Calling all /6 engine designers.

Some engine parts are at the machine shop and I'm late in designing the new engine for Big Red. While no drag machine, I want to maximize street performance. Being for street, I'm looking at manners at low RPM as well as performance when I step on it.

Engine control system: continue with SDI's MPFI and prog ignition
Supercharger boost at 10psi

Basic engine Info:
225 in3
Block: early 70's, 3.4 bore, little wear, no deck milling
Head: 1976 milled to 50cc chambers - plan for 1.735 dia intakes, 1.5 exhausts - both with 11/32" stems
Head gasket: Oz APC
Rods: Stock 6.7" or 7" K1's
Pistons: custom either way with custom compression height to dial in piston deck height for static compression ratio.

Here's my static compression calculations for scenario A below (I've done them for both 6.7" and 7" rods producing static cr of 8.5 and 9.1 in the scenarios listed below)



Firstly, here's my "blower friendly" (Jerry at Engle) cam card with larger lobe sparation, minimal overlap to prevent blow through.


I'm running through different scenarios to determine dynamic compression ratios at:

http://www.rbracing-rsr.com/calculations.htm

Scenario A
Camshaft, Rod Length, Boost – 10 psi, 3000 ft Altitude Correction to Compression

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 7 inches, (0.18 deck height) with a static compression ratio of 8.5 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 84.01 cc's. With this camshaft your dynamic, or effective stroke is 3.69 inches. Your dynamic compression ratio is 7.11 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 136.28 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 11.95 :1.

Scenario B
Camshaft, Rod Length, Boost – 10 psi, 3000 ft Altitude Correction to Compression

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 7 inches (0.14 deck height) with a static compression ratio of 9.1 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 77.79 cc's. With this camshaft your dynamic, or effective stroke is 3.69 inches. Your dynamic compression ratio is 7.65 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 149.99 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 12.85 :1.

Scenario C
Camshaft, Rod Length, Boost – 10 psi, 3000 ft Altitude Correction to Compression

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 6.7 inches (0.14 deck height), with a static compression ratio of 9.1 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 77.79 cc's. With this camshaft your dynamic, or effective stroke is 3.70 inches. Your dynamic compression ratio is 7.67 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 150.50 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 12.89 :1.

Scenario D
Camshaft, Rod Length, – 10 psi, 3000 ft Altitude Correction to Compression

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 6.7 inches (0.18 deck height), with a static compression ratio of 8.5 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 84.01 cc's. With this camshaft your dynamic, or effective stroke is 3.70 inches. Your dynamic compression ratio is 7.13 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 136.78 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 11.98 :1.

What range should be targetted for dynamic CR?
Where do you think my challenges will be?
Wiseco - can your pin location be moved sufficiently to produce the required deck height with a 50cc head?

_________________
Cheers!
Al T

Al T I think I would mill the deck instead of moving the pin. Also are the cam numbers from a V8? If so you may have some disappointments. I would PM Doc and or Lou (Dart 270) and get some more cam Ideas.
My02.
Frank

_________________
Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered

First thing is that I would make int/exh duration equal at 266. Actually, 232 @ 0.050" is a bit much for a low end and low comp motor. Surprised it's 266 advertised for 232 @0.050". I'd actually go for 224-228 @0.050 with 108-110 LSA myself. A NA Slant wants 4-10 deg more on the intake, so blower will want less intake, but not that much less. 225s can take more overlap (lower LSA) than most V8's due to the valve sizes vs. displacement ratio.

The cam you mention will be too much high end. Drake's have had this issue where COMP recommended a similar cam to yours (slightly diff for turbo), but it made it's power too high for what they wanted to do.

I agree you want to be around 8.5-9.3:1 static comp. Do not go below 8.5 or low end will suffer.

I haven't used the dynamic comp caluclators - do it by experience. I've used about 6-8 different cams on Slants with various compression ratios, and talked to a lot of experts...

So, you are upping the boost? I thought you were around 4-5 lbs.

Let me digest the rest. Any budget constraints?

Lou

_________________
Home of Slant6-powered fun machines since 1988

Lou, I was running this cam before I blew the head gasket . . . and I was liking what I saw. My understanding . . . turbo's have back pressure on the exhaust exit, blowers don't. This creates a different set of conditions and/or opportunities in the cylinder. I'm trying to determine how to take advantage of this.

I was running the Comp Cam 264S before at about 7 psi max. This cam had similar characteristics to what you reference.

I went for the larger lobe separation angle / less overlap because I felt I was blowing mixture through into the exhaust.

If you don't mind, I'd like to pm you some other details about dynamic compression.

_________________
Cheers!
Al T

Al~ we haven't been properly introduced, but I have a Megasquirt EFI and am currently building a supercharger system with a m90.

