (side exit, one per 'bank') are 2 1/2" and the space through the chassis and bodywork is only going to allow 2 1/2" pipe. Maybe in a few years I might get round to some chassis/bodywork changes, but for the time being the silencers and the last few feet of the system are 2 1/2".
Oh, and there is no real space for a cross-over, so both left and right banks are independent through to their own silencers.
So, here's the decision to be made. I can go straight to 2 1/2" pipe from the collectors onward for the full system. This makes routing a bit simpler, and I've seen a few systems with a venturi at the collector so maybe its best to get the size reduction done early and hope for a nice fast gas flow through the system.
Or, since there's a 180 degree turn after the collectors, make the 180 degree turn in 3" to cut down resistance in the bend, then drop to 2 1/2".
Or run 3" as far as I can. only dropping to 2 1/2" just before the silencers.
Or go down in stages. I could do the bends after the collectors in 2 3/4" then drop to 2 1/2" after that?
Anyone any comments? Best to drop sizes in one go or do it progressively via 2 3/4", and do it early on in the system or late on?
The cost of getting custom-made headers was crazy money, but I found a set of off-the-shelf up-and-forward headers designed for a turbo installation that will fit. So, constraint number 1 is these exit (forward, at the front of the block) in a 3" v-band fitting and expect 3" pipework.
Constraint number 2 is the silencers (side exit, one per 'bank') are 2 1/2" and the space through the chassis and bodywork is only going to allow 2 1/2" pipe. Maybe in a few years I might get round to some chassis/bodywork changes, but for the time being the silencers and the last few feet of the system are 2 1/2".
Oh, and there is no real space for a cross-over, so both left and right banks are independent through to their own silencers.
So, here's the decision to be made. I can go straight to 2 1/2" pipe from the collectors onward for the full system. This makes routing a bit simpler, and I've seen a few systems with a venturi at the collector so maybe its best to get the size reduction done early and hope for a nice fast gas flow through the system.
Or, since there's a 180 degree turn after the collectors, make the 180 degree turn in 3" to cut down resistance in the bend, then drop to 2 1/2".
Or run 3" as far as I can. only dropping to 2 1/2" just before the silencers.
Or go down in stages. I could do the bends after the collectors in 2 3/4" then drop to 2 1/2" after that?
Anyone any comments? Best to drop sizes in one go or do it progressively via 2 3/4", and do it early on in the system or late on?
stevieturbo said:
If you think the turbo manifolds are restrictive n/a...then stick a turbocharger on them 
The turbo headers are 3" outlet, so seems fine to me. I do cubes, not turbos stevieturbo said:
As for the 2.5" per bank....This is a n/a LS7 you're talking about ? How much power do you think you're going to make that 2.5" per bank will be too small ?
Bench dyno'd at 630hp. That was on basically open pipes though, and I want to lose as few ponies as possible through the exhaust.You sure they're turbo headers ? Cant think of any sensible company making a turbo header with such a large pipe on them. Even more so for a single bank.
At only 300hp per bank...I really cant see 2.5" posing any restriction worth worrying about though. And who knows, a well designed system might actually help.
At only 300hp per bank...I really cant see 2.5" posing any restriction worth worrying about though. And who knows, a well designed system might actually help.
stevieturbo said:
You sure they're turbo headers ? Cant think of any sensible company making a turbo header with such a large pipe on them. Even more so for a single bank.
Looky see http://www.obxracingsports.com/products.php?pk=204...More importantly, look at the price. Even with duty and tax they're still waaay cheaper than getting something custom made. Quality looks very good, but obviously not fired the motor up on them yet.
They'll be cheap chinese stuff. Still not bad for the money if they do fit. Tube size etc is fine though.
I really dont see them being an issue in terms of diameters. Actual design...who knows really. Long tubes are preferred...then mid lengths, then shorties.
But there really are dozens of designs available, from OEM to aftermarket.
Hell, you could even just adapt the original TVR stuff ? Are the port spacing centres vastly different from the previous engine ?
First time around I just opted for a cheap set of Pacesetter steel long tubes, although these needed modified. Eventually I bit the bullet and had a set of stainless custom made. Can fully recommend Lance at OJZ Engineering if you do decide to go that route.
I really dont see them being an issue in terms of diameters. Actual design...who knows really. Long tubes are preferred...then mid lengths, then shorties.
But there really are dozens of designs available, from OEM to aftermarket.
Hell, you could even just adapt the original TVR stuff ? Are the port spacing centres vastly different from the previous engine ?
First time around I just opted for a cheap set of Pacesetter steel long tubes, although these needed modified. Eventually I bit the bullet and had a set of stainless custom made. Can fully recommend Lance at OJZ Engineering if you do decide to go that route.
stevieturbo said:
They'll be cheap chinese stuff. Still not bad for the money if they do fit. Tube size etc is fine though.
I really dont see them being an issue in terms of diameters. Actual design...who knows really. Long tubes are preferred...then mid lengths, then shorties.
But there really are dozens of designs available, from OEM to aftermarket.
Just to be clear, these are the headers I have - now bolted up to heads I really dont see them being an issue in terms of diameters. Actual design...who knows really. Long tubes are preferred...then mid lengths, then shorties.
But there really are dozens of designs available, from OEM to aftermarket.
They were certainly cheap (price includes both sides of the v-band connector), and probably Chinese but welds look good quality and they're nice and shiny! The question was where best to make the tube size reduction in the system.Dozens of designs? I only have space for up-and-forward, and so for off-the-shelf options there seems to be a choice of 2 - OBX (which I have) and Stainless Works, with Stainless Works being way more expensive. I spend ages looking for headers that would fit and there were just 2 options I could find.
The LS port spacing if very different to the Small Block that I've swapping out - that was my first idea - just cut the SBC headers I had off the existing flanges and re-weld on to LS flanges but they're very different.
BUT, back to the original question folks - given I have to reduce the diameter of the system from 3" to 2 1/2" per bank at some point along its length, am I better to do it immediately after the headers or as far away from the headers (so as close to the silencers) as I can go?
Big cams are more sensitive to exhaust restriction. I've got a Comp 294S solid cam in the Cobra and had a set of pipes fabricated with 3" straight through baffles and proper merge collectors to get the most from the motor. On a milder cam with less overlap, it seems exhaust restriction is much less of an issue.
GasMunkey said:
I got a set of LS9 block hugging manifolds that might interest you
Thanks for the offer, but....tvrolet said:
Just to be clear, these are the headers I have - now bolted up to heads
I ended up buying the bends after the headers at 3" then I drop down to 2 1/2" for the rest of the system. On;y one more cut/weld to do, but I ran out of time at the weekend. Hopefully get it finished one evening this week.
If you feel the modifications you've made to your exhaust system may be short of optimum, go to www.maxracesoftware.com . Order Larry Meaux's 'PipeMax' software program. The best exhaust system software on planet earth. He can transfer the package to you right over the Internet. Cost is about $50-$55 U.S. -Dave-
We run very similar headers on Craig's race sagaris , but only 1 3/4" into 2.5" straight from the header into twin 2.5" system . They are way big enough and Dyno proven not to restrict the motor ( we ran open headers which lost a few hp . Ls motor don't seem to need massive headers / systems , I tried on my own car going from short 1 3/4" to long tube 1 17/8" headers with no real gain and it seemed to harm the torque . I know they are not equal length but they don't bother the motor at all , even if they cost 4-5 bhp who cares with 600. )) just don't use the gaskets they come with they are junk use oem ones
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