Poor low end response...

[DocDirk]

Hi! This is the end of my second year of working on my build, a West Coast. I've read about every thread I can find on this awesome forum about HP/Torque/Intake manifolds, exhaust impact on performance, dyno vs chassis dyno, rear end gear preferences, cam choices, etc. but as an amateur cobra builder I'm still stumped. I've a 533BB in my West Coast, built by Ford Performance Solutions in Anaheim. Intake is Victor Jr. with a Demon 850 annular single carburetor. Engine dyno'd about 650 HP at 5200 and about 500 torque around 3500 maxxing about 640 (where is that sheet..??). I don't have the cam specs right now. Transmission is a built up C6 (by the same shop) and I believe the ratios are 2.46, 1.40 and 1.00. It has a Ford 9" rear with a 2.75 gearset (recommended as optimal by the kit mfgr). Tires are 295/50/15 rear and 265/60/15 up front. I set the timing at 15 degrees, with 32 degrees total advance. Kitcarbp suggested I really won't know how it can behave until I've had it tuned on a chassis dyno.

I've only driven it a few times so far but under 3500 RPM the engine feels "like pushing a rope". I've considered changing over to the Performer RPM intake manifold (the kit manufacturer recommends the Torquer II for hood clearance), but my engine builder doesn't think that will help as much as I think, while costing me a lot at the top end. I'm planning on changing my rear diff from an open one to a posi, so the rear ratio might be raised in the process (3.08? 3.25?) I'm planning to drive mostly street and cruising on trips, so I'd hate to push the gearing to the point of having to run 3K RPM on the freeway. There doesn't appear to be room for a GearOver between the transmission and the rearend, and they're pretty expensive. Restrictive use of my ankles after many surgeries leaves me unable to confidently use a manual transmission. The exhaust is collects into 3 1/2" pipes with inner baffles the mfgr supplied, long with fibreglass wrapping outside of a 2" inner diameter. Have I built a car that's only any good at high RPM's? I haven't weighed this car but with the beefier chassis and added length and width (6" and 4") it'll surely be heavier than most other cobras.

Well with all the uncertainty brought on by my inexperience I wonder what any of you might do to make this car more fun to drive - it just doesn't seem to "launch" at all, doesn't have the kick in the pants I was expecting from the setup. As usual my enthusiasm has exceeded my wisdom and experience by quite a long shot.... Any suggestions / feedback would be appreciated!

Dirk

[Double Venom]

Doc,
I'm going to jump in here with my limited technical knowledge. To me it seeems like you have a very high rpm set up. True as the gentlemen suggests, you will loose some high end preformnce at the top end-(meaning wide open throttle DYNO numbers) changing to a different intake, but you will gain a massive amount of lower end torque. You would be basically trading one for the other but how many times does a Cobra guy go for a "Bonneville" type run?

2.75 with your set up doesn't seem bad but a 3.08 to me (granted I am a torque fanatic!) seems the better choice, especially since you are looking for that "kick in the pants" feeling. Being a WC cobra you are even hauling more weight around than a CR's Cobra. I wouldn't be surprised to see 2,700 lbs plus.

Another major option, pricey by any means is switching gears to 3.25 and a T-56 tranny. Reading your posts about your ankles makes me wonder if a properly working hydrulic clutch may not work for you? With the 6th gear (OD) then the 3.25 would certainly work OK.

Exhaust and all other criteria you have listed sounds good.
You asked for "opinions" and feedback.
My 2-cents!
DV

[vector1]

The exhaust is collects into 3 1/2" pipes with inner baffles the mfgr supplied, long with fibreglass wrapping outside of a 2" inner diameter.

what kind of baffles we looking at here? sounds as if the o.d. collector size is 3.5" and the inner part is only 2" for the exhaust to go through?

[DocDirk]

Yes, the OD on the exhaust pipe is 3 1/2" and into it inserts a long 2"? ID multiply perforated pipe with a 3 1/2" multiply perforated flange at the engine end, a 6" long solid flared cone towards the rear, and fibreglass wrapped around the length of the baffle about 1/2" thick. Do you think it's too restrictive?

You know, I thought it was a 2" ID inner baffle pipe, but haven't seen it since I installed them a while back, perhaps I misremember the spec....I bet it's 2 1/2" ID baffle and I was wrong in my post Car's at the upholsterer's atm so I can't check til next week.

Dirk

[392cobra]

What is the stall of your converter ?

