[matt4723]

So if i ran 50/50 mix "cam2" What would u set timing at??I don't want to pull the motor..to change the pistons...maybe i may change the heads to 72cc but not right now....I just got it built and yes...i was stupid not to think about compression...but have to live with it for now..cause i blew $5000 on this motor...Oh yea thinking about it i didnt even think about this but when i put gas in it it was 87 octain...so if i put 92 octain in would it run better...Or do u think i still need Higher Octain..and ajust timing accordingly

 

[camaroman7d]

The quote you responded to was a question for BartonekDragRacing about the 350 he was running at 11.5:1 with iron heads on pump gas with no problems.

92 octane would be better than 87 and should let you have a little more timing (maybe). There is no way to tell how much timing you will be able to run, the only way to find out is to tune it and see what it likes (and can handle). IF the heads you have are new, maybe you can sell them or trade with someone looking to go the other way (more compression). In the end that will give you the best performance and be cheapest.

 

[BartonekDragRacing]

I had a 3000 stall. compression was a mathematical calculation..it was at least @ 11:1. This was goin by the book looking at the piston specs, head gasket thickness, cc of the head, zero deck block. btw, I meant to say, it was a 355. Cam was CompCams XE 294

We're building a 396 SBC for my brother.. 11:1 or so CR, Dart Iron Eagle 215cc heads, scorpion or victor jr intake..its going in the 73 Camaro.

 

[camaroman7d]

Are you guys using the offset ground crank to build the 396 SBC? Or did you go with an aftermarket block. I don't know how you are getting away with 11:1 ++ on pump gas with iron heads. Maybe if you runn them real rich, big cam and take it easy on the timing. If it works for you keep it up.

 

[thrasher]

Originally posted by BartonekDragRacing:
I meant to say, it was a 355. Cam was CompCams XE 294

Mat-
A 11:1 355 with a XE294 is going to have a lot less effective compression than a 11:1 383 with a XR270.

The duration of the XE294 will blow much of the compression out the exhaust since it is designed to make top end power by means of somewhat of a sucking effect at high speeds.

(Don't know how to explain it in short detail.Don't know if I explained that verry well or not either)

The XR270 is designed to make lots of torque and power in the low and midrange by more or less trapping the cylinder pressure more,wich in effect creates higher cylinder pressures with a given compression ratio.

Make sense

[ 01-07-2004, 07:45 AM: Message edited by: thrasher ]

 

[camaroman7d]

I come up with a DCR (dynamic compression) of 10.464 in the 383 with the XR270 cam (that is way high for iron heads)

In the case of the 355 in order for me to even get to 11:1 I had to assume zero deck, flat top pistons, .039 head gasket, 64cc heads and no valve reliefs (with a 4cc valve relief and a .041" head gasket it was closer to 10.4:1).

With the XE294 and a static of 11:1 the DCR is 8.178

With the XE294 and a static of 10.4:1 the DCR is 7.765. This would explain why it ran fine on pump gas.

As you can see the cylinder pressure in the 383 is WAY to high to get by with. I will take this one step further and see what the DCR would be with the XE294 in the 383.

The DCR would be 8.288 still pushing it for pump gas (IMO).

Take this for what it's worth, I am not trying to prove anyone wrong or right I am just trying to make sense of the situation. Hope this helps to clear up things a bit.

 

[Eric68]

Yes, the cam makes all the difference with this 11+:1 350.

My 383 runs premium unleaded and is 11.3:1 static compression but I have aluminum heads and am running a 294* Comp Cam. I can also tell you that I am also close to the edge for pump fuel --- Hot weather, Hot coolant temp, and cheap gas will make the plugs START to show signs of detonation if I run full timing. I only had this happen once under extreme conditions so I don't worry about it, but its nice to know where the edge is.

PS. My cam is actually a little shorter than 294* if you measure it at the valve --- because its a solid FT cam lash effects adv duration and lift.

 

[Mousehouse]

Matt I would suggest getting a different set of rods from Scat or Eagle like their I-beams. I see them all of the time on e-bay for around $200. I would also buy something a little better than proform rockers. Maybe Crane or Comp cams.

