al8429

Wondering what the max CR for 93 pump gas. Building a vortec 350 and ordered wrong pistons. Using 7cc flat tops, vortec heads, .015 deck height, .026 gasket thickness. Says my SCR will be about 10.1:1 with a DCR at like 8.5:1 using lt4 hotcam. Cam says it has 37.5 IVC abdc. Hoping I can use the pistons.

86LG4Bird

iTrader: (1)

No, you ordered the RIGHT pistons. You're just on the conservative side of perfect
I would not want less than 10.0 for the Hotcam with those fast burning heads. I'd even prefer slightly tighter quench and higher CR.
Install that cam at 106-107 ICL, just dropping it in will be about 109 ICL. The earlier IVC will give it a better street & dragstrip powerband. That cam was originally produced for GM for their LT1 "production" roadracing program, thus the 109 ICL which eeks out a couple of extra ponies at the upper rpms at the expense of lower rpm which roadracers don't care about.


Edit: I believe you're using .050" tappet lift numbers rather than .006" in the DCR calculator. My calcs show you at 7.9 DCR for 109 ICL and 8.1 DCR for 106 ICL. Hell, you could run 87 octane with it! In fact, I'm running 8.1 DCR on 87 octane with the Vortec motor in my sig.

jokerZ71

You should be fine as long as your cooling/tuning is spot on.I doubt your actual DCR is even quite 8.5:1.It will actually be closer to 8:1 as the Hot cam has some fairly long lazy lobes.That cam actually needs 10:1 to perform well.

86LG4Bird

iTrader: (1)

Yup.
OP, see my edit. The Hotcam's .006" duration numbers are about 278/288 deg.

jokerZ71

Yep. IVC @ .006 is about 68*. The calculators that use @ .050 IVC plus 15* don't work well with cams that have long lazy lobe profiles.You really need to add 20 to 25* to get accurate.They are good with fast ramped cams like the VooDoo,or,Extreme series cams.If you use the actual .006 IVC,DCR is below 8:1 for the Hot cam,which is why,you're suggestion of some advance would help out on the bottomend.

al8429

So you mean I shouldn't just install cam straight up and down but instead install the cam a tooth or two more counter clockwise? Yes I guess I was using .050 figure

jokerZ71

You will need to degree the cam,or,use a timing set that allows adjustment.

86LG4Bird

iTrader: (1)

Yes, either an adjustable timing set (multi-keyed crank sprocket), or use offset bushings in the cam sprocket. One tooth would be WAY too much!

al8429

Ah ok I see. Looks like I have some more researching to do. Timing set I have looks to be a replacement stock set. Thanks for the help fellas. Which would be better easier route? New timing set? Timing wheel expensive?

86LG4Bird

iTrader: (1)

Since you already have the timing set, offset bushings is the cheap route. Google it

al8429

I'll look into that thank you. So you mentioned earlier you would have a tighter quench. How much?

86LG4Bird

iTrader: (1)

You can run all the way down to .030" quench on that engine IF you measure all 8 holes. If shooting for an average, .033 to .035 is a good number.
Is your block already decked?

al8429

Yeah had blocked shaved down. To 9.005. My pistons were .010 further in the hole then stock. So I'll be at .015 piston to deck height. Original plan was to use .026 gasket but I havnt ordered gasket yet. Should be getting block back from machine shop today

86LG4Bird

iTrader: (1)

You're so close to optimum quench already, I wouldn't sweat it. I believe .026" is your thinnest choice without going to something expensive like custom Cometics. The .015" shim gaskets would make me pucker ....unless you measure and find .015" is your MINIMUM deck clearance hole.

al8429

Yeah I saw those cometic prices. They were like $100 per side. The .026 Clevite was $20 a set. Which bore gasket should I use? I'm .30 over

86LG4Bird

iTrader: (1)

I believe 4.100" is your only choice, which is good.

al8429

What about a .021 copper head gasket. 4.060 bore. They are $100 for the set. The .026 Clevite was 4.125 bore also after looking at it

86LG4Bird

iTrader: (1)

Nope, do not run copper on a street engine. You WILL have coolant leaks.
If it's composite with a copper fire ring, that's ok. 4.060" bore would be great.


