If the tune is setup for 93 octane, is there any benefit of running 111 octane? One of the gas stations by my house sells both 111 and C16, so when I filled up this past week, I filled up with 111.

 

You'll actually have worse performance with 111 on a 93 octane tune. It'll be safer - but because you aren't getting a complete burn, it won't run as well.

 

Glad I know that now. But, if after the heads are installed and the car is re-tuned, I can let my tuner know to tune the car for 111 octane, which will in turn, give me better performance, correct? Any idea what the HP/TQ difference would be bettween a 93 octane and 111 octane tune, given that both tunes were maximized correctly?

 

Depends on how much more timing you can add. Probably a good 2-3%.

 

How much is 111 octane?

 

So do you know what the exhaust clearance is? The intake is the one that chases the piston, the exhaust on the other hand is fighting the piston for the same space. .060 Int and .080 exh are pretty good safe number in general especially for a street engine.

 

I had .101 exhaust clearance with this cam and my stock 241 heads, so I should have .080 or more on the exhaust side with the heads being milled to 60.5cc. I had e-mailed Phil the intake and exhaust clearance numbers with the stock 241 heads, so that is how he determined what cc size to mill the AI Dart/RHS heads down to. The AI Dart/RHS heads allow for more PTV clearance than stock 243/799 heads, so at 63cc they have the same PTV clearance as 243/799 heads at 64cc.

 

$6.35 I think.

 

I'm surprised you got those heads, as I was going to get as well but they were out of stock and wanted an extra 225? to be able to get another set. I ended up going with a set of TFS 220cc

 

You mean through Advanced Induction? I got mine for $1,595.00 (without springs because I already have them) plus shipping. I e-mailed AI yesterday and they said I should get them in 2 to 3 weeks.

 

Gotcha, I thought you were going through TEA

 

No, these are the Advanced Induction Dart/RHS (aftermarket casting) 223cc heads. To my knowledge, I may be the first person on here to run them. Phil says they are good for about 10 hp over their proven 226cc and 232cc ported 243/799 heads, so I'm looking forward to getting them put on.

 

Here is a good visual about how quench effects the burn rate and efficiency of the combustion chamber:

You have a roaring bonfire going. In each hand you have a coffee can full of gasoline. To demonstrate how quench effects combustion we take one can full of gas and slowly pour it on the fire. The fire flares up slowly, and only flares up as you pour gas on the fire. This demonstrates a loose quench figure. Too loose and/or in this visuals case, pour too slowly and it never really even flares up, just fizzles.

Now, in the other hand you take that can full of gasoline and you baseball pitch it with all your might at that bonfire. The bonfire explodes with combustion as soon as the can full of gasoline hits it. This is from the gasoline being tossed and tumbled around with oxygen right before combusting which in turn is exposing more surface area and making for more "droplets" of fuel to be burned which causes the fire to flame up very quickly. This demonstrates tight quench where the air/fuel mixture is "squished" together by the quench pad/surface of the piston and cylinder head causing the air/fuel mixture to be tumbled and tossed around exposing more surface area and "droplets" of fuel before the spark plug fires causing the air/fuel mixture to be ignited.

Now that we have this visual, too tight of a quench figure can cause the combustion event to go out of control just like a wildfire when too much wind is present and cause detonation and or total meltdown of your engine internals to happen. Too loose of a quench figure and the fire never even flames up at all. You need to find a balance point for your application whether it be N/A, Nitrous or boost. N/A engines can tolerate more quench because there is no oxidizer present in the combustion chamber/cylinder like there is in a nitrous engine. Heavy nitrous engines need a looser quench figure to become tunable on large volumes of N20. Boost likes to be treated like a N/A motor when it comes to quench as there is no oxidizer chemically and physically speeding up combustion and the flame front, just immense cylinder pressure.

I always urge my N/A customers to run a .040" gasket for added quench in lieu of milling their heads or in conjunction with milling their heads. What's done is done since you already ordered them Nate, but I would of opted for the 63cc chamber and a .040" gasket.

Either way it should run great!

 

^Good visual.

 

Thank you for that detailed explanation Martin. So in regards to PTV clearance, there will be no difference between the heads being 63cc and using .040 gaskets or having the heads milled to 60.5cc and using the OE gaskets? I understand that it would have better in regards to quench to go the 63cc route and run the .040 gaskets, but like you said, I already have the gaskets and I can't imagine there is going to be a noticable HP/TQ difference.


Martin, care to make any guesses at what type of HP/TQ I'll end up making with the AI Dart/RHS heads. Compression, according to Phil, should put me right at 11:1.

 

I wouldn't let stock gaskets keep me from optimizing my setup...

 

But will the HP/TQ difference be worth the additional cost? I'm not opposed to getting the thinner gaskets and changing my order with AI (if I still can) if it's going to be a noticable difference). Remember, this is just a fun, street car, that will see very minimal track time.

 

It probably won't matter. But if you're running 111 octane, you can run the thinner gasket and the milled heads. You might crash the valves into the piston, but eh.

 

I probably won't have my tune setup for the 111 octane just because the only gas station I know that sells it is right by my house and if I take the car on the Power Tour or out of state, who knows if I can even find 111 octane. Right now, the car is tuned for 93 octane, so I guess it was dump on my part to even put the 111 octane it it (I did that before you educated me that it's actually counterproductive if you don't have a 111 octane tune).

My PTV tollerances, with the 60.5cc heads, will put at above .060 on the intake and above .080 on the exhuast, which I'm ok with. I think that's safe. I know a lot of guys run a hell of a lot tighter clerances than that and don't have issues, but I really don't want to chance it.

 

Each cc removed equals .006" of clearance removed. So if you go from 63cc chamber and a .040" to a 60.5cc chamber and a .051" gasket the 63cc and .040" gasket actually would have .004" more P to V than the 60.5cc chamber and .051" gasket.

I would say you'll gain at least 40rwhp with the new cylinder heads, possibly 50rwhp+. I would think that you're around 390-400rwhp right now.
Here is where it gets good. I had a customer the other day who had his engine blow up on him. He re-built it with the EXACT same parts meaning cam, heads and intake, bolts were all the same etc. etc. The only change was with his new pistons he used he actually lost 2 tenths of compression, BUT he also tightened his quench up at the same time .011". He gained 11rwhp and 7rwtq with less compression and tighter quench.

This is why I urge my customers to run a thinner gasket even with the added cost of the Cometic MLS gaskets.

I wouldn't even worry about race gas. You're not going to need it.

Your P to V clearance will be fine. If Phil was comfortable with it, then if I were you, I'd be comfortable with it as well. I feel like you'll have no issues to speak of.