 

[BartonekDragRacing]

yes, you two/three are correct (mousehouse, camaroman7d, eric68)....

Camaroman7d: the crank is offset ground and the pistons are .060 over.

 

[SLEEPER 86]

hey matt;
maybe you should consider some sort of"water injection"setup.this has helped some friends of mine who were running around 11:1
Eric

 

[matt4723]

I think i know what you are talking about...If i am right i can buy it through jegs....don't u get it as a kit...like a adapter that bolts under the thermostat housing...and it has two treaded holes...where the hoses hookup...then from there it goes to each side of the head??...maybe i am wrong not sure.......

 

[Eric68]

Matt, no, its a special injection system that uses a separate pump and nozzle that actually injects water mist into the carb. The fine water mist cools cylinder temps during combustion. Usually the water is mixed with some type of alcohol to keep it from freezing and to assist the burn. I do not personally know anyone that has used a water injection kit successfully on a street car - that is not to say it cannot be done . . .

 

[SLEEPER 86]

you would,of course need to make sure you didn't run out of water on the street.i remember some guys using aquarium pumps for experimental purposes back in the day.you would probably want something more reliable than that,as i don't know how they would handle vibration.
as far as the water source goes,a wiper washer bottle would be a start,but you might need more capacity to get you thru a tank of gas.the trick setup would be a knock sensor attached to a solenoid to activate the pump(electric fuel pump?dont know if they can do water),and a fuel injection nozzle to mist the water.
although it would be sweet to use all aquarium parts! i can see the 5 gallon aquarium water supply in your trunk now
good luck!
Eric

 

[matt4723]

Ok Guys.....Use 92 octain and adjusted timing..and it pings worse now...So i am either going to change the heads if i can find some to trade for...If not i will end up pulling the motor again and sticking differnt pistons in it before it ruins all my hard work...Found some pistons i was thinking of Hypereutectic Pistons with coated skirt P/N through Jegs is 844-H859CP30...0.110 dish piston,4-Valve Reliefs 9.63 with 64cc heads...little spendy @ 43.00each....Or how about these Hypereutectic Pistons by Silvolite Approximately 10.3:1cr with 64cc heads little more on the cheaper side @ $18.00ea but just as good??

 

[69RS/SS350]

Just run a 50/50 mix of C12 and premium like I do and you'll be fine!

 

[BPOS]

Originally posted by matt4723:
Found some pistons i was thinking of Hypereutectic Pistons with coated skirt P/N through Jegs is 844-H859CP30...0.110 dish piston,4-Valve Reliefs 9.63 with 64cc heads...little spendy @ 43.00each....

That sounds like a Speed Pro Hypereutctic part number. Look here:

www.dirttrackthunder.com

They have coated Speed Pro Hypers to fit your motor for $189 delivered to your door for a set of 8.(Exact same piston that you found at Jegs) Look at part # H602CP - it has been replaced with part # H859CP. The "30" at the end means .030 oversize.

 

[matt4723]

Ok...not sure what i am going to do yet....I talked to my machinest were i bought the block from...and he also did all the calculations...and he came up with 10.7cr...Like u guys said the cam is a little small and he agreed...he said that maybe why it pings...to high of compression for that cam.....So if i went with a bigger cam would that make it more effincent with out pinging....or should i just get some 72-76cc heads?Sorry i know now that i need to pay more attention to compresson...And now i am paying for it "Live and Learn"...I do not want to run race gas cause i would like to drive it....without breaking my wallet..Any more info would be great...I am willing to spend $600
on heads..Or if i can get away with putting a bigger cam in..I would do that...Thanks
ps..head gasket was .035

 

[matt4723]

Would need to be a roller cam so i can reuse my roller lifters

 

[matt4723]

Called comp cams...they said i should be fine with the cam i all ready have....Confused on what to do....maybe just change the heads and be done with it??

 

[travis]

Geez, seems like their "tech" support (and I use that term loosely) is getting worse every day. Way too much compression for that cam...and having iron heads isn't helping any. Swapping to a set of 72cc heads, with a 0 decked block and .038 quench, will put you just a hair over 10.0-1. Still high IMO for that cam. A set of KB dished pistons (or the speed pro's you listed) would get you right in the range you need for that cam.