Im thinking of building a new street motor on dope really soon and i know that a 1.8 exhaust valve would be killer but that 8nt gonna fit..so would going to a 1.94 intake and 1.625 fit on a 4.04 bore.Really not worrying about shouding just physical fitting..

 

So, you guys are saying to use a 1.94 intake and a 1.94 exhaust

I have considered a 1.94" exhaust on my big block

 

Only if the intake and exhaust pressures are equal.

 

is there a way to really figure out the exhaust pressure?

 

Aren't we talking more about volume of gas than the mass flow?

Adding N2O and extra fuel increases the exhaust gas flow probably in proportion to the extra power produced. To some point, a larger exhaust valve, and more exhaust cam duration help when the engine is being bottle fed.

Many SBC heads have a 1.86 inch center-to-center of the valves. Using .050 clearance between the valves, that leaves 1.81 for valve radii. If you double that, you have 3.62 inches which can be divided between the intake and exhaust.

2.02 +1.60
1.94 +1.68
etc.

This spacing increases for race heads up to 1.955 for some GM 18 deg. heads. That gives 1.905 x 2 or 3.81 to work with. The problem is that the bore should probably be at least 4.06 for these heads.

My $.02.

 

Yeah, you'd want the 1.935 valve center heads for a bore under 4.06, although some guys run the 1.955 on the smaller bores... but they usually notch the bores.:blah:

No problems with a 1.94/1.625 combination in either head.

More response than I got from you, right Greg?

-Mindgame

 

1.625 would be nice to work with..The blocks arent bored as of yet so a .060 punch isnt a problem..

I could care less about the mass of atoms and what not.. This is an automotive forum.Motors on dope need as much exhaust help as they can get..Hench the need for N2O cams being the rage these days..Chemical/forced induction acutally increases displacement and you still have a valvetrain and head ports for a smaller engine..Its horsepower not the periodic table of charts..Put down the beakers and flasks and pick up a wrench sometime..( iremeber my professors at LIU still being intrigued how its hard to figure out a female..And they helped me get my Masters..Many of them were experenced srinks to boot.Anyways

Ive been talking this over with Pat Musi Warren Johnson and his head guys, as well as the guys from Al Ventura for the last few months as well as a few head guys that i know of..David Vizzard visited this subject lightly in a few of his books and went into detail about it in a manual he never published but in the manual it was on 4.125+ bores..

Only problem i see is finding a shelf 23* piston that will clear such a large valve with a big roller..640/690 or so lift wise.Since the valve spacing isnt changed i wonder if teh valve pockets in most shelf slugs would clear.Im thinking of possible contact around teh leading edge of the valve reliefs during dwell.Valve angles are the same so it should work within reason..This is gotta be a shelf parts engine so it stays cheap..Im projecting no more than$1500 dollars for the longblock and the only costs would be pistons fasteners and valvetrin parts.The plan is building a killer small block that would make a killer PRO cheap street engine if the need arises.Albeit with a illegal camshaft.

 

If you're getting information from that caliber of individuals then you shouldn't even need to come to this forum for "advice".

Pistons are simple, have WJ or Musi fly cut em for ya.

-Mindgame

 

Wish it was that easy..Pats back up north and hasnt tryied it as of yet..WJ and his boys are hard as hell to get a hold of for more than 10 mins..I stopped by there yesterday around lunch but they are so used to big blocks and big chiefs the wouldnt comment on the physical part of the idea.Not saying that they didnt know but they sure didnt seem to want to tell me.Pat looked into it a while back ( I rented his dyno when i lived in Philadelphia) when i was there a few times..He doesnt seem to keen on the idea..His reasoning is that your better off with more exhaust lobe..Wich is true but im not interested in a dual purpose engine..This will be my last hurrah for the baby engines..Im looking at the cost of making small block power and its acutally a joke unless weight/packaging is a problem..

 

Second that one.

Good luck with .060 over and lots of juice if it's a production block.

Time for lunch. Damn, David V. was busy today, or I could have asked him. I don't think he celebrates July 4 like we do.

 

I'm with them on just having WJ do the valve reliefs for you.

The camshaft is the only good place you have to play with here for N2O. The point of having a larger exhaust valve seems stupid here on a BUDGET engine. $1,500 is a budget, but what are you going to do for heads? A 60/40 spaced head like a X series from Brodix is probably the best bet for large exhaust valves. Then again if you went that route it would be pointless to do a LT1.

