|
|
|
|
Thread Tools | Display Modes |
11-18-2004, 01:13 AM | #1 |
Scooby Specialist
Member#: 37196
Join Date: May 2003
Location: WA state
|
RS DOHC vs SOHC heads
anyone got statistical evidence to show which flows better? DOHC or SOHC heads. ive heard conflicting arguments w/o numbers.
(unsung)
* Registered users of the site do not see these ads.
|
11-18-2004, 01:31 AM | #2 |
Scooby Guru
Member#: 39936
Join Date: Jul 2003
Vehicle:99RS TWE&SCAT EJ257 Hydra+HMist+PPG+35R=DEATH |
hehe
|
11-18-2004, 01:39 AM | #3 |
Scooby Guru
Member#: 36333
Join Date: May 2003
Chapter/Region:
NESIC
Location: East Kingston NH
Vehicle:98 RS GT30R, closed deck madnes |
DOHC all the way
|
11-18-2004, 02:00 AM | #4 |
Scooby Newbie
Member#: 71141
Join Date: Sep 2004
|
DOHC has many advantages but mostly in two areas. Valve angles are not limited and can be placed wider apart. Also since the cam can be made to directly depress the valves (bucket over valve) reciprocating mass is reduced allowing for greater rpm before valve float.
SOHC has one advantage alone, reduced cost through reduced number of parts. |
11-18-2004, 02:03 AM | #5 | |
Scooby Specialist
Member#: 2279
Join Date: Sep 2000
Chapter/Region:
South East
Location: The MIA
Vehicle:2000 Slingshot Pastelito Racing |
I'm lazy so I just cut and pasted my reply from the other board.
I don't remember Cobb posting any tests about DOHC vs SOHC. But I do know they tested the SOHC vs the old Legacy Turbo SOHC heads. The 99+ SOHC heads even flowed better than stock LS1 heads, IIRC. Here is the link to their writeup : http://www.cobbtuning.com/tech/sohc/index.html I dunno about DOHC being better than SOHC, who knows, they probably flow the same. But, I do know that the internal workings of the SOHC heads are MUCH better since it uses roller rockers, and has screw type adjustment, instead of HLAs. Here is an excert from their site : Quote:
|
|
11-18-2004, 05:13 AM | #6 |
Scooby Newbie
Member#: 71141
Join Date: Sep 2004
|
I'm not comparing particular heads since the original post didn't refer to particulars. I was referring to overall design potential. How often to you see SOHC on any sort of competitive race that allows the use of DOHC ?
|
11-18-2004, 08:22 AM | #7 |
Scooby Specialist
Member#: 11931
Join Date: Nov 2001
Location: Winter Park, FL/ SMU @ Dallas,
Vehicle:2001 2.5 RS Turbo 257/FMIC/T3-T04S |
Good power can be made with both heads, in the long run. However, adjustments to the internals may also be necessary. i.e. cams or stiffer springs. To say that one is better than other out of the box is just a bit arbitrary and there is not a whole lot of evedence out there to support one or the other. Besides COBB, who has done a real intensive analysis of either head flow rate? And COBB only did the SOHC. For something that flows better than an LS1 (is that 5.8L, ) head bone stock, there is not much to complain about.
But, most EJ22T who have undergone a swap seem to prefer using the DOHC configuration, but many high HP SOHC RS's still abound. The real debate about heads on the RS is the issue of what to do about a cam..... Graham |
11-18-2004, 10:18 AM | #8 |
Scooby Guru
Member#: 39936
Join Date: Jul 2003
Vehicle:99RS TWE&SCAT EJ257 Hydra+HMist+PPG+35R=DEATH |
have u picked up some cams yet graham?
