Super Jet Porting or High compression & girdled head. Where should I start?

[Roseand]

Alright guys! Looking for a little advice here. With my budget, I can either do one or the other. Porting would be through zack @ PHP, and the head would be an ADA girdled head with either 33 or 35 cc domes. I'm looking for more bottom end and mid range, but lots of reliability. This motor has to last me at least 4 years, roughly more or less 100 hours a season.
In terms of current driveline mods, I have a b pipe with a limited chamber, protec adjustable cdi @ 7750 rpm, will be running dual cooling, have a 9/15 hooker, & worx 201 intake. This is on a stock 61x 44mm carb 701 engine out of my 95 SN.




First of all, how much of a performance increase does increasing compression give you? What kind of difference do you feel?
33cc compared to 35 cc domes?

What about porting? Way bigger difference than higher compression?

Also, in terms of performance increases, the only thing I'm able to compare stuff with is a hooker prop. The previous owner installed a b pipe, so I have know idea how much power that added, but I did install the hooker prop. Going from a stock aluminum prop to a 9/15 hooker was a night and day difference, and I was amazed at the bottom and midrange power I gained. It was instant throttle response, and woke every aspect of performance up.

But here's the more important question.
Wouldn't it be a not so smart idea to get my cylinder ported & stick with stock compression & a stock head? Would I be missing a lot with stock compression? But more importantly, is a girdled head truly that important?
I know it's extra insurance, and I sure would be pissed if my cylinder cracked, but is it necessary?

What should my priorities be? The prices are around the same..

Thanks for the insight ahead of time

 

[Harbor]

How about do the port work and mill your head, then you'll have nearly both and the milling of the head will be much cheaper than the ADA, later when funds allow you can upgrade to that head.

 

[IS0LD0UT]

If you port the cylinders you may want the cases ported too. My maniac motor hits nice and hard for a 735.

 

[Lumpy]

http://www.x-h2o.com/index.php?threads/ada-racing-girdled-head-701.145357/

Used ada girlded head(not mine) just posted a couple hours ago

 

[chadman154]

port and shave the head, you can build off of that platform

 

[Roseand]

I'm going to talk to zack at php again about all of this probably , but he did recommend getting a girdled head before porting and putting more money into your engine.
But I'm still interested in other people's experiences too.
But I really want to know how much of a difference high compression makes too..

Sent from my XT907 using Tapatalk

 

[Quinc]

Girdled head. Don't want to crack your cylinders from all that extra torque after getting them ported. I have a protec half girdle kit that might work for you if you do port first.

 

[Harbor]

Within limits compression is directlty proportional to power output. Compression is so important its fundamental to the internal combustion engine. We need in the correct amounts, compression, air/fuel and an ignition source for the thing to even run. To help undersatnd the relationship compression has on power lets reverse the situtation and consider this: --------- Instead of raising the compression from 150 to 180 lets take the compression from 150 to 120
Now what could we expect?? _____________________
In this senero the ski's engine went from good power output, great running ski to one that might not even start! Compression has that much effect on power, its huge

How much cranking compression do you have now?

 

[Mdavies_02]

I can't recall the performance gains of the ADA Girdled head because I did multiple mods. No way to know what did what. However, I bought a JM 781 that came with a head, so I have one for sale. PM me if your looking for a deal with 180 psi domes.

 

[Roseand]

Within limits compression is directlty proportional to power output. Compression is so important its fundamental to the internal combustion engine. We need in the correct amounts, compression, air/fuel and an ignition source for the thing to even run. To help undersatnd the relationship compression has on power lets reverse the situtation and consider this: --------- Instead of raising the compression from 150 to 180 lets take the compression from 150 to 120
Now what could we expect?? _____________________
In this senero the ski's engine went from good power output, great running ski to one that might not even start! Compression has that much effect on power, its huge

How much cranking compression do you have now?

I understand that compression is very important to engines. I'm not engine illiterate. I know the importance, but I don't know what kind of proportional effect raising compression has on the power of a ski. I'm into more specifics.

Right now I have 0 cranking compression. My motor is completely stripped apart and my cylinders are soon going to be off to PHP to be bored to the next oversize(81.5)

 

[Roseand]

How about do the port work and mill your head, then you'll have nearly both and the milling of the head will be much cheaper than the ADA, later when funds allow you can upgrade to that head.

How much of a risk is there that I would do all of this port work all in order to have my cylinder inevitably crack and ruin the time and effort I put into it?
I doubt I would have the patience to do that, nor the expertise either. I trust a builder's port design & work quality like PHP over sportport and my amateur dremel tools & skills. I can't risk messing up my engine, especially on a tight soon to be college student budget.. Plus, going through a builder like PHP definitely helps in the tuning process, because he knows exactly what my motor needs, and he's somewhat local too.

Do you personally port your own engines?