[vector1]

considering each primary should prob be 2" on something that big and you're running 4 cylinders through one 2" or 2.5" pipe, i would think would be restrictive.

if the transition from collector to muffler is not smooth there could be some reversion there also.

like 392cobra said, if your convertor is loose your motor would rev but not accelerate, if it is tight you could be bogging the engine down at lower rpms, but something that big should be able to go through a set of tires pretty quick.

considering your complaint is at 3500rpm where the engine wants to breath....., and at that rpm your convertor should be pretty much locked up.

at 3500 rpm with your tq and hp you should be able to get sideways pretty easy in 1st or 2nd gear, prob 3rd gear also.

[Ron61]

This may not help much, but if you are running a single plane intake, changing to a dual plane will help your low end but may take away some of your top end. Also your rear end ratio is high even for that car. I don't know about later years but in the 64/65 Galaxies which were heavy cars, Ford put 3:00 gears in them stock and you could order down to 3:56 very reasonable. I ran a 418 stroker in mine when I had it with 3:27 gears and a single plane intake and it was sluggish and the 5th gear was worthless for anything but cruising at 70 MPH plus. If and when I ever get my Coupe back I have a 408 stroker in it with 3:56 gears and a dual plane intake and it is great around town and still has a reasonable top end. Not anything like the 180 MPH plus cars here but it will get me a ticket in a hurry. D.V. has good advice and you should listen to him and what the rest have said. I also had the horsepower on mine cut down from around 530 to around 470 as I don't race any more and to be truthful, just driving it I never noticed the difference. Good luck on whichever combination yo decide to try, but lower rear end gears will give you a quick feel of the pants feeling.

Ron

[DocDirk]

The converter's 2400 RPM I believe. Yes, the engine really starts to breathe at about 3500 and gives me the old 2-stroke dirtbike feel that something's finally lit up.... I appreciate all your inputs, I'm going to go with the dual plane Performer RPM, maximize my exhaust baffle diameter and stick in a posi with at least a 3.08 in it....looks like 2600-2700 RPM freeway cruising will be part of the picture, but then I figure I can't have everything in one package can I?

I don't know enough about clutches to know if a hydraulic would be workable for a guy who can't stand a lot of pressure pushing something. Does anyone here run a hydraulic clutch? Is it a lot easier to deal with than a mechanical?

What an adventure!

You folks have been wonderful in your time and attention to the ignorance of this newb....thanks!

Dirk

[decooney]

Dirk,
Before you choose your Cobra, I recall your NorCal Cobras breakfast visit in Rocklin and us talking about this very topic of differential gear ratios, transmission choices, and what you were going to do manual vs. automatic transmission. As I recall, we discussed the taller gearset in your differential but you were considering going with a 5-speed manual trans with a lower 1st gear - but then again you were not sure about automatics either back then.

We also discussed the WC Cobra being a bit larger, maybe even smoother, and definitely heavier than other Cobras and that was one of the factors you were looking at, and "room", as I recall.

Maybe you can answer this - perhaps there was a bit of mix and match of components that occurred later on down the line then when the car got built, thus (maybe?) keeping the tall axle ratio rear then possibly switching to a C6 automatic somwhere along the line instead of going with a lower gear 5speed manual trans? Did this possible scenario occur in the end?

I ask these questions because I went through a similar situation with a friend who HAD to go to an automatic, with a little bigger cam. He later removed the torque converter and went with a 3,000 rpm stall speed. It definitely helped but it was not "snappy" with the low end grunt he was looking for either. After him trying various things he went back to a manual and with a lower first gear was able to get the extra little low-end grunt he needed and sold the car because he hated to shift. You give away something on both sides of the equation I guess.

Based on what cam/axle ratio/trans specs you've noted here, (Unless you go with a Richmond 5speed say with a low 1st gear and) I'd pitch the tall gearset (If you keep the automatic trans) in the rear and go to at least a 3.25 rear axle ratio (with posi) and try that first. I recall you wanted something you could still drive on the freeway; with the automatic the 3.25s are not bad and with a bigger cam it works out okay. It won't be a rocket ship off the line with the heavier Cobra weight there, but it should do better than it is now that's for sure. I don't work on other peoples cars, but you might consider bringing it to a friend I can refer you close by to where we do some project collaboration together. He does a lot of Cobras and troubleshooting and reconfigurations... particularly in this area we are talking about here.

