SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: SoCalPSD on June 14, 2013, 08:07:29 AM
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So I was able to work out a deal with a member and picked up a tunnel ram for my olds from jpro ( josh ) thanks bro by they way. And I'm hearing a lot of mixed things between stuff I'm reading online and from some of the old school old timer car buffs I know. So not really knowing whats in my motor it's kinda hard to get an idea of what i need to run this thing but it runs great with the torquer and 850dp that's on it so atleast I won't be without a boat till I decide to put this think on.
So my first issue is carb selection, I have a pair of 660 center squirts (list # 4224s ) sitting in a container in my garage soaking and the TR came with a set of vac secondary carbs that the choke horns were cut off so they are a mystery to me. So I'm unsure if I'm able to use either of the pairs I have and if they will be to much for my olds.
Second is ignition, I'm hearing and reading I need to run a high power setup different range plugs and blah blah blah, then contradicting info on that saying I'm fine pulling the vac module off my current dizzy and converting from the points to electronic and ill be good to go?
So I know a few of you guys here run a tunnel and theres quite a few very knowledgable engine guys and if I'm not mistakin crew chief is thee carb guy. So hopefully you guys can chime in and point me in the right direction
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Ray has had great luck with twin 750 vac secondaries list 3310
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I was told that the 660s cs I had were to much wouldn't 750s be going the wrong way?
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Search for rays tunnel ram theory on here
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What are you looking to gain from the tunnel ram? More speed or is just that they look cool? O0
I have an Olds tr and 2 750 double pumpers. I don't have a lot of knowledge or experience except for what I've read and been told.
I've heard many times " you should get rid of the second carb" ," why so much carb", 'that's way too much cfm".
I went to a performance carb shop and he said he could change my 750's into 650's and that would be better.
From what I've read, tunnel are a benefit at higher RPM's. Olds are not a benefit with higher RPM's. ;D
Mine runs good (when I run it :banghead:). Would it run better with 1 carb? I don't know.
For what you have, basically, I would say stick with the torker and 850. It'll also be a lot easier on gas.
Sorry I'm not more informative. Just my 2cents.
Good luck.
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Here's the thing with Tunnel rams.
Yes they're cool, they come from the old Pro-Stock cars from the 70's, and made their way onto the street accordingly. For decades they were written off as a waste, but no one understood them, including Hot Rod Magazine back in '82...........
Now, not gonna get into street tuning one of these monsters, a subject unto itself, but what we do with Jet Boats, in particular.
For Jet Boats, these things are absolute TITS! Given the right setup! Most that do it, on BBC or BBF either or, don't realize what's involved and could realistically attain greater results with a single carb situation, in 90% of the cases.
What everyone misses is that these are VERY specific engines. Much like a Blower engine. Forged and/or Billet rotating assemblies, and premium hardware throughout. The difference is to realize the benefit from a tunnel rammed engine, compression needs to be at the extreme high end that fuel will allow, vs much lower compensating for boost on a blower engine. Reason being, more compression equals more "Suction" on the downstroke, intake cycle to take advantage of the plenum volume and velocity incurred past the intake valve. Blower cams tend to work OK with them, but more specific cams are out there to take far more advantage of this phenomena.
Two carbs are almost never better than one. Unless what's underneath it built with that reason in mind.......... JMHO. ;)
Ray
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I was told that the 660s cs I had were to much wouldn't 750s be going the wrong way?
I have a set of boost referenced 660's in Havasu (Harry has them) I ain't never seen, welcome to them. Another set of 660's I had I tried with disastrous results on Moo. 750 Vac Secy's were the choice, and I was running 11.5:1 Compression, and a 301* Solid lifter cam.........
Ask Nordie how well it ran......... ;)
Ray
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So pretty much what your saying is I'm better off just sticking this thing on the shelf?
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if your motor is all stock yes thats what hes saying. all intakes have a rpm range that they are premium in, a tunnel falls usually under 3500 to 6000 . That not going to work on a stock olds , or most stock motors. compression needs to be around 10.1 to 12.1 or higher. and your cam has to follow the intakes rpm wants. another words if you want to use the tunnel you have to build the motor for a tunnel.
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Well I'm not gonna build an olds when I have 3 Chevys and 2 ford blocks sitting in the garage. I was just gonna run this till I blew the olds then drop in a bowtie or blue oval.
Any one looking for a tunnel ram for an olds?
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yes! i was actually looking for one. what do you want for it???
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Pm sent mobboss
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if your motor is all stock yes thats what hes saying. all intakes have a rpm range that they are premium in, a tunnel falls usually under 3500 to 6000 . That not going to work on a stock olds , or most stock motors. compression needs to be around 10.1 to 12.1 or higher. and your cam has to follow the intakes rpm wants. another words if you want to use the tunnel you have to build the motor for a tunnel.
Pretty much the jist of it. And it's the details of the engine build that determine whether a tunnel ram is advantageous or not. One fortunate thing with jet boat engines using them is we can get away with far more compression than a street engine, since we have much lower operating temps, and even more if using aluminum heads, thereby increasing not only the cool factor, but gaining everything the tunnel ram has to offer up! ;)
I should have been more specific on the cam selection process though. Yes, historically, blower grinds tend to work OK. But more specific off the shelf grinds are out there built on 110* or 112* centerlines with nearly non-existent overlap that are a far better choice than a blower cam at 108* and those usually have a TON of overlap (Blower pressure being constant, helps the scavaging and pushing out of the exhaust gasses as well as the new air/fuel mixture for the next cycle.....not needed or wanted on any N/A engine)
Now on an Olds? Nothing would be cooler, short of a blower! And it would take dedication and loyalty to the Olds to justify the cost in that. In point of fact, I may well do one or the other on MY Olds powered turd with an Energized Jacuzzi YJ just simply because no one else has! ;)
You have to bear in mind, I built and drove a boat for years painted like a Chik-Fil-A billboard..........so my pride level is a "tad" lower than most of these cats! :sly:
Ray