m20 power confusion

[Milehigh30]

ok. i have a 87 vert. it has probably around 280k. i recently was driving and the car made a crazy noise i can't explain now and the power out put was no longer the same. i decided to buy everything for a head gasket change and i had a spare 885 head that is basically brand new that i resurfaced and put on. in the process of the swap i found my exhaust to be rotted at the muffler and at the connection to the manifold both welds broke. explaining why it sounded like a harley. i finished the job and got it running. but there is still a big loss of power.

cold compression check.
1-149
2-154
3-150
4-150
5-149
6-154

i haven't checked while hot. the battery was bad and i just replaced it.
i only have the down pipe fro the manifold on because cali laws make exhaust so expensive and the setup the muffler shop will do is no where near correct.

my question with the little info I've given.
Could the exhaust be a factor in power loss? or could it be worn piston rings that are showing good cold but they really are bad.

[Madhatter]

good above 150 is the general rule. It's all within a few % of each other two, so I would be suggesting the compression isn't the issue if you think it's down on power.

If you have pretty much no exhaust fitted up and just the manifold with a short section of pipe, it will feel like there is a big loss of torque. Fix your exhaust then start thinking about anything else.

[Milehigh30]

thats what I've been thinking was that the exhaust is the issue. but the shop told me it wouldn't make much of a difference so it made me very skeptical about paying $350 for an exhaust setup that is not what i need but california law make it difficult to do correct. the shop can only do a cat that is duel inlet to single outlet. idk if that would be much of a problem. id prefer to stay duel all the way.

[Madhatter]

They can't find any dual in, dual out cat's? or they just can't do it for $350?

[Milehigh30]

the guy said he can't find any. I'm just checking craigslist and such in hopes of finding oem exhaust to put on. i should add the car idles great around 600rpm. I'm very confused in what to think at this point. could the exhaust be the cause of huge power loss. i mean it takes some time to get up to speed now.

[Madhatter]

There are new california approved systems on ebay for like $500, so someone must make them. Try a different exhaust shop.

It's not a power loss you are feeling, if you ran it with straight headers and put it on a dyno you might even find it has picked up a little bit of peak horsepower. But if you have very little exhaust connected you will lose some scavenging effect created by the exhaust as the gas is pretty much just venting out into atmosphere. Normally it runs through a tube and if you size it correctly you keep the gas velocity up which helps with scavenging and draws the spent charge out the exhaust ports. When you size up to too big a pipe diameter (essentially the same effect as you have created), the first thing you normally notice is it doesn't seem to have the same mid range pull it used to have. People usually equate this with a loss of power because it physically doesn't feel like it accelerates as hard, but what you are really feeling is the loss of torque at the same rev range as before.

Though completely illegal for you, if you just replaced the whole lot with 1.5" or 1.75" dual pipe, aside from the terrible noise, I think you would find it's accelerating as hard as it ever has.

And fyi, if they leave the secondaries (ie the pipe length from the manifold) sufficiently long enough before they install the new cat and run a single exhaust system from the cat back instead of the dual, it might even pick up a little bit of power, it certainly shouldn't be worse than before and you shouldn't have too much to worry about other than the look and sound. Might be a little loud unless they spec the mufflers/resonators correctly. Probably wouldn't suggest going smaller than 2.25" single from the cat back either, 2.5" for sure if you have anything in the way of modifications (or just want to play it safe).

[Milehigh30]

so at this point I'm feeling its safe to say its the exhaust. i want to get it done correctly so i am probably going to hold off and save to get a whole new set up. I'm temporarily living in cali and will be moving in december back to my home state of colorado so I'm not worried about california laws. my cars not registered here either. just gotta find the right cat.

[Madhatter]

Im not going to say the exhaust will solve all your problems, but it's pretty evident you need it fixed regardless. It does have an effect on how the car feels to drive though, so the shop was wrong about that.

If it's not registered there, maybe you have to go interstate and pick one up or something? can you buy non approved systems and have them delivered to a CA address? I thought they didn't allow that sort of thing.

[Milehigh30]

none of the websites I've seen will ship to ca unless its approved. so i may wait till i find a car being parted and get the exhaust. cheapest way to find out if its the issue

[Madhatter]

your compression figures are ok, so I wouldn't expect there to be anything drastic wrong with the motor based on that. Run it again with a fully charged battery and put a few squirts of oil down the spark plug hole of each cylinder. If it jumps a whole lot you'll know your rings are shot. If it stays pretty close I reckon your motor is still fairly healthy.