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I'm not sure the conclusion you are drawing then. If you ran 180*F on the freeway with a 180*F thermostat, and now are running 150* with a 150* thermostat, then all that tells you is your radiators performance is capable of cooling the thermal input of your engine while cruising on the freeway.
I'm sure you know that if you were running coolant temps higher than 180* during your mile competitions, then running a 150* thermostat will not make the engine run cooler than those (>180*) temperatures at WOT.
I'm not sure the conclusion you are drawing then. If you ran 180*F on the freeway with a 180*F thermostat, and now are running 150* with a 150* thermostat, then all that tells you is your radiators performance is capable of cooling the thermal input of your engine while cruising on the freeway.
I'm sure you know that if you were running coolant temps higher than 180* during your mile competitions, then running a 150* thermostat will not make the engine run cooler than those (>180*) temperatures at WOT.
Even in the mile it's still not steady state thought. Block, oil, rotors, shaft, manifolds, coolant and radiator are still all in a transient, if you you start 30C cooler you have that little bit more margin to allow better thermal flow from housings, plates, rotor faces, exhaust ports.
If you were talking endurace racing at Le Mans/Sebring/NB yeah it's not going to matter.
Even in the mile it's still not steady state thought. Block, oil, rotors, shaft, manifolds, coolant and radiator are still all in a transient, if you you start 30C cooler you have that little bit more margin to allow better thermal flow from housings, plates, rotor faces, exhaust ports.
If you were talking endurace racing at Le Mans/Sebring/NB yeah it's not going to matter.
Transient as in the temperature have not reached equilibrium by the end of the mile?
Makes sense to want to start the run at a lower temp. I would consider an air to water or oil to water heat exchanger and ice the water reservoir.
at first glance you might be wondering why you are looking at an 12 psi boost chart.
a few years ago i did a small production run of my welded CPR manifold.
an engine customer is running one with an EFR 9180. a few days ago he decided that running in the high 30s probably wasn't a great idea w re to longevity so he decided to do a bit of wastegate spring swapping. the log above is the result.
12 PSI on an EFR 9180!
i have always run two red springs and w my 9180 or the G40. w the boost controller off i generally see 16/17. i have often wondered what my boost would be w less spring.
question answered.. to me that's a big WOW.
the CPR manifold was designed for max flow with the exhaust flow biased towards the turbo not the wastegate.
any article written on wastegate positioning guides you to positioning it in the flow. to the extent you do that you lose flow to the turbine.
the above log proves you can have effective wastegating while not interrupting the main event... power to the turbo.
the point being, whether you are running a small or large turbo you can dial in pretty much any boost level you want w my manifold.
it will be interesting to see how much power he can make w just the one small spring..
stay tuned.
Last edited by Howard Coleman; Aug 20, 2025 at 01:56 PM.
hidden somewhere beneath the G40-1150 is my SS cast CPR manifold. tomorrow i turn the key. unfortunately the car will remain in the stable as i await the arrival of my new coil overs.
i was able to do an initial run today and now have some comparative data. this comparison is between my welded manifold and the newly tuned up w SolidWorks cast manifold. i am happy to say that the cast manifold beat my welded manifold as to crossover and backpressure.
comparing two runs off the wastegate spring.
6-14-25 welded manifold
cast SS manifold 9-16-25
two things catch my attention:
the welded manifold delivered more boost than backpressure until 6510. the cast manifold delivered more boost than backpressure until 6770. an additional 260 RPM. both numbers are sensational compared to other manifolds but the cast is even better.
at virtually the same RPM (7276-7285), back pressure was 24.2% greater than boost on the welded manifold and was 17.0% on the cast. Solidworks magic.
while this is low boost the same dynamic advantage will occur higher up the scale.
i am delighted and plan to start production tomorrow..
+1. I am excited to get my build going using this manifold. I have the turbo and manifold already, just nee the remainder of my parts to start the build.
BTW, for the curious, here's a 677 rwhp third gear pull w the steel manifold.
this is the other end of the spectrum. 23.7 psi with 37 psi backpressure, 56% over boost.
more boost than backpressure until 6257.
Borg Warner estimates that it takes 100 hp to drive one of their turbos to the point that it makes 500 rw rotary... so there is bound to be some backpressure build as flow increases.
the high power at lowish boost is due to Garrett's cutting edge aero and the fact that my G40-1150 is a pretty large turbo.
i am quite interested to learn what the cast manifold delivers at this power level.
Last edited by Howard Coleman CPR; Sep 17, 2025 at 01:34 PM.
