ive been doing some reading and seen a whole bunch of different ways people select their powervalve. every motor is different and i know it depends on a lot of variables for the right powervalve, but the ways people test to see what powervalve they need just doesnt make sense to me. how do you know what your primaries need vs. secondaries?

whats your way of doing it?

i imagine i have stock powervalves in my 750 dp carburetor, i just put it on, but my cam gives me hardly no vacuume and i have a stumble if you nail the gas..(im thinking bigger carb cam will take care of that)

 

First thing, get your timing right. If you have a big cam in a 350 that generates real low vacuum, you will need alot of initial advance, a good bit of vacuum advance and an aggressive mechanical curve. More engine details would help.

As for the power valve, I use my narrow band O2 and a vacuum gage. If you watch closely as you are driving around, you can get a good feel for when the primaries are coming in on the PV and when the secondaries are opening. I don't buy into the theory of "half of your idle vacuum" for power valve sizing. Why? Because when my car is idling, it only pulls 11". When I am cruising and getting to where the PV will kick in, my vacuum is closer to 20". I have a 9.5 PV in my primaries and my secondaries have no PV. Also, use the main jets to get your AFR where it needs to be. Then correlate your new jet size to the PVCR size. This will tell you how much the PVCR needs to be opened so you can drop your jets back down.

There are plenty of guys on here that can help you through this. First, post more about the combo and where your timing is at now.

-JEFF-

 

there is no vacuume advance with my motor its a full 39 degrees all time..

350 brodix 180 cc aluminum heads
srp forged pistons 10.5 compression
xtreme energy hydraulic roller comp cam
Operating Range:2200-5800 RPMDuration Advertised:282° Intake / 288° ExhaustDuration @ .050'' Lift:230° Intake / 236° ExhaustValve Lift w/1.5 Rockers:.510'' Intake / .520'' ExhaustLobe Separation Angle:110°
holley 750 double pump
rpm air-gap
stock bottom end (balanced crank)

ill probably not need that big of a PV though if im maybe pulling 7 lbs of vacuum correct? id have to get out and drive it and recheck but im thinking a 4.5.. my AFR was on average when i checked with my wideband a 13.0-13.5 so im probably going to take my jet sizes down 2 numbers first and see how that is

 

That's not a very big camshaft. I am surprised the vacuum is that low at idle. I would first make sure that you don't have a vacuum leak. Second thing I would try...warm the car up and let it idle. Bump the timing up until it reads about 48* advance. See how that affect your idle and vacuum. Don't drive it like this...it is just a test! I have never owned a car that didn't run better with vacuum advance. Locked out timing is close, but not the same.

Our combo's are similar. I have a little bit bigger hydraulic roller cam and ported AFR 190's. My car likes 52* advance at idle (22* base mechanical) and 37* total. I pull 11-12" at a 1000RPM idle.

 

I would check to make sure that's all the vacuum I have but it's snowing and cold so I'll wait for a sunny day.. What are you running 1/4 mile times out of curiosity? My best was a 12 50 but I haven't had a good tune on it yet. The last pass I made I had 40 degrees total timing and it seemed to like it. It feels like it could have more power through 60 ft and it stumbles off the start but again that could be carb cam.. I'm just wondering if that could be PVs but I guess I'll cross that bridge when I get there. First things first I need to see how much vacuume my motor is pulling.. My brakes are terrible so I wouldn't be surprised if it was 7. There are no vacuum leaks I checked that

 

The best I have managed is an 11.89@116. That was on a very hot, humid day.

My advice would be to get a vacuum gage, a dial-back timing light (if you don't already have one) and an O2 monitor if you can afford it. A cheap narrow band is all I have and I am satisfied with that. These things will make tuning the carb a lot easier. Start with the timing curve, then dial in the idle mixture and then dial in the WOT (easiest to do at the track). WOT is the easiest to get right. After that, you can concentrate on the cruise and transition areas. These take a lot more work. Take lots of notes and try changing only one thing at a time.

When you are ready, let me know. I can walk you through the methods I used.

 

There's a sticky on Holley tuning at the top of this page that, although written by an idiot, the process works flawlessly.

Try that.

 

Locked-out timing and no vacuum advance are for track-only cars. If you're driving on the street, use both mechanical and vacuum advance. Dead spots disappear, and fuel economy reappears.

 

I have vacuum gauge and Wideband lm-2 I'm playing around with..might be a few months before the old girl comes out again lol it's crappy weather so no use in getting it dialed in for this air

 

Yeah I read that but some of his words he used confused me on what I should be looking for

 

The only place it stumbles bad is when I'm at the track and really this is more of a strip car and when I drive it on the street there's usually somebody wanting to race ( I can't say no) lol

I had this set up with a 650 double pump and it worked fine just needed more cfm

 

Which words are you having trouble with?

 

Yours should run fine with the stock power valve in it.

Ive gotten both sides of the "half of vacuum"=PV size and also 1.5-2" under vacuum for PV sizing from Holley techs.

Running a 250ish @050 SR cam, makes 10" at 1000 rpm.

The 6.5 PV worked the best so far, is cleaner all the way around.

Tried the 4.5 last night lopes too much at lower engine speeds. Might just try an 8.5 for the hell of it. I dont understand, would seem the lower one should be better but it is what it is.
Also pay attention to the motor, give it what it wants, where it runs the best. AF meter is an aid for comparison

Dont know if that helps or not.

As said above get your timing curve nailed down first, dont go too crazy with the advance curve. Then play with the carb. Squirter size and pump cams make a big difference. Make sure where the pump arm contacts the lever theres no play or slop it should be a very slight preload on there otherwise youll get a hesitation. Holley sells a pump cam kit which will give you endless options. Id bet the stock cams tried (pink) in differnet positions will get you what you want.