IMHO LT1 heads are not the best heads to start with in any PRO Cheap Street engine.

BTW If I was WJ I don't know If I would be so talkative to a guy with a $1,500 budget all the time too.

Bret

 

IMHO LT1 heads are not the best heads to start with in any PRO Cheap Street engine.

BTW If I was WJ I don't know If I would be so talkative to a guy with a $1,500 budget all the time too.

Bret

Bret maybe you need to look at the rules for PRO C.S. The fastest cars run comp launchers so thats what i will probally go with.With such a mandated low lift rule lobe contour is all i have.60/40 heads are illegal..Lt1 heads sneak past since the casting is about the same as the vortec..Id say they are the very best heads avail for a cheap street engine..Doesnt make much sense to buy the e tec edelbrocks for a grand if you cant rework the ports when Lt1 heads are dirt scheap used and vortec are 500 dollars brand new..As for Warren, I understand he is a very busy man, but the budget for this engine has nothing to do with it.When it comes to him im a lot more than just some shmo off the street..$3000 is a long block claim thats allowed..I dont plan on running the engine that much.Nor do i feel that one needs to spend that kind of cash to get a motor on dope to nine nines @ 3000 lbs..Just for the sept meet in atlanta..After that ill reinstall the big roller and drop it something to sell.

 

I doubt Bret is competing and if he was I can assure you he'd read and understand the rules..... IMO, YOU are the one who should read the rules again, for there you shall find the answer to your original question......

1.17 HEADS
HEADS, GENERAL: Cheap Street is intended for street performance cast iron or aftermarket aluminum cylinder heads.
1.17a) HEADS, PERMITTED: Original manufacture, generally available heads, accepted by PRO, permitted. External modifications prohibited in port area. Spark plug placement and depth must remain stock. Billet or fabricated heads prohibited. Cylinder heads must be overhead valve single spark plug per cylinder design. One-off or custom made cylinder heads prohibited. The PRO director must approve new cylinder heads or any changes to accepted heads in writing prior to competition.
1.17b) HEADS, MASS PRODUCED: Any mass produced, commercially available, PRO accepted, commonly available, cast aluminum or cast iron cylinder head is permitted. Low volume, one off, aluminum cylinder heads prohibited.
1.17c) HEADS, BOLT PATTERN: Cheap Street class is only permitted OEM standard bolt pattern for cylinder head, intake manifold, and header/exhaust bolt pattern. Adapter plates may be utilized on exhaust side, and may utilize aftermarket bolt pattern.
1.17d) HEADS, PORTING: Prohibited. Port matching also prohibited. **Certain PRO Accepted "out-of-the-box" cylinder head part numbers contain minor porting/port matching by manufacturer. These heads are accepted "as supplied" only, and no additional porting/modifications/cleanup can be performed.
1.17e) HEADS, WELDING/EPOXY: Prohibited. In case of a needed repair to an isolated area of the cylinder head, contact PRO tech director to determine legality.
1.17f) HEADS, VALVES: Any aftermarket steel valve permitted. Stock stem diameter (in guide area) required for head used as supplied by manufacture. Maximum head diameter of intake valves is 2.025"; maximum head diameter of exhaust valve is 1.610". Bronze lined or replacement guides permitted. Valve guide location must remain stock.

Good luck.

-Mindgame

 

and where in the rulkes does it say that the larger exhuast valve will fit?It just says that it is allowed..

Opinion, a very highly used word to help people give advice wich they actually cant provide from experence..

 

Anyone with experience building sbcs would know that a 1.625 valve will fit. Nice try though.

All this talk of building a class engine yet you don't know the rules. An "illegal" camshaft, a "1.625 exhaust valve would be nice to work with".



Fit or not (which it does).... what does it matter? Since you didn't get this in the rules posting....... the rules state that you cannot use a valve with a head diameter larger than 1.61". Wasn't Reading Comprehension 101 a required course in like..... elementary?

In my opinion, chocolate ice cream is better than vanilla.

Just debunked "your" definition.
I gave no advice and having tried both, I simply spoke from experience.

Try insulting someone elses intelligence sometime.

-Mindgame