Time for some upgrades....

[BattlestarGalactic]

Fought through some carb issue yesterday.  Front carb was not moving much fuel.  Seems i needed to play with float arm to get enough travel and shut off.  Seems fine now, but now needs some jetting.  Its up through mid range, just need to get peak numbers up.   Baby steps.

I know the old motor had flow rate differences between carbs.  We think the tunnelwedge is the problem.  Pulsing between carbs.  Anyone with input on that?

[Drew Pojedinec]

With the pulsing issue....
Are those four hole spacers?  Have you tried other spacer?

Have you pin gauged the high speed air bleeds?
I’ve seen 1850’s vary from .028-.033 would seem to make a difference.

Is the pulsing any time the boosters flow or just at a certain rpm?

[Joe-JDC]

It looks like two different carb bodies in the picture, and a 1" spacer.  What is the spacer?  When I raced my tunnel wedge, I used a two inch spacer and mounted the carbs forward.  That gave me room for the distributor, and better carb selection.  I never had an issue with pulsations using 600s, 660s, or 750s.  I finally settled on the 660s due to better launch control.

I would try a 1" super sucker type under those carbs if you have them.   Joe-JDC

[Drew Pojedinec]

Good eye Joe. Early and late main bodies.

The earlier one will have an emulsion tube in the metering block and have smaller air bleeds.

[BattlestarGalactic]

We actually blueprinted them 6 years ago.  Used brass set screws and drilled them to get them both the same everywhere.

I have 1" open hole phenolic spacers.

The fuel rate has a dip through mid range in front carb.  Rear carb stays pretty even linear.

The front carb is 1850 -2, rear is -4.

[BattlestarGalactic]

My guess Joe is that 2" spacer really gave it some volume to play with.

We have it closing in.  Open secondary jet, decrease primary jets.   Smoothed the power and a/f throughout the rpm.   Just opened hs air bleed .001 to  .032 and it liked it.  We dropped timing 2, didnt like it, back to 40.  We will do air bleeds tomorrow.

[Drew Pojedinec]

We actually blueprinted them 6 years ago.  Used brass set screws and drilled them to get them both the same everywhere.

Not to keep nagging on it.... so you removed the emulsion tube from the -2?  Did you plug the air feed for it in the upper dogleg?

[BattlestarGalactic]

Keep nagging!  You are one of the biggest carb gurus I know.  I'm only into basics101.  Fuel goes in here, air comes in there kinda thing.  The shop I use is good, but they don't know everything.  I run a real old setup and they are not well versed and we did what we could with the knowledge we had.  Throw a single carb and they can dial it in.  With only one flow meter per carb you can't really tell which end is doing what.  We were just guessing.

6 years ago the local roundy round carb guru helped get the two set as close as possible.   One was eating more fuel than the other, like now.  We blueprinted the air bleeds, compared metering plates,etc to get them as close as possible.

We knew they were different body numbers, but didn't know the differences.

Through jetting and drilling the secondary plates, we were able to flatten the a/f curve.  It pulls the same through the entire rpm band.  Though the front carb(-2) still does not use the same amount of fuel as the back(-4).  The front carb fluctuates slightly about 5k rpm.  Then recovers flow rate again.  The rear pulls smoothly up through.  We just figure that is from the design of the intake.

The HP curve has a slight dip, about the same rpm as that front carb drops.  Don't have those sheets in front of me to confirm.  I'll take any input I can get.  I don't plan on making any changes, I'm just going to run it for now.  It's been that way for 6 years, and has run great overall.

[blykins]

What’s the power so far?

[BattlestarGalactic]

I was not really expecting a big jump and it didn't.  Though I'll agree(along with shop) that we did kinda think it would be maybe 40 hp.

The new motor had about 20 more HP starting about 5K, but 6500 was only up about 10 HP. 

The conversation went towards the cam choice.  I specifically stated I did not want to turn it harder then 6500 rpm.  It's a bracket car, I want a solid, bracket car motor.  I don't want to deal with higher rpm and the issues that come with running it that hard for years.   Am I being a bit too conservative?  Maybe, but I am one of the very rare racers that isn't born with the "I gotta go faster" gene.  The shop talked with Comp about what I wanted and they hit it on the head.  Is this motor an over achiever when it comes to HP?  No, the shop agrees it is not quite an optimal build.  We adjusted timing and fuel til it just repeated a good number.  It still has a dip in the power curve(is that from the front carb?), but the a/f is near a dead straight line.  We didn't want to lean it out much more because it's summer and in the fall we wanted it to still be in a safe zone.

I could have just sleeved the old block and ran it for years longer.  But, I've always wanted a new block and the situation came upon to do it.  Now I have a solid foundation "IF" and "WHEN" I decide to go ahead and start making more HP.

[My427stang]

Did you try both sets of your carbs?  Seems to me there may be more there.

How about torque, did it go way up?  If torque skyrocketed with inches and airflow, then I would blame the power numbers on too small of a cam, but if it is 20 hp more at the shift recovery, it should be quicker

Any wiggle on the curve that may indicate valve float?

FWIW, one of my close buddies has a rectangular port 460 inch Rat motor, single plane, Dominator, similar head flow, similar cam, and similar power but at a little higher RPM. 

[Joe-JDC]

Two things come to mind, the timing and flow numbers on the reworked heads.  It is a bit odd that the aluminum Edelbrock heads wanted 40* timing, and if the flow went from 280 to 320, then there should have been a definite increase of horsepower on the order of 40-50 hp.  What was the airflow at your camshaft lift?   Joe-JDC 

[blykins]

I agree on the timing.

Also keep in mind that he added a lot of displacement. 

Camshaft duration or head flow increase is necessary to offset a displacement change.  I think the head work made the hp change but the camshaft is just small for an engine that’s almost 500 cubes.  I understand that high rpm was not a goal, but in the overall scheme of things, that’s a small camshaft.  A lot more  overlap is necessary.  Also if you look at the rule of thumb of 2 hp per cfm, he’s pretty much there. 

I’m not being critical.  He had a goal and he met the goal. 

[blykins]

BTW, those lobes are Comp XX lobes and are very aggressive. I hope you’re using EDM lifters that oil.  Valve spring pressure requirements would be high as well.  Sure you’re not getting into any valve float issues?

[Joe-JDC]

Not denigrating the build, either, but all things being equal, the first engine made 1.35 hp/ci, and the 496 would come in at 670 with the same hp/ci.  Better heads, bigger cam, more cubic inches, and less hp/ci?  You may be on to something with valve springs giving up early.  The timing is a bit worrisome, though.  I just want the best for him with the new build.  Joe-JDC