Where'd the horsepower go????

[Poundz9oh9]

Engine

ZZ4 block bored .030

Complete roller cam setup (474/510 - I believe w/o checking my build sheet)

1.5 ratio aluminum roller rockers

Vortec Iron heads

Airgap intake

600cfm Edelbrock carb

Hei with 50,000 volt upgrades

2 1/2 dual exhaust

Rated at about 385 hp with matching torque(ish)

700R4

3.54 R200

 

My question is this, can I be losing a great deal of horsepower through the transmission? I mean the motor seems to be running great, maybe a little rich sometimes but other wise fantastic. I have great throttle response and the car is quick. My problem is off the line, it seems to be a dog, compared to my higher rpm ranges. Can the trans really be stealing this much horsepower? I mean, with this setup I should be able to burn the 205's off the back of the car right? I barely can get a little screech from the tires off the line and then another shifting from 2nd to 3rd. What do you guys think?

[jt1]

Are you absolutely sure it's going into low gear? When I had the 700R4 in my car you had to be just right on the shifter and TV adjustments or it wouldn't shift into first, and acted just like you describe. You should be able to blow the tires off the car in first with that setup.

 

John

[Poundz9oh9]

Yeah, I'm sure it's going through all the gears. 1st is often shortlived at light throttle but it stays there when I step on it and it's shifting good through all the gears especially when I stand on it. Now just light throttle, that's a different story, the shifts are, in my opinion are coming way to soon and I tap into 4th at low speeds which bogs it down just a little. But hey that's at light throttle whose trying to go fast at light throttle..

[Mikelly]

I'm with JT... You should be roasting those rear tires... something's up...

 

Mike

[boodlefoof]

Too tight a torque converter? Timing outta wack?

[Poundz9oh9]

Timing is good, but the torque converter may be another story, it's supposed to be a stock corvette 2500 s/s. Would that really restrict the motor that much?

[Scottie-GNZ]

Test the converter by slowly brake-revving the engine and seeing how high the RPMs go before the torque tries to overcome the holding power of the brakes. Of course, if the brakes are crappy it kinda makes this test difficult.

 

Having a big cam, overrich condition and too tight a converter will make the engine feel like a dog off the line.

[Guest zfan]

My Good friend has the ZZ4 crate motor in his Jensen Healy with a 700r4/3.55 gears and can roast the tires anytime under 40 mph. He runs a 24-2600 rpm converter.

 

Could be tranny/converter. Motor is fresh? Have you done a compression test? Checked a/f mixture. May need a dyno tune.

 

Mike

[Pyro]

What is the cam duration and lobe separation?

 

Yes, a stock converter can make a big cammed engine a dog at low rpms.

 

What is your initial ignition timing at?

 

Are you using the vacuum advance?

 

What is the total timing?

 

Bigger cams need more initial ignition timing. Try 20 degree initial.

 

Then the vortex heads don't need much total advance because of their fast burn design. The total timing should be about 35 degrees. You may need to weld up some of the advance slot in the HEI to get a curve like that (15 degrees of advance).

 

Then use a medium light springs on the advance weights. Mr. Gasket sales a recurve kit for the hei, but don't use their weights because they get stuck. Use the factory advance weights with the medium Mr. Gasket springs.

 

Edlebrock carbs suck. You should get a Holley or get a Q-jet.

[Poundz9oh9]

What is the cam duration and lobe separation?

 

Yes' date=' a stock converter can make a big cammed engine a dog at low rpms.

 

What is your initial ignition timing at?

 

Are you using the vacuum advance?

 

What is the total timing?

 

Bigger cams need more initial ignition timing. Try 20 degree initial.

 

Then the vortex heads don't need much total advance because of their fast burn design. The total timing should be about 35 degrees. You may need to weld up some of the advance slot in the HEI to get a curve like that (15 degrees of advance).

 

Then use a medium light springs on the advance weights. Mr. Gasket sales a recurve kit for the hei, but don't use their weights because they get stuck. Use the factory advance weights with the medium Mr. Gasket springs.

 

Edlebrock carbs suck. You should get a Holley or get a Q-jet.[/quote']

 

initial timing was set at about 12 degrees (20 degrees??? won't that hurt something?)

 

vacuum advance is hooked up

 

using the 2 light duty springs (have the complete set) that was included with a mallory HEI distributer that's on my fathers engine

 

carb is tuned the best I could get it (so far) without getting a *gasp* when accelerating from about 50 mph

 

I don't know off the top of my head the total timing or cam/lobe seperation

[Pyro]

A cam with more than 220 degrees of duration at 0.050" lift really likes a lot more initial timing. Your cam sounds bigger than that. 20 degrees initial is very common setup with bigger cams. However, more initial timing will also add to the total timing which is not a good thing. That is why one of the advance slots in the HEI need to be shortened to limit total timing to 35 or so. You need a timing light with a degree knob on the back or use degree tape on the balancer to determine total timing.

