If it's less than a half a point, I doubt you'd ever tell a difference....
Even then, I bet you're a shave and adj. cam gear away from stock compression levels.
+2. Excellent question. I was going to ask the same thing, but been busy here today.
My Menegon 91 casting 287 head has a 56cc combustion chamber, and my JE pistons have a 23cc dish.
I'm using a Cometic MLS gasket of unsure thickness and the static compression ratio is around 8.2:1
Brian did want to have about 8.5:1 but we fell short of that by my piston choice that had already been purchased.
When i need a new headgasket, maybe we can get closer. I've heard you can get Cometic gssketd in custom thicknesses.
It seems the combo is working well enough, with the other parts of the complete package. This is not turned all the way up yet, but i feel i may be getting close to the intercooler being more of a limiter.
I should try to get my other dual thermocouple gauge kit installed so i can get some efficiency data.
Wayne H.
'91 Dodge Spirit ES 2.5L turbo 5spd
'05 PT GT 2.4T HO autostick (RIP)
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MeanMini dragracing videos: https://www.youtube.com/playlist?lis...URZLB1RxGYF6vw
and other cars, trucks and motorcycles
https://www.youtube.com/user/SlugmobileMeanMini
Dynamic compression ratio is what really matters.
http://www.wallaceracing.com/dynamic-cr.php
If I remember right I think around .060 reduction in area from the whole bore is worth around a full point increase or just a touch over that. Using the whole bore area for removal of area/material as in thinner head gasket has a greater effect on raising the compression ratio than what shaving the head only would have. Although my head has now been shaved .020 as well. So with a .042 reduction from the stock head gasket thickness of I think it was .069 (been awhile on remembering all this stuff) along with .020 taking off the head, the total is a .062 reduction. I had my compression figured to be 7.9 to 1 before. It was at 7.9 because off the chamber work and from using swirl head type forged pistons with a G head. My new compression ratio should be around 8.5 to 8.6 to 1 or so after the reduction in area. And good point "cordes" an adjustable cam gear will be needed to keep the same cam timing as before.
Last edited by glhs875; 12-24-2016 at 08:34 AM.
I wasn't trying to single anyone out, I was just trying steer the thread back to the topic of head I mean cylinder heads
I too worried about CR reduction when cutting back the valve shrouds and other areas in the chamber especially since the head I started with was already heavily cut in the wrong places and I knew I'd be cutting more so I did some research into how much CR reduction I should expect. OK, I actually just called a guy here on the board that's way smarter than me(thanks Todd ) and not only did he have a decent rule of thumb formula for decking the head vs CR increase but he made a good point I hadn't thought about. Going with the larger valves (that have increased mass in the chambers) makes up for a good portion of what was lost with the cutting. He also told me to CC each chamber in the head if I really wanted to know what my final CR was gonna be. Not sure if I'm gonna take the time to do that or not yet. Wanna get it bolted on RedBox before 2017
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There is a reason I chose to run t3 pistons (other than being cheap) with my ghead... Hoping to try it out with a swirl head next...
With the research I did and the 10 thou I took off the deck to get about 5 thou pop out, I was figuring 9.2 to 9.5 Ish, stock head. Hoping to maximize the quench and squish area, and give me some room for decent compression when installing either of my ported heads with modified chambers (one overly deshrouded ghead, and a tvaliant swirl). I'm worried with the swirl I will have to fly cut the pistons tho, I'll be doing mock up soon as a pull it apart again. I might just run the swirl head on my forged 2.5 tho depending on the condition of the "t3" piston engine. Destroyed the headgasket when I lost an injector but kept pushing it while racing a new sti, I had to rub it in when he wouldn't stop racing me... bad move
well, kind of a lot... ill "try" to explain.... also, I planned on running e85 and did, but still made a crap load of power on 87 and mp stage2 tune (actually I never really got my 3 bar tune how I wanted it honestly)What kind of performance increase if any did you realize with the use of T3 pistons along with the G-head?
so, it fired up quicker (on cold start gas and e85), idled smoother at lower rpm, quicker off idle rev, boost was full song (20ish psi) by 2500 rpm, got 28-32 mpg with e85! torq was actually too much, but it was more the combination of parts that I used, ended up rushing the build quicker than I had wanted and ended up with a few comprimises. it was only supposed to be a quick spooling daily, turned out it ran way better than I had hoped with too quick of spool. never saw knock on 87 up to 14 psi with the stock intercooler (but never wanted to push it harder obviously). I had also welded the intake and ported it heavily, plus I HEAVILY ported the exhaust manifold too
Had to many unfortunate events before realizing its full potential, but it was always going to be hinderd with a stock turbine housing and wheel mated to a Chinese 60-1 comp wheel and housing. blew up 2 early 523 transmissions (I'm an idiot, but they just stripped out 3rd gear rolling into the throttle), lost an injector that took out the headgasket (and I'm hoping not a piston), someone stole the large intercooler I was going to install so I just parked it behind my shop til I could work on it again.
same car before this motor, I also ran e85 on ghead pistons with a swirl head and log intake to 18 psi for months with no intercooler til I blew up the 525 (what an idiot again)
I was already at full QWERTY when I heard talk of people retarding cams being re..... Or were they sad that a little junk setup mitsu makes power up top when sorted and toyed with.
Very enjoyable to see a swing at someone's 20 year old work. Excess deshrouding where its gonna make very little difference while not attempting to find the easy gains closer to the valve. Obsession with a "good look" vs optimal performance. Customers look for something pleasing to the eye. Really hard to sell potentially your best to work to someone who can't appreciate it. I wouldn't want to explain every little secret just to make the complaints stop. Everyone has their lazy day too.
