pawnstar12

how much does the 3.5 heads lower compression?

SR20DEN

iTrader: (7)

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

pawnstar12

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

IceY2K1

iTrader: (3)

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

krismax

iTrader: (15)

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

IceY2K1

iTrader: (3)

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

pawnstar12

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

SR20DEN

iTrader: (7)

Those heads are already spoken for.

IceY2K1

iTrader: (3)

Money talks...BS walks.

IceY2K1

iTrader: (3)

High compression head gasket?

SR20DEN

iTrader: (7)

Really?

chris'smax

iTrader: (3)

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)

pawnstar12

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

IceY2K1

iTrader: (3)

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.

pawnstar12

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 ?

stephenlc

iTrader: (1)

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.

IceY2K1

iTrader: (3)

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.

pawnstar12

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

pawnstar12

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

IceY2K1

iTrader: (3)

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?

pawnstar12

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

pawnstar12

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

IceY2K1

iTrader: (3)

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.

pawnstar12

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

kenji

iTrader: (1)

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

SR20DEN

iTrader: (7)

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

kenji

iTrader: (1)

Holy racegas batman!

IceY2K1

iTrader: (3)

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

kenji

iTrader: (1)

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?

SR20DEN

iTrader: (7)

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.

SR20DEN

iTrader: (7)

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.

Larrio

iTrader: (10)

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

kenji

iTrader: (1)

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? ...