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Discussion Starter #1
I promised PaulNY that I would analyze his dyno charts. It took a lot longer than I thought to get it done, not only because Christmas events and job hunting got in the way, but also because the results were not what I would expect given the mods that Paul has made. Fortunately, there is an explanation.

First, let’s review what Paul has done. Paul has a 5.3 Liter SSR, and says he did the following:

- Stroked the engine 9mm. Since the stock stroke is 92mm, Paul has added 9.7% displacement, or made his 5.3 liter engine into a 5.8 liter (356 cu in), still 3% smaller than the 6.0 liter LS2 engine in the 05 / 06 SSRs.

- Installed CNC-ported Z06 heads, which are the same heads as on the LS2 engine, except machine ported for even better flow. Regrettably, these heads have 64cc chambers versus the 61cc chambers on the stock LM4, so he dropped compression from 9.5 to 9.0 doing so. I know that Paul thinks this was good (getting lower compression for a supercharged engine), but since the Magnacharger was engineered for stock compression, I view this as a loss.

- Replaced the mild 5.3 liter “truck” cam with the Z06 cam, which is not only MUCH hotter than the stock LM4 cam, but also hotter than the cam in the LS2 engine. He apparently did also properly change to longer and stronger pushrods (the Z06 cam has a smaller base circle diameter, so needs longer pushrods, and the stock pushrods are weak at high rpm, especially in a supercharged engine). I ASSUME he upgraded the springs to at least Z06 springs, and hopefully stronger than that for this application.

- I am confused as to what boost Paul is running. He says 18 psi, but I doubt that the engine would stay together at that boost without high quality aftermarket forged pistons, rods, and crank. He HAS apparently changed the crank and rods (that’s how you get the extra stroke), but did not mention forged pistons in his last posting. Since he had the entire guts of the engine out to do the stroking, it would make sense to have done the forged pistons, but he did not say so. He says he is getting this 18 psi boost by using a 2.5 inch pulley from Magnacharger, but I think he did his math wrong. A stock Magnacharger kit for any model SSR makes about 6 psi boost, and if Paul is using a smaller than standard pulley on the supercharger, he is getting more boost than that. But, since the standard pulley in the Magnacharger 03 / 04 kit is 3 inches, I’d guess he has maybe 3.0/2.5 = 20% more boost than normal, or 7.2 psi. 2005SSR6speed tells me that Magnacharger itself says each 0.1 inch drop in pulley size can give up to 0.5 psi, so using even THAT more optimistic formula, you only get 8.5 psi. Paul’s belief that the numerically higher rear axle ratio spinning the engine faster under most driving conditions increases boost at WOT is conceptually just wrong.

- Paul has wisely changed to higher quality aftermarket connecting rod bolts – a MUST do if going much beyond 500 hp, and easy if you are changing the crank to stroke the engine anyway.

- He is running an intercooler as provided by Magnacharger.

- He has installed Dynatech Supermaxx headers, which is good. He has also installed a Corsa catback exhaust, which as you will see below was a big mistake.

- He had his stock torque converter modified to a 3800 rpm stall speed. A higher stall speed is required to get decent low speed acceleration in an automatic-equipped SSR. A stall speed of 3800 rpm is normally reserved for drag strip use, but is defendable for street use if you don’t mind lots of transmission heat (Paul has installed a tranny cooler) and non-linear throttle response. I would personally have gone more like 2600 to 2800, but I am somewhat conservative. Getting the stock converter modified though, instead of buying a new one, was an error. To get the best combination of torque multiplication, heat control, and fuel mileage, you need a physically smaller diameter converter with vanes optimized for the desired stall speed. Modifying a stock one produces a less than optimal converter that is also physically weaker than a purpose-built hi-stall one.

- Paul apparently could not get adequate results out of the Superchips microtuner normally provided with the kit. This really confuses me, as Magnacharger will custom produce a tune for you based on your specific engine mods, and will provide that via the microtuner (i.e. using the microtuner purely as a “diskette” or “CD” for data transfer to your PCM). I don’t know why Paul didn’t ask for this service. Instead, he purchased HP Tuner tuning software, which is GREAT, BUT he does not specify who did the tuning for him using it. As it arrives from HP Tuner, it has absolutely NO reprogramming included in it. It simply ENABLES you to re-program the PCM, on the assumption that you know what you are doing. Whoever did Paul’s re-programming apparently did not detect and grasp that there is currently a PHYSICAL shortcoming in Paul’s engine air flow.

Paul’s dyno results, which he sent me, were inadequately handled by the tuner. The results that Paul quoted, 454 rwhp and 445 ft lb torque, were from a chart that had NOT been corrected to standard ambient conditions (i.e. it was a chart of “raw” results), and is therefore not an accurate statement of the power output. His highest CORRECTED result was 442 rwhp and 432 ft lb of torque, corrected to SAE STD (SAE STD gives results about 4 to 5% higher than SAEJ1349 used by the manufacturers, but is so commonly used by dyno operators as to effectively be the reporting standard). I would not put too much emphasis on the precise numbers, as I have shown in my book that it is extremely unlikely that any two dynamometers at different facilities, on different test days, can produce anything RESEMBLING comparability. Instead, we look at th relative shapes of torque and power curves. This is where it gets interesting.

