Hello, looking to maybe get some ideas about performance upgrades. My car has 250k miles on it with a manual and a 2.93 open diff. Now what makes me wonder here is that I just also got a 87 325e with 150k miles and the same diff but is way more pepy on power. Is it the difference In miles that make it quicker or should I replace some engine components. All the hoses with the exemption of coolant hoses and are the original and are hard. The car also has a rougher idle then the 87. Someone before me has obviously been in the engine bay before me based off of a zip tie(seen in the picture attached) holding the spark plug plastic (that should be bolted to the top of the valve cover) just to the intake bracket, and there is a random (seen in picture attached) blue ground wire from the valve covers to where the top of the shock towers bolt in. (No idea why it’s there). I’ve done normal and needed maintenance to the car, oil and filter, front and rear shocks, front brake disks and pads, new radiator and coolant, new radiator hoses and thermostat, new v belts aswell as timing belt, cleaned idle control valve, obc screen repair, mileage gears, and other interior accessories. So back to the original question, any ideas on the performance difference? I would happily change anything that needs to be changed. Thanks.
they just added an extra ground. its not a bad idea to do that one a lot of cars.
maybe the 87 has a chip in the ecu?
both of those have 2.93 rear ends? one isn't 2.72 or whatever the other one is? that would make one feel slightly faster
its odd, they should really feel quite similar having same set up engine and drive stuff. are the tires and rims the same size?
No e30s again.
no dragging brakes or e-brake? bad bearings?
sometimes same model vehicles can be set up identical and one is just faster. no idea why but maybe during the build one was put together on Wednesday and one on Monday or Friday and the assembly mechanic was still hung over or something so the rings are at the largest gaps everything was not built as tight as the other? you never know but with the mileage being 100k different, lots of things could have happened since they were built and the miles racked up.
No e30s again.
The rough idle is an indicator that you should do a compression test
The engine may be down on power due to low compression. Run a compression check first before doing anything else, or spending any money on chips, exhaust, intake, etc.. to make sure you have a good foundation to improve.
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Idle may or may not be from low compression, but I agree.. run this test first..
Ya, the 1987 325e is actually a 2.7L with a longer stroke than the 2.5L, but only revs to ~4500rpm.
All things being the same, torque = acceleration.
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Are you checking the compression on both engines to compare ? Otherwise I would be checking for fuel delivery which would be pressure and volume. Pressure I would check with a gauge but you have to check the volume by doing a flow test some how into a container. I would do both of these tests on both vehicles for an accurate comparison
Last edited by msservices; 02-21-2019 at 09:44 PM.
Compression pressure specs from Bentley is 142 - 156 for these engines - and your 250,000 mile engine is reading better than new..
if the numbers are accurate - the 8% drop between the cylinders is within the rule of thumb of 10% - although something is causing the erratic difference..12psi difference in two cylinders is concerning (valve leakage - head gasket).. Valves not sealing can create low power.
Can you run a vacuum gauge onto the plennum?
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Is the two cylinders located next to one another?
Last edited by 95BMWIC; 02-21-2019 at 09:48 PM.
I would think you could also swap the DMEs in those cars just to see if one has a chip or if one is not advancing timing correctly
the vacuum gage is a great tool for this kind of stuff. they are not expensive and can be bought at the counter from your local auto parts place. if you google, you can see what each reading you could possibly get on a vacuum gage means. they are one of the best tools you can have for trouble shooting a vehicle.
No e30s again.
Your numbers suggest good high compression - the anomaly of having two cylinders next to each others suggest a head gasket issue - however I wouldn't worry about it unless the compression begins to drop (check it again in 6 months). A vacuum guage hooked up to the plenum could indicate whether the valves are sealing - you should get a reading around 17 (maybe a bit lower in California) (15-22 is consider normal) and a nice steady reading at idle. If it is not steady and bounces around - this suggests a few different things but probably a leaky valve or two. If you have a leaky valve or two - then I would do a head job first. Personally after doing the head on my 91 325i, I saw a dramatic difference in power. Power loss in old engines can come from wear on cylinder walls, piston rings, valves (its just natural - they don't last forever)
If your vacuum gauge is low (below 15) and steady - then it points to a low compression issue.. and I would double check your compression numbers. Make sure you crank over 4-5 times each cylinder (all spark plugs out) and have throttle wide open.
If you get a high steady reading on the vacuum gauge- I would move forward on looking for power increasing measures. I personally would start with a 4.10 LSD diff (provides a bit quicker around town driving) and next a chip (which most people say is the cheapest 10-15 hp gain..
Last edited by 95BMWIC; 02-22-2019 at 11:36 AM.
I suppose it could just be a crap load of vacuum leaks also, I dealt with that on mine until every last gasket and seal was replaced. In terms of the compression loss on the two cylinders, you could try replacing the head bolts, assuming they are the old style. If you check the torque on them I would not be surprised if they are a bit “loose” compared to what new ones would be torqued to, and that would allow the head gasket to leak without being completely blown. Granted, the head should be rebuilt by now anyway but that’s not the mission you are on atm
a 4.10 made a heal of a difference for my son's 325e. on a totally stock e, that is a great mod if you do more in town driving than highway driving. he said he saw his first 300 mile tank the tank after putting the 4.10 in. he does 0 highway miles though
No e30s again.
I was thinking they were both eta
Then motors lol
Could be completely unrelated, but I blew the HG in a 99 528iT with 217k on it. I swapped in an engine and trans with 170k and it was absolutely faster. I chalked it up to mileage since that was the only variable.
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