tunnel ram

mdlahotrod said:

If I rejet the 390's down, will they work sufficiently?? I realize this tunnel ram set up is mostly for looks and I really do like the way they look however, not bein a mechanic, I don't wanna compromise reliability and performance just cause they look cool.....but I really do like they way it looks......Oh...did I say that already??
I do have an Edelbrock Performer intake (Single carb) that I can use and will if it really will make that much more of a difference. If I do go back to a single carb, using a mild thmpr cam, what size would be good for performance and reliability?

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Man, if you want to run a tunnel ram then, by all means do so. It's your ride and the only person you have to satisfy is YOU.
Put it all together and then start tuning. If you don't like the setup, you can always change it.
If you change later and the Performer intake is not an Edelbrock Air Gap then, try to get one. With the Comp Cams h268ex, the Air Gap intake and a 650 Holley you'll be surprised at the performance and relatively good economy.
I too understand the Thumper cams are not that great. Hear say!!!
Best cam I ever had was a 290 Lunati solid lift. Hardly ever had to set the tappets.

Tunnel ram

I really do appreciate all the info yall are given me. This is the first car I'll be building from scratch. I'm just starting with the engine, then it'll be the frame, then steering, etc., etc.
I get it about the thumpr cams. I'll start considering others. Of course the ones I know are Crane, Isky, and Edelbrock only cause they appear to be the most popular. I will try and make it work with this tunnel ram and like you said old iron, I can always change it later.

I have a 2x4 tunnel ram for a SB Chebby that I picked up cheap. I am thinking of running adapter plates and a pair of deuces on it. With a big intake/air cleaner on it who will know. Right.

Have any of you kids tried this?

I haven't tried the 2-deuces deal, because I don't think it looks right. It should work pretty well though.

I've done a ton of work with tunnel rams. I have patent 8,733,312 issued for my Real Street Ram.

What you are proposing should help fix up the fuel distribution, which is one of the big problems with the tunnel ram, especially at part throttle. When you run 2-fours on the tunnel, and you only have the primaries open, there are some runners directly under the open venturies that wind up sucking in a lot more fuel than the other runners. Fuel absolutely hates to turn a corner - if it has a place to go in a straight line, that is where it will go. Dual plane manifolds achieve good distribution between the cylinders because every cylinder has to draw out of the plenum by pulling fuel sideways out of the plenum. No cylinder is favored. Now on the tunnel once you get the secondaries open you get reasonably even distribution, because every runner is pretty directly under a venturi that is open. I know about this stuff because we did a huge amount of development work on the RSR with a wideband oxygen sensor on each individual cylinder.

The 2-barrel solution has you putting the fuel discharge pattern such that fuel is spraying down exactly between the runners. This is true if you are using a Weiand or Offenhauser base, where the runners are grouped symmetrically right under the carb. On an Edelbrock small-block tunnel ram, the runners are offset - the driver side runners are forward of the passenger side runners. So even with the 2-barrels you will get a weird fuel distribution pattern.

The best manifold for what you want to do would be an old Offenhauser. They have a divider down the middle that keeps the fuel separated left and right.

Willowbilly3 said:

For the street most tunnel rams are more for looks. Run your 650s and unhook the secondarys. I'm not sure if that comp # is for their thumper cam but they have one that's designed for that rumpy sound. Also if you like noise, a gear drive for the cam is pretty cheap. Don't forget about the convertor, nothing worse than having a mismatch there.

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As someone who has a very similar combination I have tried to run a big mutha thumper cam and let me tell you it ran like crap on the street with a tunnel ram
With 450's
It was a nightmare to tune and cruising speeds pretty much sucked but it sounded good.
I had to lock the distributor at 36° with no advance to even get it to run.
I also had a gear drive which I have since removed (broke a tooth when I jumped on it) fortunately the piece fell straight into the pan and didn't cost me an engine so I'm no fan of gear drives anymore either.
I ended up getting a comp cams 268XE kit in and what a world of difference still sounds great lopes and has more power than I'll ever need i'd highly recommend the 268
I believe you're going to need some more gear though.

Couple videos one with tunnel ram and big thumper
http://youtu.be/ApNOBvCaddc


Second with 268 and dual quads
https://m.youtube.com/watch?v=WorS7j6CcG8

I did make some changes the distributor and timing are different with the 268 I put a full exhaust on and went to the dual Quad set up I think it sounds just as good and gobs more power

the t-bucket folks run them all the time and for the most part they run ok. most run the vac sec and play with the sec spring to set the back barrels and use large jets and squirters. try to go with the edl. tr1y or tr1yx as they seem to have smaller runners. i do know a lot of folks that run them and was gonna run one myself, but i sold it to a member here and waiting to see it on his ride.

