Kurt04

iTrader: (2)

I'm ready to select my heads for my 383 build, pretty sure I want AFR Eliminator 195cc, but I'm still looking. The short block is 3.75 stroke, 4.04 bore, 4cc flat top Probe SRS Pistons, pistons are .002 in the hole. I'm some what at a crossroads with the SCR and quench.

From what I figure, with a quench of .040 (.038 gasket) and and 65cc cambers I should be about 11.1:1 SCR.

If I go with the 75cc's and get my quench down to .030, that will put me at 10.1:1.

Is 11.1:1 too much SCR, for a daily driver? With MPFI, Aluminum heads, and 91-93 octane I should be ok, right? I know DCR is what really matters so, with a good cam to compliment that, I figure I shouldn't have too much to worry about.

Note: This is going to be a daily driver ('92 S-10) that will see the track as much a possible. It will have a Accel Pro-Ram intake setup controlled by a 1227730.

rgarcia63

I'd think twice before using a .030 quench regardless of the CR.
I run .043 quench @ 10:1 SCR with alum fast burn vortec style heads.

Sonix

iTrader: (1)

You didn't mention cam. If it's a fairly big cam, i'd do the 11:1 setup.
If it's not THAT big, then i'd do the latter choice, but do a .035" quench or so, .030" is a little too close for comfort. That'd put you closer to 9.99:1 sorta thing, but i'd still sleep well at night.
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.
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Just re read your post there. With fuel injection, and in a light vehicle like an S10, if you have a decent sized convertor, I think the 11:1 should be alright.

327???

I think 11:1 will be ok.

F-BIRD'88

11:1 is too high for a SBC on pump gas. A good cam combined with a good induction and exhaust system {that actually works together to fill and empty the cylinders (reguardless of the cams intake closing point) can and should very well create in excess of 100% volumetric effiencly at peak torque. That means you'll have a lot of cylinder pressure at peak torque. ( and you'll make a lot of torque and power.
That high cylinder pressure (when the motor is running) has no colilation with the cranking cylinder pressure that popular "dynamic compression" proponents push, is what determines the octane requirement of a particular engine.
Are you going to select and cam with timing to kill off volumetric effientcy in a hope to allow a 11:1 cr on pump gas. You're going to end up with a less powerfull engine than you could have. And it will be a fuel pig, to boot.
make the motor have high volumetric effientcy. Fills, traps and emptys air better. Then give it a static cr that works within the physical limitations of the available fuel taking in to account the actual in cylinder "mean effective pressure" at peak torque.
Around 10.5 with aluminum heads. .030" quench clearacne is a little too tight. have the large chambered heads milled to adjust the combustion chamber volume. or open up the small chambered heads to the required combustion chamber volume.
You're not building a LS-1 type motor. Don't try to do what is done on those motors.

A motor that detonates at WOT (even a little) does not make power and will live a short life. The required tuning compromise (richer AFR and reduced spark timing) kills off more power than you actually would loose by limiting the mechanical cr.

Make the head 70cc and the quench clearance .040"
by the way, which is it? 91 or 93 fuel? If you'll actually be using 91 octane fuel, make the cr under 10:1.

Kurt04

iTrader: (2)

You make a good arguement and I think you are correct. I guess I was blinded by trying to get what I want with out milling the heads. In the back of my head I knew that 11:1 is really to much, but I didn't want to belive it. I also know that .030 quench is a little close, especially when I have a used shortblock that I haven't even seen in person yet.

I think 10.5:1 and .040 quench is nice and safe.

Jens J

If you havent seen the shortblock yet i would wait to order the heads untill you check the deckhight unless you know its zero deck!

Kurt04

iTrader: (2)

Its not zero deck, it 9.002. Thats why I said pistons are .002 in the hole.

Kurt04

iTrader: (2)

Well, I emailed AFR to see what their options are as far as angle milling or flat milling the 75cc heads, having them open up the chambers on the 65cc heads, or even if they have any other options to get a 70cc chamber. But no reply yet.

Now I'm kinda debating if the extra .5:1 C/R is really worth the hassle. Would I really see a that much of a difference? I'm not really concerned about the cost or the wait time, but if the gains are not going to be that big, I'll just settle for the 75cc's and 10:1 (.038 thick 4.060 gasket).

F-BIRD'88

You can order your heads finished to a specific chamber volume.
Its a extra cost option. To mill your heads from 76cc to 70cc is a flat mill operation. Not very involved or expensive. Just tell them when you order your heads direct from AFR.
The difference between 10:1 and 10.5:1 is 2% power or less.
But having too much compression even alittle too much will kill power a lot faster. Not to mention shorten the life of the motor.
If you will actually be using 91 octane go easy on the finished cr. 91 is not the same as 93.

