Porting vs Oversized valves

[Tegetus25]

Hey folks!
Im very new to the whole DSM scene. I was raised mostly on muscle cars until I realized the actual HP you can get from a DSM. My question is that cams allow more air flow just the same as oversizing your valves. Is camming easier or better to do? Cheaper? Which one will give you the most gain?
-Matt

 

[Tegetus25]

Oh gosh, first post and I mess up the title !!

 

[ApexVIII]

cams will do more for the dollor, well probably more overall being that you would not do oversized valves unless you had some large cams,

replacing the cams=
price of cams + price of timing belt

larger valves=
new head gasket+intake/exhaust manifold gaskets+new Fluids+timing belt+resurfaced head+over sized valves+valve install(valve seat)


i dont think you would really even need over sized valves on a stock bottom end... but im not sure anyone?

 

[crimsondragon]

They're usually 1mm oversized. The gains are minimal. It's only for people looking to get the most out of the engine.

 

[Staytuned]

Cams = easy afternoon job.

Go for cams first and do your homework on the right ones for your application.

 

[mach4g63t]

When it comes to cams, you will also maximize the increase in horsepower by upgrading from the stock intake manifold to something a little more bulky like a sheet metal intake manifold. Those two together will yield lots of top end power vice doing one at a time.

 

[andy4g63]

You could do 1mm OS valves, it is OK. Make sure if you do that, you port and polish the head, change the HG, guides and seals and bolt it on. After that, whatever you need to do to the head, no removing of it is nesessary:
You can change anything, while head is on the car: cams, lifters, springs, rockers,etc.

 

[Defiant]

I was raised mostly on muscle cars

Welcome to turbocharging. Most of what you knew will be different. Some things very, very different, and others simply nuance.

 

[92_6bolt_1290]

if you don't NEED to take your cylinder head off then I would not even bother with more than a mild cam upgrade(264 or 272 depending on what supporting mods you have). my question to throw into this would be if I needed to take my cylinder head off anyway would it be WORTH porting the head and getting 1mm oversized valves to use in a road driven car or will the porting/oversizing put a damper on low rpm drivability?

 

[jazzfoxx123]

cams are a good idea for quick easy horsepower depeneding on which cam duration you chose it can greatly increase higher rpm's. If i were you get cams, the cam gears and then port your head not very hard just get a dremel and sharpie and mark how much you can take out, as for oversized valves, it's very difficult to do unless you send your vavle head to someone with a cnc machine and knows what there doing and prbably costing a good $1000 for porting and polishing job.

 

[92_6bolt_1290]

i'm good friends with someone that does all that fun machining stuff himself and he just built a 91 talon and even offered to do my head work for way cheaper than a shop could so is it worth doing while I have the cylinder head off because oversized valves cost the same as stock size? i want a slightly bigger cam eventually but its nowhere near the top of my list right now.

 

[rarson]

if you don't NEED to take your cylinder head off then I would not even bother with more than a mild cam upgrade(264 or 272 depending on what supporting mods you have).

I agree, although I'd go a step further and say why not upgrade the valve springs and retainers and go for an aggressive cam while you're at it? If you're using the stock valves, you still don't need to take the head off. I'd go with an aggressive cam and test how it works before even thinking about a SMIM.

my question to throw into this would be if I needed to take my cylinder head off anyway would it be WORTH porting the head and getting 1mm oversized valves to use in a road driven car or will the porting/oversizing put a damper on low rpm drivability?

I would think that a larger cylinder bore might actually help better than larger valves due to unshrouding. Larger valves would actually be a step in the opposite direction. I can't imagine that with an aggressive cam setup with a ported head is going to gain a whole lot from 1mm oversize valves. I'd probably undercut the stock valves or buy an aftermarket set of the stock size first before going to the trouble of trying oversize valves.

Then again, I'm of the opinion that the 1g head ports are entirely too large...

 

[92_6bolt_1290]

i need to take the head off ### my valves are bent... and since i NEED to buy valves i was thinking why not go bigger, unless it really won't do me a thing considering i want this car as somewhat of a daily driver. so i guess you really did answer my question and oversized valves are pretty much a total waste and a small port job with a cam is more of a step forward

 

[Nati0nalxCrisis]

Well, if your taking it off and your looking for more HP compare the prices of doing it and not doing it. Either way it'll net you HP.

If you got a few extra hundred smackaroos then go for it. Beats redoing it all over again down the road if you ever are looking to make a drag car or something like that.

I've always been the kind of guy interested in doing those things first.

 

[92_6bolt_1290]

if the car was perfectly drivable, you bet i would go with something like 272 cams and brian crower springs but it needs valves. i think i'll just go stock size stainless valves and bronze guides with a minor port job if anything ### those intake ports are huge. its like they took the outside dimensions of a honda intake mani and made them the inside dimensions of the 1g dsm intake mani

 

[rarson]

Well, if your taking it off and your looking for more HP compare the prices of doing it and not doing it. Either way it'll net you HP.

Has anyone ever done a back-to-back comparison of power with stock-sized valves versus 1mm oversized valves? I find it hard to believe that they would make a significant difference on the average engine, especially with the stock bore. Granted, I haven't really been doing much with DSMs in the past 4 years, so I might have missed a lot.

The natural inclination for performance enthusiasts is to hog everything out as much as possible, and in my experience that this isn't the best way to go about things. When I started modding my 2g over 10 years ago, 2g heads were worthless because everyone wanted the 1g head with the huge ports in it. I was convinced that they were too large and that the 2g head was the one to go with. Now it seems like more and more people are putting 2g heads onto 6-bolt blocks (I also refuse to get rid of the perfectly good 7-bolt that has served me well over many years).

Point is that when it comes to heads, people tend to look towards the flow bench to decide what is best, but there's a whole lot of other things to consider than just flow numbers. Copying what is common isn't how guys like Curt Brown break records.

 

[92_6bolt_1290]

of course not...breaking records required big money as well as a crew of people working together to figure out what exactly will work the best. obviously in a daily driven stock internal 6 bolt car only running a few psi over stock settings, i won't see a bit of difference with bigger valves. maybe a tiny difference with a port job, if any difference at all. i haven't done much work on dsm's so i figured i would ask instead of doing what i would have done with my old honda.