OK, now that my car has been on E85 full time for a couple months I have really been wanting to get high compression pistons put in the car. You know from my other thread about 10:1 pistons that I have been getting prices for them and the lowest is right around $600 for a set. This car is my daily driver and my goals are not high hp. I run an 18g turbo right now and I am after a higher torque quick spooling setup for daily use with a max hp of around 350-380. For the duty that this car sees it is much more fun to have off turbo and mid range performance than a car that pulls up top. Given all of that, I decided to pick up a G4CS block for a couple hundred dollars and put my 4G63 head on it for ~11:1 compression. I have read all the hybrid 2.4 threads and everything makes sense as far as the build up goes. It seems one or two guys ran with the stock pistons and 4G63 head, but not with E85. The one thing that does not make sense to me from those threads is that the pistons in the G4CS have valve reliefs for a SOHC engine and are flat in the area that a DOHC engine would normally have reliefs. I plan tonight to start checking piston to valve clearance without a head gakset on the engine stand. I am curious at this point if I will have to clearance the pistons myself or maybe they will be OK with a stock cam. I would like to go to a 272 type cam with the larger displacement and high compression so I don't end up with really high cylinder pressure. If anyone has run with the stock G4CS pistons and 4G63 head let me know. Also if you ran larger than stock cams let me know.
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Nope the combustion chamber size of the various 2.4 heads are the same as a 4g63 (47cc). . . So there is no compression increase beyond stock for a 2.4 (9-9.5CR) by putting a 4g63 head on it.
You can try looking for a 1.8L 4g67 head. They have 43cc chambers and have the wide 1g intake ports. If you have one of the 9:1CR 2.4 motors, this will raise the compression up to about 9.4:1. If you have one of the 9.5:1CR 2.4 motors, this will raise your compression up to about 10.7CR.
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Matt
dd '90 GST, Holset H1C
Interesting. This was never mentioned in the several other threads that claim putting a 4G63 head on a stock G4CS with stock G4CS pistons yields 11:1. Hmmm, I guess I will just pick up a little compression from 7.8:1 and displacement. I will also verify the combustions chambers are the same size tonight. I have talked to more than one person locally that did this and increased their compression to about 11:1.
How do THEY know the compression went up to 11:1??? A compression tester doesn't read in CR .
Did they cc their head volume? That is what you should do. Especially if you have both heads. Cc them both so that if your measuring wrong or using an inaccurate dropper or graduated cylinder, you'll see what's important: the difference between the head volume. Use the numeric difference measured and get a percentage and apply that percentage to the formula to calculate CR. With a little algebra, the percentage difference of the head volumes, and knowing that a g4cs has 9.0:1 CR; now you can figure out what the CR will be with the 4g63 head.
So what was the head volume measured of both the heads? I'd like to be wrong. It would be great to raise the compression that high for those that want to build an n/a motor.
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Matt
dd '90 GST, Holset H1C
So what was the head volume measured of both the heads? I'd like to be wrong. It would be great to raise the compression that high for those that want to build an n/a motor.
Here are the results and pictures of the two heads side by side. I had to use a very small amount of RTV to plug the air injection point in the 2.4 cylinder head. The 4G63 head measured 43cc for me and the 2.4 G4CS head measure 66cc. There is no doubt looking at the two that the 2.4 head is a much larger chamber but I measured them just for fun. These may be accurate enough numbers to calculate a new compression ratio.
I should also mention something about head gaskets. All the G4CS threads say that a 94 Galant GS 2.4 head gasket is required for the larger bore or a cometic, etc. I have what I believe is a felpro on the wall and it has the same bore size as the stock 2.4 head gasket. I will verify by purchasing a new gasket. That only helps for people that want to run felpro gaskets and I know a lot of people don't like them.
THANX! now we know that some of the web sources for the head volume are wrong. Does your 4g63 head have a 1.6 or 1.8 or 2.0 on the CAS side? We need to know if you have a 4g61 or 4g67 head since you measured out 43cc. 47cc / 43cc = 109.3%. If not we need to assume that the actual head volume of the g4cs head is the same percentage larger than your measurement.
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Matt
dd '90 GST, Holset H1C
Does your 4g63 head have a 1.6 or 1.8 or 2.0 on the CAS side?