 

Also, big cams with low (stock) timing makes the headers glow red.

 

No, 20 degrees will not hurt anything. I run 20 on my sbc engine with a 242 degrees of duration at 0.050". 20 degrees is recommended in "how to modifiy sbc books". BTW, that is the factory timing for a L28et.

 

Wider lobe separation will make a carbed engine feel sluggish. Cam overlap helps the carb fill the cylinder with fuel. 108 to 110 is about ideal for a carbed street engine, 112 is getting too big, and 114 is weak. EFI does better with wider centers (112 to 114).

 

Where is the vacuum advance connected? It should be on the ported vacuum source on the carb. The ported source has no vacuum on it at idle. You should set the timing without the vacuum advance connected. And little to no change should occure to the timing when the vacuum advance is connected to the ported source.

 

If you have the vacuum advance on manifold vacuum then the timing will retard when the throttle is opened which will reduce off idle torque.

[v80z]

Pound

 

I am very interested in what you find. I am running a similar setup. The questions I had have already been asked. From my L28 racing days I know that a carbbed and cammed machine will limit performance to various ends of the power band. I initially have gne with a top end cam .508 lift ~250 duration thinking there would ber plenty of low end torque considering the cars starts out stock with very little anyway. On the race setup L28 I ran a 602 316 duration which would not make power below 4000 rpm. We had to run an initial 20 -22 degrees with a mechanical advance of 12 for a total advance of 30 - 32degrees. I am also thinking that at the top end I am going to be under carbbed and would like to get at least an 850 cfm.

 

Can one buy different jets for an edlebrock carb or is meter adjusted? Wonder what jets you have.

 

Anyway please update this thread and I will do the same as I progress.

 

350 .030 over

600 Edlebrock

.508 solid

Edlebrock roller race rockers

HEI proform billet

Performer airgap

[zeeboost]

My cam has 230* duration at .050" of lift -- I'm running at 20* initial timing and it runs cooler and sooo much better than when I was running at 14* initial.

 

ALSO

 

Be DAMN sure that when you mash the accelerator pedal to the floor, your carburetor is opening all the way. SBC engines need those secondaries opening up as far as they can.

 

You could also try disconnecting your vacuum advance and just plugging it up -- I know it helped my acceleration as well. I've always heard that for I high performance engine, you shouldn't run a vacuum advance on your timing. Good luck with it.

[BRAAP]

Yes, advancing the ignition timing will allow your engine to run cooler and the engine will also perform better. These results are indicative that original timing settings were not optimized for that particular engine. As a note to those who are new to engine tuning, be careful that you don’t advance your ignition timing too far as it can be harmful to your engine. Typically you’ll find on most ‘70’s and ‘80’s era vehicles, the OE ignition setting is not quite ideal, from a performance stand point, and in some instances a very noticeable and measurable performance gain can be had just by adding 5 or so degrees of ignition advance without any ill affects other than maybe it is not as emissions friendly now.

As for your vacuum advance affecting your acceleration, it really should have absolutely no influence on your WOT performance at all, unless something is amiss with your ignition system. Typically the vacuum advance is connected to a “ported” vacuum port somewhere at the base of the carb and only sends the vacuum signal to the distributor at part throttle which adds more ignition advance which in turn improves part throttle drivability AND mileage. There were some vehicles that were set up to have their vacuum advance connected to full manifold vacuum, i.e. some Chryslers etc. so most aftermarket carbs have provisions for either “ported” or “full” vacuum for vacuum ignition advance.

Now if you were setting your initial advance at idle with the vacuum advance connected, (particularly if you had it connected for full vacuum at idle), then in reality your initial ign advance will be too far retarded as idle vacuum has advanced the timing and as you open the throttles, the timing then retards from the initial set point and performance will suffer as compared to the ignition timing being set with the vacuum advance disconnected.

In short, a correctly connected vacuum ignition advance that is properly timed, (set your initial ignition timing with vacuum advance disconnected), will not hinder or take away any power from the engine but will improve the part throttle manners of that particular engine, i.e. driving around town, cruising the freeway etc. in a full out race car, part throttle smoothness and mileage is not a concern so vacuum advance is typically omitted for this reason.

To take ignition tuning to another level, if you wanted to extract the most performance from your particular engine, one of the steps we tuners use is to find out exactly how much ignition advance that particular engine prefers through its entire operating range and then we recurve the mechanical advance via springs and heavier/lighter fly weights to deliver that optimized ignition advance curve. Every engine’s ideal ignition advance curve is different so what works best for one engine may not work so well for another. Even changing mufflers can have a small influence on the perfect ignition curve for a particular power plant.

