how much does the 3.5 heads lower compression?

 

A rough estimate using the VQ35 heads and matching head gaskets takes it down to 8.9:1

 

i was bidding on some 350z heads but they sold for $450 i put in $300 so i lost ....oh well

 

http://forums.maxima.org/showthread.php?t=349665

 

What would the compression be with a 3.5 head on a 3.5 block with vq 30 crank and rods.......

 

krismax - I believe that setup would be around 9.37:1(VQ35 with VQ30 rods/crank) vs. 9.02:1 for VQ35 heads on VQ30 short block using *ROUGH* guesses and this online calculator....http://www.turbofast.com.au/TFcomp.html

 

thanks man ... i can always count on you. the only thing is im gonna need the fab a high compression head gasket because i have 9.1 pistons

 

Those heads are already spoken for.

 

Money talks...BS walks.

 

High compression head gasket?

 

Really?

 

so using the 3.5 head on 3.0 block works if you use use the 3.5 lower intake manifold(or am i way off base)

 

i dont think the lower IM matches up...at least it thought i read that some where

 

Nobody has definitively proven what is involved with putting VQ35 heads on a VQ30, however at least the lower/upper intake manifold would be needed since the VQ35 intake ports are a different size and angle.

 

if you split apart the head gasket you lower the compression. so if you add layers you would raise the compression. am i right or wrong? so being that i bought forged 9:1 compression pistons and planning on using the 3.5 head, i would want to raise the compression because it would be way too low. or am i missing something ?

 

Why would you need a high compression head gasket whatever that means. You could use the nismo one, I think it is thicker. You just need a thicker one but I think you would be fine even with the lower compression pistons, that would bring you down to about 8:3:1 which isn't that bad. More boost for you on pump gas.

 

Auuuugh, it's the other way around. Thicker head gasket lowers compression. However, from what I believe SR20DEN has said, that won't work on VQ engines or if did, it would screw up cam timing.

 

i thought it would be more like
10.5 stock
- 9 forged
________
1.5 difference

9.37:1= stock VQ30DE bottom end, 3.5 head
7.87:1= forged pistons,VQ30DE bottom end, 3.5 head

 

oops... *made an @$$ of myself*

 

Stock VQ30 is 10:1.
Stock VQ35 is 10.3:1.

Why would you want to use forged pistons with the VQ35 heads unless you're trying to RAISE compression by using say 11.5:1 or higher pistons?

The VQ35 heads lower compression to an acceptable pump gas ratio and the stock VQ30 pistons are tough enough to tolerate 18-20psi or so on FIs. Are you building a 20-25psi FI motor here?

 

well now that you ask....yeah i am

 

where the hell did i get 10.5:1 from???? hummmmm oh well.

 

All motor forum......so I don't want to go any further. Post in the FI guys territory.

Just follow Mardigrasmax lead, he'll show you the way shortly.

 

well the reason i post here is because i feel you guys are way more knowledgeable about our motors i feel so if i pick your brains it will very beneficial to my build.... and for the record i never like to follow

 

I think there are plenty of wise people in F/I forums.

 

VQ35;

Swept: 583.0704
Total Chamber: 62.6957
CR: 10.3:1

Alternate
CR: 12.0:1
Total Chamber 53.0064


VQ30;
Swept: 497.9202
Total Chamber: 55.3245
CR: 10.0:1

VQ32:
Swept: 525.0499 (95.5x73.3)
+4.2978 chamber
CR: 8.8:1 (VQ35 heads, pistons, gasket)


VQ30DE with VQ35 heads/gasket
Swept: 497.9202
Total Chamber: 62.6957
CR: 8.94:1

 

Holy racegas batman!

 

That's with the NISMO heads, however Tilley is around 11.5:1 without issues on pump gas.

 

Daaaayum. I only get 91-92 here in Oregon. I can't see 12:1 without high octane fuel or some kind of anti-detonation injection system.. Well who is going to pioneer that one or will it have to be me?

 

That 12.0 is just a number i pulled outta my **** and typed on my scratch pad when I was working a bunch of equations the other day.

 

I know of people that can design engines to run 14.0+ on pump gas. It's no big deal. My brothers '93 Pontiac Grand Prix runs at 12+:1 on pump gas just fine.

 

the toyota matrix also runs on 12.0 compression and i forgot which company even turbo'ed it

 

Well the engine in question is the VQ. So what parts (that already exist pref. oem) would be needed to eliminate detonation, or would custom cams have to be made? ...