12secformula

Alright, I am building a 385 stoker, but am kind of caught in the middle on some issues. First the block is .040 over, and zero decked. I was going to run my AFR 190's w/ 54 cc chambers so I ordered SRP pistons w/ a -16cc inverted dome. Now I have decided to get a set of Trick Flow R-series 215's, they are going to be hand ported and should flow about 310cfm@600 lift, and will be milled to a 64 cc combustion chamber, now my problem is that the guy designing my custom cam says that with a cam as big as he is designing I will want a static compression ratio of 11.8-12.0:1. Now I will be returning my SRP's beacuse the inverted dome is obviously too much to be close to the ratio I am striving for. Now I cannot find pistons that I can use to accuire the needed ratio....well at least not in flat-top pistons. I have always been told, and read to run flat-top pistons for the best combustion, and quench. Will there be any adverse affects of running a dome with a 2 or 4cc volume, I know that is small but according to my calculations it should put me were I need to be w/ a .040 head gasket, also would a 0cc flat-top piston be ok to run? I thought about that, but now I am worried about piston to valve clearance if there is not any valve reliefs? What do you guys think....please help!! If I am mis-informed, pleae staighten me out!!

Streetiron85

I'm not the expert on this, but I have a feeling when the other guys do post it will be a similar response.
First question, is it a race only car?
Why such a large cam that you'd require 11.8+ CR?
It seems like more cam than what is commonly used by most guys with street driven 383s.

brutalform

That does sound a bit stout! What kind of induction are you planning? Depending on the rest of the combination, it may not be that radical so to speak. I get away with pump gas on my 11.2 C/R with aluminum heads, but Im also running EFI. A large cam will bleed off some of that cylinder pressure. What are your intentions with the car?

12secformula

Yes the engine should be quite stout. My goal is about 525+ at the crank N/A. No this is not a race only engine, actually it is more of a street car than anything. This will be more of an all around performer than anything else. Suspension wise it is set up like an auto-x vehicle, but will make it to the strip a few times a month, along w/ alot of street racing. I am running EFI also, I am running a Mini-Ram intake that will be ported to match the heads. The cam profile I will be using is quite aggressive, Bret Bauer is designing it and Lloyd Elliot, who is a very common LT1 head porter is doing my heads. The cam should have peak power somewhere between 6600-6800 rpms, I wa also told that w/ a cam like this we are much more worried about dynamic compression ratio being at 9:1 than what the static ratio is for running pump gas. I don't wanna mill the heads to 62cc or less due to the risk of intake and accessory fitment issues, so I believe a small dome is my only way to go. However I don't wanna go that route if I will have adverse Issues due to the domes. If I calculated correctly if I kept the heads at 67cc it would take a totally flat piston w/ no reliefs to put it at 11.8:1, now i don't want piston to valve clearance issues....so I don't feel that this is reasonable. But if I have valve reliefs, I think a small 4cc dome would give me the room for valve reliefs and the right compression ratio. Would a small dome like that have any adverse affects?

brutalform

When my engine went together, we decided to use Manley valves, because of the concave design on the bottom of the valves. This took a bit of compression out of the engine, Im not totally sure on how much, but it was worth doing, I remember.

Why not go with a flattop? It would allow for a better burn in the cylinder. The better you can control the flame front, will enable the detonation factor to lower. What C/R do you calculate with the flattops?

I think if the quench area is kept tight, you should have no problems. My engine is 500 hp, and 570 lb ft at the crank.

Maybe the Manley thing might work for you also.

12secformula

I calculate 11.8 w/ a 64cc chamber, and a flat-top w/ no reliefs...do you think it is safe to use w/ no reliefs?

12secformula

Oh, the cam is a hydraulic roller.....around .600" lift

12secformula

TTT....come on guys, someone help me out and answer my question. Will i have any problems or adverse affects of running a small dome piston w/ a volume of 2-4cc's? Or would there be a problem w/ running a 0 volume flat-top piston w/ out any valve reliefs? What would you do? HELP!