Tunnel ram

An edl. Tri-Y is the tunnel ram I'm using. I'll be lookin at the comp cams 268XE cams next. Also gonna use the 50cc accelerator pumps on the 390's. I'll have to check the squirters once it's running.
Hopefully it'll all come together.
On those heads. Did any of yas get a chance to look at em. Should I trash those and find another set er what? I think I may have gone too far on the intake side from what I'm hearing.

mdlahotrod said:

An edl. Tri-Y is the tunnel ram I'm using. I'll be lookin at the comp cams 268XE cams next. Also gonna use the 50cc accelerator pumps on the 390's. I'll have to check the squirters once it's running.
Hopefully it'll all come together.
On those heads. Did any of yas get a chance to look at em. Should I trash those and find another set er what? I think I may have gone too far on the intake side from what I'm hearing.

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If the intake runners are too shiny, maybe you could blast them with really coarse sand to roughen them up. Just leave the seats alone. This is 90% guessing, mind you. Either way, don't feel bad, I did it to a set of '70 high compression 440 heads when I was learning.

This is a recipe for a helluva lot of fun.

A good set of 64 cc sbc heads with 1.94 intake valves and 1.54 exhaust valves. You don't need 2.02/1.60 valves.

Just deburr the runners, match the intake ports to the manifold ports. Heads are done!

Use stock FelPro auto parts head gaskets (they are .036 thick)
The heads and the '78 350 block will bring your compression ratio up to around 9 to 1 and the engine will run on regular unleaded pump gas but, run 91 octane premium pump gas.
Comp Cams 268ex stick with new hydraulic lifters (the break in is critical *** see below).

If you want to run the tunnel ram go ahead. They are cool.

If and when you get tired of it, buy an Edelbrock Air Gap intake, a 1/2" phenolic 4 port spacer and put one of your 650 double pumpers on it.

This combo creates torque which is what pulls your butt down the road.

***Put breakin additive in the oil, prime the engine with the oil pump. When you fire the engine, immediately run it up to 2,000 rpms for at least 30 minutes varying the rpm up and down a little every few minutes.

After break in:
Set the distributor to 40 degrees of total timing, all in at 3000 rpm.
Don't be concerned with initial timing.

Opinions are like belly buttons, everybody has one
Ok, here's my 2 cents worth.....
Tunnel rams look awesome - yes they were originally designed as "race" manifolds so there is some low RPM power loss in trade for high RPM gain - but they look awesome.
Lots of good advice, small carbs, big accelerator pumps, etc., also progressive linkage is a good idea as well as vacuum secondaries.
Having used a Thumper cam in the 454 in my 36 Packard, I can tell you it is a turd at low RPM but I also had 2.75 gears in the rear on a heavy car, stock stall converter. But it sounded awesome!. I didn't care about the negatives because it just sounded so wicked.
It boils down to what you are willing to live with, everyone has their own opinion on what is tolerable, overkill or too tame etc.
We've all become too used to modern cars that you just pour gas in and go with little need to really pay attention to what the engine is actually doing, they are just to darned civilized!
I love having some involvement in really driving a hot rod - babying it till it warms up, fiddling with the choke, feathering the gas so as not to bog, feeling the rise and fall of the power curve as it winds up, just listening to the engine do its thing, hearing the gears whine.
Go with it and have fun. [cl

Thanks Old Iron. That's exactly what I needed for guidelines.
I will certainly take your advice and go with it.
ZZrider and old iron, I really plan on havin a lotta fun with this car and lemme tell ya, doin all this for the first time is a really great learning experience that I'm lookin forward to accomplishing.
I really appreciate all the help and will keep you posted on my progress.
Thanks again.

You're welcome
ZZ is right about opinions.
There's a lot more to building an engine than what time and space we have to post about it.
I don't think any of us asked if you are planning on running an automatic or a standard tranny. This will make a little difference what cam you run too.
The specs I gave you, are the most friendly street application plus performance combo.
If you run an auto, get a 2800 stall converter for it. It'll be fine with the stock converter but the 2800 will be more fun.
I suggest you read this article. It's a great read on this exact subject.
http://www.hotrod.com/how-to/engine/113-9604-choosing-the-right-camshaft/

mdlahotrod said:

On those heads. Did any of yas get a chance to look at em.