My initial impression of Paul’s reported results was fairly positive, but then I looked closely at the data compared to other supercharged SSR data I have seen, and realized there is an issue. To see the issue, look now at the attached chart that compares the following SSRs:

- Paul’s supercharged 5.8 liter SSR (5.8, not 5.3 anymore) with headers, catback, Z06 ported heads, Z06 cam and valvetrain, and MORE boost than normal

- Magnuson’s own data for a supecharged 5.3 liter SSR, as published on their website

- Steve Rainwater’s supercharged 5.3 liter SSR with Dynatech Supermaxx headers (notice that Steve’s supercharged SSR has headers as well, but still irrationally shows lower power than the Magnacharger kit alone on Magnacharger’s chart (shows how dynos can differ DRAMATICALLY in calibration and accuracy)

- 2005SSR6speed’s supercharged 6.0 liter SSR

- My own NON-supercharged 5.3 liter with Z06 cam and valvetrain, headers, and true dual exhaust with crossover

Note that Paul’s SSR breathes notably better than either of the other supercharged 5.3 liter SSRs, but is weak in low and mid range torque and power, and also runs out of air between 6000 and 6500 rpm. (My chart, limited to sampling at 500 rpm intervals, unfortunately doesn’t show that his engine actually peaked at around 6300, not 6000, before rolling downward due to limited air flow). Note that 2005SSR6speed’s engine, withOUT the hotter Z06 cam or ported heads, and with only standard 6.0 psi boost, is still climbing at 6500 when he bumps his factory rev limit.

With everything that Paul says he has done, the shape (not absolute values!) of his power curve should be more like the shape of MY non-supercharged curve. Note that my curve is PROPORTIONATELY stronger at both 3000 rpm and at 6500 rpm, even though my numbers are of course lower without having the supercharger.

It is my theory that there are 3 things screwing up Paul’s results:

1. The modified torque converter: That modified stock converter is turning way too much of the power into heat until it gets well past 3800 rpm. In fact, I am puzzled as to how it could be properly dynoed at all, since under full throttle, it would not match engine rpm to transmission shaft rpm anywhere even CLOSE until it exceeded the stall speed of 3800 rpm. (Think about it – that’s the PURPOSE of a hi-stall converter – to allow the engine rpm to get much higher than the road speed would normally compute to). I think with this converter in place, this engine will never show good low to mid rpm torque and power on a dyno.

2. Unoptimized tuning: Paul did not say who did the dyno TUNING using the HP Tuner software, but whoever it was clearly did not know as much as he may have claimed to know, as he evidently did not mention to Paul that the engine is visibly running out of air at 6300 rpm DESPITE the CNC-ported heads and Z06 cam. I should in fairness point out that the air/fuel ratio print out WAS provided for this dyno run, and DID show a very uniform 12 to 1 ratio from about 3600 rpm up to 6500 rpm, where the testing was cut, so the tuner DID get good A/F ratio. But, a knowledgeable tuner would have seen that this combination of engine parts should have done better.

3. Inadequate exhaust system: Here is where the big deficiency is. As I recall, I had pre-warned Paul a long time ago that a true dual exhaust with crossover is essential to get the potential power out of a Gen III engine (you guys with 05 / 06 SSRs ALSO have a Gen III engine, despite some GM marketing guy’s stubborn use of Gen IV for the LS2 – a true Gen IV engine is one that has displacement-on-demand (DOD) included). This is because an engine is an air pump. Paul has studiously and dramtically improved the INTAKE of the pump, has has left a major “cork” in the OUTPUT. The Supermaxx headers WITH hi-flow cats were a GREAT idea, but that Corsa catback is lame. Catback systems are good mostly for improved SOUND, and rarely allow a properly modified engine to breather anywhere near well enough.

My recommendation is that Paul dump that Corsa system and get an exhaust that is true dual, has a proper engineered crossover device, and is of sufficient engineered diameter to match the engine’s breathing needs.

If Paul does that, I see the power output going WAY up, and I see the mid range torque and power improving a lot too, despite the fact that a dyno may not show the results accurately at rpm below 3800 due to that modified versus optimal torque converter.

For those of you who have noticed where my Unsupercharged power curve sits relative to the other two 5.3 liter supecharged curves: don’t et too excited – remember dyno results from different dynos are rarely accurately comparable. But, yes, my curve is the shape I was shooting for (not yet falling even at 6500 rpm), and it IS easy to imagine what it would look like with a supercharger attached . . .

Jim G


Premium Member
3,926 Posts
JimG - Very nice analysis of the results given the information you were provided. I agree that the exhaust after headers and the torque converter are what is holding his SSR back.

Once he gets beyond the flash point of the torque converter you can see his torque curve rise quickly. I am unsure of what the stock stator is in the torque converter but you can get stators as high as 2.1 for torque multiplication and still have a 3000 or less stall.

The engine is running out of air in the higher rpm's and that I would also attribute to the after cat exhaust.

Thanks once again for a great writeup!
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