Borla ProXS mufflers installed, and dyno tested
 

After several weeks of bad weather and bad luck, I FINALLY got my T/A clone back on the dyno today.

To recap, LOW budget, Low compression 455. Unported pressed-stud HUGE chamber 66 heads, basic shortblock, Performer intake, Q-jet, HEI.

Last round of testing had the Tribal Tri-Ys (1.75" primaries) hooked up the exhaust that came on the car. That system consisted of 2.5" pipes going into 40-series 3" FlowMasters, exiting through compression bent 2" tailpipes. The transitions between sizes was abrupt and ugly.

New system is all 3", H-pipe, and Borla ProXS mufflers.

I posted a video on FB, and you should be able to view it at https://www.facebook.com/DynoTune/vi...9873204735140/

I'll have to look at my notes later, but I had to richen the carb quite a bit.

Results summary:
- Peak RWHP gain 14.44
- Peak RWTQ gain almost 9
- HP gain at 4500 rpm ~17
- TQ gain at 4500 rpm ~ 20

Nice!

Here is the graph comparing the performance with the log manifolds and old exhaust system, to the Tri-y headers and new exhaust system.

Beyond a doubt, the higher the rpm, the greater the loss of performance from log manifolds.

Wow, that's a big difference for that power level. Nothing like real world data.

Nice numbers Lee...!!!!
The exhaust is it mandrel bent 3 inch tails.....???? And mufflers are they off set /centre outlet mufflers

Thanks, I'm happy with it at this point! With the compression so low (114cc chambers, .022" avg piston down the hole, beveled edge pistons) I wasn't sure if the motor could break 250 at the wheels.

The tails are mandrel bent. They are Steve Coombes' old tailpipes, from a previous system he had on his car. My exhaust guy had to make a couple of cut/twist/rewelds to get them to fit the way he wanted with my mufflers and nuances to my car.

The mufflers are offset inlet, center outlet. The headers have slip-on collectors, so my exhaust guy installed flanges at the muffler inlet to allow the system to be dropped from there. Flanges were also added to the muffler outlet side to make the tails removable. I may test that later on.

Thanks for the info.....great build and nice looking car ......

How do you like the sound of the Borla’s? I bought them my current project but they are not installed yet.

I like them. Compared to the RacePros I have on my other car, the sound is much "smoother". You hear them outside the car much more than you inside the car. Under light throttle under 2300rpm, it is rather quiet inside the car.

A set of decent heads would give 50% more power at least.

Engine management (EFI and Ignition) are the next step for me.

After that, I may test some different intake manifolds.

Whenever the balance in my "Play money fund" recovers, then I'll do a head swap.

But for now, I'm having fun seeing how much performance I can get out of a engine that is basically a stock low-compression base engine, with a few bolt-ons and a cam designed to make the best out of what it has.


Side Note: I had a conversation yesterday, and the topic was "Engine dyno compared to Chassis dyno results." I've stated for years that there is NO simple formula, as there are so many variables. My engine has made 225hp with the stock log manifolds and old exhaust, 270 with headers and old exhaust, and now 285 with headers and improved exhaust. At any of those points, if I had pulled the motor and put it on an engine dyno with dyno headers and open exhaust, the "flywheel HP" would have been the same (after carb tuning).

There is no formula or "rule of thumb" that I have ever seen, that would have given the same "flywheel" HP when applied to those three different test results.

Nice results! Now the car has exhaust that will handle much more hp in the future.

What are you considering for a head swap? Just a basic low 90's cc iron head unported?

Nope, I'll be gunning for YOU ;-)

Realistically, if a nice set of ported heads in the lower 90cc's range comes my way, I'd probably snag them and run them for awhile. Maybe keep the same cam but increase the rocker ratio.

But I DO plan to eventually get some aluminum heads that will put me in the low/mid 11's on compression, and an HR to match. It seems like chamber design keeps improving, porting as well, so I'm not rushing into that purchase. As you surmised, I'm making changes with other long range improvements in mind :-)

Very nice. Love the sound too! And the bumper sticker!

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I wasn't too sure on your plans ,it would be interesting to show the difference going to smaller chamber iron heads.

Thought those looked like Torque Tech tailpipes.

Good job!

Damn Lee, that sounds great and the results are impressive.

You have the same exhaust system I'm putting on my '73, including the Tri-Ys and x-pipe except I have some Dynomax Ultraflow mufflers. I wonder how the sound will compare?

Do you have a thread or a link where you discuss your cam choice? I just popped over to your blog and read what you have and I'm curious how/why you decided on the specs you went with.

Thanks for posting all of this, Lee. It's great to see the real world results!

I'm beginning something very similar for my 72 LeMans GT, starting with a nearly identical low compression combo. After the engine install, exhaust will be next, so this is fantastic to see the details of your improvements.

Thanks again, and keep it up! :)

Will, thanks! It will be interesting to see/hear how your muffler choice will compare.

I've discussed the cam a few times, but I'll give a quick summary. I got a CHEAP 455, and the heads were set up for the .454" lift cam that was in it. The lobes and lifters were perfect, so I knew the valve springs/heads were sufficient for that lift - so that established that parameter of the cam design.

With so many people losing lobes & lifters with "modern" aggressive cam lobes, I thought it would be interesting to see what I could do with much less aggressive profiles, and decided to go even lower on the lift. The heads have pressed-in studs, so that was further impetus to keep the lifts on the low side.

