Advice on camshaft for 3,0 RSR Engine

[stein johnsen]

I am building a RSR 3000cc MFI engine and need advice on type of camshafts . The engine has today the sprint cams . I will use this engine / car on the road .
I noticed that Supertech used a DC 62 cam from Dougherty . Do anybody have some experience with a detuned RSR engine . Would be grateful for any advice here.

Stein Johnsen

[MST0118]

I personally have had better luck with the sprint cams in generating more power and drivability with MFI than using a more modern cam like the DC80 that I’m still trying to dial in. I think a lot of this is due to the fact that the space cam in a 3.0 rsr is a v-109 which generally provides a good matching fuel in the pump to the sprint cam in the engine and not to other modern cam profiles.

While the DC-62 has more lift than a sprint cam, the intake and exhaust duration is much less than an rsr cam. Thus, if you already have an rsr pump built, you might need to change the space cam out or have it modified and change pump timing.

It can be done but can be a tuning challenge. If you haven’t built the injection pump yet, then I’d recommend going to MFIWerks or another pump specialist that would know how to calibrate your pump to make a dc62 cam work with your 3.0 displacement. Are you going with traditional slide valve which many 3.0 RSRs had or using throttle bodies? This may also play into which option is best.

Finally, if this is a real 74rsr motor, those heads had huge 43mm ports so you probably want to have cams that will help the engine breathe. If it is an original case and heads, the engine is worth big bucks, another reason to go with sprint cams.

[faapgar]

Check and see which Sprint cams they are.Shrick made a set that timed at overlap from 6-6.3mm.They are a different color from the factory grind.Fred

[lvporschepilot]

I have used the DC65 camshaft on two motors, both had 39-40mm intake ports and 38mm exhaust ports. Timing was set to 5.7mm. The engine made max power at about 7500rpm. Redline set just a little above that. Idles ok around 1200-1300rpm.

[Edelweiss]

We have a profile that made 370 plus hp on a 3,5l engine using 41 / 49 mm Std. valves.

It is hollow bored with internal oiling to the ground circle.

Modern design with a good lobe area and acceleration fitting to the application.

On demand we have the correct springs and rockers also - all made in Germany 🇩🇪🔔♠️.

Best reg.

Dirk

[stein johnsen]

Originally Posted by MST0118

I personally have had better luck with the sprint cams in generating more power and drivability with MFI than using a more modern cam like the DC80 that I’m still trying to dial in. I think a lot of this is due to the fact that the space cam in a 3.0 rsr is a v-109 which generally provides a good matching fuel in the pump to the sprint cam in the engine and not to other modern cam profiles.

While the DC-62 has more lift than a sprint cam, the intake and exhaust duration is much less than an rsr cam. Thus, if you already have an rsr pump built, you might need to change the space cam out or have it modified and change pump timing.

It can be done but can be a tuning challenge. If you haven’t built the injection pump yet, then I’d recommend going to MFIWerks or another pump specialist that would know how to calibrate your pump to make a dc62 cam work with your 3.0 displacement. Are you going with traditional slide valve which many 3.0 RSRs had or using throttle bodies? This may also play into which option is best.

Finally, if this is a real 74rsr motor, those heads had huge 43mm ports so you probably want to have cams that will help the engine breathe. If it is an original case and heads, the engine is worth big bucks, another reason to go with sprint cams.

My idea was to select cam first and then let MFIWerks build the pump .
My engine unfortunately do not have the original heads.
RSR valve size .
I will try to build an engine I can use on the road ,no competition. I was of the opinion that with the sprint cams it would be nearly undrivable in traffic.

[stein johnsen]

Originally Posted by faapgar

Check and see which Sprint cams they are.Shrick made a set that timed at overlap from 6-6.3mm.They are a different color from the factory grind.Fred

I have the original RSR sprint cams .

