Piston Slap: Tunnel vision on tunnel rams?

Wesley writes:

Hi, I’m really hoping you can help me with this. I have a ’68 Chevelle with an Ultra Street 540 built by Shafiroff Racing Engines out of New York. I am wanting to put a dual quad Tunnel Ram on it. I want to do this for two reasons:

1. I love the look! LOL
2. The engine has 650 lb-ft of torque and 648 horsepower. The low-end power is there, big time, but the upper end seems to run out. I feel like the ram and dual quads would provide improved breathing and better gas distribution across the cylinders at the upper end. I understand that my low-end torque will be compromised to some degree, but I’ve got more now that I can deal with. So I feel like I can afford to lose some of that for a better top end.

This car is mainly just street driven but I do plan to drag it every once in a while at a track near my home. So, would the ram help my upper end? Would it be drivable/reliable on the street? And how many carbs would I want? Feeling like two carbs would more evenly distribute the fuel, but there might be some tuning issues, I hear, although I really don’t know why that would be the case.

Sajeev answers:

Your question is both exciting and ironic for me, so thank you for asking it. The exciting part is pretty self-explanatory, considering the vehicle and the technical specs of that engine. The ironic part is that one of the big-block Lincolns in The Mehta Collection was purchased with a motor in your dream configuration (dual quad carbs, stroker, race cam, etc.), and we subsequently converted it back to a more streetable affair so we wouldn’t lose to V-6 Toyota Camrys at a stoplight. (Those V-6 Camrys are pesky, lemme tell ya!)

You suggest you have an overabundance of low-end torque right now. That’s a very fair point, but odds are you will be slower both on the street and the track if you do what you suggested. The only way to know for sure is to dyno-test both setups, but there’s truly no need to do your own research when the writing is already on the wall. Therefore I want to dissuade you from doing dual-quad carbs/tunnel ram intake on your Chevelle for these reasons:

1. If your Ultra Street 540 is anything like the one on Shafiroff’s website, your Chevelle is “under cammed” for the operating range of a tunnel-ram intake.  While I don’t know the cam’s specs, Shafiroff Racing says it uses “a mild, street roller-cam profile” and that the motor has a 6200-rpm power peak. Most tunnel rams make power from 3500 to 7500 rpm, which means something like an Edelbrock Performer RPM intake with a 1500 to 6500 rpm range is a far, far better choice.
2. Maybe a tunnel ram will allow your car to pull harder above, say, 5000 rpm, but you’ll already be losing to better-optimized cars, because you aren’t cammed correctly for the breadth of intake’s powerband.
3. Switching to a hotter camshaft will “fix” the problem; it will be appropriate for a tunnel ram intake. You will still lose torque, but you’ll gain tons of top end. Problem is, you’ll degrade or destroy the streetability you currently enjoy in your car. It’s probably not a trade-off you want, much less something you’d spend money to make happen.
4. If off-the-line traction is a problem right now, switch over to drag radial tires and practice your 60-foot times.
5. Dual quads certainly look awesome, but they are a nightmare to tune compared to a modern, single four-barrel carburetor with enough CFM to feed that beast. And two carbs are unnecessary, as tjm73 from Jalopyjournal put it: “Multiple carbs made more power when the single carb options weren’t big enough for the engines they were trying to feed.”
6. You don’t need a tunnel ram with dual quads to look cool. I understand that you “love the look,” but that’s just tunnel vision (so to speak). I propose that loving a stroker rat motor with the right combo of camshaft and induction is the coolest look of all … and isn’t that the type of cool we truly lust for?

But don’t take my word for it; I’ll bet the folks at Shafiroff Racing would happily advise you on the best combo for that motor. And, with any luck, you’ll get more opinions in the comments section that will help you make an informed conclusion. Don’t let me down, Hagerty Community!

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