Simon y
Full member
Hi Guys,
this is my first post, I'm looking for anyone who has gone through a 911 engine rebuild, built in some hot parts and actually made it work. I have gone through a string of experts and apart from spending more on the car, than I originally paid for it, I still haven't got a result.
I started with a 2.7 Ltr engine from 1975 911, ran the car for a while and loved it, but decided it was time for a rebuild, and started to look around for someone to do the work. After a chat we got started, and decided to up the output a bit with a few mods.
1. 2.7 Liter engine bored to 2.8
2. J.E. pistons to give 10.5:1 compression
3. RSR camshafts
4. Twin spark conversion
5. Lose the Zenith carbs and fit fuel injection
The first attempt used a 996 turbo inlet plenum, but with the long duration cams, it was awful. We dropped the RSR cam and fitted one from a GT2 Evo (porsche super cup)
I drove it for a while and it was low on power, so after a couple of years we had another go.
1. found that the heads were from a 2 liter engine, so I got a set from a 2.7 and put them on
2. re-installed the RSR cam.
3. Fitted high rate valve springs and titanium retainers
It was really bad again so we put the GT2 cam back in.
I drove it for a while (6 months) and then decided on yet another attempt
1. installed individual throttle bodies (Jenvey from the U.K.)
2. Installed a DC40 cam from Dougherty in the USA. immediately got 20% more power , but still a huge flat spot in exactly the same place.
I noticed that the inlet manifold was 33mm and the inlet port was 36mm so I decided to sort that out
Bored the inlet manifolds to 36mm and blended everything with a die grinder so no steps or rough surfaces.
Had it re-mapped again and still can't get power, and there's a huge mid range flat spot. It makes plenty of torque at about 3000 revs, then nothing until about 5000 revs, and both peaks are about the same.
Is there not a tried and tested formula for tweaking an engine like a 2.7L? There must be thousands of these out there, and even Porsche made the 2.7RS and then based the 2.8RSR on the 2.7 so there seems to be plenty of examples to follow.
Has anybody got any idea why I can't get more than 120 Kw at the back axle (on a chassis dynamometer) I am testing at 5800 feet altitude (Johannesburg) so allow 18% for that, and about 12% losses for the drivetrain. This means I should get around 158 Kw at the crank, if I was at sea level. The standard 2.7 could do that back in the day. With all the hot cams, fuel injection, high compression, twin spark stuff I ought to see a lot more, and that big flat spot is killing me. If anyone has "been there, got the T shirt" and has any ideas why a straightforward "old school" set of modifications like this, no turbo, no nitrous, just elementary stuff which ought to be a piece of cake, won't work, please repond.
Cheers guys,
Simon.
this is my first post, I'm looking for anyone who has gone through a 911 engine rebuild, built in some hot parts and actually made it work. I have gone through a string of experts and apart from spending more on the car, than I originally paid for it, I still haven't got a result.
I started with a 2.7 Ltr engine from 1975 911, ran the car for a while and loved it, but decided it was time for a rebuild, and started to look around for someone to do the work. After a chat we got started, and decided to up the output a bit with a few mods.
1. 2.7 Liter engine bored to 2.8
2. J.E. pistons to give 10.5:1 compression
3. RSR camshafts
4. Twin spark conversion
5. Lose the Zenith carbs and fit fuel injection
The first attempt used a 996 turbo inlet plenum, but with the long duration cams, it was awful. We dropped the RSR cam and fitted one from a GT2 Evo (porsche super cup)
I drove it for a while and it was low on power, so after a couple of years we had another go.
1. found that the heads were from a 2 liter engine, so I got a set from a 2.7 and put them on
2. re-installed the RSR cam.
3. Fitted high rate valve springs and titanium retainers
It was really bad again so we put the GT2 cam back in.
I drove it for a while (6 months) and then decided on yet another attempt
1. installed individual throttle bodies (Jenvey from the U.K.)
2. Installed a DC40 cam from Dougherty in the USA. immediately got 20% more power , but still a huge flat spot in exactly the same place.
I noticed that the inlet manifold was 33mm and the inlet port was 36mm so I decided to sort that out
Bored the inlet manifolds to 36mm and blended everything with a die grinder so no steps or rough surfaces.
Had it re-mapped again and still can't get power, and there's a huge mid range flat spot. It makes plenty of torque at about 3000 revs, then nothing until about 5000 revs, and both peaks are about the same.
Is there not a tried and tested formula for tweaking an engine like a 2.7L? There must be thousands of these out there, and even Porsche made the 2.7RS and then based the 2.8RSR on the 2.7 so there seems to be plenty of examples to follow.
Has anybody got any idea why I can't get more than 120 Kw at the back axle (on a chassis dynamometer) I am testing at 5800 feet altitude (Johannesburg) so allow 18% for that, and about 12% losses for the drivetrain. This means I should get around 158 Kw at the crank, if I was at sea level. The standard 2.7 could do that back in the day. With all the hot cams, fuel injection, high compression, twin spark stuff I ought to see a lot more, and that big flat spot is killing me. If anyone has "been there, got the T shirt" and has any ideas why a straightforward "old school" set of modifications like this, no turbo, no nitrous, just elementary stuff which ought to be a piece of cake, won't work, please repond.
Cheers guys,
Simon.