i ordered my twes the other day...i had to do it |
11-18-2004, 12:39 PM | #9 |
Scooby Guru
Member#: 832
Join Date: Jan 2000
Chapter/Region:
RMIC
Location: Teh Ghetto Garage, CO
Vehicle:99 2.5RS, '85 911 '73 914 and 2012 BRZ |
http://www.wrxforum.com/cgi-bin/ulti...=000917#000000
Read this. If we are talking fully built and ported heads, then the potential of the two designs are equal. They each have advantages and liabilities. And one of the things you will discover by reading that thread is that the roller rocker design of the SOHC boxer heads allows quicker opening and closing of the valves than the shim over bucket design of the DOHC heads... |
11-18-2004, 02:24 PM | #10 |
Scooby Specialist
Member#: 2279
Join Date: Sep 2000
Chapter/Region:
South East
Location: The MIA
Vehicle:2000 Slingshot Pastelito Racing |
Awesome link Matt, thanks!
|
11-18-2004, 02:37 PM | #11 | |
Scooby Newbie
Member#: 71141
Join Date: Sep 2004
|
Quote:
|
|
11-18-2004, 03:03 PM | #12 |
Scooby Guru
Member#: 39936
Join Date: Jul 2003
Vehicle:99RS TWE&SCAT EJ257 Hydra+HMist+PPG+35R=DEATH |
unless u get stronger springs and
u dont need a shim under bucket conversion |
11-18-2004, 05:22 PM | #13 | |
Scooby Newbie
Member#: 71141
Join Date: Sep 2004
|
Quote:
|
|
11-19-2004, 12:26 PM | #14 |
Scooby Guru
Member#: 832
Join Date: Jan 2000
Chapter/Region:
RMIC
Location: Teh Ghetto Garage, CO
Vehicle:99 2.5RS, '85 911 '73 914 and 2012 BRZ |
revving to higher rpms before valve float is a discussion in mental masturbation. How high are you gonna rev? A SOHC EJ25 head with upgraded springs can rev to 8000rpms, no problem. Sure, a built DOHC head can rev to 9000rpms without float, but unless you spend the big $$$ on a bucket over shim conversion, you are gonna spit shims at that rpms. Otherwise, with upgraded springs the max I would personally rev the shim over bucket heads to is about the same 8000rpms.
AND, you had better have a monster freakin turbo on there if you are going up there or there is just no point. Most of the turbos that most people are using around here don't blow enough cfm's up there to be efficient up there and 7500 tends to be the number where most people redline around here. If you have enough $$$ you can build anything, but I prefer to keep my tech discussions grounded in the world of mortal working man and human horsepower desires... |
11-21-2004, 04:11 PM | #15 | |
Scooby Newbie
Member#: 71141
Join Date: Sep 2004
|
Quote:
Learn to participate in a discussion without putting your own narrow mindedness into it. READ THE ORIGINAL POST. Point out to me where it said anything outside of dohc vs sohc. |
|
11-21-2004, 04:19 PM | #16 |
Scooby Guru
Member#: 39936
Join Date: Jul 2003
Vehicle:99RS TWE&SCAT EJ257 Hydra+HMist+PPG+35R=DEATH |
jesus angry
|
11-21-2004, 06:04 PM | #17 |
Scooby Newbie
Member#: 4133
Join Date: Feb 2001
Location: St. Albert, AB, Canada
Vehicle:'01 2.5RS Sedan '05 LGT Wagon |
I hope this answers the question in the original post... klug Last edited by klug; 11-21-2004 at 06:29 PM. |
11-21-2004, 06:11 PM | #18 | |
Scooby Newbie
Member#: 71141
Join Date: Sep 2004
|
Quote:
|
|
11-22-2004, 12:13 AM | #19 |
Scooby Newbie
Member#: 4133
Join Date: Feb 2001
Location: St. Albert, AB, Canada
Vehicle:'01 2.5RS Sedan '05 LGT Wagon |
Bump...for edited previous post with good info.
klug |
11-22-2004, 12:30 AM | #20 |
Scooby Specialist
Member#: 2279
Join Date: Sep 2000
Chapter/Region:
South East
Location: The MIA
Vehicle:2000 Slingshot Pastelito Racing |
Nice find klug!