 

[Big Kahuna]

Honestly. Zach knows his stuff. Talk with him. Set some goals. If he says get a girdled head first. Do that. Run it his season then get him to port it next. You don't have to do everything at once. Do it in sensible steps. More compression will make a stock motor wake up. So will porting with a stock head. Typically you want a girdled head with a modified motor. Hence, Head first. Then do the port work.

 

[Harbor]

I know youll be going to school to study engineering. Your question on how much performance gain will you gain with raising the compression is a good one and a bit abstract, you said your self you dont know how much compression you started with, so when its all siad and done you wont know how much effect it had either. We are all in that same boat. I deal with compression on a semi weekly basis so i thought the reverse compression post would help make clearer its effect is direct in both directions. There is almost, within limits, no subsitute for cc's or compression.

Porting, depending mind you, can normally lowers compression say around 10 psi so really the question may be how youll raise raise your compression not if youll raise it.

My last ski i sold last year a 96 RN with 701, high compression none girdled head with a type 4 dry pipe bolted to it been cylinder crack free and running strong going on 8 years. The b-pipe is alot less stressfull on the cylinder since it doesnt bolt to the cylinder head too.

A girdeled head could be important insurance, we dont want to invest a bunch of money into a cylinder to only have it crack, but exactly how common is the cracking? Mine hasn't cracke in 8 years. So porting while its appart now and milling head makes sence with your budget, then when funds allow you add the bolt on ADA girdled head. What makes less sense is putting it back together with a girdled head only to tear it doen again to port the cylinder.

If your #1 concern is the cylinder forgo the porting and get you a girdeled head, personally i think the risk is low, port, mill, then add the bolt on head when your budget allows

 

[Roseand]

Well before everything I did start with 150 PSI. I should have mentioned that. So that's where I'm coming from.
Yeah it's not all that common, but it's common enough that there's a legit risk of it. And yours is a good case of it not being all of that common, because that pipe is a heavy sucker, isn't it?

I believe I heard that as long as you don't raise the exhaust port, you won't lose compression.
I'm not worried about tearing down an engine to port the cylinder. Taking a cylinder off would take less than an hour probably, just would need a new cylinder base gasket I believe. Bleh! Priorities. It's frustrating at times
I appreciate all of this insight though.

 

[Roseand]

Honestly. Zach knows his stuff. Talk with him. Set some goals. If he says get a girdled head first. Do that. Run it his season then get him to port it next. You don't have to do everything at once. Do it in sensible steps. More compression will make a stock motor wake up. So will porting with a stock head. Typically you want a girdled head with a modified motor. Hence, Head first. Then do the port work.

Yeah he sure does.. Awesome guy to talk to too.

Who here has went from a stock engine to just putting on a high comp head @ 185 psi?
What was the power increase?

 

[Quinc]

My motor is completely stripped apart and my cylinders are soon going to be off to PHP to be bored to the next oversize(81.5)

If he is going to bore it you might as well have him big bore it to 754cc. =)

 

[Harbor]

Your welcome

 

[Roseand]

If he is going to bore it you might as well have him big bore it to 754cc. =)

Already bought pistons. Oh well!

 

[kevbo]

More compression will make spool up faster since it increases power mostly at low rpm. It wont make it go any faster, that comes from the pipe and porting. I once installed a stock head/gasket on a high port 701, it cranked 120 psi. It took a full second to get on the pipe from idle although it was still fast. At 200 PSI it became very snappy. I settled at 165 psi and found I could tune the carb for peak rpm on pump gas without melting a piston. This setup could run full throttle all day turning 6900rpm at 48mph. Throttle response was fine for general riding. A freestyle port job should get you noticeably more power without hurting response for a given compression. I would not bother with an ADA head until timing is advanced and/or compression gets over 170. You will never get your small engine nearly good enough for what most people here want to do. You will however burn up your engine trying. Just keep it mild and reliable and go to the coast if you want big air.

 

[JetManiac]

ADA head is not just about raising your compression. Different dome shape and squish band angle and tighter squish size all work to incease power over a stock or stock milled head.

Porting for freestyle will not lower compression, that is with race porting and raised exhaust ports. You are on the right track though. Pick a good builder and follow his recommendations.

Also raising compression will lower engine life somewhat as will widened exhaust ports lower ring life somewhat. However, the way you care for your motor is also very important. We have customers on their 4th year with fully ported motors with high compression, but this isnt advisable. Best to teardown and inspect every season or 2 depending on hours and type of use.

How many hours used, how motor is dried out between uses, how much water is injested during use especially saltwater, heat/overheat developed during use, etc. all affect reliability.

If you want ultimate reliability, then remove bpipe and install stock pipe, cdi and jetting.

If you are building a ski for freestyle, then understand you are will be making tradeoffs for power gains. That said, you can still have a reliable freestyle motor, just understand that it will be higher reving, higher compression, higher performance motor that must regularly drink water that gets run hard so preventative maintenance becomes more important to longevity.