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.