Need opinions from h/c guys
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Need opinions from h/c guys My mods are in my sig. The 2 changes are I am now running Jesel SS's undercut for my springs, which are stock PP Gold's but shimmed .060", and I also have Ferrea hollow shaft lightweight intake valves. This is what I'm planning:
DCR is now 8.62:1. I want to bump it to 8.82. My deck height is -.004" (pistons out .004"). I am running .040" Cometics which gives me a quench height of .036".
What I'm thinking is to pulling the heads and replacing my Comp 850's with the Cadillac lifters and when I replace the heads, put on a Cometic .036". This will reduce my quench height to .032" and bump my DCR to 8.72:1. Then I'm going to advance my cam from +0 to +1 which will bump my DCR to 8.82. I can get 93 octane all day so I'm not worried about ping and don't get any now with 28 degrees of timing.
I don't care about the expense of the gaskets and I'm already changing the lifters so what I need are opinions on the .036" gaskets. PTV is no issue either as I have flycut the pistons. Is .032" quench height to tight? I am rev limited to 6800rpm's.
DCR is now 8.62:1. I want to bump it to 8.82. My deck height is -.004" (pistons out .004"). I am running .040" Cometics which gives me a quench height of .036".
What I'm thinking is to pulling the heads and replacing my Comp 850's with the Cadillac lifters and when I replace the heads, put on a Cometic .036". This will reduce my quench height to .032" and bump my DCR to 8.72:1. Then I'm going to advance my cam from +0 to +1 which will bump my DCR to 8.82. I can get 93 octane all day so I'm not worried about ping and don't get any now with 28 degrees of timing.
I don't care about the expense of the gaskets and I'm already changing the lifters so what I need are opinions on the .036" gaskets. PTV is no issue either as I have flycut the pistons. Is .032" quench height to tight? I am rev limited to 6800rpm's.
.032 is extremely tight and youre pistons better be very tight in the cylinder bores or else the rocking of a piston at TDC can cause the piston to crash into the valve. How tight are the pistons in the bore? I dont see internal motor mods inj your sig so i am assuming your bottom end is stock, if thats the case I would surely not go .032 quench because the pistons are probably too loose.
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Read this http://www.nitrophotos.com/240z/nitrous.html
Last edited by brad8266; Jan 9, 2007 at 12:37 PM.
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Yes, it's a stock bottom end. I'll have the heads off so I can have them do a clean up of .006". Without advancing the cam I'll be at 8.82... And I'll use my new .040" Cometics.
.032 isnt absurdly tight, though i wouldnt really push any further. Im surprised you get no ping. You shoudl be right on teh edge even for 93. Bumping to 8.8 DCR might push you over and youll have to take out a bit of timing. Might be worth it, might not. Could always try the toluene/xylene mixed with gas.
Originally Posted by ArKay99
Yes, it's a stock bottom end. I'll have the heads off so I can have them do a clean up of .006". Without advancing the cam I'll be at 8.82... And I'll use my new .040" Cometics.
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Originally Posted by GuitsBoy
.032 isnt absurdly tight, though i wouldnt really push any further. Im surprised you get no ping. You shoudl be right on teh edge even for 93. Bumping to 8.8 DCR might push you over and youll have to take out a bit of timing. Might be worth it, might not. Could always try the toluene/xylene mixed with gas.
As far as ping, maybe the valve reliefs are keeping the DCR a little lower than I'm calculating?
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Originally Posted by lilbuddy1587
Or you could just advance the cam 2 degrees and have 8.82 DCR
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Originally Posted by ArKay99
So, in your opinion it would be ok, clearance wise, to use a .036" gasket? I already have a case of Torco in the basement.
With the smaller duration advancing it might limit how high you can take it. Installing the cam straight up and raising the compression is there the power is at, however its not easily reversable if you went too far. If youre not opposed to losing some timing or having to mix in a hint of race gas, id go for it.
Originally Posted by ArKay99
So, in your opinion it would be ok, clearance wise, to use a .036" gasket? I already have a case of Torco in the basement.
As far as ping, maybe the valve reliefs are keeping the DCR a little lower than I'm calculating?
As far as ping, maybe the valve reliefs are keeping the DCR a little lower than I'm calculating?
It might be Ok but it might not, especially if those weak stock rod bolts stretch a little bit.
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Originally Posted by brad8266
If I were you I wouldnt dare go .032 quench with a stock bottom end. Now if you get forged bottom end with tight clearanced pistons and rods, then i say yeah no problem, but the stock bottom end parts are not most presice parts out there and have some slop in them.
It might be Ok but it might not, especially if those weak stock rod bolts stretch a little bit.
It might be Ok but it might not, especially if those weak stock rod bolts stretch a little bit.
Originally Posted by slow trap
just mill the heads some,use the .040 cometics and be done with it.
I agree with the above.
What's the risk / benefit?
How much HP gain for the slight increase in DCR and Risk of Detonation ?
Street driven? Mileage?
Well the .032 quench would bump DCR up slightly, but the real advantage of it is the great amount of turbulance that would be caused in the chamber, which would make it LESS prone to detonation as well as giving it better heat dynamics and creating a extremely quick flame front.
The downside is that it would be so close on a stock bottom end that some bolt stretch or just the piston rocking in the bore could cause a crash.
The downside is that it would be so close on a stock bottom end that some bolt stretch or just the piston rocking in the bore could cause a crash.
Originally Posted by brad8266
Well the .032 quench would bump DCR up slightly, but the real advantage of it is the great amount of turbulance that would be caused in the chamber, which would make it LESS prone to detonation as well as giving it better heat dynamics and creating a extremely quick flame front.
The downside is that it would be so close on a stock bottom end that some bolt stretch or just the piston rocking in the bore could cause a crash.
The downside is that it would be so close on a stock bottom end that some bolt stretch or just the piston rocking in the bore could cause a crash.
However if the rods stretch youll probably have plenty of other issues like spun rod bearings. IMO, I dont think a motor will run very long with stretched bolts regardless of the quench.
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Not to mention the factory deck are usually not perfectly square which could mean the pistons are .004 out of the hole on one end or on one side and maybe .006-.008 out on the other end or other side. Have you checked all of them, or at least one on each end and on both sides?
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Originally Posted by BOWTIE
Not to mention the factory deck are usually not perfectly square which could mean the pistons are .004 out of the hole on one end or on one side and maybe .006-.008 out on the other end or other side. Have you checked all of them, or at least one on each end and on both sides?
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Originally Posted by GuitsBoy
Thats how I feel. The tighter quench will help the motor to actually run without pinging on 8.8x dcr.
Originally Posted by GuitsBoy
However if the rods stretch youll probably have plenty of other issues like spun rod bearings. IMO, I dont think a motor will run very long with stretched bolts regardless of the quench.
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Originally Posted by brad8266
I would be most concerned with the piston rocking in the bore and bumping the head because remember a stock bottom end piston will come out of the hole a slight bit.
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I'm also concerned about a piston to head crash. That's one of the reason's for this thread. I needed some opinions as to whether I'd definitely be ok, or I'm playing with fire, so to speak.