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Sorry to go back to posts from August 2019, but I was looking through the full thread and came across your hood vent posts. Did you ever do any testing to determine how effective the location you used is? I installed vents a year or so ago, based on this aero diagram. It shows up on this site in a 2014-ish thread.
I finally got around to checking to see if air is actually coming out. I taped a bunch of pieces of yarn to the vents and went to the track. The yarns consistently were sticking up in the air. Not straight up obviously, but definitely up off the hood. Maybe 30 deg angle. Seems like that should be good. That hood isn't legal for STL or ITA, but just fine for enduros in the desert (that is pretty much all we have here in SoCal. I have an unvented hood for SCCA races.
On another testing front, I found that my new-ish airdam didn't like going over off course and over a curb. Mashed up the drivers corner. Not sure exactly how it happened, since I was not driving at the time, but looked like a pretty innocuous spin. Anyway decided that I don't need it after all ;-)
We have the same vent installed in the same place. It helped. We have now leaned the radiator forward as well to help aim the exiting air at the vent. We'll see this season if that helps.
I didn't get to do a yarn test with my vents last year. Too busy just trying to get my heap to finish a race!
Carl, based on that image my vent location may not be ideal. I am hoping that the current placement vents air out of the inner fender area. I will try to evaluate that this year. The STU rules just changed and now we can have louvers as a part of the vent. So if what I have works, I will extend it forward and add louvers to it. Otherwise I will be cutting some new holes!
Regarding your air dam drama, I get it. At Indy I spent allot of time driving off the track and really got tired of fixing the damage. This off road driving thing is a new development for me. I have always been pretty clean in that regard. Not anymore. I am blaming my age.
I have decided the best approach is an air dam and splitter that I can keep on the car. Even a splitter that is 4ish inches off of the ground helps by speeding up the air under the front of the car.
I didn't get to do a yarn test with my vents last year. Too busy just trying to get my heap to finish a race!
Regarding your air dam drama, I get it. At Indy I spent allot of time driving off the track and really got tired of fixing the damage. This off road driving thing is a new development for me. I have always been pretty clean in that regard. Not anymore. I am blaming my age.
I have decided the best approach is an air dam and splitter that I can keep on the car. Even a splitter that is 4ish inches off of the ground helps by speeding up the air under the front of the car.
Interesting. We have basically the same air dam...well as close as we could get copying your design (thank you). We've been impressed with how durable it is whilst going off road. Every other design we tried usually was destroyed after an hour or two of running. Your design has lasted us two seasons with minor re tweeks.
Interesting. We have basically the same air dam...well as close as we could get copying your design (thank you). We've been impressed with how durable it is whilst going off road. Every other design we tried usually was destroyed after an hour or two of running. Your design has lasted us two seasons with minor re tweeks.
It was fine until I added a splitter and then started driving like an idiot. I noticed that one of my competitors had an air dam and splitter similar to mine only higher off the ground. Which I dismissed at first glance but later noticed that it survived his off road excursions just fine.
so the splitter makes you drive worse? i should really go find the pic, but we did hood vents on the green miata, and one weekend it rained and the driver went off (because of the splitter) and it scooped up a bunch of mud and it went through the hood vents and into the drivers lap.
so the splitter makes you drive worse? i should really go find the pic, but we did hood vents on the green miata, and one weekend it rained and the driver went off (because of the splitter) and it scooped up a bunch of mud and it went through the hood vents and into the drivers lap.
No the driving idiocy began before I ripped off the splitter and continued after it was completely removed. See this is the reason I have a car with a proper roof. When ever I drive off the track the grass clippings go over the roof.
I was going to replace a gasket between my RB presilencer and the back part of the exhaust. Of course, snapped off a stud. When pulling it all apart to repair noticed that the guts of the presilencer are gone. Apparently early ones were stainless on the outside, but the perforated tube inside was mild steel. Ordered a new presilencer late on Friday afternoon. Thinking about it after the weekend, I realized it is probably time to upgrade the exhaust from the header back, especially now that I am running a street-port 12A not the stock-port that I ran for about 20 years. The presilencer order is on hold. The current exhaust is the short RB collected header going to 2-1/4" tubing through a 4" round x 14" long Magnaflow, over the axle to a stainless turbo muffler. This configuration is quiet and allows me to run Laguna Seca enduros at <90-92 dbA.
The old stock-port 12A made 135HP with a stock Nikki and same exhaust. Currently with a stock Nikki, same exhaust and street-ported 12A, I make 138HP. With the street-port and a modified Nikki (primaries opened from 119mm to 124mm) I make 150HP with the same old exhaust. I am guessing there is some more HP available by opening up the exhaust.
