C4: "Ten Times The Torque....Take TWO!" AKA, "Hot '80's intakes Test"....

[Tom400CFI]

C4 owners....you're getting it all here, first, on VetteMod!

I'm sure that every C4 owner has seen the famous "Ten Times the Torque" article, done by Richard Holdner (see attachment). He did a VIDEO RECAP of the article a few years ago on his YT channel. Freiburger did a similar test also, I believe, in the '90's. These test/articles became fodder for all of us, and established a hierachy of available intake options for TPI and how each/all of them ranked. None of us know squat back then, EFI was rather new, tuning was not readily available....so ALL of us wanted to know which of these new-fangled EFI intakes really worked on a TPI car. These articles shed some much needed light on the matter and became the "holy grail" of TPI intake info. The only problem was...all of the available test then, up through now, were done on "500 hp" motors. Holdner had planned on doing the test on a medium 350, but that engine blew before testing began (I have read), and they had to shift to using a fairly radical 383 to test the intakes on. Freiburger's test used a similar 383. The data is good, but it's probably not aligned with what most C4 owners have when they buy an intake, and it's certainly not the motor most of us had in the '90's when we were in early stages of learning EFI, intakes and mods....all w/basically no tuning. Maybe a Vortech FMU!

With this in mind, and a stock L98 at my disposal (in my '89 "Vette Kart"), I embarked on some dyno testing which has evolved into essentially re-testing most of the intakes from "10x the tork"...but doing it on a stock engine. At the onset of the testing, I expected gains from all of the intakes over stock. I expected the order of "winners" to be different than on the old big-engine tests....I expected my testing to favor the lower performing intakes from the original tests.








The test mule:



The car (Kart) is...was an '89 Corvette, Z51, 6 speed. The engine was bone-box stock except for the following:
True dual exhaust, no cats, bullet muffs
Under drive pulleys
No air filter
160 stat
It was in that configuration for all intakes/tests, and base timing and fuel pressure were adjusted to optimize results for each intake. ECM/"Tune" was not touched for any intake. This was simply an intake R&R and fuel pressure and timing adjustments....pretty much like we'd all have done back in the day.
All pulls were done on the same chassis dyno, I requested all pulls start "at idle", or ~500 RPM so we could see the WHOLE tq curve. I hate pulls that start at 4000 RPM...what is that? Anyway, due to the coordination of the dyno op running the car, the dyno etc. none of the pulls actually "hit" until about 12-1500 RPM, so that is what you'll see in the graphs, but they DO give a darn good look at "low end torque" for each intake. I hade the op shut it down "before 6000 RPM" on all test because there were zero intakes that would make any power that high, on this stock engine. No point.

With all of that covered.....how'd they all do?

 

[Tom400CFI]

The first test...and not surprisingly, the lowest performing intake, was the stock unit. The small diameter runners hurt even a stock 350. Still, this ~160k mile, poorly maintained dog did impress on it's first trip to the dyno.





241 RWHP @4200 RPM and 342 RWTQ at (no surprise) 3280 RPM.
I found that to be quite stout for RWHP&TQ numbers that matched the original engine crank rating. Torque peaked right on schedule at just above 3200 RPM. The engine was making about 280 lb-ft from the start of the pull, about 1200 RPM, I think it's fair to say that it was doing ~300 crank tq from the start of the pull. Not really "sports car" stuff here....GM should have stuffed these into the '88^ GMT400 trucks.

 

[Tom400CFI]

In the original 10x the tork" article, the TPIS Mini Ram smoked 'em all, with 505 hp on Holdner's 383. As mentioned in post 1, I assumed the order of output would be changed up on a stock engine and sure enough, the Mini Ram performed the worst of all the aftermarket intakes, bettering ONLY the stock TPI by 17 hp. The Mini Ram made less torque everywhere until ~4200 RPM, and only then started to exceed the tq of the stock intake...although at that point, both intakes' tq output was dropping anyway. The Mini Ram did hold on and raise peak power to around 5000 RPM and carry decent power to about 5500 or so.



258 RWHP @ 4920 RPM and 321 RWTQ @ 3550 RPM.
It's not surprising that the intake with the shortest and biggest runners didn't perform well among it's peers, on a stock motor with mild cam, smaller displacement and weeny heads. I expected it to pull a little more RPM, but it wouldn't do it. Another interesting thing is that I've ready many-a-time on "the forums" that "an L98 with a Mini Ram is the same (power) as an LT1". No, it's not. Not even close. My own LT1, which is bone, box stock make 279 RWHP, so no, an L98 with a Mini Ram is most definitely NOT an LT1 or in LT1 territory. Even with the benefit of good dual exhaust.
Still, a 17 hp increase from a simple R&R of an intake....that's not bad. It's an easy intake to install/own and it's one of the more affordable intakes, as well. This intake did require a significant increase in fuel pressure to get a reasonable A/F ratio and still, it's pretty lean as you can see in the graph.