Optimizing ignition timing is just one of the many things tuners use to extract the most from their performance engines.

 

Sorry for the long rant,

 

WOT till you see God, then lift…..

 

Paul (BRAAP) Ruschman

Rusch Motor Sports

Sandy Oregon

 

 

77 280Z hybrid, Mopar 440, FOR SALE…

[zeeboost]

I should have specified that the difference that I felt in acceleration with the vac. advance plugged was from a part throttle acceleration, and not WOT. Correct, at WOT, the timing should not change if the vacuum advance is connected or not. Then again, I'm still playing around with springs and weights, so my ignition system still may not be up to par.

[datsunlover]

I'm curious too, as I'm having a similar problem in my rx7. My engine is basicaly stock (350 TBI from an old police car) and I have a 700r4 tranny. I have very similar issues at light throttle, and unless I stomp it too the floor, it really doesn't like 1st gear. As you describe, it does go into 1st, but aside from WOT, it shifts into 2nd almost instantly, and quickly gets itself up into 3rd then 4th.. boggggg.... For now, I've started shifting to 3rd (instead of D) and let it go up to 3rd, which is 'ok' around town, and if I'm on a long stretch I'll click it into 4th manualy. I've been thinking it may be something to do with my fuel injection/computer but if you're having the similar issue and runing a carb, I'm thinking this is a tranny issue...

[Poundz9oh9]

I have very similar issues at light throttle, and unless I stomp it too the floor, it really doesn't like 1st gear. As you describe, it does go into 1st, but aside from WOT, it shifts into 2nd almost instantly, and quickly gets itself up into 3rd then 4th.. boggggg....

 

HA!!! Exactly!!!

 

Thanks guys, you've givin me a lot to think about and check................

When I can get some time....

[Poundz9oh9]

ok guys, here's the complete cam specs:

 

The duration at lash point in degrees (intake/exhaust) is 275/280; duration at .050" tappet lift (intake/exhaust) is 208/221; and maximum lift with 1.5:1 rocker ratio (intake/exhaust) is 474/501. Valve lash is zero/zero and lobe centerline is 112 degrees

 

The suggested timing is 10 degrees initial @ 800 rpm (where it is now and set with the vacuum advance disconnected)

Suggested Total timing of 32 degrees @ 4,000 rpm (no idea what I'm getting exactly)

 

So where do I go from here timing wise? Do I stay with the suggested or take it up to 20 like mentioned before?

 

Anybody want to go in depth as to how exactly to limit the total advance at the vacuum advance assy.?

 

Would something like this work for the total timing adjustment.

http://www.jegs.com/cgi-bin/ncommerce3/ProductDisplay?prrfnbr=3315&prmenbr=361

[datsunlover]

A little good news from the RX7 camp here... I re-set my TV cable yesterday, and it seams to shift a lot better. It still gets into 4th and bogs, but not as quickly. (So I'm still shifting it manualy and holding it in 3rd till I WANT 4th) I think part of my problem is electrical though, as I'm running a TBI system and it takes a speed sensor signal from the back of the spedo. I think because my spedo is reading WAY to fast (have to change the gear in the tranny) it's confusing the computer, and making the tranny shift up.

 

I have a link for a site describing how to properly set the TV cable, and it gives a good run down of how/why it works. Acording to that site, there is no such thing as 'adjusting' the TV cable, only a 'setting' of it. The way it was described it made sence to me.. And following the distructions has made a definite improvement on my car.. Unfortuantly, the site seams to be down right now..

 

Basicaly, it is a simple thing to 'set' it properly;

-you unhook the TV cable from the throttle

-push in in the little D shaped 'button' on the cable sheth (where it clips to the bracket on the intake)

-then push the little square piece (that the actual cable runs through) all the way inside. It's like a little racheting mechanism..

-re-attach the TV cable to the throttle, and open the throttle all the way.

-just before WOT it will have resistance; force it past that, and the little square piece will ratchet out, and that's that. It's set.

(Oh, and make sure the pedel in the car is able to push the engine side to full throttle too.. that was oart of my problem as well.)

 

Not taking credit for anyone's work/words there, just thought it might help.

[Poundz9oh9]

Yeah I've done the TV thing. It got a little better but sill not the best, just like you said. I think part of my problem with that is that the linkage hole for the TV on the carb is a little bigger than the end of the cable that slides into it. I need to find a bushing or something because it looks like the cable is just kinda dangling in there as opposed to having a nice tight fit. I mean, I'm not getting too bent out a shape because hopefully I won't have this Trans long, I'm still looking at going back to manual. I just don't feel right driving this car with an auto. Anybody got a spare T56 they wanna trade for a "race prepped" 700R4?

 

Needless to say I still want to get things set up right for the time being.