Interesting results on the dyno . We've played with different manifolds and systems on our race tuned mk1 Escorts and they don't normally change power levels too much . We've also tried straight through pipes without silencers but you need the pipe to be a tuned length for it too work properly .
Best way is to bolt on a long pipe and then drive the car flat out through all the gears and then switch off the engine . Where the pipe starts changing colour you chop it off at this spot and that's the correct tuned length for that level of engine tune . Hope that makes sense .
Not tried it on a Porsche but an engine's an engine .
1971 911E Hot Rod Special , Atmo cosworth mk1 Escort , 900bhp per ton Fiat 600 Abarth , R5 Gordini turbo , Mk1 Cortina , E28 BMW Alpina and few more !!!!
"We finished off the tests with a run with my original megaphones on, fantastic sound but a power loss of nearly 25hp........
so they've gone in the bin! At the end of the day back pressures a wonderful thing....."
Mike, this is an interesting finding. Could the poor performance of the megaphones be due to the way the 993 test engine is set up (i.e. for an exhaust with back pressure)? Would this be repeated if you tested your RSR engine in the same way? If yes, why did the factory use megaphones in competition? Could understand that you would get more mid range torque with a silencer box but not more ultimate power.
As i've said , open headers and pipes need to be the right length for the engines level of tune . The original porsche sports exhausts look terrible inside but work but i'm sure something better could be used with a bit of thought .
When i do mine next year then we'll see on my mates dyno-dynamics rollers . I'll do a test with the Porsche bits on and then with some re-designed manifolds and exhaust system fitted . Hopefully see a decent power increase over the Porsche bits for sure .
1971 911E Hot Rod Special , Atmo cosworth mk1 Escort , 900bhp per ton Fiat 600 Abarth , R5 Gordini turbo , Mk1 Cortina , E28 BMW Alpina and few more !!!!
Also find the 25bhp loss with the megaphones fitted a little surprising - with the 'flaps' open on the RSR 'muffler' the system is effectively 'straight through' ...
Did Neil offer any explanation ?
Andy
“Adding power makes you faster on the straights; - subtracting weight makes you faster everywhere”
The test were just to see the back to back difference between the exhausts with no adjustments, primarily to test the flaps for power loss.
You would normally adjust fuelling, ignition and cam timing to suit each setup and optomise performance but we just stayed with how it had
been done for the 993.
The main point to make is that the RSR box with flaps open though still in effect an open megaphone style system, still has a crossflow of
gases from side to side. The flaps are central in the pipes and so the box is open to allow the gases to balance, this is the most crucial bit.
We will try the mega's again when my engine finally goes on the dyno, and then test differing setups which hopefully will then show why the
factory used them for racing. I suspect it might show max hp but real loss of torque and a very small usable rev band.
cheers, Mike.
previously..
1994 968 Club Sport Riviera Blue
1994 993 C2 Carrera Riviera Blue
1972 911S to Martini RSR Prototype Spec
1973 911E to RS Lightweight Specification
1981 924 Carrera GT ex Mexborough car
3.2 Carrera Sport x2
Mike wrote:
We will try the mega's again when my engine finally goes on the dyno, and then test differing setups which hopefully will then show why the
factory used them for racing.
Weight saving probably and not extra power unless they are very long and stick out about 4 feet !!!
1971 911E Hot Rod Special , Atmo cosworth mk1 Escort , 900bhp per ton Fiat 600 Abarth , R5 Gordini turbo , Mk1 Cortina , E28 BMW Alpina and few more !!!!
mk1gaz wrote:unless they are very long and stick out about 4 feet !!!
what, a bit like this you mean..........
cheers, Mike.
previously..
1994 968 Club Sport Riviera Blue
1994 993 C2 Carrera Riviera Blue
1972 911S to Martini RSR Prototype Spec
1973 911E to RS Lightweight Specification
1981 924 Carrera GT ex Mexborough car
3.2 Carrera Sport x2
mk1gaz wrote:unless they are very long and stick out about 4 feet !!!
what, a bit like this you mean..........
Look a bit too short to be any good . Best weld another 2 foot on and then try it flat out through the gears and cut off where the metal changes colour . Might work then instead of losing 25bhp .
1971 911E Hot Rod Special , Atmo cosworth mk1 Escort , 900bhp per ton Fiat 600 Abarth , R5 Gordini turbo , Mk1 Cortina , E28 BMW Alpina and few more !!!!
mk1gaz wrote:unless they are very long and stick out about 4 feet !!!
what, a bit like this you mean..........
That engine looks rubbish, what a waste of time and effort.
It would be an embarrassment putting that in your nice silver car.
I tell you what I've got a nice 3.0SC engine that is original factory built and stamped and would be more suited, I'll bring it over and we can do a straight swap, I won't even charge you any extra.
Honestly, doing you a big favour here Mike....just GIVE ME THAT ENGINE!
----------------------------------------------------
Jason https://www.SweepingHand.co.uk
Rolex & Omega Watch Purchases & Sales
A road going engine, say a 3.2, will work well and 230 bhp ish.
Remove the exhaust system and fit the freest flowing system with 'minimal' silencing (but 108 dB). Will you see a power drop due to loss of back pressure and all the effects of the factory stock exhaust system?
How much is the cam timing (overlap) influencing the power output?
.
