SBC tunnel ram

[555RAT]

Well I finally got this to the track, not what I was expecting.

What were you expecting ?

Randy

I was expecting an increase in MPH and maybe similar 60', not a slower mph and more consistent 60'. The intent of this endeavor was to determine if my combo would be more consistent with the tunnel ram and maybe a bit quicker. Needs a little more carb work and see if the next race will go a little better.

[F-BIRD'88]

The 750 dp carb is a better start point for this.
I know you probabily don't want to hear that as you are already commited to your 950 carbs...
It will be more difficult to get there with the 950's vs the 750 carbs... But you should still get there..
It takes a bit of work either way.
Good luck. Hang in there.

[randy331]

Well I finally got this to the track, not what I was expecting.

What were you expecting ?

Randy

I was expecting an increase in MPH and maybe similar 60', not a slower mph and more consistent 60'. The intent of this endeavor was to determine if my combo would be more consistent with the tunnel ram and maybe a bit quicker. Needs a little more carb work and see if the next race will go a little better.

Did you get a manifold vacuum reading with your single 4 set up ? I'd say the 1.45 x 1.75 carb is a little on the small side.
Likely been some power with a Braswell 4825 type carb or a 1050-1250 4500 carb.
I just tried a 4500 carb on the dyno on a 660 HP 383 and it added some power.
Your results and rustbuckets are typical of what I'd expect.
Now if you take something screwed up off,.. the results could be much different.

Randy

[PRH]

Just a WAG here........

There is a formula in the SF flow bench manual(I don’t have one anymore)to help figure the peak rpm based on a few criteria....... one of which is runner length.
I think if you found that formula and plugged in the specs of your motor combo and runner lengths....... you might be surprised at where the theoretical peak should occur...... and how that relates to your results from trying different shift points.

I’ve had motors on the dyno with certain TR manifolds where once you got outside the operating range, the power would drop off like a rock.
To the point of suspecting a serious valvetrain stability issue.

However, swapping to a single plane single 4bbl, the top end power didn’t behave the same way at all, and while the single 4bbl made less peak power...... it did peak at a higher rpm, and at the very top end of the curve made way more power than the TR.

Basically, my thinking is that particular manifold could have an operating range...... on your motor...... that’s not as high as the single 4bbl piece you removed.

[555RAT]

PRH, thanks for that, I'll look into it. This being the 7070 victor ram I would think it would pull clean to 8k at least given the rest of the components, but every engine being it's own animal you never know. Still a bit of tuning so I'll keep at it and see where I end up by end of the season.

[In-Tech]

Hiya,
A couple things I can offer is a single carb tune doesn't work on a tunnel ram especially when you are taking a perfectly running single carb and add another exactly the same.

Think about it for a bit, although you have given the engine the ability for atmospheric pressure to get into the engine easier, the signal across the booster has dropped, especially at the hit. Most tunnel ram stuff requires an increase in main jet to aid signal and then requires a larger MAB as the signal starts to come back. Kinda how yours lost mph because it went dead fat on the top end.

I'll be quiet now since f-bird will be along shortly to tell you that AVS and smaller carbs and a supercharger will fix the world.

[naukkis79]

Think about it for a bit, although you have given the engine the ability for atmospheric pressure to get into the engine easier, the signal across the booster has dropped, especially at the hit. Most tunnel ram stuff requires an increase in main jet to aid signal and then requires a larger MAB as the signal starts to come back. Kinda how yours lost mph because it went dead fat on the top end.

What longer runner intake manifold do is delay flow changes. At high revs that means that air incoming is delayed to have shorter but faster intake flow pulse. To get that work there has to be enough flow capability. If engine is head flow constrained longer manifold runners won't increase power but decrease it as there's shorter time to flow. Same applies for carbs, as actual flow pulse is shorter for same volume carb flow needs to be higher, especially if plenum is also tuned - small volume.

With long intake runners there's also possibility to use much longer intake valve open time, with short duration cams engine peak power always rises by shortening runners as more of that short valve time is used to fill cylinder.

[In-Tech]

Who said anything about longer runners with this tunnel ram he is using?

oy vey,

[naukkis79]

Who said anything about longer runners with this tunnel ram he is using?

oy vey,

There's not much difference between tunnel ram and single-plane intake if runner lengths are same..... but you are right og poster seems to be using 10k tuned ram with only 7K revving motor.

[F-BIRD'88]

The supercharger WOULD fix your world..!!!.
Just saying...ha ha

I agree with In Tech, you are going to eant to dial in the 2 carbs for the tunnel ram now..
And single 4 bbl thinking will not work.

Move the cam to straight up too,
The tunnel ram (that 7070 tunnel ram) is all about top end power and rpm. You want to keep the motor up there.. Too bad BIGJOE1 is no longer with us.
A real expert on this stuff.

The aVS2 carbs are super easy for street stuff.
Not for you... Hit taken and noted..
Back to regular programing...
It will come around.. You have a baseline now.

[In-Tech]

Move the cam to straight up too,

It will come around.. You have a baseline now.

Agreed.

An inexpensive datalogger and wide band will really help with the carb tuning. If interested I will reply with some part numbers.

[rustbucket79]

Did some dyno work on a couple of GM LSX 454's this week, first one had a GM single plane, second one started with a pair of Demon 750's on a tunnel ram and finished with a CNC ported single plane and a 950 UHP Holley (Aftermarket intake)

The 2 engines were within 15 HP, and overlaying the 2 race intake pulls shows almost identical HP and Torque curves from 4000 to 6000 RPM. The T/R did make 2 more HP at 6200. I don't know what stock jetting is supposed to be in those carbs (Demon) but I was down to 77 primary and 80 secondary jets to get 12.8 to 13.1 AFR.

[ClassAct]

Move the cam to straight up too,

It will come around.. You have a baseline now.

Agreed.

An inexpensive datalogger and wide band will really help with the carb tuning. If interested I will reply with some part numbers.

I'm interested in an "inexpensive" data logger because I've never seen one yet. Unless it was used and I don't trust buying that stuff used.

[JES]

All you need is an SP2P intake and your good to go

[In-Tech]

Move the cam to straight up too,

It will come around.. You have a baseline now.

Agreed.

An inexpensive datalogger and wide band will really help with the carb tuning. If interested I will reply with some part numbers.

I'm interested in an "inexpensive" data logger because I've never seen one yet. Unless it was used and I don't trust buying that stuff used.

Innovate ssi-4 part number 3914 $106.99 at summit, 4 channel https://www.innovatemotorsports.com/pro ... _4plus.php
Innovate pl-1 part number 3875 $75.99 at summit https://www.innovatemotorsports.com/products/pl1.php

If you don't already have a wideband and want straight plug and play, https://www.innovatemotorsports.com/products/lc2.php $154.99 at summit.

You have 4 channels so after rpm and wideband you still have two to do whatever, fuel pressure, oil pressure, wheel speed, etc etc etc.

Note, I do not work for summit nor innovate, I just noticed these a few weeks ago and thought I'd pass it along. The price is definitely right.