1989GTATransAm

iTrader: (3)

Here in warm Southern California I'm running 10.70:1 compression with .035" quench and 91 octane. I think you will be OK with 10.5:1 compression, .040" quench and 91 octane.

You are only going to build the motor once hopefully so get it right the first time. Just have AFR mill the head to the desired cc's as was stated above. By the way you will need a custom tune.

Kurt04

iTrader: (2)

So since I started this thread about choosing a cam, alot of people have said I need to bump up the compression to make good use of the cam.

So I'm trying block static compression out of my mind right now and only think about dynamic.

So for the Crane cam I'm looking at they list the valve timing @ .050" lift as 8-42-56-2. If I use this calculator and take 42+15=57 (because "ABDC @ 0.050" lift plus 15 degrees") I get 8.4. But to me using "ABDC @ 0.050" lift plus 15 degrees" isn't very acurate. I have no clue where they come up with + 15 and with higher ratio rockers your off even more.

So I downloaded the program from this site. To get the "advertised" valve timing, I punched in the @ .050" lift duration numbers and LSA, then fudged the Intake centerline number till I got the 8-42-56-2 valve timing, ICL was 107. Does this sound right? Or am I way off course here?

If that is right, the numbers it gave me were 39-73-87-33 valve timing @ advertised lift (which for a crane I think it is .004", still much closer than .050"), overlap of 72, and total cam advance of 5.

Now input to figure dynamic stroke, 3.75" stroke, 6" rod, 73 ADV intake closing angle, gives me effective stroke of 2.69". Plug that in the CR calculator as stroke and get 7.45:1 dynamic compression.

So two different calculators, two different numbers, which, if either, is correct?

And am I right to say that with alum heads, EFI, clean air, and proper cooling, I should have no problems running 91 (or possily lower) octane at 8.5:1 dynamic compression?

Kurt04

iTrader: (2)

Oh, the cam is Crane P/N 109661
230/238 Duration @ .050
292/300 Advertised Duration
.539/.558 Lift with factory rocker ratio
112 LSA

Guest

I have the first cam that Comp recommended:
P/N 08-467-8:
230/236 Duration @ .050
280/288 Advertised Duration
.576/.570 Lift with factory rocker ratio
113 LSA

Running ported AFR190's in a heavier car with a 350 with TPI (Edelbrock base, stock runners, plenum, 58mm TB), 1 5/8" headers into a mix+match exhaust, 200-4r, 3000 stall, 3.42 in the back and right at 10:1 and I'm absolutely certain it would benefit and run with more compression just fine. It'll run fine on 87 octane depending on the weather conditions. Figure with the Pro-Ram and those heads (little better than mine probably), you should be nearing 400 at the wheels I would think. Maybe more.

I'd go for .035 quench. .030 is doable, but for how long? I think playing safe is better in this case. Get AFR to mill the heads to the cc you want, thats what I did although I had my shop mill the heads. I'd go with around 10.5 and it should be just fine.

Damon

If you milled a measly 2cc out of the larger chamber heads (down to 73cc) you'd be back up at 10.1:1 with .041" quench distance (Fel Pro .039" head gasket).

I'm not a big fan of high compression on pump gas street motors. They work fine until you get some mileage on them with the pistons and chambers starting to carbon up a little- you end up with a ping monster. Then you start to have to pull the timing back to stay out of detonation and you end up with less power than if you had just gone with a lower/safer compression ratio but with optimal spark advance to begin with.

Kurt04

iTrader: (2)

Ok, thanks guys but what about my calculations (post #12)? Thats why I brought this thread back.

Guest

My DCR using Kelley's calculator comes out to 7.82 IIRC and I have no problems with 91 octane at all.

You're not going to get an agreement on DCR with different calculators, unfortunately. Actual dynamic compression is a guessing game with more factors than just the cam and displacement.

I think Allen's (89GTATransAm up there) DCR with Kelley's was around 8.4
He runs 91.

1989GTATransAm

iTrader: (3)

I more thing about quench. There is a theory going around that if the quench is to tight it might actually quench the flame front in the far reaches of the cylinder. So I would try to stick with a .035 quench for a number of reasons including mechanical.

As to my DCR using Pat Kelly's calculator Madmax was pretty close as mine works out to be 8.5:1. I was trying to squeeze every last horsepower.

SpitotRs305

when i was telling you to get your comp up there... i didnt mean 11:1 just above 10.5:1..10.8, 10.9 would be a good area for 91 with AL heads...

those cams you are looking at are rather large... even for a 383. which well it wont really be a dog cause its a 383 down low. but it will be an underperformer...


what you are trying to build here has a pretty good chance of being difficult on the street.

if it were me building this engine... i would forget about spinning this to 6500 that wont give to many smiles on the street and with a T56 isnt nessecary
torque is what you want and the 383 will have it... but it wont have as much in the normal street range if you plan on making power til 6500...