 

[Tom400CFI]

Next in line? After seeing how the Mini Ram did in this test as compared to Holdner's 383 test, it's not surprising that the second best intake in his test, was the second worst of the aftermarket intakes, in my test. Next up was the Holley Stealth Ram, AKA Weiand Stealth Ram. This intake was, like the Mini Ram, easy to install and affordable. Unfortunately it will not fit under the hood of a C4 Corvette w/o modifications or a cowl hood, which complicates "easy to install".








Anyway, after some fuel tinkering, here is how the HSR looked on the rollers....

273 RWHP @4970 RPM and 343 RWTQ @ 3600 RPM.
Now we're getting somewhere! This is a very solid, 32 hp gain over the stock intake....R&R only. I paid $300 for this intake and $100 for the rails/regulator. 32 hp for $400 bucks is some pretty fantastic bang for the buck. The Tq basically matched the stock intake, peak for peak and was 20 over the Mini Ram, and it was making ~310 ft lbs at only 1200 RPM. The HSR also carried power out about as well as the Mini Ram, peaking just about 5000 RPM, and still making about the same power at 5500 as the Mini Ram did at it's 5000 RPM peak. This intake was a huge improvement over stock and a big improvement over the Mini Ram, for about the same money and effort. (Corvette hood, not included in that last comment!)

 

[Tom400CFI]

What came next? How did IT do? You'll have to wait and read. Time for bed, tonight! I'll write and post more, later.

 

[Red77]

I remember the Accel SuperRam being pretty popular back in the 90's until the LT1 took off. Looking forward to see what it actually does on a stock L98. Thank you for sharing this with us.

 

[69427]

Hey, Tom, good to hear from you!

 

[Tom400CFI]

Thanks ! Nice to see you too.

Moving on to the next intake, this one was a real surprise that kind of came out of nowhere. Someone had this thing....I have no idea how they got their hands on it, and unfortunately, it's rarity makes it rather unatainable for most folks. But it's super interesting (to me, at least), so when the owner offered to share it with me for a while for testing toward this "article", I accepted. The intake, is a prototype, GM made "Big Mouth" TPI intake. The thing is, IMO, GM's in-house version of the TPIS Big Mouth intake. In this case, it appears that GM took a stock base, (casting number the same as my '89 stock base), cut the runner roofs off, starting about 1/3 of the distance from the head flange toward the runner flange and raised the runner roof and then welded the roof back on. Then they ported it. The bolt-on runners are oval, to increase cross section, and the plenum appears to be hand ported to match the runners' mouths. Here is a pic of the prototype, sitting next to the stocker...




And here are a couple pics that show the radical increase in runner cross section...






I measured the runner cross section, where the bolt on runner meet the base. On average, the ports are 2" tall, 1.6" wide, have flat sides between upper and lower .8" radius top and bottoms. That works out to a 2.01" sq circle, plus a 1.6"x.5" rectangle in the middle of it, for a total CSA of about 2.81" sq.

This intake was a total PITA to install. It was as hard or maybe slightly harder than putting a Super Ram together...partly because the "fat parts" caused interference, and partly b/c of it's hand made nature. You can see that I obviously had to make my own gaskets, nothing fit exactly right and the end result was some vacuum leaks that showed me that thicker gaskets should have been used. Oh well.




Due to the size of the runners, both in the base, and in the bolt-on runners, things get real tight, real fast, during assembly. I found that basically, the fuel rails/injectors, runners, gaskets, and some of the bolts, all need to drop onto the base at about the same time. Runners won't fit under the rails....rails won't fit under the runner flanges. The small cap distributor won't fit in the "right" orientation, it has to be installed with the plugs at the base, facing rearward. Pics of those idiosyncrasies for your viewing pleasure.








But man, when it was finally together, my god it looked amazing!!......








So the question at this point is....DID IT WORK!? Is it worth it? Well, that's debatable. Here's how it did:




276 RWHP @ 4400 RPM and 373 RWTQ @ 3510 RPM.

It beat out the HSR by a pretty meaningless 2.5 hp. However, it decimated the HSR in mid range and peak torque, beating it by ~ 30 ft lbs! That isn't going to win a race, but it makes the car FEEL AWESOME! Interesting to note that "Low end torque" -measured at about 1200 RPM, it was doing a bit less than the HSR, as the prototype was right at 300 lbs at 1200 RPM. It pretty handily smoked the Mini Ram, even making about the same hp at 5000 RPM, as the Mini Ram made at 5000, it's peak....but of course the Prototype made more power everywhere, below 5k.