Back between welded production runs I wanted a manifold. Howard directed me to a person that had tried to get it to fit on a RHD. He was selling it because he was unable to make it work.
Since the dimensions are very very similar I wouldn't expect the cast one to work on RHD.
I'd love to be able to fiddle with one on a build I'm doing though I'm afraid the intake manifold setup I've put together wont clear the compressor - the LIM to UIM flange has been moved down a couple inches. Is there any way (and would you mind) that you could give dimensions from the top exhaust manifold studs plane to the plane of the LIM/UIM surface? Congrats on the great work.
I'd love to be able to fiddle with one on a build I'm doing though I'm afraid the intake manifold setup I've put together wont clear the compressor - the LIM to UIM flange has been moved down a couple inches. Is there any way (and would you mind) that you could give dimensions from the top exhaust manifold studs plane to the plane of the LIM/UIM surface? Congrats on the great work.
Shortened runners to lift peak power rpm? Did you take any out of the top section too?
Shortened runners to lift peak power rpm? Did you take any out of the top section too?
Yeah, the goal is to play with intake designs on boosted applications (already have loads of work on the ITB and race side of things)and do testing on my dynos - it wont be empirical per se since many things are being changed up but I think with the experience I've got I can use it as a good learning exercise. It's been converted into a plenum'd manifold on top of the shortened LIM - the runners end at the LIM after a plate to receive said plenum is bolted on. Just writing the CAM as well as playing with the transitionswhen I have time to keep moving forward.
Sorry to pollute the thread - mainly wanted to give context as to the 'why' I'm asking for the dimensions I've asked for since I've always liked Howard's design. From the last photo it's very obvious that at least the compressor (and maybe turbine) would interfere with what I'm putting together. I keep meaning to make threads for my own projects but photos are the bane of my existence.
"dimensions from the top exhaust manifold studs plane to the plane of the LIM/UIM surface? " will PM you tomorrow. i did a bunch of NA work on runner length in the 70's. my SCCA B Sedan motor. single OHC, 2 valves, two DCOE 45 Webers w really large chokes. really big results from changing the runner length. ultimately, 205 flywheel hp from 122 cubic inches and 10,000 rpm. my buddies at Ford sent me ROLLER cam followers. no part numbers on them.
Last edited by Howard Coleman CPR; Oct 18, 2025 at 08:43 PM.
as far as the engine flange design/leakage, I never understood why nobody used separate flanges i.e. no cross-connection. Artec did it on their cast 321 manifold though, not really comparable otherwise to the CPR design imo:
thanks for the initial response re the first production of my manifold. for those onboard production starts Dec 22 and the process lasts a week. final machining another week. of course this is right around Christmas so we will see how busy Santa is...
i am now taking single orders so don't hesitate to contact me. the greatest interest, so far, has been 347. 316L and 321 are tied.
bottom line, you are looking at 10 weeks from placing your order... $850 initial payment.
If you're struggling trying to decide which grade SS to choose from among 316L, 321 or 347, the attached Google AI generated response might help. I asked it "Which is the best stainless steel grade for a cast exhaust manifold application, 316L, 321 or 347?".
The take away I got from all this is that 321 or 347 are about equally suitable for a cast exhaust manifold application, while 347 has an edge if you're going to need to perform welds on it in the future (e.g., sensor bungs, crack repairs?). FWIW, I chose 321 because Howard's mani has all the bungs I'd need already, and I doubt it's going to need any crack repairs in the future.
The take away I got from all this is that 321 or 347 are about equally suitable for a cast exhaust manifold application, while 347 has an edge if you're going to need to perform welds on it in the future (e.g., sensor bungs, crack repairs?). FWIW, I chose 321 because Howard's mani has all the bungs I'd need already, and I doubt it's going to need any crack repairs in the future.
Why didn't you go with 347 for essentially the same price? What would be the downside?
Why didn't you go with 347 for essentially the same price? What would be the downside?
That was a tough decision, and because of the minimal price difference, I almost opted for 347. What decided it for me was that in addition to that AI result I posted, maybe another 60~75% of the internet research query results I got back comparing SS grades in a cast manifold application were agreeing that cast 321 is slightly better than cast 347 for prolonged exposures to high temperatures, i.e., 321 can withstand temps in the ballpark of 1600*F/870*C while 347 withstands temps in the ballpark of 1500*F/815*C. In the scheme of things with a rotary, I'm more concerned with high EGTs than future weldability of the cast manifold, so I opted for 321 over 347.
