home register FAQ memberlist calendar

Go Back   Turbobricks Forums > Mechanical > performance & modifications

Reply
 
Thread Tools Display Modes
Old 07-01-2018, 06:14 PM   #1
papsimagoo
Delicious Boost! Nom nom
 
papsimagoo's Avatar
 
Join Date: Jan 2007
Location: Portland, OR
Default Another Cometic MLS Gasket Thread / Dished Piston Measurement

Heads off, this is my first cometic replacement. Don't know what thickness originally was used. If they print any ID/PN on them let me know, I didn't see any.

Piston to deck measurements- ~ 0mm-.4mm below block deck height on cylinders 1 and 4 averaged out...

So I believe it goes .003" for every 1000 rpm, redline 7k so 7x.003=.021 +.003" for safety puts me at ordering around a .030" compressed....BUT i have waveguide/large valve relief pistons..want/wanted to make sure I am doing this right before trashing a motor. Do the pros factor reliefs/dished pistons into their CRs?

BTW going to use real hylomar.

Engine Specs:
2.5l B230F + T by RSI
RSI 86mm Billet Stroker Crank
RSI 158mm H-Beam Connecting Rods
RSI Waveguide 8v Turbo Pistons
Cometic MLS Head Gasket
RSI Stage 2+ Cylinder Head Prototype
RSI Race Valvetrain Kit
RSI Stage 3 Turbo Cam Prototype
RSI Square Tooth Adjustable Cam Gear
RSI Twin Scrool SS Turbo Header
RSI Poly Engine Mounts
Twin Tial MVS 38mm External Wastegates
Greddy Type S Blowoff Valve
Holset HX40/Garrett Hybrid Turbo
Isuzu NPR Intercooler
NIW Motoring Intake Manifold
Megasquirt 2 EMS
Mitsubishi Coils
Injector Dynamics 1600cc Fuel Injectors

Head off1
__________________
89' RSI 245
Delicious BOOST! Nom Nom Nom

Last edited by papsimagoo; 07-02-2018 at 01:31 AM..
papsimagoo is offline   Reply With Quote
Old 07-02-2018, 11:25 AM   #2
shoestring
Board Member
 
shoestring's Avatar
 
Join Date: Jun 2009
Location: Beverly, 01915
Default

Yes, you must factor piston dish volume.

The formula is:

(Cylinder volume + combustion chamber volume + head gasket volume + piston dish volume (whether positive or negative) + piston deck volume + ring land volume)/(combustion chamber volume + head gasket volume + piston dish volume (whether positive or negative) + piston deck volume + ring land volume)=compression ratio

Any machinist will tell you that both the block deck and head deck need to be cleaned up to use an mls gasket, but I have gotten away with just doing the head every time in N/A applications.
shoestring is offline   Reply With Quote
Old 07-02-2018, 12:24 PM   #3
DET17
Reformed SAABaholic
 
Join Date: Nov 2009
Location: NW Georgia
Default

Been running a MLS gasket for 20K miles with a planed and polished head, block just wet sanded with 400 and 800 grit on a flat steel plate. Remember, the head being aluminium is what needs to expand with its 2.5x thermal expansion rate vs. steel/iron (or thereabouts ).

Below .036" there is negligible gain per the SAE.
__________________
Project "cheap thrills" build thread: http://forums.turbobricks.com/showth...67#post4211467

Feedback thread: http://forums.turbobricks.com/showthread.php?t=198746

Last edited by DET17; 07-03-2018 at 12:57 PM..
DET17 is offline   Reply With Quote
Old 07-04-2018, 01:48 AM   #4
papsimagoo
Delicious Boost! Nom nom
 
papsimagoo's Avatar
 
Join Date: Jan 2007
Location: Portland, OR
Default

Went with .030" cometic, old looks like a .027”. Will report back. If anyone reads this and knows a hylomar source in PDX... I'd like to know.
papsimagoo is offline   Reply With Quote
Old 07-04-2018, 06:47 PM   #5
Stiggy Pop
Board Member
 
Stiggy Pop's Avatar
 
Join Date: Feb 2011
Location: Granville, MA
Default

Why do you think you need hylomar? Properly prepped and cleaned surfaces make an MLS gasket happy.
__________________
'79 242
943 pickup
Stiggy Pop is offline   Reply With Quote
Old 07-05-2018, 08:19 AM   #6
chirish1234
Board Member
 
chirish1234's Avatar
 
Join Date: Jan 2009
Location: NJ, US
Default

where do you guys source your MLS gaskets?
__________________


1989 Volvo 245-GO FAST DRIFT CAR!
1988 Volvo 245/ B230FT, 16T @ 13PSI, G80, M46+Craving boost short shifter, Battery relocation, 15x7 ARES, Ecodes, Euro front end, 25/21 sways, too much to list Sold
1971 Volvo 144/ project

CoconutLeah:~Hes not afraid to hang out the window with a camera while passing you on the right at 70mph
chirish1234 is offline   Reply With Quote
Old 07-05-2018, 08:26 AM   #7
GTJordan
Been here for too long
 
GTJordan's Avatar
 
Join Date: Jul 2002
Location: Edmonton AB
Default

Quote:
Originally Posted by chirish1234 View Post
where do you guys source your MLS gaskets?
Cometic. Jegs sells them cheaper than the home site. Atleast when I ordered mine they did.
__________________
80 242- 2.5L, T5, Porsche brakes, short billies and kaplenkhe suspension, trutrack.
Project Thread- http://www.turbobricks.com/forums/sh...d.php?t=324470
GTJordan is offline   Reply With Quote
Old 07-05-2018, 12:29 PM   #8
DET17
Reformed SAABaholic
 
Join Date: Nov 2009
Location: NW Georgia
Default

Quote:
Originally Posted by Stiggy Pop View Post
Why do you think you need hylomar? Properly prepped and cleaned surfaces make an MLS gasket happy.
Because StealthFTi recommends it. Just use a light coat of hylomar.
DET17 is offline   Reply With Quote
Old 07-05-2018, 01:09 PM   #9
GTJordan
Been here for too long
 
GTJordan's Avatar
 
Join Date: Jul 2002
Location: Edmonton AB
Default

From Cometic

WHY DOES COMETIC RECOMMEND MLS GASKETS TO BE INSTALLED DRY?
Cometic Multi-Layer Steel (MLS) head gaskets go on dry because they are coated with a sealant. Each MLS head gasket is coated with a .001" thick Viton rubber that is bonded to the outer stainless steel layers. Adding an additional sealer can hinder the performance of an MLS head gasket.
GTJordan is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

Forum Jump


All times are GMT -4. The time now is 11:46 AM.

Powered by vBulletin® Version 3.8.11
Copyright ©2000 - 2018, vBulletin Solutions Inc.