This intake did pretty good. I'd bet that it was about the same as you'd see from an TPIS Big Mouth intake, although that one is much more readily available, affordable and would assemble much more easily and with less leakage than this interesting and unique one-off. It was a really cool piece, I feel honored to have gotten a chance to touch it, feel it, see it and try it on the Kart.

 

[Tom400CFI]

Long out of production, and hard to come by, the next intake I tested was an intake that was basically my childhood lust item. From the moment I read about this intake (and the car that it came on), I thought it was probably the king shit of all aftermarket intakes for a stockish 350 chevy! When one came available in the early '00's for $1200 with all installation items, bits and pieces, I passed on it thinking that it was too expensive. Instead, I waited for another to come along, partially complete, and paid $2500 for it, instead!!










The intake in question here, is the SLP T-Ram, found first on the '91 Firebird Firehawk, then later available through Summit Racing. In the day, it was cheap; only ~$550 for the basic intake. Now days? Good luck! Bolstering my childhood readings/beliefs and fantasies, the SLP T-Ram laid down the highest horsepower in these tests, yet....though only by a slim margin.



276.47! .47! It beat out the GMProtoype by a scant...1/2 horse!
276.4 RWHP @ 4660 RPM and 356 RWTQ @ 3700 RPM.

Like many of the other intakes, this one blew the stocker away in the low end, doing about 305 RWTQ at 1200 RPM. The torque was way down compared to the Prototype, but the trade off was made at the upper end where the T-Ram went another 200 RPM to it's peak, and had a slower drop off after that...although by 5000 RPM, both intakes were making about the same power and both were falling fast. The T-Ram was easy to install, the integral fuel rails were nice and save some money. I always LUSTED for the looks of the T-Ram...loved the unconventional runner and plenum layout, loved the side tanks....but when it was installed in the Kart, my lust for it's looks faded quick. It's rather dull looking (yeah, you could polish it), it's kind of a big slab looking thing, and it covers the nice 'Vette valve covers. It kind of dominates the appearance of the engine but not in an awesome way...more like "plastic engine cover" kind of way. When I was done testing, I pulled the T-Ram and sold it. It was way, WAY too expensive to own for what it does and how it looks. It was super cool to get to try one, have one, finally, but for me, on this car the value wasn't there.

 

[BBShark]

Interesting info. Is there a general rule that you could apply to a TPI design (for any engine displacement) for optimum plenum volume, runner length/volume?

I ended up making a plenum for a 502 starting with the design of the Ramjet, and using a Ramjet intake, but with the requirement that it would fit under a stock C3 BB hood. I have not dyno tested so it's an unknown at this point.

 

[Tom400CFI]

Is there a general rule that you could apply to a TPI design (for any engine displacement) for optimum plenum volume, runner length/volume?

No idea. That would be a good topic for another thread; this thread is more simply about existing, "TPI" replacement intakes and how they perform on a stock or stockish 350.

 

[Tom400CFI]

Looking at the trend in power output from our test mule turd it seemed like perhaps we were reaching a plateu; we had already seen a healthy baseline for the motor, and then a substantial ~35 hp gain over that number with a single bolt-on part? Add to that the trend in power gains for each intake; 17hp for the first -the Mini Ram. Then the HSR did 15 more than the Mini Ram....the Protoype/"Big Mouth" did only 2.5 more than the HSR....and finally the T-Ram...only 1/2 more than the Prototype. See the trend there? A wise forum member pointed out that head flow would cap the hp, b/c most if not all of the aftermarket intakes outflow the 113 head. That makes sense and therefore, we might have already maxed out any gains that we could see from the available intakes....on a stock motor?

It would appear that harmonic ram tuning would be the only contributor to hp at this point. The MR has ~3.5" runners....that thing would be "tuned" to hit the 3rd harmonic at something like 9000 RPM. HSR has longer runners but is also likely tuned to hit a resonant frequency that is above the operating range of this cam/head/exhaust engine. Once we get into the LTR intakes, we see an increase in power (and torque in the mid range), likely due to harmonic resonance. Anyway, although it seems like a plateau had been reached, we move forward.

The next intake was a Accel base, using Arizona Speed & Marine's siamesed runners. This was on an Accel base and used a commensurately ported/matching plenum.








