Upstate

Just how important is quench when super charging with regards to preventing detonation? I am starting my engine building plans and all this math is driving me crazy and leading to more questions. I'd like to get it right and not blow things up. My (simplified) plans are as follows:

427 short block from Bill Mitchell, Brodix Track 1's CNC ported, Jebs single plane, and yet to be determined cam and SC. Doing the math with the advertised specs I have come up with the following:

Bore: 4.125
Stroke: 4.00
Head CC: 67
Head Gasket Bore: 4.155
Gasket Thickness: .042
Piston Volume: 20 cc Dish (-20)
Deck Clearance: .025

Equates to 9.6:1 comp ratio and .067 quench if I've done my math correctly. I would like to have my compression ratio lower than 9.6:1 but the only option I'd like to exercise is using a thicker gasket. I am open to a different head but I really like the Brodix and don't want to get crazy with combustion chamber size.

Changing the compressed gasket thickness to .060 (the next size I could find in the summit catalog and assuming I can use copper gaskets with aluminum heads) brings my compression ratio down to a more friendly 9.28:1, but increases the quench to a staggering .085.

Ultimate effiency, street manners, and fuel mileage I could care less about. I don't want the engine to detonate itslef to death though and all of the searching and reading I did today says increasing quench promotes detonation.

So, I am sure I could be safe with 9.28:1, even 9.6:1 should be alright, but am I looking for trouble with that much quench?

Thanks Fellas

tjwong

How much boost are you planning on running? At 9.6 you can't crank up the boost much beyond 6 or 8 psi. Which is what most kits are good for that are designed for a stock high compression engine. You should run your quench down to about the thickness of the headgasket, meaning that you would have to deck the block down .025 or get a custom piston to raise the piston deck up that same amount. If you go with the piston route you can order a piston to give you 9:1 compression allowing you to have more boost and be more detonation tolerant. This of course would be the more expensive route to follow, but if you are building a 427 it sounds like its a high dollar engine anyway, so why not do it right

I am running a .039 quench which is the thickness of my head gasket. My deck had been machined down to 9.015 and I have custom pistons from Lunati to give me zero deck at that block deck height. I am running a 396 with a blower as well.

Upstate

I am not totally informed about what's out there for SC's but was planning on 10 PSI output from the SC. Between an intercooler, belt slippage, and the increased volume over your typical 350, I was guestamating at least a 2 PSI drop for 8 PSI total, which I am interpreting as being on the ragged edge.

For simplicities sake only, If I started with 8 PSI, and ended up with 6 PSI, how safe would I be with the afformentioned and way less than optimal quench of .085 and the 9.28:1 compression ratio? I can surmize that face value says I'd be better off than 9.6:1 and .060 but in reality I don't have a clue.

My ultimate goal is 500 chp n/a and 700+ boosted. I think with the right cam my n/a HP goals are pretty attainable. Advertised increases in HP from the SC are on the order of 50% but I don't think I've seen anyone get it. My 40% percent goal may be a little lofty too. If the quench is that much of an issue with regards to preventing detonation I will go throught the expense of correcting it, but having a stout preassembled short block to build on is very tempting.

tjwong

The pressure drop is about right going across an intercooler. However there are other factors such as intake efficiency at the blower intake, for instance the Vortec intake hat is very restrictive and these centrifugal blowers don't like any kind of restriction at that point. I have redesigned my intake with a new sheet metal intake hat. However I haven't had a change to install it as I have been so busy trying to get the shop and the new dyno together. It was to be a winter project, then a spring and now where we are nearing fall. I hope to have the new T trim done over this winter for testing on the dyno. Plus any extra elbows in the discharge tract will also add pressure drop points to the equation as well. Not to even mention what you cam can do to boost.

As for quench the whole idea of having a idel quench demension is to create high velocity turbulance as the piston comes up to TDC to enhance the A/F mixture for a better burn. This also deters detnonation as well. And if you do plan on staying with a relatively high compression its better to have the correct quench demension than to have both a higher than normal CR for a blower application and improper quench. As I mentioned before it sounds like you are planning on spending a lot of hard earned cash to build this engine, so I see no reason not to do it right to get all the performance out of it for the money you're spending.

With the right combo 700Hp is attainable. A friends 355 at 9:1 pushing 8.5 PSI at the intake with a T trim Vortec, made just shy of 600Hp at the wheels in a 93 C4. The cam was a Comp Cams custom grind cam with around 222 degrees of intake duration. He was also running a custom made 8 rib setup.

Upstate

Thanks for letting me pick your brain, it's very appreciated and now I am getting way out of my league. I've made some revisions to the above calculations using a 0 deck height, and Brodix M2 T1 227 heads with 68cc chambers, and slightly revised off the shelf JE piston with a *gasp* 36 cc dish. I have a good quench at .041 and good static compression ratio of 8.74:1. I started looking at cams with respect to supercharging and this is where I got really lost. Most cams I looked at were aimed at smaller cubes with much shorter duration figures.

I know that big cube engines can eat up more duration and still have some assemblance of an idle. But what to choose I don't have a clue. Lets use Ski_Dwn_It's cam with some assumptions as I don't know his full specs but it seems to work pretty well n/a.