Then, if you still absolutely must keep the automatic trans, you could look into what someone else suggested with a higher stall speed with your converter but I'm not sure you'll be happy with that either - gets a little sloppy and irritating at times zinging the motor up a bit before you take off. Maybe first decide if you must keep the automatic or not, then start making other changes. If you are not sure what to do about keeping the auto trans or going with manual trans, and decide to go manual, you can come up here and we can send you to a local shop here in Sac. Gary works on Graydon's West Coast Cobra and has it setup nicely for him to shift, custom hydraulic setup (basic) and it works well. Perhaps I can hook you up with Graydon E. and he can share with you how his car West Coast Cobra runs/shifts. We've gone through all the same exact discussions on his car, numerous times. Let me know and I can have him call you. DC

[DocDirk]

Duane, wow you remembered a LOT of our conversation of almost two years ago! Yes, I was undecided about the transmission at that time, but the 2.75 rear end was the idea of the manufacturer. He uses the C6 with a 514 crate engine, a Torker II manifold and the 2.75 rear ratio and likes it. As for me, I have definitely been disappointed in the low end performance. I put in the automatic because of ankle problems I have and figured I couldn't push in a clutch any more and wasn't aware of the hydraulic clutch option. I presume it's a very light action hydraulic assist sort of thing?

Actually the lure of a manual transmission in the driving experience is far greater for me than the automatic. Years earlier I drove nothing but manual transmission sporty little cars (even my 1962 Jag Mark II saloon has a stick shift). Even when I'm slowing for a somewhat spirited turn with my Towncar I sometimes find my left thigh rising and my right arm reaching for the nonexistent stick in order to downshift...haha!
I've looked at a lot of rearend gear options using gear calculators that will show RPM at a given MPH or MPH at a given RPM and no rear ratios work very well with the limitations of the C6 to give BOTH quickness boost AND low tension freeway cruising. From what I can tell, the Tremec TKO with the overdrive would do wonders with a 3.55 rear end ratio but then that's just my conjecture... been wrong before.... It looks like a manual will be in the works for me soon. The Tremec TKO was rated as handling up to 600 ft. lbs of torque and I wonder whether with such a beastly engine I should be waiting on the Magnum? I haven't looked at the Richmond yet, will do that soon as I finish this post. So many variables, so few years in which to sort them all out

Yes, please do hook me up with your friend who is familiar with this problem and might be willing to share some hard earned wisdom! I can't wait to get on the road, I'm still troubleshooting a steering rack leak and the rear suspension problems inherent in the kit. I'll PM you with my personal information

Dirk

[wtm442]

Dumb question. I'm not interested in peak HP and TQ if the problem is below 3500 RPM.

What does the dyno sheet show for the air/fuel mixture when you stomp on the gas pedal in 3rd gear at about 2K RPM? Does it go lean? Does it go rich? Maybe its just a few carb adjustments. Disconnect the secondaries and see what happens.

If you have an ankle problem, I'd suggest holding on to the automatic for now. If the carb is OK, the next thing to do is change the rear end gear and/or the first gear in the tranny. Then you could try the dual plane manifold. But before you do that, you could retard the cam to make more lower end HP, but it would decrease your top end HP.

[DocDirk]

No doubt a chassis dyno tuning would be a smart thing to have done before I conclude I understand what the current setup has to offer. That information is not available to me from the engine dyno of course.

Anyone know of a Northern California shop that does a good job of that?

Dirk

[wtm442]

Engine dyno'd about 650 HP at 5200 and about 500 torque around 3500 maxxing about 640 (where is that sheet..??). I don't have the cam specs right now.

Find those sheets?

One pull on a chassis dyno will tell you whether its lean or rich or good at low RPM's. But once its on a dyno, you want someone who is a very good tuner. A couple of hours of tuning by an "expert" can save you thousands of dollars in un-necessary parts.

You might want to fool around with the total advance to something more than 32 degrees. Bring all your carb parts with you when you go to the dyno.

[DocDirk]

No, have to clean out a room we used to clean out our house for company omg! Yes, we have to be sure our home looks like nobody ever set foot in it before someone can come over to visit The engine dyno sheets are in there I just know it... well I DO recall that the pull graph ran from 3500RPM up, so I got no engine dyno info re lower rpm's. Just have to find a professional who knows what he's doing... I obviously don't!

Dirk

[decooney]

Dirk,

I sent you a PM and tried your house phone and was not able to connect... I'm fairly sure we know what the problem is and why a few different things are working against you, making you feel a bit "underwhelmed" about your results at this point. Rather than trying to explain it in more emails or posts... just see my prior PM reply back to you and you can go from there. If you drop your car off at Gary's place at GT Auto, I'll stop by and check it out and reconfirm a few of my own suspicions; just send me a PM. Remember, this is like a 3,000lb Cobra, and it needs to be set up as such and based on your driving style and needs. I believe there are a few more key changes needed for the remaining stars line up. I think you'll be pleased once those are completed. Then you can go race the SS and see how it all pans out.