Even extra special since I have Stg. 1 heads. |
09-10-2005, 06:39 PM | #21 | |
Scooby Specialist
Member#: 8828
Join Date: Jul 2001
Chapter/Region:
MWSOC
Location: K-Town
Vehicle:01 BRP 2.2T Hybrid 08 Tundra |
I'm in the process of buying the TWE stage II SOHC setup and they are bascially telling me that it's not ideal due to SOHC combustion chamber size (99MM) in realtion to the EJ22T combustion chamber size (97MM) and should go with DOHC. That's more work than I care to do with this project, but has anyone heard anything similar?
Quote:
|
|
09-10-2005, 07:04 PM | #22 |
Scooby Specialist
Member#: 1366
Join Date: Apr 2000
Chapter/Region:
VIC
Location: Delta, BC, Canada
Vehicle:2000 RS-T -> RSTi-8 Blue Ridge Pearl |
Unless you swap out the pistons, your compression ratio will be below 8... using a thinner head gasket is not even an option and hence if you have the stock EJ22T and you mate it to the RS SOHC head, you get something like 7.7:1 compression which would make the low end gutless. I believe the only DOHC head worth using is the JDM STi heads, otherwise it's not worth the trouble - even JDM heads are just too pricey to come by itself.
|
09-10-2005, 09:07 PM | #23 |
Scooby Specialist
Member#: 9861
Join Date: Sep 2001
Chapter/Region:
RMIC
Location: Colorado Springs, CO
Vehicle:1999 2.35 RS-T w/NOS Hybrid Rally Blue Pearl |
I ran mid 12's at 5000 ft above sea level with a stock block ej22t and stock SOHC heads. It was hardly "gutless"
|
09-11-2005, 03:11 PM | #24 |
Scooby Specialist
Member#: 8828
Join Date: Jul 2001
Chapter/Region:
MWSOC
Location: K-Town
Vehicle:01 BRP 2.2T Hybrid 08 Tundra |
I have Pauter Rods and CP pistons designed for 8.0:1 compression based on stock SOHC RS heads and longevity isn't a critical priority since it won't be driven that much.
RS heads are not that far behind the big port STI heads in stock form from what I found on this board. It’ll be interesting to see what the setup does with a GT35. |
09-11-2005, 06:56 PM | #25 | |
Scooby Newbie
Member#: 43114
Join Date: Sep 2003
Location: Pownal, VT
Vehicle:1998 Legacy GT Turbo Green |
Quote:
Also, the coolant and oil passages don't seem to perfectly mate up. Finally, on the potential debate. This is definitely an old debate, and cobb has written articles about this on their website. Apparently, from their point of view, the SOHC has just as much potential, if not more, than the DOHC. Valvetrain mass is not so different, since you have all the shims and buckets going on all the valves, and an extra pair of cams, with an extra pair of cam sprockets and bearings. Also, the lobes have to be bigger on the DOHC cams, because it is a 1:1 ratio to the valve. The rocker arms on the SOHC have a higher ratio, like 1.4:1 or something similar (don't quote me on this number....I just know it's more than 1:1). The larger lobes mean less centralized mass on the cam, meaning, more relative valvetrain mass. Basically, just use whatever you already have, ha! |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Swapping from DOHC to SOHC heads???? | chevynut | Normally Aspirated Powertrain | 23 | 03-30-2010 07:00 PM |
dohc vs sohc vs phase I vs phase II | spdracr00 | Normally Aspirated Powertrain | 3 | 01-23-2006 02:53 PM |
DOHC and SOHC Heads | Cossey | Normally Aspirated Powertrain | 3 | 06-08-2004 10:41 PM |
Iridium spark plug DOHC vs SOHC Theory | yebokmj | Normally Aspirated with bolt-on Forced Induction Powertrain | 9 | 05-09-2003 07:56 AM |
Let's start the DOHC vs SOHC ALL over again ;) | jetfreak | Normally Aspirated Powertrain | 8 | 03-17-2001 10:31 AM |