How much HP is porting/polishing 2000 head worth?

GoldHawg · Post by **GoldHawg** » Mon Aug 07, 2006 11:42 pm

For a stock datsun 2000, how well does the head respond to porting/polishing? What about porting/polishing plus a mild cam upgrade (one that hopefully wouldn't change highway mileage? All these ??s assuming stock SUs, plus maybe a header (recommendations?). I don't want to give up torque, but do want to pick up HP

Thanks for your thoughts

spyder · Post by **spyder** » Tue Aug 08, 2006 2:06 am

It all depends on where you want to make power. Porting, polishing, cam upgrade (bigger lift and duration) and headers will affect economy mileage in a negative way. These modifications allow the engine to have more power at higher RPMs but you also should increase the compression ratio to take advantage of the mods. Think of it this way, more power means more fuel burned. The faster you can spin an engine the more energy it creates. However if you design the engine to have a high RPM powerband it usually has crappy low end unless it has a variable cam timing operation, think VTEC.

Post by **spl310** » Tue Aug 08, 2006 11:48 am

What is your horsepower goal, and what kind of mileage do you want to have? I have talked to several solex 2000 owners that report getting 30is mpg at 70mph.

SLOroadster · Post by **SLOroadster** » Tue Aug 08, 2006 2:40 pm

The bigger question is how much money are you looking to spend on it. I get about 25 mpg at 80 mph turing 5K rpm with my 4.11 rear end. Porting and pollishing the head might increase your mpg due to the head being more efficient. Again, a big cam might hurt economy, it might not. I run a BIG cam, and I still get resonable mileage. You wont loose much in the low end department, and you will gain some in the midrange. If you are going as far as the machine work, you might as well opt for some lighter weight valves to help your timing chains last a little longer. If you are interested, Email me and I will tell you what I have.

Will

DatsunBucky · Post by **DatsunBucky** » Tue Aug 08, 2006 5:56 pm

I'm not too sure about the "latest and greatest", but "back in the day", the wisdom was that a highly polished surface didn't flow as well as a surface with a little "character". The thinking was that the texture in the surface tended to break up the boundary layer a bit, so the air flow increased. Similar to how the sharkskin pattern on the bottom of an America's Cup boat lets it slip through the water easier.

What did we know? We also thought that a light coat of black paint on a radiator increased the ability to shed heat better than even a bare metal surface.

spyder · Post by **spyder** » Wed Aug 09, 2006 1:48 am

30mpg with solexs! I never got that with the SU's and with the solex the best I got on the hiway with lean winter jets was 24. Presently I do not care about mileage because I live about 5 miles from work. So anything I can do to make it faster I have done or tried. Once again it depends on what you want. Good, Fast or Cheap? Pick only two!!

P.S. Lightweight valves? Gratuitous name drop alert!!! Ed Iskiderian told me that the stock valvetrain should be good to about 8500 rpm with his cam grind. He called my answering machine and wondered what I wanted him to do with the two cams I sent to his company. His people had advised me to send the cams and they would regrind them for me. I guess they did not inform him they were coming his way. Three guesses which cam I use and the first two don't count.

SLOroadster · Post by **SLOroadster** » Wed Aug 09, 2006 2:31 pm

Yes the stock valves are good to 8500, however why bother with those heavy things (unless its all you have). The head that is on the car now is a pretty special creation. Lets just say a stock head flows about 160 on the intakes, and roughly 110 on the exhaust. Mine is 212 on the intake and 173 on the exhaust. If one has the $, chevy race valves can be recut to fit, and the results are impressive. The stock valvetrain while bombproof, is heavy. The valves are heavy and the rockers are even heavier. It has lots of inertia, and running a big cam with a heavy valvetrain is going to stress things. With the lighter valves, you can run lighter springs without worry of valve float. This in turn places less load on the chains, tensioners and gears.

Will

GoldHawg · Post by **GoldHawg** » Sat Aug 12, 2006 4:47 pm

Thanks for all the thoughts...

However...my original ? remains. If I just ported the head, what performance increase could I expect? The reason I ask is that I have a friend that ports heads as a hobby and I could likely get him to do it gratis. I was just wondering, how much that is worth. If stock HP is 135, does it get me to 145? What if I then add a mild cam? I was wondering about the numbers one could expect to these type changes. Anybody w/any experience that actually bothered to dyno?

Thx!!!

Post by **spl310** » Sun Aug 13, 2006 2:06 pm

Porting without knowledge of the needs and capabilities of the engine can be counterproductive. Conventional wisdom is that bigger is better, but that is not always true. Look at the Boss 302 Ford engine. When Shelby's team was campaigning that engine in the Trans Am series, they determined that the ports were WAAAYY to big, and they were losing power keeping them in the stock configuration. They actually added material to reduce port sizes.

The only real way to know what you will gain is to test with a flow bench as you go, and test on the car.

Dave · Post by **Dave** » Sun Aug 13, 2006 4:59 pm

Sid has a very good point. The bigger is better motto is not always correct, especially if you are running stock carbs (SUs I'm assuming) and cam. Also, you need to view your intake system (carbs, manifold, valves, ports, cam) as just that, a system. There are good power gains to be had by going from the SUs to the Mikuni/Solex/Weber carbs. A bigger cam will also get you a nice bump in power. What this means is that the stock ports are large enough as is to support those mods. The ports are not the limiting factor in the intake system. If the stock ports were woefully undersized, none of these guys would be bothering with B cams and carbs.

I understand you have a line on some cheap port work but until you upgrade the carbs I honestly don't think you will see any performance gains. As Sid mentioned, you may actually hurt performance.

However, if you're Hell bent on doing it, go for it. Be sure to do a before and after dyno session as anything less will just lead to more speculation on whether or not porting a stock U20 is worth it!

Post by **dbrick** » Sun Aug 13, 2006 10:32 pm

I'm with Sid and Dave, I usually look at the history and see what others did. Have you looked at the Competion prep manual? They had alot of R&D money behind them.

Is the black paint thing a myth? I thought it worked? I paint my pyramid hat black in summer to disapate more heat.

SLOroadster · Post by **SLOroadster** » Mon Aug 14, 2006 12:28 pm

Bigger is not really better on the U20s. My valves are stock on the intakes and just a hair larger on the exhaust (to the point that you need a set of calipers to tell.) Its the shape of the exhaust ports that makes the biggest deal. You are shooting for an exhaust flow thats roughly 85% of the intake flow. The stock port size is good, the shape is what needs to change. A flow bench is a must. When the guy who built my head did the final flowbench test, he was blown away on the exhaust flow. Infact he triple checked it. Another thing is if you do the work to the head, you need to redo the exhaust to make use of it.

just my $.02

Will