100hp/L - How to questions?

[tom1394racing]

"Here is a straight forward build that makes 95? hp/litre.. at the crankshaft anyways."

Another RSR Clone Project - Dyno Day

The motor in my RSR is close to 100 hp/lt and it is pure joy to drive on both the street and on the track.

John D made me a set of DC-60 cams and the motor is very tractable from 1000-4000 RPM and just screams from 4000-7500 RPM.

With twin plug, RSR heads and 10.5 CR, it was not inexpensive to build but it is well engineered and great fun.

[tomkirkcis]

Tom,

I had read your enginedyno post previously. Congrats on a great build. I have a 3.2 of similiar specs. I am juststarting to drive it and am sorting it out and have not had it on a dyno yet. I have read several posts about twin plugged motors and the correct timing advance. Are you runing 25 - 26 degrees which seemns to be the common wisdom, or have you found something else that works for you. thanks tom

[bob barnes]

I should be at the track this evening but I have to pipe in. I have had five motors in my lifetime that have made 100HP/L. One built by R. Ginther-rebuilt by Andial. One built by Woods-2.9L. Three built by me-3.0L, 3.4L, and last 3.6L. Three of these were dynoed on Woods dyno to allow good comparison and all had Carbs.
All of these motors were expensive and tuned on a very conservative dyno.

These numbers I see quoted and the Cams used are very questionable. Trying to get Torqued spread over a large RPM range usually means that Peak Power is also reduced over the upper range. A peaky cam will make power over a narrow range and get boasting rights, but won't win many events. But now I see boasts of wide torque and high HP with low Compression. Yes 10.3 to 1 is low compression trying to make competitive power unless all you are doing is running against other Porsches with the same parts.

Guys are being mislead to think they can build 100HP/L with standard heads, small ports, not very aggressive cams, and inexpensive add-ons and very liberal dyno readings. The Cam makers are being too kind to blast some of you on your postings of unbelievable claims of wideband HP on small lift cams.

Bob

[davidppp]

Hello all.

This thread is revealing quite a few bits of hard-won tuning tricks!..typical of Henry's generosity..

A litle math shows us the Factory ports are generally bigger than needed for peak power, even at 8000 rpm.

For example, the gas speed of the 2L FIA race engines is only about 390ft/sec in a 30mm port.
Plenty of these engines make well over 100bhp/L...

Put another way, gas speed at intake charge temperatures becomes a blocking factor on flow at about 690 ft/sec..at 8000 rpm a 2L motor will pull enough air to just reach this speed thro' a 27.7mm hole..

Note I am neglecting boundary layers, and obstructions in the port here..

And we know thwe Factory used much bigger ports, and this was surely the product of some dyno work..

But its pretty clear we are wise to look elsewhere than simply bigger ports to make more power...and torque spread, gas mileage, and mixture quality all will surely benefit from keeping up gas speeds.


kind regards
David

[Henry Schmidt]

Small, high flow ports seem to be a key component in our unexpected results.

Reread my post "36mm intake port" on a 3.0. 3.0 factory RSR intake ports were 43mm. yikes!!!!!

[Flieger]

sub'd

36mm ports are early 911S spec?

[kenikh]

I'd venture to suggest that port size is overrated. Who cares what the aperture size is?

Every infinitely small increment behind the intake port is an aperture when you cross section a head. Performance is about port design which maximizes velocity as a function of air volume, not a static diameter reading. The below heads measure at any given diameter on the intake port between 39mm and 40mm. The air flow was modeled to my specific displacement (2.3L, 85mm x 66mm), camshaft (DC44 on 102 lobe centers) and top engine speed (8000 RPM). I provide this example as a counterpoint to the above discussion on "small" ports: it ain't the ports as much as what is behind them (between the port and the valve).

Credit goes to Herr Weiner for the work below.

[304065]

Here is another good thread on the subject.

Race motors, Steve, Henry and the lot

[Steve@Rennsport]

Originally Posted by kenikh

I'd venture to suggest that port size is overrated. Who cares what the aperture size is?