Streetiron85

I wouldn't consider using a 0cc flattop even with a stock cam, let alone the cam that you want to use.
There are guys with cars running in the 11s with lower than 11.8:1 CR. It seems to me like some more research would be a good idea. You're wanting to build a street motor with a race cam in by the sounds of it, and creating problems for yourself.
A 64cc chamber with a 16cc dished piston and a milder cam sounds like a much more practical combo.
I think most other guys would agree.
Your combo is over the top.

12secformula

I understand what you are saying, but I am curious why you think this is a race engine? Yes the cam is gonna be fairly large, but it will match perfectly w/ the heads. These guys designing told me to what I need to do to get this to perform, on pump gas and make good power. Its a big cam as far as lift but it won't be outrageous thats for sure, they said that I need a static ratio of 11.8:1 and I want it to perform like they think it will. Really I have a combo in mind, as do they....and it could easily make more power, but we went milder. I just basically need to know if you think a small dome on the pistons woould be a good way to do this. I guess I could have the heads milled right down to do it, but I don't wanna have any fitment issues w/ the intake, and accessories. What would you do if you needed the ratio to be that high? Also I have done a ton of research, and that has led me to use the people I am using for my combination. Thanks for your responses though.

Streetiron85

Why do I see it as being a race motor?
Because there are guys who take racing pretty seriously, meaning they do drive their car on the street, but the car's purpose is to win races. And it seems like the combo you're describing is one for that type of car... Pro Street.
Milder combos than yours are running in the 11s.
It just seems like the car you're designing is going to be a total ANIMAL..
But maybe that's what you want.
I kinda think you'd be happier with a milder combo though... it's not as if it would be slow.

Streetiron85

What are the duration #s for your cam BTW
The cams that I've looked at that require 12:1 CR are all in the range of >255deg@.050

brutalform

I would not use the dome under any circumstances, when you can use the flattop and eliminate any detonation problems. It just does not make sense today with the combustion chamber designs with todays cylinder heads. Keep it simple. Have a moderatley high compression engine, that makes killer power on pump gas. Keep a flattop design to keep the flame travel in the chamber under control. Dont add to the problems of inefficient combustion.

forums_suck

yip i'd keep it down to flat tops with at least the two valve reliefs or even a 12.5cc dish would be fine.My zero decked 400 is running flat tops with a .610 lift cam 250@.050 and cranking compression is just over 200psi on all 8 cylinders.Comprission i think is around 10.6 and it wont run on anything but premium
a question i have it with your monster heads if im not mistaken an intake port that large runs a felpro 1206 medium race intake gasket which you might find your intake maybe too small and result in sealing problems along the top of the intake gasket .I know heads that large usually require a intake port equivilant to the edelbrock super victor intake.I tried running a rpm manifold on my 230cc heads which used the 1206 intake and it was waaay too small,you could still see into the intake runner with the intake inplace it was that bad,just something to keep in mind.

Cheers and good luck with the build sounds like a great engine

12secformula

Ok....Now where do I start....The camshaft is not very radical it will have a decent amount of lift, around .600" lift, and we are not set on the exact duration yet, but it will be in the neighborhood of 235-240/240-250, there are def. alot more radical cams out there, think about this.....a CC306, is 230/244 w/ 544/576 w/ 1.6rr's, now would you call that a big cam? I wouldn't, I was set on buying that until I started doing some research, that lead me into some Lt1 forums, were I really learned about the CC306, its a very old cam design and there are newer designs that have alittle more lift, and a bit more duration, that run smoother and are much more powerful. So I was torn, so I continued to search for a good off the shelf cam that would suit my needs, and have a broad, flat powerband that would work perfect w/ my everything I had so far. I noticed that many Lt1 4-th gens were deep in the 11's w/ cam and head work done, and stock bottom ends. I continued my searches and found Lloyd Elliot and Bret Bauer, Bret is actually a local boy, so I gave him a call, and he went to work designing a cam for my needs. this cam is FAR from pro-street, it is nasty though from what I have heard from The LT1's running something similar. This is all purpose built, to be a sweet all-around car, more for road-racing than drag-racing but should be sweet for both. They said get that comp. ratio and I'm trying to get the info needed to do it, thats is why I come here to the Thirdgen gods, that will surely have the answers.