Speaking to Alan's point about a "ported" head, I worked and flowbenched a TIII head that was off the shelf supposedly big name ported. With the valves removed I really hoped that wasn't true. Apparently TIII heads can have large casting "cornflakes" hidden behind the valves and a pro headporter wouldn't leave those...
I am assuming the 8v head I ported from a 2.2 TII forged crank Shelby Z was a 782 head. I wish Gary would make his head section a little more dummy friendly for understanding what is what. Seems like some years of the same style head are better but its all very unclear.
Assuming 782 head, all I remember was that the intake port looked like a C-clamp. Junk.
Regarding SMP's old posts, I believe he would have had a nasty ignition system, no blowing out the spark for him on a swirl head.
He also raised the ports on his heads so any head with a better angle/radius to the valves would have been his head of choice. When I say he raised the ports, I believe he basically built a new ceiling and extended that into his own intake manifold design. Better if he did this with both the exhaust and intake. One of the poor aspects of the old Hemi heads were terrible exhaust port angles. Same problem on 3.0 heads. Floor drops right after valve. The Gen II hemi (427 I think) was less of a hemi than the older 1950's 390somethings but it had a better exhaust port. Get the idea that the crossflow design was the real improvement aspect and the chamber gimic was not as important as a good port.
I have said before that a "chambered" piston would cost nearly the same, nobody wants to do the work to make it all jive. There is certainly a good point to having a nice burn near the plug. It is also very true that when you are running exotic fuels, you don't care about a little sensitivity improvement. I will defend exotic fuel use in that its not just for hiding problems. Methanol makes 20% more power minimum off the bat. Thats got nothing to do with all the people who cover up with excess octane.
Side note, I see some camshaft issues people long argued over have more to do with running a sketchy turbo than everything else. Crap turbo on iffy head with according to myth marginally better camshaft is nothing to bother writing about. People still pass around fraudish t3t4 turbos in stock housings that perform worse than S60's.
I also have never really seen these large turbo high timing projects that did well at low boost and failed at high boost. I would assume they ran poorly at the start and never got much better. I would also not blame the turbo. I love big turbo with fun timing. Its insane common on other platforms, or domestic v8s. Its something you do on an engine that was not factory turbocharged. It makes little sense on a low compression slug lacking supporting mods. Neither the junky factory turbo engine, or the factory n/a engine will handle the rigors of high boost levels, so either one has to be fully modified to bother with big boost #'s.
That last point brings me to think about Gary's comment on cylinder head sealing. That could certainly be more important than anything else. Lots of high power turbo import motors don't bother porting heads. The n/a guys have to, but for the turbo guys, sealing the head is a much bigger deal. They can always throw insane boost levels to make up for flow, but if the combustion pressure won't hold, its game over.
For true high power, I would first want to be able to seal the head. Screw flow. You can always make more boost, and on the right fuel you don't care so much about a little extra heat, especially since you won't be lacking intercooler in a high level race setup. Once you can seal the head and have a turbo falling off the boost pressure map (but still having flow potential) then optimized ports will bring more power. If the turbo dies off at 60psi, you probably want to make that same power at 45psi with improved headflow assuming your turbo flows more there. Very interesting to see SMP ran a bone stock head during an event on the same exact setup. Thats info you would never get your hands on otherwise. Shows ability to perform, yet still a huge bottleneck. Realize that he ran the same boost level, he always ran conservative boost #'s compared to his rivals, and I bet if he cranked that turbo hard he could have brought his times down near ported levels if the head would seal. All that really matters is if his class legal turbo was off the compressor map either vertically or horizontally. Thats how you maximize power for a turbo class racer. Knowing how easy he ran his turbo, he certainly could have made that stock head run fast. I feel Stephane did a lot of things to avoid weight penalties and keep his costs down. Go slower and be consistent. Never turn things up. Never show your MPH until some ridiculous SDAC pass. Make one fast pass at an event and you are gonna get slammed with weight. He was allowed back then to be very very light. Near lightest in the class I believe while having more displacement than the legal B series Hondas. Probably all down to saving the transmission.
Last edited by Ondonti; 01-02-2017 at 08:54 AM.
Brent GREAT DEPRESSION RACING 1992 Duster 3.0T The Junkyard - MS II, OEM 10:1 -[I] Old - 11.5@125 22psi $90 [U]Stock[/U] 3.0 Junk Motor - 1 bar MAP [/I] 1994 Spirit 3.0T - 11.5@120 20 psi - Daily :eyebrows: Holset He351 -FT600 - 393whp 457ft/lb @18psi 1994 Spirit 3.0T a670 - He341, stock fuel, BEGI. Wife's into kid's project. 1990 Lebaron Coupe 2.2 TI/II non IC, a413 1990 Spirit 3.0 E.S. 41TE -- 1993 Spirit 3.0 E.S. 41TE -- 1994 Duster 3.0 A543 1981 Starlet KP61 Potential driver -- 1981 Starlet KP61 Parts -- 1983 Starlet KP61 Drag 2005 Durango Hemi Limited -- 1998 Dodge 12v 47re. AFC mods, No plate, Mack plug, Boost elbow -- 2011 Dodge 6.7 G56
Found an interesting cylinder head picture.
http://www.turbo-mopar.com/forums/ga...vehicle&id=142
that thing looks crazy? it was milled so much theres no more "pad" left to tell how much "life" is left. wonder how it did? any more info on car?
fingts is from Finland with a Lancer. The pictures I linked is all you have to go with.
http://www.turbo-mopar.com/forums/me...=user_vehicles
http://www.turbo-mopar.com/forums/ga...vehicle&id=142