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Yes, I was wondering what your compression ratio is with those heads and pistons.

tunel ram

8literbeater.
Not sure what the compression is. I tore down this motor before ever hearing it run. I got it used on a trade for a Pontiac 400 and didn't wanna take any chances but after seeing how clean it was inside, I started doubting myself about rebuildin it. Oh well, got 30 over pistons for it now. It had 20 over when I took em out. I'm thinkin whoever ran this engine before me, may have recently rebuilt it. Oh well......I'm goin through quite a learning process now but I think it's gonna be worth it in the long run. That way if anything goes wrong with it, I'll be able to fix it.
Ya know....I have people here with drag cars and hot rods. Of course when they wanted "A Buddy deal" when pinstripin their cars, I was right there. Now that I need some assistance on buildin this motor.....seems nobody's got time to give me a hand or even advice. That's ok though, what goes around comes around. Any of yall that need some stripin, lemme say thanks for the advice and just gimme a call. One hand washes the other.

mdlahotrod said:

8literbeater.

Ya know....I have people here with drag cars and hot rods. Of course when they wanted "A Buddy deal" when pinstripin their cars, I was right there. Now that I need some assistance on buildin this motor.....seems nobody's got time to give me a hand or even advice. That's ok though, what goes around comes around. Any of yall that need some stripin, lemme say thanks for the advice and just gimme a call. One hand washes the other.

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Feel your pain........keep your head up and keep scratchin' , I think
all of us here have felt that way at one time or another....
most of the guy's on here are more than willing to help so keep
asking ? and stay positive you'll get there.......

The compression ratio, not the compression pressure. The late 70s engines had low compression, like around 8 to 1. Those heads look like low compression heads, but it kinda depends on the pistons you're using. You could possibly have a bad combination, and the compression ratio would be miserably low. I've never put a tunnel ram on anything, but I suspect that an engine with a tunnel ram and low compression would be nearly undriveable on the street, especially with ported and polished intake ports. Porting and polishing generally sacrifices lower RPM torque for higher RPM horsepower.

If you can tell us exactly what pistons you're using, and the casting number on the heads, we can probably help you out. Your heads might work fine, and you might just need to get pistons to match. Some of these other guys with more experience than me can advise.

The casting numbers on the heads are 3998993, under that is L5 2.
I've got new Mahle 30 over pistons to go in. 20 over pistons is what came out of it.
According to an online guide the valves are suppose to be 1.75/1.5.- 75cc However, they measure 1.94/1.5. 75cc. I think the optimum compression ratio would be 9 to 1 right (9-1/2 to 1 Max). 10 to 1 would be too much according to what I've been reading.
I'm also running a turbo 350 tranny.

mdlahotrod said:

The casting numbers on the heads are 3998993, under that is L5 2.
I've got new Mahle 30 over pistons to go in. 20 over pistons is what came out of it.
According to an online guide the valves are suppose to be 1.75/1.5.- 75cc However, they measure 1.94/1.5. 75cc. I think the optimum compression ratio would be 9 to 1 right (9-1/2 to 1 Max). 10 to 1 would be too much according to what I've been reading.
I'm also running a turbo 350 tranny.

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From what I can find, the heads have 76cc chambers. http://www.chevytech.com/3c3998993.html

The pistons can be deep dished, shallow dished, flat top with 2 valve reliefs, flat top with 4 valve reliefs, small popup, big popup, and all variations in between... There is more to a piston than just the diameter. If they're flat tops, you'll probably be around 9:1, maybe 8.8, maybe 9.3. I guess if you're just using what ya got, then it is what it is. Although, you could choose your head gaskets to work the compression a little one way or the other. You could also have the heads milled to bump it up a little.

I run 10.09 to 1 with iron heads in my big block, on pump gas, in 110° heat. It works, but it's right on the fringe edge. I probably would have been happier around 9.8:1.

3998993 heads aren't worth the price of milling.

With the 3998993 76cc heads you have;

If you use dish top pistons, .036 thick head gaskets then, you'll have right at 8 to 1 compression ratio.

If you use flat top pistons with 4 valve reliefs, .036 thick head gaskets then, you'll have 9 to 1 compression ratio.

If you use dished pistons with 64 CC heads, .036 thick head gaskets then, you have 9 to 1 compression ratio.

If you use flat top pistons with 4 valve reliefs, 64 cc heads, .036 thick head gaskets then, you'll have 10.2 to 1 compression ratio.
With the pump gas we get nowadays, 10.2 to 1 is a little risky unless you back the timing off to around 38 degrees total and run 91 octane

Some thoughts on porting/polishing.....
Cleaning up the valve bowl irregularities and smoothing the combustion chamber is always good, just don't cut down the short side radius where the port makes the tight turn to the valve seat. Clean combustion chambers reduce hot spots that can cause detonation. I wouldn't worry about ports being too shiny, the exhaust ports will get a coat of carbon on them right away and even the intake ports will get some skuzz buildup especially with a lot of overlap on the cam and just from everyday puttin' around in traffic. Real flow improvements can be found by port matching the manifold to the heads and often overlooked is matching the header pipes to the exhaust ports.