Anyways, one thing I want to tell you about for the cam is what is called a Miller Cycle. It closes the intake valve 70deg ABDC, instead of the typical 35deg ABDC. I couldn't read your current numbers very well, so maybe this has already being taken care of.
The idea is that the effective compression ratio is reduced by changing the dynamic compression ratio (as you had metioned). The benefit is with the fixed displacement it can fill the cylinder, while reducing the heat of compression. I'm still wrapping my head around this, but it should work well with the Root's style blower.

Wes

Hi Al,
If you do decide to go with a custom piston, please PM me or call me @ CP (949)567-9000]and I can help you out with the paticulars.
I can design almost any bore size, compression ratio & pin hight that your engine comb will need .

Mike @CP

Al,

I am happy to discuss by PM, or on the site. Good to know that bigger cam was working well for you. 225 can handle quite a bit of duration compared with square or oversquare engines.

I still think a bit less duration and smaller LSA would be better for lower RPM usage based on conversations with other folks, but you seem to be in good shape.

What's your max planned RPM at WOT?

Lou

_________________
Home of Slant6-powered fun machines since 1988

Discuss it on the site! This is good stuff!

_________________
66 Lil' Red Piggie Valiant (Mater Crusher) - Thanks Zilla!!!!! 72 Demon (Number 1 Son's)

Lou, I expect to cruise the highway, come up to a slow car, stomp on gas and blow by it. I want to create maximun cylinder pressure in the 3000-5000 rpm range. Its torque I'm after.

I've attached some of my calculation in picture form. Double click on them to make them legible.

Firstly, here's my thoughts on intake closing. This 1st calculation seems to indicate that under boost conditions, I don't have to be too quick to close the valve because boost will keep the mixture in place and actually pack in a bit more mixture as the piston is coming up. Therefore, I'm comfortable with the intake closing at 44' ABDC. I've listed my assumptions. Let me know where I'm off.



This graph is simply a plot of the equations.



Secondly, the overlap. Since I'm using boost to fill the chamber and since my exhaust is free to escape, this can be minimized. I don't want A/F mixture blowing through into the exhaust.

That leaves the exhaust opening. Need to take advantage of the longer stroke. With my current cam opeing at 55' BBDC (0.050"lift), there's 0.88" of stroke left. However at 0.020" lift, the angle is 74' and about 1.48" of stroke are left from the 4.125" total. This seems a little early to me and my gut tells me I might be leaving too much energy in the exhaust.



Wes, best of luck with your setup. BTW, I didn't know what I was trying to do had a name but here's what wikipedia has to say about the Miller cycle http://en.wikipedia.org/wiki/Miller_cycle
This is what I'm hoping to get. Time to read more about the Miller cycle.

_________________
Cheers!
Al T

Al, I love your attention to detail and thought process... thanks for sharing your thinking with the group.

I have to say that I do not have as much "hands-on" knowledge with pressurized SL6 engines as I do with N/A Slants... so take my comments as speculation only.
(all the pressurized Slants I have built over the years... have blown-up relatively quickly )

Your cam logic is sound.
A number of top notch cam grinders have told me that there are 3 important cam events:
-Intake closing
-Exhaust opening
-Overlap duration & positioning
In that order...

As you already know, finding the "best" place in the 4 stroke cycle, for each event, is a challenge, especially for us folks with limited time and $$$.

As you are doing, use "known" info. as a baseline and adjust from there.
It is tempting to make a lot of changes but try not to, single changes give clear results.

I agree that delaying the exhaust opening (blow-down) event is the biggest opportunity for you, followed by a decrease in overlap. Look at shifting the overlap event so the exhaust valve closes right after TDC... but let the intake open at the same place. An even profile or RDP cam will help, allowing the exhaust valve to open a little later (blow-down) and close a little sooner. (overlap) Your current cam, with extra exhaust duration, is throwing cylinder pressure (power) out the exhaust pipe.

I would try to keep your current intake events the same... just to reduce the number of changes.
Just my 2 cents...
DD

Al,

I've read through your calculations and the Miller Cycle site, and they seem reasonable. I think these should provide some guidance, but also used with caution.

However, there are a LOT of assumptions here, as in any description of an internal combustion engine. This is where you can get into trouble in trying to design the perfect cam.

A good example of faulty assumptions made by "the best" cam grinders led people to recommend more EXH duration than INT on NA Slants. This has been shown to be wrong by many experiments, and as I understand it is due to the assumption that the int/exh flow ratios on a Slant head are quite different than most other engines AND that we have a more undersquare engine than most.

I think this topic is definitely still not settled. There is still so much we do not understand theoretically in complex interdependent systems like an IC engine. Boost, almost always variable with RPM or other factors, throws in another group of variables.