[stein johnsen]

Originally Posted by Edelweiss

We have a profile that made 370 plus hp on a 3,5l engine using 41 / 49 mm Std. valves.

It is hollow bored with internal oiling to the ground circle.

Modern design with a good lobe area and acceleration fitting to the application.

On demand we have the correct springs and rockers also - all made in Germany 🇩🇪🔔♠️.

Best reg.

Dirk

Dirk
I am not after max BHP but Torque on a 3000 cc engine . Do you have anything in cams for this purpose ? I am using original RSR springs and rockers .

Syein

[stein johnsen]

Originally Posted by lvporschepilot

I have used the DC65 camshaft on two motors, both had 39-40mm intake ports and 38mm exhaust ports. Timing was set to 5.7mm. The engine made max power at about 7500rpm. Redline set just a little above that. Idles ok around 1200-1300rpm.

Do you have the torque figures for your engines ?
It would be interesting to see .
It is drive ability that is my goal .

Stein

[lvporschepilot]

It's a very docile engine to drive, but torque is pretty high and the idle is somewhat rough. It really is user preference, I personally don't mind an engine the requires a lot of revs. A good compromise is the DC40 'mod S' cam, or DC44. Both of these are, without going into too much depth, just better versions of the early S camshaft.

[stein johnsen]

Originally Posted by lvporschepilot

It's a very docile engine to drive, but torque is pretty high and the idle is somewhat rough. It really is user preference, I personally don't mind an engine the requires a lot of revs. A good compromise is the DC40 'mod S' cam, or DC44. Both of these are, without going into too much depth, just better versions of the early S camshaft.

I have used the DC40 on 3 engines. 2300 on Webers and is building another 2300 cc MFI , A 3400 cc EFI has these cams also . I would like something “hotter” for the RSR . Therefore I thought the 62 could be the ticket . I appreciate your input here as here in Costa Rica it is not much help to get . I will use the RSR 2800 cc butterfly system and a 935 distributor ,8 plug ignition .

[lvporschepilot]

It sounds like the 62 or 65 will be just what you’re looking for then. These are the hottest cams I would run in a motor seeing any street use.

[Mark Henry]

I have a 3.0 with 40m webers, twinplug, RSR style Mahle pistons* set at 10.1:1 CR, I'm using the WEB camshafts 120/104 hot street/track grind.

The engine so smooth you would think it's FI, except for the 3 pumps at cold start and feathering the throttle at hot start. None of the popping or farting I've seen with too hot for street cams. Pulls hard from 3k rpm and sings at 5K+ rpm.

I'm leaving a lot on the table with the 40 Webers and 1-1/2" headers, I should move up to 46mm and 1-3/4" headers, but it drives so smooth it's hard to justify the $8-10K Canadian to do so. I'm guessing I'm about 250hp in a 2200 lbs narrow body 914. Some day I might do couple pulls at a dyno day, but it's real low on my priorities list right now.

* Not sure on the origin of the new in box Mahle pistons I used, defiantly the 3.0 RSR wedge style dome. The best guess was they were made for a stock head chamber to be used for a backup and/or practice racing engine and never used.
Real 3.0 RSR pistons have to be used with RSR heads, which have a smaller cc head chamber.
Also note I've seen other 3.0 RSR style Mahle pistons (claimed) that at look like a regular high CR dome.
Below is my piston dome shape.

[mikedsilva]

Camshafts are a real mystery to me. Still trying to understand how the duration and lift affects characteristics and output.

My motor is a 3.0 single plug with stock "big port" heads.
42mm ITBs.
COP ignition using AEM Infinity
1&5/8 headers.
10.2:1 compression

First cam I tried was Webcam 464/465. Felt very strong above 4k.
Second cam I used is the GT2 with 108 lobe centres. Torque comes in earlier, nicer to drive around town. Idle is much smoother. Feels a little softer above 5k. I could be imagining it, but doesn't feel like it wants to rev to 7k as quickly as the 464/465.

