Hardcore advise

[Anonymous]

Execute (or others)
Sorry to keep all the questions rolling on. Just looked again at your post on getting 14.2 quarter with 205 hp. Quite frankly I would value your advise on how to do it, it might take a lot of the guess work out.
When you say with a good cam, what peak 4800, 5000 even 5500 to get those figures. If I go above 5000 with the peak, then I think I should go to the 200 rods with ACL pistons. With rod bolts it will cost me at least 600 to 700 Aust with a balance. Seems a lot of money to justify and then probably should go even further with cam maybe 6000 to get the benefit with diff change to 3.5.

 

[xctasy]

With short rod engines, the rev range is limited by the side thrust thing. Lobe separation, duration have an effect on the rpm peak. The faster an engine revs, the more inertial 'ram' that takes place.

From prevoius posts, I have used a composite number which is proportinal to brake mean effective pressure and volumetric efficiency.

You take the revs at which maximum power occurs, multiply it by the cubic inches, and then devide that by the net Hp at that point.

E.g 1 Geelong cross flow EFI 4.1. For a 111 kw (149 hp) 4089cc (249.5 cid) engine, maximum revs is about 4000 rpm at maximum power. Thats 249.5*4000 all divided by 149 hp. The composite number is 6700,

or, in metrics, 4.089*4000 all divided by 111. The composite number is 147.5

E.g 2 351Cleveland 4v HO, dynoed by Mick Webb in the early 70's.For 260 kw (350 hp) 5766 cc (351.9 cid) engine, maximum revs is about 5800 rpm at maximum power. Thats 351.9*5600 all divided by 350 hp. The composite number is 5630,

or, in metrics, 5.766*5600 all divided by 260. The composite number is 124.2

E.g.3 Pinto 2.0 with 500 cfm Holley 2-bbl. For 102 kw (138 hp) 1.993 cc (121.6 cid) engine, maximum revs is about 6500 rpm at maximum power. Thats 121.6*6500 all divided by 138 hp. The composite number is 5728,

or, in metrics, 1.993*6500 all divided by 102. The composite number is 127.0

E.g.4 Boss 290 quad cam 5.4 V8. For 290 kw (389 hp) 5.408 cc (330 cid) engine, maximum revs is 5500 rpm at maximum power. That's 330*5500 all divided by 389 hp. The composite number is 4666, or 102.6 in metrics.

E.g. 5 302 AVESCO EFI Windsor SVO V8. For 462 kw (620 hp) 4.942 cc (301.6 cid) engine, maximum revs 7500 rpm at maximum power. That's 301.6*7500 rpm all divided by 620 hp. The composite number is 3648, or 80.4 in metrics.


From this 'rpm times capacity divided by power' rule, just gather every engine known to man, and you soon see that low stressed engines rate above about 5500, and as the engine gets more high tunned 4500 is about it for a really good streeter, but the factor drops to below 3500 for a super hot race engine.

Okay, the profound part is that this sets up limits for maximum power because there is no way you can create extra power without turning rpm. It's simply not possible to get a 3500 factor on a stock 250 Falcon engine unless its turbo charged. 4500 is about it, and it would need an independant runner EFI or triple IDA/IDF/DCOE/DHLA set up to do so.


E.g.6.Setting rpm at 6000 maximum, and power at 5500 rpm, then 250* 5500 rpm all divided by 4500 is 306 hp, needing triple Webers or a Haltech F9 EFI system. With a lessor factor of about 5000, this is about 275 hp, which would be a really well cammed 250 with mods to raise the rpm maximum power peak to 5500, and power to 6000 rpm.

Phone Crow cams, and you can even feed in the 200 Falcon rods and ACL low deck pistons into the equation.