My plan is to keep the short collector RB header that I already have, cutting off the existing flange to transition to either 2.5" or 3" single pipe back to and over the axle. I plan on using a RB univeral silencer somewhere between the header and the axle and a stainless turbo muffler behind the muffler.
Does anyone have any experience/opinion on whether I should use 2.5" or 3"? The header pipes are 2" OD with 1.75" ID. A single 2.5", 16ga tube is a little smaller (flow area) than the two header pipes. Of course, 3" is slightly bigger.
Just did a closer calculation. The 3" flow area is 35% bigger than the 2" primaries and 2.5" is 10% smaller. Not sure which way to go. Of course, the volume of the exhaust drops (by a lot) as it goes through the system. Velocity drops by 20% by the collector (short style) and at least 50% by the axle. Not sure what that means though.
I googled rotary exhausts and megaphones a week or so ago and got some hits on Rotary race car exhaust systems. From that I gathered that you don't want a restriction down stream of a rotary. You might want to look that stuff up. The posts covered the difference between long primary and short primary systems
My system consists of old ISC 12A stainless header that was modified to fit my 13B. I believe the header has 2OD tubes but has a larger ID (thinner tubing). I had a NASCAR 2 into 1 collector adapted fit the header which created a step increase in the primary tubing to 2 3/8" OD just ahead of the merge that opens to 3" OD. I then run 3" OD stainless all the way to the back over the axle and to a Magnaflow 3" round muffler that is 5 x 14 inches. It's loud but makes sound everywhere but CA.
I would like to get a better header with 2.5" tubing to see if that makes a difference.
before you get the hammers out, you might just put some kind of pressure fitting in the exhaust after the collector, and get some kind of exhaust backpressure reading. the rule of thumb is if you have more than ~2psi of restriction you're loosing power. if there isn't a restriction, then playing with the tuned lengths might be a better way to go
Endurance racing, I managed to destroy pretty much everything I put on the car when I was trying to use mild steel, and standard mufflers you can buy from Summit. Even managed to set the car on fire when I destroyed the muffler, which then destroyed the heat shield, and got the fuel in the cell so hot it boiled out the vent tube…
One thing for sure is that I never want to deal with that Racing Beat 6 bolt flange under the car ever again.
I ended up going ahead and spending the money to get the right stuff, 100% stainless from front to back, all v-band connections instead of bolted flanges, Racing Beat rotary specific pre silencer and muffler. You can even get stainless hangers which I highly recommend.
It is still possible to get stainless versions of the old ISC header, Steve Eckrich has the tooling, but he doesn’t make any effort to sell them. he can make them with the 6-bolt flange, but I got a 2 inch to 3-inch merge collector which I could then use with a v-band. The merge collector should be better for power and definitely easier to work with.
Carl, depending on your stash of housings and rotors, you may want to consider building a system that would work well for a 12aSP and/or a 13b motor. May want the 3" for the 13b, especially if you are going over the axle(restriction/turbulence from close elbows).
When I was running in IT I had a long primary system made out of mild steel. I spent allot of time welding patches to it everywhere. And the repair just made it more likely to crack again. Also had RB mild steel header crystalize at the bend just after the exhaust port.
I built what I have using ebay stainless steel straights, bends and unions. Pre-covid this stuff was not expensive and it was easier to weld on than mild steel. My stuff is not as pretty as MR650s...(really cool looking stuff) but it works and is lighter than the mild steel exhaust it replaces.
And like Kurt, v-band clamps for the win. No gaskets
Last edited by mustanghammer; 02-01-22 at 01:16 PM.
Thanks for the info/help guys. It definitely has helped me figure out how to go forward.
My plan is based on some basic pragmatic concerns. I already have a RB collected header that has an "industrial strength" ceramic coating that still looks new after 2 years. I am planning on cutting off the 2" collected outlet and converting it to 2.5". I have already shaped some 14ga 3" tubing to modify the collected portion. I hadn't realized until this morning (after going down the internet rabbit hole that Scott pointed me down yesterday) that RB makes a fully SS presilencer identical to the one that I have been using since 2006, but with 2.5" internals instead of 2". It is for the 2nd gen collected system. This silencer has worked well for me, with the exception of the recently broken stud and realization that the internals are gone. According to RB, the presilencers from 15-20 years ago had a mild steel perforated pipe core, which explains why mine was burned up. They have since changed to a stainless core, so I think it should be good for a long time. From the outlet of the presilencer, I will go with 2.5" 409SS tubing back over the axle. The final muffler will be the same as the Mandrel Bending Solutions SS muffler that I have been successfully using for 5 years. Just 2.5" instead of 2.25". If I need to add it for Laguna sound, I will install a 4" round muffler between the presilencer and the axle. The configuration is the same as what I have now and I have easily made Laguna sound. I am hoping that the new presilencer will allow me to eliminate the intermediate muffler for simplicity. Except at the presilencer, I will be using v-bands as necessary. They look really slick.