12secformula

This is very true, what do you think I'm looking for?

Yes my Mini-Ram intake can use a fel-pro 1206 perfectly, actually it could go a little bigger, and my heads will only be 215's either way I go. They will just be ported slightly in the runners, further in is where the magic will happen.

Thanks guys, for your responses. I guess popular concesus is to go a bit milder w my combo, I will talk to these guys doing my stuff and found out more, if they say I won't be giving up much by being a bit milder than I will def go that way.....I will let you know how everything is going as it develops. But keep em coming, let me hear what you think about my build-up, the pistons...whatever.

forums_suck

hey for what its worth the combo i listed in my camaro has a good size cam (mechanical roller) and when the engines idling it purrs like a kitten you wouldnt know the car goes like a raped ape until you actually drove it,almost sleeper like and thats with large tube header and 2.5" exhaust through flow masters

12secformula

I am sure that your engine does run like a raped ape, and it purs like a kitten. Mine runs through a long tube header and a mufflex 4" w/ a flowmaster also. I think we are on a different page here, my engine is a hydraulic roller not solid, and the engine is set up for road-racing and auto-x more than anything. Power should start down low, but to really launch this at a strip it will take a high rpm dump of the clutch to put this thing in its strong powerband. From what I have read, I could run 13:1 on a street engine and it more or less depends on dynamic compression ratio, not static compression ratio. I will try to get as close to my 11.8:1 target ratio, to keep the planned 9:1 dynamic ratio that we planned on. Which just happens to be the highest dynamic ratio you can run on pump gas. I think I will see about having the heads milled more just to find out what exactly i should do. But if I find out that I can't mill past say 60cc, I will infact run a tiny little 2cc dome. Which would probably look like a tiny bump on the piston to compensate for the needed valve reliefs. That is if the experts that are designing my cam, valvetrain and doing my heads approve. I am told this is the easy way to make big power w/ out some monster duration cam w/ out streetable manners. Thus the reason I am trying to balance the piston dish/dome with the correct head cc needed to perfect this combo, w/ out detonation or other issues usually associated w/ a very powerful, high compression street machine.

Streetiron85

The numbers you posted for duration look very reasonable.
I was just having a hard time figuring out the part about the 11.8-12:1 CR and needing domed pistons...
I was under the impression that maybe you asked the guy to grind you a cam that's too big.
But the grind you've chosen seems like it ought to be compatible with some flattop pistons and the heads you have in mind.

12secformula

Thanks man, I thought once I showed those numbers you might understand what I meant. The cam has big lift, but the duration is fair. This is a whole package custom for me, and they have a custom they have in mind but nothing totally set in stone yet. They just say that this should be everything I want and more if I get it to that ratio, more compression: I would be giving alot up, and less compression I would be giving up some. Thats the "happy" medium I guess. If I can get the heads milled to 62cc, I could run a 1cc dome to compensate for the valve reliefs and put me right where I need to be....11.8:1. I think that would work, thats only like .075 dome pop-up....hell, I got zits w/ more dome volume than that!!

Streetiron85

One of the problems with domed pistons is getting a dome that fits within the space of your chamber. The modern head designs are meant to be used with flat pistons, and to find a dome that will go into the chamber without making contact can be tricky.
My guess would be that milling the heads would be a better solution, if you insist on maxing out the CR.

ross

Mill the heads. If you have to mill a lot off (ie) over .040 you may want to do a combination angle mill and flat mill so that you dont have to worry about intake fitment. as for the no valve relif piston good luck. Just about every eng combo with a big cam needs the ex side fly cut things get a little tight in there. I had Total Engine Air Flow do my afr heads worked out great.