Just remember that the rpm range is limited more by crank windage, lifter pump up, valve train limits, and harmonic balancer and timing gear durability. Rod ratio is also a big factor. Going from a 1.5:1 to a 1.61:1 rod ratio may liberate another 500 rpm at the top end. Engine Analyser territory, it would tell you. When you change the rod ratio, the cams lobe centres and overlap needs to be altered so that the piston is moving away at maximum speed when the intake charge is comming in.

For 205 hp, you could rev to less than 4600 rpm even with a conservative factor of 5700. And a 250 like that would sure last a long time!

 

[Anonymous]

Thanks, I would be more than happy with that. I am surprised that it possible to get 205 hp under or at 4600 rpm. I am pleased with this because it should still have heaps lower rpm grunt and tractability (which is great fun and usable) as well as run fairly efficiently. And I dont not need to worry about the longer rods.
It makes me wonder if Ive got the most out of what Ive got at present. I would not have thought pushing the peak around 600 rpm up from 4000 rpm would have made that much difference.
Thanks.

 

[xctasy]

I did lots of reading of Formula One engines, US race cars, and anything to do with engine hi-po mods I could get my hands on. Soon, a pattern emerges, and you can realy on that pattern as sure as you can that the sun is goning to come up.

I learned this from Holden Engineers Ray Borret and Warrick Bryce in 1989-90. When the Group A Holden Commodre with those 8000 rpm NASCAR rods was released. There was a need for more power for Group A racing, and Warrick Bryce was qouted as saying the only why the'd get more power is if they pulled more revs. Power is revs times torque.

What he said wasn't exactly right, but his point is once you've done everything practical to the head, cam and block,the bore and stroke, and that you've decided not to go turbo or blown, the only other extra is to pull more revs in the pursuit of power. And an extra 600 rpm is 22 hp if you do bare minimum. Of course, the cost of getting a 250 to rev past 5500 rpm reliably is significant.

 

[6bangerbill]

I always thought that hp was also a matter of improving intake and exhaust port flow and port cross section area to maintain correct air flow speed at the desired rpm. How does this fit into building hp? I have completed welding my ls1 hibred head for my 300 six and also comparing cam requirement for different head flows from 250cfm to 322 cfm.Using several engine analysis programs i have found that with an rpm limit of 7000 the best hp under the curve occures with close to 230 deg at .050".
It seems that low head flow numbers require much larger duration numbers. The result is a less "streetable" combination for a given hp level. With a 300 we are talking 400 plus hp with a flat tappet solid lifter cam with close lobe centers ( 108 deg) and .600 lift. Another interesting result was that hp improved with smaller valve sizes if flow could be maintained.
Does this fit the established engine theories?

 

[xctasy]

Absolutely!

The equity equation Flow = Volume times Area (Q=v.a) formula should create a target gas speed of about 250 feet per second at peak power, but the chamber design may allow for 300 feet per second, and still gain power. The are a raft of other items to then consider

I could go on about the vast raft of other factors.

The best method of flow assesment is a kind of "Simpsons rule" a measurement of area under the intake and exhast cfm curves. (Mathmaticians use it for integrating an iregular curve to find the area) The degree of valve overlap or lift is not as important as the bulk mass of flow inducted at each intake cylce. The intake valves need to be wide open when peak cylinder speed is reached. The old saying is that that all valves are half open twice ans many times as they are fully open, and peak cfm figures are not the means of creating a wide torque curve.

Balancing the exhast flow to 80 to 65% of the intke flow is a key point, and that can be done via a cam, rather than port mods.

Shape and cross sectional area are important, runner volume is important.

When drag racing, though, the peak power rules. On the streets, the brake specific fuel consumption drops when the focus is on increasing the the port sizes. Air flow drops, fuel falls out of suspension, and we are loosing mixture motion.

Each has a part to play.


Lastly, the key acid test of finding out if you've hit pay dirt on airflow management is calculating a Aspiration Factor, which is a Brake Mean Effective presure calculation.

Or the

composite number which is proportinal to brake mean effective pressure and volumetric efficiency.