Amen, to that!!

Its all about throat shapes and volumes between the port openings and the valve seats,....

[911pcars]

Beautiful head work Steve. Given these are heads destined for a track engine, would you care to comment on the +/– issues of abbreviating the length of the valve guides on a 911?

Thanks,
Sherwood

[jpnovak]

Herr Weiner, Could you elaborate on throat shape and volume? Obviously from the pictures of Kenik's heads a streamlined shape around the valve guide boss is important for flow. How does intake port volume help? I assume it is related to engine and intake pulse frequency tuning. This would be why you want to maintain a constant diameter throughout the section.

IN addition, how much does the loss in length of the valve guide affect service lifetime?

I am learning a lot.

[kenikh]

Sherwood, those heads are for a street motor. It may never see a track...ever. The cams and heads mean it will pull harder than a stock 'S' low and as hard a 906 up high.

[bob barnes]

Thanks, it's about time someone sheds some true light on the Head/port size myth. This is why a good Race Engine isn't cheap because there usually is a good head guy waiting in front of a good Cam Grinder! Someone spent hours on those ports.

Novak, your Desktop dyno made lead you astray. I have 60hours of work with that software but I also have three engines to compare the results against real dyno data on Wood's dyno. Someone before told you that you have to do baseline work on a known engine. You are going to spend more money experimenting than paying a good Race Engine builder to build you a motor. The real Builders are not sharing their secrets just sitting back laughing at the bull of
Thermodynamics 101 and Fluid Dynamics 202. Past Racers running 3.0L engines trying to make 100HP/L were not using RSR Cams or those who were making power were not using them! If they were that good, Elgin, Woods, Schrick would not have been needed.

Bob

[Steve@Rennsport]

Sherwood,

Shortening the guides a little (as pictured) has not proven to reduce their lifespan. As long as one uses a good guide material, installs it properly, and hone it to fit, guide life is really excellent.


Jamie,

Without dilvulging specific data, I can tell you that such heads represent many thousands of hours on a flow bench and engine dyno with the objective to maintain sufficient velocity at all valve lifts and volume for improved HP and torque. One uses special pitot tubes to measure boundary layer airflows at many points in the port and around the guide boss as part of the process. You get to ruin a LOT of heads during the course of development, too. Patience is a big virtue in this endeavor,....

Those heads are equally at home in a race engine as well as a high-performance street one,...

Mister Barnes speak volumes of wisdom; making a real 100+HP/litre is an involved process involving custom cams, pistons, headwork/valves, induction, exhaust system configuration/design, windage and extensive oiling modifications so that the whole thing may live. Years ago, we had a 3.0 RSR motor making over 400 HP but it was a 24 hour engine and FAR FAR from stock RSR spec,...

[Facey]

hows does honda achieve 100hp/l at their price point?
just new design and stuff like vtec?

[kenikh]

Originally Posted by Facey

hows does honda achieve 100hp/l at their price point?
just new design and stuff like vtec?

First, scale - they make a LOT of cars. Scale allows them to drop Titanium rods cheaply into an S2K, after all.

Then there is technology; it has moved on. To name a few things:

1. Water cooling; easier to make power on a cooler running motor
2. VTEC - variable valve timing gets around SO many of the power generation issues in older cars
3. Multi-valve heads - It is easier to spin high revs on a car with two lighter valves on the intake and exahust side versus the monolithic single valves on old Porsches (and the 4 valve heads are much more modern and volumetrically efficient)

Then there are things like bearing technology, modern casting and forging techniques, direct fuel injection, etc...things that cannot be economically back engineered into a 50 year old engine design.

I could go on, but you get the picture.

[cgarr]

Are those valves 8 or 9mm?

[cnavarro]

6mm even!

[cgarr]

Originally Posted by cnavarro

6mm even!

Perhaps, Not 9 for sure, there is a lot of meat in those guides.

[kenikh]

Which valves? Mine? Stock! Perhaps not for long, depending on some news. We'll see.