If headers are added to stock motor how much more horsepower is added 1987 suzuki samurai?

It really depends WHAT power you want to increase...high revs top end, or low end crawing torque. The header will help with the high end, and hurt at the low end.

If you are trying for better high end power at high revs, then the header might help, incrementally. If you are trying for more low end umph when 4-wheeling, it probably won't help much as it will NOT help power at low revs, it might even cost a smidgen of low rev torque. Tricking engines with aftermarket exhausts or different camshafts tends to move power up or down the rev band...there's no free lunch, and you are dealing with a pretty low power engine. MAYBE I got 5 HP at top end by replacing my whole exhaust system...a guess on my part.

If you have a damaged exhaust manifold that needs replacement, if you want to setup your exhaust so you can use $80 after market flanged catalytic converters instead of $700 stock catalytic converters, if you want to increase high end power a bit by also replacing the rest of your exhaust, THEN an after market header might make sense.

Otherwise, it probably isn't worth the money or effort:

1. If you don't replace the rest of the exhaust you won't see any benefit because the stock exhaust and tailpipe will prevent increased flow.

2. If you DO put on a less restrictive exhaust you will increase top end power some, but also at the cost perhaps of low rev torque. If you want to drive 70mph on the highway, great. If you want to crawl up that steep rocky slope, not so useful.

I DID put a header on my main Samurai...that I retired with 250,000 miles, and it had been used as a daily commuter as well as for week long off road desert camping trips a couple times a year. I did increase my top end power a little as I also replaced the rest of the exhaust...at a cost of low end torque. But since I also had changed the gear ratiOS of the transfer case and both differentials, the loss of low end torque did not adversely affect me. (My "crawl ratio" was about 78:1 in low range 1st gear, 78 revolutions of the engine for every revolution of my wheels...would idle at 1mph, redline about 5mph, so a slight decrease in low end torque didn't matter.)

On the other hand I did NOT replace the exhaust header on my son's Samurai...I would have done so if his original exhaust manifold cracked and needed replacing, or if we were going to change his catalytic converter. But since neither was needed, we kept it stock. And he had about 180,000 miles on his when we retired it.

Hope that helps,

Paul