I'm not unhappy with the performance.
But I feel that maybe there is something better?

[Jeff Alton]

Email John at DRCamshafts.com and/or speak with WEBCamshafts about your specific needs. You need to speak with people that grind and spec custom cams for their living. These are the people that can guide you to the right solution for your SPECIFIC needs and build specs. Reach to them and report back.

I am yet to be disappointed with the above process in my dealings with John at DRC. Every time we engage in a discussion over the build specs and needs he has delivered a product that exceeds our expectations... I can tell you what works on the motors we build, but we haven't built a motor to your specs. So please, reach out to the experts in this area of engine design....

It actually takes less time than posting a question on this forum. But please, post your experience and results to help us all build a database of known good combinations.

Cheers

[mikedsilva]

Originally Posted by Jeff Alton

Email John at DRCamshafts.com and/or speak with WEBCamshafts about your specific needs. You need to speak with people that grind and spec custom cams for their living. These are the people that can guide you to the right solution for your SPECIFIC needs and build specs. Reach to them and report back.

I am yet to be disappointed with the above process in my dealings with John at DRC. Every time we engage in a discussion over the build specs and needs he has delivered a product that exceeds our expectations... I can tell you what works on the motors we build, but we haven't built a motor to your specs. So please, reach out to the experts in this area of engine design....

It actually takes less time than posting a question on this forum. But please, post your experience and results to help us all build a database of known good combinations.

Cheers

Appreciate this.

[stein johnsen]

Originally Posted by Jeff Alton

Email John at DRCamshafts.com and/or speak with WEBCamshafts about your specific needs. You need to speak with people that grind and spec custom cams for their living. These are the people that can guide you to the right solution for your SPECIFIC needs and build specs. Reach to them and report back.

I am yet to be disappointed with the above process in my dealings with John at DRC. Every time we engage in a discussion over the build specs and needs he has delivered a product that exceeds our expectations... I can tell you what works on the motors we build, but we haven't built a motor to your specs. So please, reach out to the experts in this area of engine design....

It actually takes less time than posting a question on this forum. But please, post your experience and results to help us all build a database of known good combinations.

Cheers

Jeff.

I have mailed John a few months ago but no answer ,therefore my post here . I will try to mail him again for advice .

[stein johnsen]

Originally Posted by stein johnsen

Jeff.

I have mailed John a few months ago but no answer ,therefore my post here . I will try to mail him again for advice .

I got an answer back from John after a couple of days .
His recommendation was.

The DC62-100. Or even the DC65-100 would work well.

Do anybody know the volume of the combustion camber from a 3000 cc RSR head .?

[Mark Henry]

Originally Posted by stein johnsen

Do anybody know the volume of the combustion camber from a 3000 cc RSR head .?

The 3.0 RSR head has a 77.2cc chamber where a stock head has a 90cc chamber. the 3.0 RSR piston has a 31.2 dome giving the RSR combo a 10.4:1 CR. (in theory you would have to do the math, shims used, etc.)
If you put RSR pistons with stock heads and do the math you get something like a 8.5:1 CR. It will run but way too low of a CR for a performance build.

My Mahle 3.0 "RSR style clone" piston with stock heads gave me 10.1:1 CR with IIRC a .25 shim.

[stein johnsen]

Originally Posted by Mark Henry

The 3.0 RSR head has a 77.2cc chamber where a stock head has a 90cc chamber. the 3.0 RSR piston has a 31.2 dome giving the RSR combo a 10.4:1 CR. (in theory you would have to do the math, shims used, etc.)
If you put RSR pistons with stock heads and do the math you get something like a 8.5:1 CR. It will run but way too low of a CR for a performance build.

My Mahle 3.0 "RSR style clone" piston with stock heads gave me 10.1:1 CR with IIRC a .25 shim.

Mark
Thank you for the information on RSR 3000 cc ,very helpful .