I'd just get this one: http://shop.mr-gasket.com/gaskets/he...chev-1-pc.html
With fresh decks, a steel shim gasket will be ideal.

al8429

That's what I will do then. You were right the copper gasket required the block or heads be o-ringed. One more question then I think I'm done. That gasket need to be installed dry with nothing on them at all?

86LG4Bird

iTrader: (1)

Yes, dry. It's embossed/rubberized

al8429

Great. I think I found that gasket in stock at local oreillys. Thanks alot for your help.

jokerZ71

Victor Rienz & Mr Gasket have composite gaskets in .025 & .026 with a 4.100 bore,i believe.

jokerZ71

Have you already had the block cut? If not, you could still take it down to 9.0" & use the Felpro .028" gasket for a quench of .038".I wouldn't wanna go much lower than that, especially if you advance that cam w/o checking piston valve clearance. Are you using 1.5, or,1.6 rockers?

al8429

I actually ordered a victor reinz .026 4.100 bore. The block is in the machine shop getting the decks cut now. Should be ready tomorrow. Should I just go ahead and cut the decks to 9? Or is that extra .003 quench gonna make a big difference

Also I am running 1.5 rockers for now till I can afford a set of 1.6

jokerZ71

That's a good gasket.I think you'll be good as is.That way, you'll still have a little deck left for cleanup at a later time if needed.

al8429

So your saying I need to get a 1 or 2 degree bushing? Then verify by degree the cam

skinny z

What kind of timing do you have in that engine? ( we may have had this conversation before...)

skinny z

Check out the Cloyes Hex-A-Just for a timing set and a means of getting the cam timing to where you want it. I'd pull up a part number but you haven't published any specs on your engine package.

86LG4Bird

iTrader: (1)

Yeah I think we did. I honestly don't know; I just give it what it wants. If I go by the marks, it's about 18 deg initial, but I know that can't be right. It has the L69 chip, which is a fairly aggressive advance curve. It runs great; it's the car in my sig. Running .015" HG's to keep the quench tight.

skinny z

For what it's, going back into my documents, my RHS Vortec iron headed 355 had a DCR of 8.4:1 and a cranking pressure of about 205 psi. SCR worked out to 10.39:1. Cam is 274/282 110/106.
THAT particular combination was difficult to tune as keeping it out of detonation meant taking a ton of timing out of it. That's despite a .040" quench, 94 octane and a cool running engine.

anesthes

iTrader: (12)

8.5:1 DCR is too high for iron heads, especially vortecs. As was with Skinny's build, you are going to have a tough time keeping it out of detonation.

The whole combo is a mess. If you've got a prepped block with forged flat tops, put some decent heads and a good cam in it. The vortec heads and lt4 cam is what you put in a tired L98.

-- Joe

86LG4Bird

iTrader: (1)

Ahem....appears you only read the opening post.
Read it all, especially post #2. He will be nowhere near 8.5 DCR
No, the combo is not a mess.

anesthes

iTrader: (12)

You are right, I didn't, and I assumed his numbers were correct.


LT4 hotcam intake valve closes at 68.5 degrees

350 cid, 4" bore, with 5.7" rods, standard 3.48" stroke.

I went ahead and calculated his static ratio assuming a .026" shim gasket at 4.030" bore, and came up with 10.0:1 rather than his stated 10.1:1.

So anyway, punch those numbers in and we get:

Static compression ratio of 10:1.
Effective stroke is 2.61 inches.
Your dynamic compression ratio is 7.73:1 .

So yes, his DCR is fine.

I still stand by what I said about the combo. Put some AFR heads on it and a comp-503 or larger cam and actually go fast.

-- Joe

86LG4Bird

iTrader: (1)

Aw come on, man, don't p!ss in his Cheerios. We're all low budget hacks here just trying to work with what we got
Money withstanding though, you ARE correct

al8429

How much of a difference are those heads and cam you mentioned? I havnt assembled the engine yet. I have been investing my money elsewhere. Although I did order a set of new scat rods and have a bit more money than when I first started. What's the price tag on a set of afr heads?

anesthes

iTrader: (12)

I'm not, but he's doing the bottom end right. Might as well buy good stuff for the top end.

-- Joe

86LG4Bird

iTrader: (1)

I wouldn't get too excited about out-of-the-box AFR heads. IMO, the little bit of performance benefit over Vortecs doesn't justify their cost. The people that really go fast with AFR heads are using their competition ported heads. Check the prices on those!
That CC503 cam is good. Standard Comp shelf grind. Good used ones available all the time too. search on LS1Tech.com right now and I bet you'll find one.