I'll have to check tonight when I get home. BTW, I plugged some numbers into my CR calculator and using a .040" thick head gasket and 4cc valve reliefs (just a guess, they are small on the 2.4 pistons) I get 8.7:1 for the 2.4 and 11.3:1 for the 4G63 head (using 47cc that you call out). That all sounds reasonable to me. The bottom line is that these tests seem to confirm this setup is going to put me in the realm of 11:1 static compression ration.
Well, you have the large port head so it can't be the 4g61 head. That rules out you having that 43cc chamber head. And, take a look here. Your head looks like the 2.0L head not the 4g67 head (based on the unused holes on the head surface at the intake side). You have the 4g63 head. Which does have 47cc volume (I've measured).
So your measurements are about 9% off. 66cc X 109% = 72cc ==> g4cs head.
g4cs==> 9.0:1CR
Rearranging the CR formula:
[Cylinder CC + Head CC - CR(Head CC)] / [CR -1] = Piston dish & head gasket CC
G4cs Piston dish & head gasket CC = 3cc
With the 4g63 head (47cc), CR will be 13.0:1 !!!
I wonder if I'm wrong about the G4cs CR. . .
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Matt
dd '90 GST, Holset H1C
I believe you are correct, my measurement was not scientific enough to get to 47cc which should be the correct measurement. I also agree with your calcs that I will be somewhere between 11:1 and 13:1. It depends on accurately measuring the chambers at this point and also accurately measuring the valve reliefs. It will be interesting to see what psi I read on the compression gauge, but also keep in mind my house is right at 6400 feet altitude. The MAP sensor on my car reads 77kpa when the car is not running. My 4g63 engine in the car right now that is all stock reads 130psi compression. My friends engine that was rebuilt 40k ago with stock parts also reads 130psi compression.
Quote:
Originally Posted by dsm-onster
Well, you have the large port head so it can't be the 4g61 head. That rules out you having that 43cc chamber head. And, take a look here. Your head looks like the 2.0L head not the 4g67 head (based on the unused holes on the head surface at the intake side). You have the 4g63 head. Which does have 47cc volume (I've measured).
So your measurements are about 9% off. 66cc X 109% = 72cc ==> g4cs head.
g4cs==> 9.0:1CR
Rearranging the CR formula:
[Cylinder CC + Head CC - CR(Head CC)] / [CR -1] = Piston dish & head gasket CC
I looked up the CR in the 2.4L rebuild manual and it is indeed 9:1. you will have closer to 13:1 CR . That should be nice. If you ahve minimal tuning issues, e-85 DEFINATELY FTW! I suggest that you run similar to stock timing unless you're going to be able to do a lot of timing tweeking. E-85 likes more timing because it burns slower, but higher CR really speeds the burn rate up. So those two extremes could very well cancel each other out for the most part.
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Matt
dd '90 GST, Holset H1C
I plan to start at the stock boost of 9-10psi and start learning about the new combo. I suspect that is going to be pretty fun at that low boost compared to my current 7.8:1 compression at 18psi. If I don't encounter piston to valve clearance problems I should have this in the car in the next couple weeks. I planned to lower the timing to more like I ran with pump gas for a start so I will keep in mind what you said about the burn rate.
Curious how much boost and timing you plan on running with that compression and pistons? What do you realistically think the lifespan of this motor will be?
And im serious, you seem to know people that have done this and im curious of their long term results as well as some spool/turbo figures
I wonder what it would make on just motor with some cams,intake,etc?
I'm not convinced yet that it will really be 13:1 once some real world things come into play like head gasket bore size, actual size of valve reliefs, composite head gasket thickness, piston to deck clearance, etc. At any rate I will do a compression check with the stock turbo cams and see how the new psi number correlates to the stock 2.0 turbo engine number of 130psi that I get. The one thing that keeps worrying me right now is ring end gap. I better pull the pistons while the oil pan is off and make sure the top ring gap is large enough.
Rod bolts shouldn't come into play since this will only see 6500 rev limit. This isn't intended to last forever, that would be icing on the cake. This car is a daily driver, but I end up working on it weekly.
EDIT: the felpro gasket is listed as .048" thickness on jegs website. They don't say felpro, but their picture is a felpro. It also says 7.4cc volume. That right there will lower the CR. I think real world it is much closer to 11:1
Last edited by mobythevan; 02-05-2009 at 02:55 PM.
The piston quality seems to concern me as well as rod bolts?
The 2.4 pistons and the n/t 4g63 pistons have weaker ring lands (from the piston top to the firts ring land is shorter). That's about it. They don't do good for surviving detonation but detonation spikes at 300whp is 3-4 times higher than normap pressure from 500ish whp.