I would focus on making peak TQ around 4800-5200 RPMs that way you will be making power to use your 6th gear... and for more traction control issues

but a idea of what i am running for CR 10.9:1 with CAST vortecs and a DCR of 8.3:1... but i religous about my gas... get it the same day every week always from the same station and always 93...

the one thing i have been wondering lately is now that they have added the ethanol to the gas wouldnt that raise the octane? as ethanol can be from 100-115...

Kurt04

iTrader: (2)

I know I won't get the same numbers from different calculators, but with the Silv-o-lite one I get 8.437, thats with 57 as the intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degrees. Because they list valve timing @ .050" lift as 8-42-56-2, so 42+15=57.

But with Kelly' Calculator I get the "advertised" valve timing as 39-73-87-33. Because I only have valve timing @ .050" lift duration numbers, I punched them and LSA in, then fudged the Intake centerline number till I got the 8-42-56-2 valve timing, ICL was 107. Was that correct? Because that would put static at 7.45. Pretty big difference, but I actually feel 7.45 is more correct, that is if the cam is installed per the cam card at 5 degrees advance (107 intake centerline.) But also, advertised duration in not [I]actual[I] seat to seat, and even rocker ratio will effect that, but its still a lot closer than "@ .050 plus 15 degrees"

Do you mean that in the sense of, "don't go past this" or ".040 isn't enough"? Because I have already decided .030 is too close, all my numbers now are with .040 for the quench. Only reason I was even thinking of going that close was because I was trying to cut corners and get the compression "I wanted" with out having to mill the heads, which I realize now, would have been a very bad idea.

You know you recommended a larger cam than Comp did at first. They recommended the same one as you afterwards and said, "if you want more RPM potential."

Just out of curiosity I asked Crane what they thought of the bigger Comp, I only gave them the specs. They said "thats too big." Did the same with Comp and the Crane cam, they said "thats too small."

I also got a recommendation from Bullet Cams (Ultradyne)
CHS 280/288 HR 12
DURATION @ .050 = 226/234
LIFT = .565/.565
LOBE SEPARATION = 112

Guest

There's 3 tabs on the calculator, one is to calculate valve timing for you based on 'advertised'. It comes up with the valve timing you listed, using 107 ICL. 107 ICL is likely correct. Is that whats on the cam card?

Kurt04

iTrader: (2)

Thats what I used. Thats what I thought, guess the "intake Closing Point (degrees) ABDC @ 0.050 lift plus 15 degree" that the Silv-o-lite calculator uses was making me doubt myself that I did it in correctly. I'm only going to use the Pat Kelly one from now on.

I don't have the cam yet, just going buy specs from their catalog.

I'm going to keep playing with the numbers, talking with the cam guys and the guys at AFR and maybe we will all come up with something.

I'm thinking if I get the dynamic up near 8:1 with the 5 degrees advance that would give me room to play, but like I say I'm gonna keep talking to the experts also.

SpitotRs305

you are right i did recommend a bigger cam than comp because i didnt know you were really planning on driving this on the street... daily, and that you understood exactly what you were building... something that you are going to want to spin til 6K+ isnt going to be much fun for a daily driven car in my opinion...that is why i am now saying smaller would be better that way you can run your 91/87 and still have the low end TQ to have fun on the street... and still be able to tell people it is a 383 at the strip..

Kurt04

iTrader: (2)

I'm not trying to purposely build something I can rev to the sky. I know that I need lower RPM torque to be a better daily, but once its altogether, I'll hit the dyno, see my power curve, decide on a rearend ratio, and pick my shift points. I would spin it till 6k everyday on the street anyways.
anyways.

How do I delete the poll?

SpitotRs305

what are you running for gears now?

you will probably need 3.73s minimum if not 4.10s or 4.56s...

Kurt04

iTrader: (2)

Right now it has a 7.5 under it, I know it won't hold up too long so I'm going to replace it with something stronger, most likely an 8.5, maybe 12-bolt, 8.8" or 9", if I were to find a great deal, but kinda doubt it.

I was thinking 4.10s or 4.56s would go well with the T56.

Kurt04

iTrader: (2)

Ok, I have decide I'm going to have the heads milled to 70cc chambers.

With the Crane Cam and the recomended 5 degrees advance and .040 quench (.038 x 4.130 gasket), dynamic calculates out to 7.8:1 with static at 10.5:1.

If I used a .034 quench (.032 x 4.060 gasket) and 5 degrees advance instead it would be 10.7 and 8.0, so thats could be a possiblitly, but I'm just playing with numbers here. Either way 70cc chambers would be best I think.