The latest Dick Johnston Racing HP320 Kw 5.4 Quad Cam V8 has arrived in Australia. It has the highest BMEP of any production engine ever.

320 kW is 429 hp, and the 5.4 is 330 cubes with maximum power at only 5300 rpm. The factor is a stagering 4077! Thats 89.8 in metrics, or a BMEP of 11.1 via a metric constant used by some European engineers.

The EFI AVESCO 302 engine, basically a Windsor V8 with NASCAR heads, runs 630 hp at 7500 rpm, or 3595.

The 850 hp at 1800 rpm F1 183 cube engines loose BMEP because of the huge airflow restriction. That's only 3875

The carb NASCAR 351 engine runs 650 hp at 8000 rpm, or 4320.

A Lamborghini LP 400 S had 375 hp at 8000 rpm, or 5120.

The 400 hp Chev Z06 only rates at 5190, or 114.3 in metrics, 8.7 via the Euro BMEP system.

In terms of hp per per per cube, the Ford modular V8 is 25% more efficient in terms of airflow management. The Chevy Z06 engine then fights back on thermal efficency, as its a much more economical engine, with better mecahnical efficiency for every hp produced. After all, it only has one cam to spin, a better igntion system, and is two-thrids the weight at about 185 kilograms verses about 290 kg for the Triton based 5.4 with Mustang 4.6 Quad Cam heads.

 

[6bangerbill]

I have to make a copy of your last few postings and spend a few hours digesting the concepts, and make a few comparisons of my own. The analysis program i use has been very useful in my hibred head project because it gives port volume, plenum volume and port length for manifold fabrication. It also gives port velocity at various lifts for a given cam duration . It seems that lobe separation is critical for max lift to occure at max piston velocity. THis program is drag race oriented.
One concern i have with the ls1 or ls6 heads is the large change of cross section area inside the port before the valve.The short turn radius is better than most production heads but at the sacrifice of port area at this point.Area varies from 2.956 Sq. in. at the valve,2.41 sq.In. at the short side radius and 3 sq. in. at the port mouth. I read that Max Hp is determined by port velocity at the desired rpm peak. Please comment.

 

[xctasy]

I can't help at all.

I just don't understand the Chevy LS-1 at all. It is a masterpiece, but in engineering, the orthodox rule is that the number of flowpaths verses the number of flow drops defines the "areodynamic' character of the port. In short, any thing that has a large sectional change creates drag. In publications on fluid flow, they used flow nets like this.

I instictively thing a wider lob sepration angle is better, as that is what Chevy uses. But its just a hunch, and that is a useless precept for you deciding to run a 112 LCA cam rather than a 108.


In port flow calculations, they mearly look for areas of turbulence, and then try the port shapes to optimise both after port mixture swirl and bulk cfm through the port. They only plot air speed if there is some kind of tricky problem. The Fluid flow in the classic Richardo models suggest 250 feet per second wet flow gives ideal power. In practice, the Chevy port is mostly dry flow, with a cooling atomised fuel flow which shrinks the fluid. The lobe anlges look to be a method of stopping backflow.


The nature of the short turn radius is the key to making any head flow. The drastic change in cross section is never good for performance, and this is the reason is that GM spent so much time working on the Cathedral intake system. I believe they looked at getting the mixture motion right, and then they took a loss on the intake profile.

The rule I've heard is that the sectional area shouldn't change much. Its fine to make wild D, apple, or Cathedral ports. The reason the LS1 ports exist because is becasue of the intake manifold on the V8. The air flow is dry air flow, and then it gets spiked by cool, very rich fuel supply, with a wide lobe separtion angle, and long rods to reduce the intake pulses. The restrictions of the hood line made the Chevy Powertrain engineers look at the intke port, an I have no idea how it works. I do know its possibly the best brake specific fuel consumption intake 2 vlave head around. It bulds on the amazing GM 3800 engine.