The thinking with these runners is of course more flow than stock, due to the larger runner cross section, but also an effectively shorter runner length and increased "plenum" volume, due to the bolt-on runner segments being siamesed for roughtly 1/2 to 2/3 of their length. This should raise the usable RPM range, and potentially reduce that mid range tq peak, compared to full length runner TPI systems. The base and runners shattered the "plateau" theory by making the highest hp so far in this testing. So? We put 'er on the rollers again to see what this intake would really do....






280 RWHP @ 4330 RPM and 375.5 RWTQ @ 3400 RPM.

BOOM!! There went the "plateau" theory! This intake blew the hp increase "trend" away, doing ~4 hp better than the T-Ram....and putting down an impressive 39 hp over the stock intake! 39 hp from a bolt-on intake....no tuning! WOW!

This intake was easy to install, everything fit well, and slipped together easily. Unfortunately, for this to work, you need to put some hours into your plenum with a grinder and also buy a big mouth base to see all of these runners' potential. That will add to the "ease" of install for this intake set up. Surprisingly, the AS&M peaked only 100 RPM higher than the stock TPI. I'd have thought that w/the shorter effective runner and the larger cross section, it (and the others w/similar features) would have really driven up the RPM range. The hp dropped off pretty sharply above about 5000 RPM...an interesting note is that in the original "10x the tork" test, even with the relatively huge cam shaft, Holdner pointed out that, "...the power curve seemed to fall off more rapidly than we anticipated". I had a similar surprise. I thought that the siamesed runners would have driven the RPM range up noticeably but it didn't really do that. It behaved very much like the stock intake...only higher up, everywhere. Even way down low, this intake did ~310 RWTQ at 1200 RPM. I find it odd that the peak hp RPM was a couple hundred below the full length runner, "prototype" intake. I don't know how to explain that one...

This was a good intake -especially if you're looking to keep your RPM range similar to stock.

 

[Tom400CFI]

With only one intake left to test, I figured that we had seen the best that this old dog of an engine would ever do. With a 39 hp gain over stock from the AS&M, no one would be disappointed with the money and effort spent to swap out the stocker! Few mods will single handedly provide such a generous gain. There was still one intake to test, and incredibly, it would do even better!



The final intake in this test** was the popular and well respected Accel/Lingenfelter Super Ram. The Super Ram was the biggest PITA to install. Maybe neck and neck with the Prototype, but that one has the "excuse" that it was basically home made. The Super Ram is mid pack, price wise, so owner ship is middle of the road once you get past the install. Install works best if you slot the plenum bolts so you can screw driver them into the plenum from above, and leave everything loose, until all hardware is started, in place. Additionally, (and you'll see this in the pic below) you have to use either the stamped steel valve covers or grind and notch the magnesium Corvette valve covers to clear the fat, cast Super Ram runners. With the stock valve covers, you can't get the cover on between the runners and the rockers....and if the cover is on (even loose), you can't get the runners between the cover and the fuel rails. The runners need to go in first, then a notched valve cover or a stamped tin one will fit between the runner and the rockers if dropped in at an angle, with the intake side down, first. Anyway....it's a "Tetris" puzzle.







I really thought that the Super Ram and the T-Ram would be neck and neck, with a slight advantage going to the T-Ram (see post 14 for reasons why). But, I was wrong. All of these companies are great at what they do; TPIS, AS&M, SLP, Holley, even the GM engineers....they all know what they're doing....but John Lingenfelter (RIP)....he did it even better. Have a look...





HOLY GEEZUM guys!!

289 RWHP @ 4460 RPM and 375 lb-ft @ 3540 RPM
I probably could have (and maybe should have?) iced the intake and gotten 290/375+, but LS's have dyno'ed less than this!
With the Super Ram, you're seeing an engine that gained a whopping 48 hp, and 32 ft-lb pund increase, from a simple, bolt on, R&R of an intake manifold. WOW!!!
Interesting things to note, the Super Ram blew the stock intake away in torque, everywhere. It smoked every intake in tq, everywhere, except the GM prototype and the AS&M where they were essentially matched down low to their peaks, and then the Super Ram beat the others out above the tq peaks. Also, subjectively, the Super Ram was the most fun to drive. IDK why...looking at the actual tq numbers (and the fact that they're matched with those other two, but subjectively the Super Ram pulled the hardest. The thing felt like an animal and from ~3000 RPM up, it was ridiculous. I didn't get that same "feel" from any of the other intakes. Super Ram for a decisive win. John Lingenfelter knew what he was doing.

 

[Tom400CFI]

Summary/thoughts....The ads!

