Sorry to bother you with another of those ”combo” questions.
Story is that Im going to tune “down” my 355 and make a nice daily driver with good idle, that can pass sniffer test here in Sweden without any drama.

I have a combo in mind that I need some feedback on.

This is what I got to build on:

1991 vette 6spd
355 forge bottom end
Converted LT1 intake
Hooker headers to hooker front y-pipe to metallic “race” cat to rear magnaflow exhaust.

Plan so far is:

Cam.

CC XFI™ Xtreme Fuel Injection 260XFI HR13

210/218 .560 .555 ( 1:6 ) lobe 113

Or:
ZZ9 cam
212/226 .483 .520 ( 1:5 ) lobe 112

My exhaust is a narrow point, so perhaps the ZZ9 cam will work better?
Also tuneability is a factor here.

Heads.

Im looking at dart pro 1 alu heads:

180cc intake port, 64cc chambers.
With my pistons I will get 9.8:1 comp.
And the 180cc intake will be a descent match for the lt1 intake I think.

I hope this will make a mild, easy to tune, drama free daily driver.

Am I way off?

Cheers

 

That looks like a good plan. Your CR is good for either of those cams.
I'd prefer the CC XFI; just make sure the valve springs will support it. Comp Cam's guide for springs is not very good when pairing a given cam with the LT1 manifold. Your powerband is going to be about 500 rpm higher than what they specify for that cam, so choose your springs accordingly.
If you decide to run the ZZ9 cam, I'd run 1.6 rockers on the intakes. Either cam can be tuned to run clean for emissions testing.

 

Thanks

Do you think I can benefit to get heads with even smaller chambers? Like 62/60 to boost up the comp?

 

Going beyond the 9.8 CR you stated is pushing it with those small cams.
It's possible, but factors such as the pump gas available to you, quench (deck clearance + gasket), piston type (flat top?), cooling, intended use,..... all need to be considered.

 

Thanks

Piston got 4 valve relife.

So going thru the process to perhaps mill the heads, to get closer to 10.5:1 is not worth it, compared to my 9.78:1 ?

Cheers

 

I'd have to say no.
What is your deck clearance (how far are pistons in the hole)?
What head gasket thickness do you plan to use?
What temp thermostat?
What octane fuel (R+M /2)?
What's your plan for tuning it?

 

Fair questions.

Deck clearance im going to measure, I will get back to you there.
Gasget thickness I havent decided yet, It will be choosen after I got the deck clearance.
Stock temp thermostat 195 f

Octane is EU 95.
EU ratings are 95/98, which are equivalent to US ratings of 91/93.
So, EU 95 octane = US 91 octane and EU 98 octane = US 93 octane

Im tuning it myself using the stock 730ecm 8d code and tunercat, datamaster and my own wideband o2.

Thanks

 

Use a .028 head gasket thickness. It will get the compression up to 10.6 to 1. This will be cool and you can use 91 octane fuel. It will also pass the sniffer too with the right tune. We do this in SoCal with no problem.

 

I measured between the center of the piston and a metal ruler that I laid flat over the block. I used a digital caliper.
It whas hard to get a consistent value, due the angel I held the caliper kept changing.

But it whas around .022 give or take..

I also saw that summit has these heads that might work better for me, and will pump up the comp to around 10.5:1 with 56cc chambers?

http://www.summitracing.com/parts/tf...make/chevrolet

And cam choise is most likely going to be the LPE211 cam:

211/219 .496/.525, with 1:5 rrs
What do you think?


Thanks

 

With .022 deck clearance, I'd run the .015" coated steel shim head gaskets http://www.summitracing.com/parts/fel-1094 and the 64cc heads. That tight quench and 10.0 CR will make a great running engine with probably only 30 deg of timing required for best power. IMO, that LPE cam is better than either of the earlier options you were considering.

 

Thanks so much for helping.

Out if curiosity and lack of knowledge.
Why would the 64cc heads and the thinner headgasget be a better choise then the 56cc heads, a normal headgasget on this setup? Is the comp going to be to much at 10.4:1 ?
Or Is it about the "quench " ?

Thanks

 

Yes, it's about the quench.
I was going from your 9.8CR remark at the top of the thread figuring the .015 gasket would bump you up by about 0.2, but I've just run the calc using the numbers you've posted since then, and yes, I come up with 10.3 CR. That will be fine with the .037" quench and AL heads, the 91 US-equivalent octane, and ideally a 180 deg tstat. sorry, but earlier up the thread I was thinking iron heads and had no idea of your planned quench clearance, thus was cautioning about going over 10.0 CR.
Your engine will require less ignition advance for best power with the better mixture motion from the tight quench, and therefore will be more detonation resistant than it would be with a thicker gasket and more timing.
Degree the cam when you install it to make sure it falls around a 107 ICL.

 

I had 10.8-1 with Dart S/R Torquer heads with the .015 shim gasket. The heads were milled from 67cc to 64cc on 91 octane and never pinged.

 

Thanks. Thats the way im going to take..

 

I've heard that in that quench range piston to valve and piston to head clearance is a really big concern, especially at high RPMs. Is there any rule of thumb about that? Piston to valve clearance can be measured, of course, but not sure what the guideline is there.

 

ahh good question.

My forge pistons has 4 vavle relife in them.

 

[QUOTE=devilfish;5497927]I measured between the center of the piston and a metal ruler that I laid flat over the block. I used a digital caliper.
It whas hard to get a consistent value, due the angel I held the caliper kept changing.

But it whas around .022 give or take.


You need to measure properly with the rings on the piston. This will cause the piston to **** in the bore. Measure at the high point of the piston not the center of it

 

It's not a concern for any of the cams being talked about here in Gen1 SBC's. You have to get up around 245 @ .050" duration cams installed at 105 deg or sooner ICL's before it needs to be looked at.
Some people mistakenly think it's the lift of the cam that is a concern; it's really the intake valve trying to open when the piston is dwelling near TDC that is the concern. Also, think about how much the valve is trying to move versus these few thousandths we're talking about in quench clearance.

 

[QUOTE=scoflaw;5499548]Rings where on. I will find the high point and re measure..

Thanks