The rules go out the window with the Chevy LS1 and ZO6 V8's.

If the program shows 108 lobe centre, I'd split the difference between the factory 114 and 116 profiles, and go for 112. The air mix is getting squeazed, and this creates a pinch point as the fuel discharges. I have no proof at all, but reckon the EFI nosel cools and shrinks the bulk mass of the incomming air, and Chevy are capitalising on that.

The LS1 engine runs very, very rich. The aftermarket chips wind the air fuel ratio from the stock 11:1 back to 12.7:1 under wide open throttle, and it gets more power!


Regards,

x

 

[6bangerbill]

Thank you for your response. After a little thought ( very painful process) it occured that the reason for the overly large port mouth was due to volume reduction caused by the injector location.The mystery of the catheral port mouth is solved,the cathedral port mouth is to allow injector clearance and explains the overly large port entrance volume at this location. I have filled the cathedral area with weld and remachined the upper port to a smaller rectangular shape for use with carburation.This still leaves the port entrance at about 3 sq in in area with no injector to fill the cavity. My next move would be to increase the area at the short radius to its maximum without lowering the floor of the short side radius. My dummy head section (this is the section of head left over from the hibred operation) opened up to about 2.56 sq in.

I hoped not to use efi but i will if required , the cost woud be a strain at this time.

The engine analyzer calls for a min 2.75 sq in. and a max of 3.9 sq in. for my rpm range. This is average area for the entire port length, so i may be in the ball park. I may weld a filler into the port section to avoid a large section variance. A port length of 15 " is also reccomended with this port volume. I may go a bit longer on length to provide torque required for transmission converter. If i do go longer do you reccomend that the same port volume be maintained, that is a smaller port cross section?

The engine analyzer reccomends a 102 lobe centers and a 101 intake lobe center location.Max piston speed is at 74.8 deg atdc when the valve is at about.600 lift. and 2.759 sq in flow area . Flow speed is a max of 420 Ft per sec with 71 1n of water vaccuum at max piston speed.all at 6500 rpm.
It seems that wider lobe centers would not provide max port flow until after max piston speed. The 108 lobe centers sacrifice some flow to provide a reasonable idle for street use. Isky cams uses 108 as their standard lobe centers for street use; comp cams uses 110 .Most drag cams seem to use 110 to 106 lobe centers but the don't have to idle.I can come close to the reccomended intake location by advancing the cam about 5 degrees to a 103 degree intake lobe center.

Do you have a method of calculating plenume volume? And do you simply use half of that volume for a two plane or split manifold .My engine anylizer shows a hp increase at all rpms when front and rear cylinders are grouped together. Street use would have to be inhanced as well.

If I am all wet on this please set me straight.

 

[Twinscrew]

xtaxi, I believe you are right on the money. As I understand it the fuel timing can be used to improve flow by adding mass @ velocity at less than peak piston speed/valve lift. My gas flow analysis skills are lacking, but it seems that the spike of fuel would also induce some resonance perhaps stabilizing flow at the short side radius??

 

[6bangerbill]

Xtaxi, I just read an article about modifications to the small ls1 v8 that may be of interest. A completely stock 5.3 ssr truck engine produced 413 hp @6600 rpm with only a cam/spring change and headers (100 hp over stock).This is with small 1.89 intake valves. This same engine with ported 2" valves, intake manifold change and injector change yielded 458 hp @ 6600 rpm. It was noted that the A/F ratio during these tests were 11.5:1.Lingenfelter Performance recalibrated the stock GM fuel map to accomplish the fuel mixture. Can these results be duplicated with a carburated ls1 headed 300 engine? The cam used on both dyno pulls was a Comp Cams 229/242 duration, .631 lift and 114.5 lobe centers.Xtaxi, you win, maybe wide lobe centers are not only for street idle purposes. Your rich fuel mixture comment was also right on for the ls1.