Edit: Oops, that wasn't directed at me. Oh well, I said it, so I'll leave it.

anesthes

iTrader: (12)

Here is a decent build:

http://www.hotrod.com/how-to/engine/...-crate-engine/

It's a 10:1 350, like yours. Forged flat tops. But they ran AFR-195 heads and a solid roller cam.

Substitute the solid roller for a hydraulic, like an XR288HR, and it will make 500hp.

Is this an EFI car or carb?

-- Joe

86LG4Bird

iTrader: (1)

http://www.hotrod.com/how-to/engine/...-crate-engine/
Magazine "test", paid for by one of their biggest advertisers. Ya don't think they might have "tweaked" those things a bit?
Results look suspiciously like their 180cc castings treated to their 195cc competition porting job. I've been around the block once or twice

anesthes

iTrader: (12)

That may very well be. I told him to use the 195 eliminators, and an xr288hr cam. It will make 500hp.

If he's using good pistons, scat rods, a fresh prepped block. Why bolt vortec heads an a take out cam.. It's gonna make 300-310hp.

In fact, the LT4 hot cam is only a hair bigger than the ramjet 350 cam in my boat. That motor is rated at 260hp. It has less compression, and again the cam is slightly smaller. I estimate a 40-50hp gain between the higher compression and slightly larger LT4 cam.

He can throw that junk out, and buy nicer heads + cam and make potentially 200 more hp.

-- Joe

86LG4Bird

iTrader: (1)

Man, I hate arguing (makes us both look bad ).
But I can't shut up just yet. I think you're really misleading him. The Hotcam is in no way, shape, or form in the same ballpark as that little Ramjet cam. Under a single plane manifold, at 10:1 compression the LT4 Hotcam makes 400 crank hp with stock Vortec ports (provided they're not the later inferior 062 crate motor castings). Unless he does something really wrong in the build, 350 crank hp with a 2-plane manifold will be a walk in the park.


OP, did you ever specify what intake you're running?

Orr89RocZ

iTrader: (20)

That i'll disagree with lol

But a vortec head refreshed with a good valve job is a great bang for buck

86LG4Bird

iTrader: (1)

Maybe I just go too fast....I mean fast enough.... with inferior parts, that I miss out on the finer stuff

Orr89RocZ

iTrader: (20)

Dabble in the finer things in life and it may spoil you lol do what works for you is all that matters

But there are applications where the afr's for the money are hard to beat for out of the box head. Most people can get away with less for their goals lol

anesthes

iTrader: (12)

We're not arguing, we're debating tech which is what the forums are for.

062 castings are production castings, I know because I have some in the shop that was on my 1998 GMC that I bought brand new in 1998 and junked in 2005 The 062s are the same as the other ones used in the 1 ton trucks, except the other ones had a longer protrusion for the exhaust valve guide to disperse heat.

You can't compare them to a decent aluminum head. Look at the flow and velocity numbers.. For the money, it's the best bang for the buck. You can cheap out other places.

-- Joe

UltRoadWarrior9

Exactly! I love reading the passing of knowledge based on experience/opinion... Going back to lurking.

86LG4Bird

iTrader: (1)

You are correct. Both production 906 and 062 castings are good and will make the power I stated. My '98 pickup also came with the 062's.
The later 062 ones used on crate motors are identified by "062 Hecho en Mexico" and should be avoided for performance use.

86LG4Bird

iTrader: (1)

not lurking. I'm actively participating...lol! What I post is pure experience....my own stuff + what I've touched and tuned.

al8429

Well I was planning on using dual plane edelbrock performer intake. Maybe the rpm airgap. Havnt decided yet. I may just put it together with the vortecs. Already had them rebuilt with better springs and valve guide cut to handle .525 lift. Later down the road I will get bored and get different heads I'm sure. Is there a better cam than the hotcam? Now would be the time to decide on it. About to get rotating assembly back from being balanced and havnt installed timing chain yet. Have a timing set that I can adjust +/- 4 degrees at the crank.

While we are talking about intakes, why do people say dual planes have better street manners. Been told I should use dual plane. Might be driving this car quite a bit

Orr89RocZ

iTrader: (20)

Dual plane fits the vortec rpm range much better