SpitotRs305

.034 is to small stick with .040


what do you get with that cam installed straight up with the .040 and the 10.5:1CR. for your DCR

Damon

`
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Careful with you cam advance calculations. The 5* advance you are calculating is already ground into the cam- you don't need to advance it any further at the chain. Dot-to-dot is how you install it to get the 5* advance on the cam card.

For calculation purposes this is probably irrelevant, but in real-world assembly that's something to keep in mind.

F-BIRD'88

"advertized duration" is just that. it has nothing to do with the actual seat to seat duration of a cam as measured in a actual motor while running.
In order to accuratly calculate the dynamic compression ratio based on intake valve closing point (when compression is supposed to start) then you have to know the actual point that the intake valve does close at in the running motor.
using any thing else as a input (advertized @ .004" or .006" or .020" or .015" or .050" or what ever will result in a garbage answer.
Even at that, this does not take into consideration the engines actual in cylinder pressure or temperture. AFR varience cylinder to cylinder etc etc.
Also Some one says I run 10.9:1 on 91, you can too.
Well his motor may be getting exhaust reversion back into the motor from excessive exhaust cam duration or a bad exhaust port shape and be deluting the next fuel air charge with exhaust gas. The resulting EGR effect is just enough to lower combustion temps enough to stay out of detonation but is also killing power output from what it could be. You cannot qualify the success of running "10.9:1 compression on 91 octane" without comparing actual power output. Are ya making more power?
or less power?
Take the whole "dynamic compression" stuff with a big grain of salt when it comes to dialing in a usable compression ratio on a specific fuel.

Kurt04

iTrader: (2)

At 112* intake centerline, DCR would be 7.4:1. Which is less than @ the 5* ground advance.



The Pat Kelly Calculator calculates "seat" timing from advertised. It may not be dead on accurate, but still much closer than guessing with SCR, or the Silv-o-lite calculator. If I actually thought that they were totally accurate I would be shooting for higher numbers, but I know they aren't so I'm staying somewhat conservative.

Really whats a guy to do? Just pull some random number out of his ****? Everyone has different opinions. It even seems like guys like David Vizard's opinions change from book to book.

If wanted to build a crap motor I would just buy some random parts, get the biggest cam I could find, shoot for the highest compression I could, and throw it altogether and wonder why it ran like crap. But I'm not, I'm thinking it through and trying for the best combo I can that will still remain streetable.

I know there is a lot that determines what octane you will need, not just compression ratio. Intake air temp, coolant temp, quench, ignition timing, ect. all play into that and I haven't forgotten about those either.

Kurt04

iTrader: (2)

Blah, I still haven't decided.

I'm still flip-flopping. I'm asking around on other forums, some say I could go as high as 11:1. Some say the difference wouldn't even be noticeable, so just play it safe. Alot of different answers. Either way it should make good power. Heck, I've even thought of just going with the 75cc's and add a little nitrous to make up the difference and then some. Even contemplated water/methanol injection.

The more and more I look into it the farther I get from making a decision.

1989GTATransAm

iTrader: (3)

Shoot for 10.25:1 to 10.75:1 and be done with it. On the quench anywhere from say .035" to .045" and call it good. Sounds like you may be on the verge of splitting hairs.

89gta383

iTrader: (5)

You are 'supposed' to pick the cam first, and then adjust the static comp ratio to equal your desired dynamic comp ratio.

All I can tell you is what I've used in the past. My current 383 is 10.5:1, hogged out AFR190's, 230-.600 107lsa cam, miniram intake, etc and it runs fine on the street, shifts at 6500, and has plenty of torque. With cat convertors, it would pass smog also. I wish I had gone with more static compression now that I want more power n/a, but I am limited to cam size because of my 10.5:1.

The problem is, you will change you mind on what you want later on, and your combo will already be bought and paid for, so the mistakes you make now can only be corrected later on with more $$$. Pick something that will get you some good power numbers, decent driveability and mileage and tune it as best you can. There is a tradeoff in going fast and using pump gas/daily driving it that you can't avoid.

I've run that comp 230-236 cam on a 114lsa in the past and it was tame. It would be good for an all-around driver though. Get it on a 110 or 112lsa for more mid-range. I even passed smog with it.

I don't know what you are looking for power-wise, but my suggestion for a good street combo would be the gm847 cam 234-242 112lsa and 11:1 comp. I would only use 93 or 91 octane and make sure you tune it. A bud is running this combo in his IROC and is pulling 3 mph more than me in the quarter. My car runs high 11's at 113, his runs mid-high 11's at 116-117.

Kurt04

iTrader: (2)

Yep, thats pretty much the area I'm in.

Thats what I'm doing. Pretty much decided on the cam, just using the chamber size to change the C/R, just don't know where I want it.

Thats whats kept me from making a decision.

Kurt04

iTrader: (2)

Thanks guys, I got what I needed here. Now we go back to this thread.

https://www.thirdgen.org/forums/tech...ht-engine.html