Going into this test, I thought that on a stock engine, the SLP T-Ram would smoke 'em all....for a couple reasons.
First, it was the only intake designed to go on a CARB cert'ed car as a factory option w/an RPO -The '91 Firehawk.
Second, (and b/c of the "first"), as such, it would be an intake optimized for that configuration, where I felt the other intakes may have been optimized for other, bigger configurations
Third, Ed Hamberger commissioned the design, casting and machining of a bespoke intake for that project and engine configuration...why do that if there are other CARB cert'd intakes that will already do the job as well or better?
Fourth, since the T-Ram got beat by a few of the intakes on the original "10x the Tork" test on a pretty big/radical engine. So...it must be the BEST on an engine more like a stocker?
Finally, there is the literature from period Summit Racing catalogs, where the script describing the T-Ram does so in way that makes it appear to be the BEST intake on a stockish 350.
Ahhhh....well....that didn't turn out to be the case, but its a great, if not expensive, intake. The Super Ram, is better.

Let's talk torque, for a moment; The SLP Firehawk was rated at 390 lb-ft. (NET tq) That's DAMN good torque for a 350 in the early 90's....damn good for a 350 any time, but it's a lot, it's always impressed me....it's even more torque than the LT5 engine. It's a lot. They got there with the T-Ram, mildly ported 113 heads, mild-medium cam and not-bad shorty headers. With the Super Ram and AS&M intakes, we were w/in 15 lbs of that rating.....at the wheel! This engine made more NET tq at the crank than the Firehawk's 390 lb rating. Stock cam, stock heads, stock shitty pinched down exhaust manifolds...wow. This turd engine made over 400 NET crank tq, with two of those intakes! Don't believe it?....
The LS2 in the C6 was rated at 400hp/400 tq...NET/Crank. I was looking at a dyno sheet that I have from back in the day when I had my '06, C6, with the (stock) LS2 engine and I had a little epiphany. I was looking at the tq curve, and I was thinking that something didn't look "right". WTF was it? The tq part of the curve looked WAY off, to me. It looked too low...way too low. How could it be that low!? Recently I've become accustomed to the Tq numbers that the Kart's been making, in the 370's, and here I am, looking at a 400hp/400tq engine that made ONLY 355ish tq!? How in the world is a larger cube, higher compression, better tuned/ECM'd engine making less tq?? Well, it did. It's pretty surprising to me that the LS2 doesn't do more peak tq, w/all of the advancements, size and compression advantages that it has. It makes it all the more impressive (to me) that with exhaust and some intake(s), this sludged up, sh!t-box 350 is doing over 400 crank tq. Probably ~420 at the crank. Damn...no wonder it's so fun to drive. No wonder the C6 felt so blase'.

To summarize, here are all the results:
Intake/HP/TQ
Stock/241/342
MiniR/258/321. 17 hp gain
HSR /273/343 32 hp gain
GMXP/276/373 35 hp gain
T-Ram/276/356 35.5hp gain
AS&M/280/375 39hp gain
L SR/ 289/375 48hp gain!

As predicted, the results on a stock motor were radically different than in the original article. Not only was the order totally different (w/the top two performers from the '05 article being the bottom two, on this engine), but the gains and losses of tq were radically different. In Holdner's article, he accurately predicted and then showed how the higher performing intakes "traded top end power for low end tq". In this test, all but the Mini Ram, made more torque than the stock intake....at ALL RPM...even right off idle! For the stock or stockish engine, you loose nothing, and gain a LOT, everywhere in the usable RPM range, with any of these intakes, except for the Mini Ram. Interesting.



**The asterisk in post #13 were in reference to "intakes tested in this test". Why didn't we test more? It would have been fun to, but the whole ordeal was costly....I have over $2000 into the testing and shipping of intakes, plus my labor of doing all of the swaps, taking off work to get the sessions in etc. But it's a hobby I enjoy...I'd have done more, but after the last test (which chronologically was the HSR), I was pulling out of the Adrenaline Dyno's parking lot, and as I rolled on the throttle in a mild fashion....this started.....

...so, that kind of concluded the "Ten Times The Torque....Take TWO!" (AKA, "Hot '80's Intakes!") testing! I have a SBC 400 that'll go in the Kart next, so that'll make anymore A/B intake comparisons useless. It would have been fun to test a TPIS Big Mouth, and a Single plane EFI intake....A dual plane EFI would have been interesting, too....but I think from the collection of intakes done, one can fairly well extrapolate how those others would have done, roughly.

So? I hope you all enjoyed the read, the data....I've had a blast doing it all and I appreciate the contributions that were made by some of the intake owners, and by Adrenaline Dyno for all of their time with my irrelevant, old-skool car taking up space on their dyno! It's been a hoot.