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Matt
dd '90 GST, Holset H1C
The 2.4 pistons and the n/t 4g63 pistons have weaker ring lands (from the piston top to the firts ring land is shorter).
I don't think this is true for the G4CS piston. The first thing I noticed when I pulled the head was the really long carbon ring from the deck down to the compression ring. Check out these two pictures of supposed G4CS piston and NT 2.0 piston. My G4CS pistons look exactly like the photo(bottom photo), but of course I can't see the ringlands except to infer from the carbon. The G4CS piston has a much longer distance from the top to the first ring. It seems to have a short distance between the first and second rings. From the photo you can see my concern with the DOHC valve clearance and the SOHC valve reliefs in the piston.
If that is the case for the g4cs, then this is my new favorite sirius shortblock! 6bolt, more displacement, same piston strength, higher compression. But when wanting to use the DOHC head, I'm not liking the idea of running THAT much compression for a pumpgas car even with plenty of timing control and water/alcy injection.
Would you be able to post a picture of yours? Turbo 63 pistons measure 5/16" from the top to the first ringland. N/T 63 pistons measure 1/4" from the top to the first ringland. It makes a big difference in surviving detonation and keeping the first ring cool. What does the g4cs measure?
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Matt
dd '90 GST, Holset H1C
I eliminated the balance shafts over the weekend and cleaned up all surfaces so the engine is ready to be assembled with the 4g63 oil pump and other parts. I got all parts on order including head gasket and longer timing belt. If all the parts come in I will swap the engines this weekend.
You need to see if you have a zero piston to deck height at TDC. If the piston tops don't come all the way to the top of the deck that will add more volume than you are calculating. I would also run the thickest MLS head gasket I could find if it would indeed be 13:1 CR with the stock headgasket thickness. FYI bikes are the only things on the road with that high of a CR not including diesel's of course.
With a 13:1 CR you would be hard pressed to have decent n/a power without detonation. That is also considering E85 into the picture. I would never build a N/A motor with over 12.5:1 CR.
But I don't think that the calculations are correct. The initial posting of 11:1 sounds more likely. In a SBC going from a 72cc to 62cc combustion chamber only get's you about an extra 1 CR on average. The biggest factor is piston size. The bigger the piston head surface the more effect you'll see from running smaller combustion chambers.
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Jeremiah
92 Talon TSi (HX52 install in works)
Wow. Well no. 14.5:1 isn't to far off from diesel compression ratio's of like 18:1 which is an average CR. You also have to realize that with higher compression ratio's comes worse gas mileage. It causes higher cylinder pressures which requires more power to get each piston to TDC. It's parasitic loss. You can get more power out of the fuel but more times than not you will see increased fuel consumption with higher than 10.5:1 CR's. I also would not use a Felpro HG on a NA motor with 12:1 CR. I sure as hell wouldn't even fathom using one in a turbo motor running "13:1". You are just going to be wasting money on that HG. Again I highly recommend the thickest MLS gasket you can get if you would indeed see 13:1 CR. The downside is the quench area is going to be ruined by doing so but it's a better trade off then having something you can't run over 13* of timing on and possibly blowing HG's on.
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Jeremiah
92 Talon TSi (HX52 install in works)
I'm part of a club at my college that is building a high mileage vehicle starting with a 5 hp briggs and stratton block. When it's all said and done, we're going to be running 16:1 CR on iso-octane (100 octane), but we only need the motor to last 4 hours of on and off testing.
Good luck with 13:1 boosted with E85! I hope it works for you.
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Wes - '97 Talon Tsi AWD
I'll measure cranking psi with stock 2.0 turbo cams when it is together this weekend and then we can try to figure a more realistic compression ratio, given that I am at 6400 feet altitude so cranking psi is already ~18% lower than sea level. If the cylinder pressure is too high for what I want then I just throw in bigger cams. Its an easier problem to deal with than having low compression.
I got the engine and tranny pulled over the weekend. The clutch was in worse shape than I expected so I put a new clutch kit on order. Other than that everything is going smooth, should have it back together as soon as the clutch comes in. It was a good time to pull out the original 2.0, the rod bearings were worn pretty good and the clutch disc/PP/TO bearing were worn to the end.
Im interested in knowing the results! 13:1 shouldnt be a problem with e85, moderate boost levels and lowish timing. Your MBT will be found at a lower timing advance number so you wont need to run aggressive timing maps. Should make for a fun car when finished.
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