Lunati 284/284 251/251@.050 .620 Lift Solid Roller are known variables. Lets make the assumption this cam has 114 degress of lobe seperation, and an ICL of 110 Degrees. This will close the intake valve 72 degrees ABDC, making my dynamic compression ratio 6.67:1, and my dynamic boosted compression ratio 10.3:1 at sea level with 8 PSI, and 9.39:1 at 6 PSI.

What that will do in terms of how I want the engine to perform and it's longevity I don't know, but hopefully you do . I also do not know if octane requirements for static, dynamic, and dynamic boosted compression ratios are the same. If they are, 8 PSI after losses seems to be a pretty safe limit with that particular cam, even with 10 PSI after losses it's still a manageable 11.21:1.

Sources:
RSR Advanced Dynamic Compression Ratio Calculator

Dynamic Compression Ratio Calculator #2

For those lurking the latter link has some nice explanations and includes a very neat program to calculate DCR, Dynamic Stroke Length, and a compression ratio calculator that will calculate your SCR, DCR based on your DSL, and effective displacement based on DSL. If you're wondering my effective non boosted total displacement from the figures above is 313 cubic inches.

tjwong

There is one more bit of concern involving supercharging a exotic stroker such as a 427 small block. And that is the piston compression height. Idealy a strong piston for blower applications should have a thicker than standard crown or dome. With a 4" stroke, and 6" rod combination for a 427 SBC built on a standard deck SBC block, it leaves a less than desirable dome thickness and compression height. With that combination it gives you a compression height of 1.025" which means that the pin will be into the oil control ring which will require support rings for the oil rings. That is not an issue as there are thousands of these out there in use today. The main concern is the dome thickness, the thicker it is the stronger it is and the more meat there is to absorb the heat created by additional boost pressures. If you speak with a rep at JE Pistons they will tell you the same thing.

The other issue is with the cam example that was giving. If drivability is not an issue then sure it would work. Not to even mention that lifts over .600 for a street care is going to have a lot more wear on the valve train. But thats the beauty of blowers a large cam isn't normally necessary to create big power numbers, especially at the cost of losing boost during the overlap period. A cam with less duration will give you much better drivability and better power. Your static compression vs dynamic compression is fine with a static number of 8.75 to 9:1. One has to remember that with a blower peak pressures peak with peak boost pressures. And with a centrifugal blower it takes RPM to build boost peak pressures will occur at a higher RPM.

Staying with a smaller cam will offer better durability of valve train parts, less chance of valve float at higher RPMs and over all better drivability without sacrificing power.

The next couple of engines I am involved in are going to be 383's using a 5.85" rod length. At that stroke and rod length I will end up with a compression height slightly less than 1.300" which is considerably more than 1.025" or .275" thicker. This will give me adequate pistom dome thickness to handle the planned boost pressures of 12 PSI or a 14 PSI maximum limit. Any more than that for the street will require O ringing the block and heads which I don't care to even go there. This is going to be a rock solid foundation for daily street use so it has to be dependable.

The cam I am looking at using is a 236/248 nitrous HP Extreme cam from Comp being ground on a 114 LSA. It has modest lift numbers with around .560/.575 which will be easy on the valve train. This cam matches the planned AFR 210s or 220s air flow rates so in theory with the 12 PSI of boost will make dependable Hp well into the high 600 regions. None of the cams mentioned, mine or yours will likely pass emissions. However I have a few tricks up my sleeve to make them pass but I think I can squeak my choice through easier that the cam profile the Ski uses, such as that big Lunati.

From my experiences a cam for a NA engine may not necessarily work well in a blown application. Where a cam with long duration and lots of overlap makes huge Hp numbers up high in the RPM ranges, a smaller cam with lots less overlap can make as much or more Hp in a blower application. With a cam with long overlap periods it is less effective in a blower application because it bleeds off that precious boost pressure during that overlap period.

Upstate

This is probably the reason why you don't see many combos like the one I was planning. Thank you though for saving me lots of money and time picking pieces of aluminum and iron up off the street .

Your combo looks pretty good, will deliver good power, drivability, and longevity. Getting into the high 600 range super charged seems a much better proposition than trying to go n/a and get that power level out of a 427. It's definitely 6 of one and half a dozen of the other .

It looks like my only safe option to get my combo to work is with a tall deck block and I don't want to go there. My only issue, which may be imaginitive, is the low end torque I'll be giving up with less cubes and an SC. It would seem to me the smaller cube supercharged engine putting out identical numbers as a large cube n/a engine (in my A4 3.07 equiped car) is going to cross the finish line last in the quarter, but will ultimately be much easier to live with on the street. I could certainly gear appropriately to get the engine in it's powerband a little quicker but I like the idea of lower cruising engine speeds.

Given I really like that low end grunt that a big cam is going to steal I think I'll have to suck it up and go with the cubes and drop the SC idea. I am willing to live with the drivabillity and tuning problems and could probably safely spray my way to 700 HP. I think a 150 shot would definitely get me there.

You've been a great help tj, and I really appreciate it, thank you. If I was on the left coast I'd definitely be coming up your way to buy you a beer.

Thanks buddy.