Because this system configuration is basically what I already have just bigger, I feel like I should have a pretty good grip on the sound levels. It is 35-50% larger than what I currently have depending on the location , which seems like a reasonable upgrade. It also is only costing a couple hundred dollars more that it would have to just repair what I already have, so I won't feel too bad if I upgrade to a ported 13B in the future.
In the meantime, I welded all the broken bits back together so I can race with my son at Buttonwillow in a couple of weeks. Kurt, I think I saw you are signed up for the race, so I am looking forward to seeing you there. I will be racing in EP, so my son can run STL. The car and driver are extremely uncompetitive in EP, but kids get priority.
As a retired engineer, I feel the need to measure the exhaust pressure of my existing system as j9fd3s suggested. Planning on drilling a hole in my current presilencer and running some tubing into the passenger compartment. Can turn a GoPro on the gauge for a session and see what it looks like.
Anyway, thanks again for the help and if anyone sees any potentially significant flaws in my plan, feel free to let me know. I haven't ordered any parts yet.
In the meantime, I welded all the broken bits back together so I can race with my son at Buttonwillow in a couple of weeks. Kurt, I think I saw you are signed up for the race, so I am looking forward to seeing you there. I will be racing in EP, so my son can run STL. The car and driver are extremely uncompetitive in EP, but kids get priority.
Cool, looking forward to seeing you! And I hear you about the kid factor. Haven't touched my car since the runoffs, just getting my son's 82 ITA/ITX/STL/ST6 ready for SCCA drivers school the weekend before. So Super Tour will be a bit of a warm/up and maintenance event for me.
Cool, looking forward to seeing you! And I hear you about the kid factor. Haven't touched my car since the runoffs, just getting my son's 82 ITA/ITX/STL/ST6 ready for SCCA drivers school the weekend before. So Super Tour will be a bit of a warm/up and maintenance event for me.
Wait....you haven't touched your EP car and you are telling me to get back to work?!
For the record I spent last Saturday removing the pilot bearing from my engine. I have a puller and in the past this job took less that 10 minutes start to finish. This time I had to use chisels and diamond incrusted dremel bits to get it out. I swear the outer shell on these bearings is harder than the hubs of hell.
I completed an inspection of the transmission and decided to change all of the bearings that support the Input shaft and the main shaft. Now waiting on Jerico to ship the bearings I ordered....stupid supply chain issues.
Wait....you haven't touched your EP car and you are telling me to get back to work?!
For the record I spent last Saturday removing the pilot bearing from my engine. I have a puller and in the past this job took less that 10 minutes start to finish. This time I had to use chisels and diamond incrusted dremel bits to get it out. I swear the outer shell on these bearings is harder than the hubs of hell.
I completed an inspection of the transmission and decided to change all of the bearings that support the Input shaft and the main shaft. Now waiting on Jerico to ship the bearings I ordered....stupid supply chain issues.
First race is in April....maybe.
Scott,
I'm curious on your transmission woes...shouldn't a Jerico by more than stout enough to deal with what you are throwing at it? I mean they are supposed to be rated up to 750hp in a 3200lbs car. For the cost involved I would expect it to be virtually maintenance free. Can you tell what I'm missing?
Sorry to go back to posts from August 2019, but I was looking through the full thread and came across your hood vent posts. Did you ever do any testing to determine how effective the location you used is? I installed vents a year or so ago, based on this aero diagram. It shows up on this site in a 2014-ish thread.
I finally got around to checking to see if air is actually coming out. I taped a bunch of pieces of yarn to the vents and went to the track. The yarns consistently were sticking up in the air. Not straight up obviously, but definitely up off the hood. Maybe 30 deg angle. Seems like that should be good. That hood isn't legal for STL or ITA, but just fine for enduros in the desert (that is pretty much all we have here in SoCal. I have an unvented hood for SCCA races.
On another testing front, I found that my new-ish airdam didn't like going over off course and over a curb. Mashed up the drivers corner. Not sure exactly how it happened, since I was not driving at the time, but looked like a pretty innocuous spin. Anyway decided that I don't need it after all ;-)
I invite everyone to look at our wind tunnel data. Not all hood vent designs are created equal. Many hood vents on the market simply use a generic 'recessed louver' design like vraptor, trackspec, etc. Our kits use a very unique design which nets double the cooling and four times the front downforce. In short, you get what you pay for... https://racelouvers.com/test-data/
01-25-22, 04:51 PM