My first reaction is that if you have a cam already that has worked well, the FIRST thing you should is intstall that and do some testing, then try another profile. Since you will be changing boost, compression, and possibly head characteristics, this will be your baseline.

Also, cam timing could be very important here. I know someone who has an adjustable billet 225 timing set from Oz who would sell it to you and you could make easy adjustments via some inspection holes made in the timing cover. I plan to do this myself and I have one of these chains.

I will think more about your assumptions, calculations, and how to modify the cam profile...

Lou

_________________
Home of Slant6-powered fun machines since 1988

I dont have anything technical to add Al........I do see you doing research and crunching numbers. That is a process that has worked very well for me. Using on-line calculaters and asking a few questions saved me a ton of money and grief. I think you are on the right track.

_________________
Yeah....Im the one who destroyed this rare, vintage automobile.....

Well, I'm glad that the Miller cycle idea led you down a good path. I don't think that you need to go overboard with it but it should help. I bookmarked it in my book because I'm using the m90 blower and it seemed like a perfect match. Some other things to keep in mind is that turbo's can respond great to a decent amount of compression so they have some pop at the lower end. I would steer clear of this for the supercharger (fixed displacement), however, I would still hug up on 9:1 over keeping it to low. My roomate with the '69 Camaro wants to drop his compression down to 7.5:1! Why??? Because once people have something in their mind that works they go overboard, bigger displacement, bigger cam ect.
So in short I would keep the lift higher, durations short, overlap minimal, and intake opening later. This should all be done in moderation, so after re-reading, the 44deg is very acceptable over let's say a stock 35ish. I wouldn't go anymore than 110 on LSA though. Did we discuss lift and duration? I'm lost in the numbers again, so perhaps your HP goal and max rpm can help me.
I really wish you the best of luck becuase I will be following a similar path. I got a stout 170 short block from Josh with the plans of: full roller cam and rockers, 1.7/1.44 valves (maybe), a forged pistons, makeshift windage tray, and custom EFI intake manifold (obviously gotta tackle that one). The goal is a 350hp at 7000rpm, hence full roller valvetrain, and to switch between 5lbs during winter and 10lbs during summer. Hopefully a 20 minute swap with pulley, fuel map, and ect.

Thanks guys for your suggestions. Based on your combined feedback, here's where my thinking currently lies for this engine.

For the "music" I want to play, I'll need a new "mystro" who should conduct the engine symphony something like this. (Click image for full size readability)



I should be able to run a higher static CR because of where I close my intake valve, the fact that I use an intercooler and because I can dial back my timing at higher boost levels. If I then aim for a static CP between 9 and 9.2, the calculator gives me . . .

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 6.7 inches, with a static compression ratio of 9 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 78.76 cc's. With this camshaft your dynamic, or effective stroke is 3.70 inches. Your dynamic compression ratio is 7.58 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 148.20 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 12.74 :1.

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 6.7 inches, with a static compression ratio of 9.2 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 76.84 cc's. With this camshaft your dynamic, or effective stroke is 3.70 inches. Your dynamic compression ratio is 7.76 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 152.81 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 13.04 :1.


If I use 7" K1's . . .

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 7 inches, with a static compression ratio of 9 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 78.76 cc's. With this camshaft your dynamic, or effective stroke is 3.69 inches. Your dynamic compression ratio is 7.56 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 147.69 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 12.70 :1.

Your engine summary is as follows: Bore 3.445 inches, stroke 4.125 inches, rod c-c length 7 inches, with a static compression ratio of 9.2 :1. Your camshaft specifications call for an inlet valve closing of 44 degrees ABDC (after bottom dead center).

Your chamber volume is 76.84 cc's. With this camshaft your dynamic, or effective stroke is 3.69 inches. Your dynamic compression ratio is 7.74 :1 corrected for cam timing, altitude, and rod length. Your dynamic cranking pressure, corrected for cam timing, rod length and altitude is 152.29 PSI. Your dynamic boost compression ratio, reflecting static c.r., cam timing, altitude, and 10 PSI is 13.01 :1.

Since its seldom going to see well above 5000 rpm, I'm leaning toward sticking with stock rods.



I'll give our friend at Erson a call about grinding the cam and I'll need to get into the piston specifics from either Mike at CP, Miseco or Ross.

BTW, what's the factory height of a block (Crank CL to top of deck)?

Any last words of advice?

_________________
Cheers!
Al T

AL
Im concerned that your DECK height changed by only .040 between stock rods and the new K1 rods. IS this correct or did I misread?
And I believe the K1 rods are 7 and some change like 7.15... Im going from memory from Docs recommendation in the K1 thread.
BTW I am really enjoying this thread and the processes you are using to get the info put together.
Frank

_________________
Scrapple: Because a mind is a terrible thing to waste.
73 Duster - Race Car
66 Dart Wagon - DD
178" FED
82 D150
All Slant powered