Alright, this is for those guys that have built or raised compression on their Sr's. I'm currently trying to decide what thickness head gasket I should run. Obviously higher compression means better off boost response and a potential for higher horsepower in at the end result.
My head has been shaved approximately .030, which isn't all that much, and the block has been decked .010 but that leaves me with .040 total gone from between the valves and the pistons. I'm not sure if I can run a 1.1mm thickness headgasket and not have valves hit pistons. Here's what each headgasket thickness will be in comp ratio...
1.1mm - 9.47:11.5mm - 9.14:11.8mm - 8.89:1
Now with that said my engine has 8.5:1 pistons in it. I'm leaning more along the lines of 1.5mm just to keep valves and pistons a safe distance from each other and still have better off boost response from the comp increase...
If you have any input, please feel free to share... Would like to get a headgasket ordered, but unsure of what I want. I know it'll be either Apexi or Cosworth.
Need some help...
Re: (Hijacker)
Yeah, I know there's a good amount of material removed, but that's ok with me as I was looking for a higher comp engine anyway... I read the article on the Cosworth headgasket, it was great and probably one of the main reasons I considered it. I ended up getting the 1.5mm, I figure I can still make solid numbers, have clearance between valves and pistons, even though they have reliefs and have faster spool on most turbo's than anyone using stock comp would. I just need to order a few more things and the motor will be done, then it's injectors turbo and a tune... I'm hoping for close to if not 400rwhp...Hijacker wrote:I vote for the cosworth. I love mine!
I would say go with the 1.5mm. Slightly over 9 is a good CR to have IMO.
Your combined metal removed is pretty significant IMO. It equals a hair over 1mm
Thanks again Hijacker for your input...
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WizardBlack
- Posts: 99
- Joined: Wed Sep 19, 2007 5:35 pm
- Car: 1977 Datsun 280Z w/ RB25DET
Re: (jr_ss)
Are those thickness - comp ratio numbers already adjusted for the fact that you shave .040 off or are those standard numbers? If they are standard, you need to select your comp ratio, look at the thickness it tells you and then ADD .040" to it and buy that gasket to get that compression ratio. The amount you shaved means you need to add 1.01mm to your gasket thickness.
Re: (WizardBlack)
Those comp ratios already take into account the amount shaved and decked from the head and block...
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WizardBlack
- Posts: 99
- Joined: Wed Sep 19, 2007 5:35 pm
- Car: 1977 Datsun 280Z w/ RB25DET
Re: (jr_ss)
Gotcha. To be honest, some of it depends on your turbo setup. Bigger turbo, lower compression. Smaller turbo, higher compression. It's a fairly small range, but I'd go with the 8.89:1 preferably or the 9.14. 9.47 might be getting a bit far out there; particularly depending on what your engine management is. If it's a factory ECU, I'd go closer to factory compression.
Re: (WizardBlack)
I'll be using an Enthalpy ROM tune, but for fine tuning I'll take it to him, he's about an hour from me. The ROM tune should be fine and Enthalpy makes some awesome numbers with their tunes so I'm not worried about it.