I've been using engine modeling software for several years now, and have found it extremely effective in dialing in valve timing events - as long as you have a fairly accurate "model" of the engine. I developed a model for my engine and played around until I had a design that created enough manifold vacuum, and maximized the average HP & TQ over my expected power band.

I then looked through Comp's and Bullet's lobe catalogs until I found lobes that best matched what I was looking for. I put the data for those lobes into the program, and tweaked the ICL & ECL to find the best positions. Then I called Bullet and placed the order.

At this point, the cam has met or exceeded all of my expectations. :-)



EDIT: Todd, you are welcome! Glad the data is helping you! Everyone else that has replied, thanks for the feedback and support!

How accurate do you think the readings at the start of the runs is? It looks like under ~3500rpm, there is a loss of power both torque and HP that is fairly significant. Do you think that there is a happy medium that could have kept the bottom end from losing as much? Maybe smaller tube headers, or longbranch manifolds, and/or smaller exhaust pipes than your upgrade? I'd keep the smooth transitions.

Trying to pick your brain as to what what longbranch manifolds and a full 2.5" system would do for my planned low CR/low rpm build.

At 225rwhp, I could floor it around 3200 and start the dyno run. At 270rwhp, I had to go to about 3500 before I floor it, or else the trans would downshift and screw the data for the entire run.
Now I'm starting the run, and just easing into the throttle. It still downshifted on me twice yesterday.

Where you see the graphs make a noted change in slope, just past 3600 rpm, THAT is when I was finally at WOT. Ignore the data at lower rpm. The car has noticeably more power off-idle and at lower rpm than what it did previously, there is NO loss!! I wish I had a manual tranny, then I could do WOT pulls from off idle.

If the cam is designed for the exhaust system you are using, then it will perform fine. My cam was designed for a really low restriction, and that is probably part of the reason I've had such gains from when the exhaust was very restrictive. If I had maximized the cam for a restrictive exhaust, I probably would not have very impressive gains with my new system.

Thanks Lee, but now I'm confused.

Everything I think I've learned over the years tells me that wide LSA splits with longer durations on the exhaust side are for "de-sensitizing" an engine to a restrictive exhaust. Such cams (the factory 068 is a good example) are less dependent on scavenging and therefore more tolerant of exhaust systems with manifolds or restrictive piping.

I have a book somewhere around here that briefly discusses some testing the factory engineers did back during the 455 HO & SD development years. They confirmed that a cam on a 108 LSA made more peak power and more overall power when running headers and low restriction exhaust but lost power compared to wider LSAs when you started bottling things up. This, along with the need for good idle quality and vacuum is why all the factory cams are on such wide LSAs compared to a lot of aftermarket offerings.

In a long-ago conversation with Dave Bisschop he stated that he usually recommends cams like the OF on a 114 LSA if running manifolds but 112 with headers.

Other dyno tests and things I've read & seen over the years seem to bear this out. The narrower LSA increases overlap which can contribute to reversion unless the exhaust system is good at scavenging the cylinders, in which case that actually promotes better cylinder filling and can extend the RPM range of a narrower LSA cam. The wide LSA cam with less overlap or a long duration exhaust lobe typically gets the exhaust pulse started earlier and gives more time to get exhaust gases out of the cylinder before the intake valve opens to compensate for less scavenging and lower overall flow.

So now we are getting back into the great LSA debate, but your statement and apparently your findings on the "desktop dyno" are running counter to what I've always believed to be true.

Care to comment further?

Lee - completely off topic - but I really like the black/red/silver bird and lettering on the early 70s car. And the YO 17” Rally’s really make the look. Fantastic car.

Here's a sound bite from my 30 over 455 with Dougs, x-pipe, and 2.5" through utraflos. Not as throaty down low as the Borlas but a bit more rowdy up top.

PDC, thanks!

Will, I pay ZERO attention to LSA as I'm designing cams. I don't even look at what it ends up, until I'm ready to order the cam - that is its sole importance to me, it makes ordering the cam easy. Once you start using intake to exhaust duration splits bigger than 8 or 12 degrees, all the "rules" go out the window. Really now, why would the engine care where the middle of the cam lobes are? There is only gross flow going on at that point. Even is peak flow did make some difference, with asymmetrical lobes the peak could be a bit before or after the cL. The opening, closing, and the overlap events are what really need to be looked at. LSA "infers" overlap to a point, but it is different depending upon the duration spread.

It bothered me, too, several years ago. Unlearning is harder than learning! I've been able to see most of these non-traditional designs tested on the chassis dyno, several times testing a conventional design first, then installing a big split, and the results have backed up the theory. Look at the GM Performance Parts Corvette Stage 3 cam - HUGE split, designed for a low restriction exhaust 7.0 liter engine, making a wide powerband - that is what GM engineers are NOW doing.

One more thing I've observed - the big splits work best with really efficient low-restriction exhausts. The more restrictive or inefficient the exhaust, the smaller the spread that I can effectively use.

All that said, I'm still learning! And unlearning :-) You know me, and saw me follow "the rules" for a long time, in cam designs/suggestions. They usually worked pretty well. My new approach to cam designs is also working, and has been working even better than the old. We are getting WAAAYYYY off topic though, so e-mail me if you want to discuss further.

Thanks Lee. Very interesting. I don't want to throw your thread off topic any more but am interested in your findings. I agree that LSA is merely a byproduct of getting the opening and closing events right. However, I don't understand why, if you have a very efficient exhaust system, such a long exhaust duration would be beneficial. That's the part that confuses me but yeah, we should talk about that elsewhere.

Thanks again!