Interesting learning curve still learning myself, its fun though.


Edit....have to eat my words!!! Maybe the 1/2 vacuum deal IS right. Found an idle air bleed issue that, now fixed likes the 4.5 better. THe 6.5 crutched the condition. My bad!

 

Raise the value until the flat spot goes away when you're in high gear and driving along at about 35 mph?
- how do you tell if you have a flat spot? and does the "half of your vacuum At idle is what your primary pv's is" method do the trick also?

Also he says when leaning out your jets keep dropping down until it starts surging
1. This sounds kinda dangerous
2. Does he mean it will be cutting out alot in other words when you start giving it a little throttle?

I gotta lotta learning to do

 

I guess I'll just have to try it out for myself if people go both ways on that..40 degrees timing is a lot I wouldn't go passed that but again it seemed to like it lol. People tell me I won't really need a pump kit but I guess if all else fails I can pick one up if I can't get the stumble out. Also I checked what color the cam was and it was pink, white, or yellow? I doubt it was yellow that's only for 50 cc pump kits I thought. It was in the lean position next time I start it up I'll put it in the fat position. What comes on those things stock? I got mine used (but it was from a relative and he only had it a week and went back to a different carb) idk if he did anything with it internally but the initial squirters are 28 in the front and 32 in the back

 

Get the list # off your carb.
Holley tech line can tell you exactly what it came with

750 DP usually comes with 70 and 80 (?!)jets if Im not mistaken could be 68 primary, its been awhile

Stock pink cams front and rear, brown usually used with 50cc pump which you dont need. 28 and 31 squirters are stock.

If you need an earlier shot move the pink cam to the #2 position. If you need a larger shot go up 3 sizes on your squirter. Cam kits are cheap
Make one change at a time. Float level can have an effect also just have to spend time playing with it.

Say your car makes 9 in vacuum at idle, divide that in half is 4.5 . Now if it was 10 it would give you 5, no such size. Use a 4.5 (next size down) follow?

Its a start.

most motors dont need as much fuel thrown at them as youd think. Takes time getting it nailed down just like EFI tuning but if you make ONE change at a time youll see what does what then youll nail it.

 

Thanks for the tips I follow on the PVs now. As it said in the sticky, I keep 6.5 in the back?

Also just to keep my AFR at cruising speed ( around 14.7 but no more)that's all in my main jets correct

 

Flat spot = you give it gas, but over some range of moving the pedal, nothing happens; or worse, the engine produces less power. Then, once you reach some "magic" point of pushing the gas, the thing suddenly snaps out of it and starts doing something.

Holley's "instructions" for choosing a PV are just plain WRONG. They are based on the idea that somebody took a REALLY sucky 60s combo and jammed too much cam in it and too much carb on it. Think, a 4200-lb 60 Chevy with a 283 2-bbl (about 8.7:1 compression), a 151 cam, a Powerglide with the stock converter, the stock 3.08 gears, and a 750 carb. They set the carb up to practically DROWN the motor in fuel, because it's going to try SO HARD to go lean at various times.

If you follow the "half idle vacuum" guide, you end up with too much jet, and/or the problem where as you slowly give the car gas, it gets leaner and leaner and leaner and leaner and finally starts to stutter and stall, because the PV setting is SO LOW that you practically have to have the gas floored before it opens. If INSTEAD OF following those 50-yr-old obsolete WRONG instructions, you set the jets for CORRECT cruise mixture (they'll end up SMALLER than Holley's stock choice), then the PV that their "rule of thumb" will select for you, will require you to be so far into the gas before it ever opens, tha tthe car will be near undriveable. Once the jets are set to the CORRECT cruise mixture, the PV needs to be RAISED to a value MUCH CLOSER to cruise vacuum than "half". Especially if cruise vacuum is high. Woks OK if you have the 60 283 situation above, and your cruise vacuum is only 12" to begin with; not so much, if you have lets' say a 80something F-body at 3400 lbs with a 350 or 383, 3.73 gears, and a modern, sensible cam.

Follow the instructions in the sticky. Your car will run better, and probably get 50% better gas mileage than what the carb will give out of the box.

If you're having trouble with "flat spot", I'm going to guess you also want to know what is meant by "surge"? That's where the car feels almost like it's hitting patches of water and being intermittently slowed down, even though you're not moving the gas. It's caused by being right on the edge of excessively lean. That's why it makes a good tuning indicator: that tells when YOUR ENGINE has just barely exceeded its most efficient cruise mixture.

On the subject of a sec PV, I often wonder why there's even one there. In a street carb or a drag race carb especially. There is NO UNIVERSE (in those applications.... professional road or paved oval-track racing, MAYBE, but not the street or strip) in which the secondaries are open, but the vacuum is high enough to close the PV. Basically, the only time the secs are open, is when you have it floored, and there's no vacuum. Therefore out here in the RW, WHENEVER the secs are open, the PV is open as well. Therefore, it's useless. Might as well plug it and increase the jets about 7-8 sizes to flow the add'l fuel that the PV would have; you'd have a carb with fewer parts but does the exact same thing. I've been known to do that as well but it's by no means necessary.

 

Yeah thats why I made this thread there's so many different ways I've read to select a PV it's really whichever method works best with your application I guess.. That does make this a lot easier to comprehend now. Wish there wasn't so much snow on the ground I can't even get there car out to try this out.. It's gettin me worked up I know there's more in this car. Once I get it pretty well dialed in on the powervalves and jets I think I'm gonna try and take that back powervalve out and bump up the jets. It's just one less thing to worry about screwing up on me. As far as gas mileage getting better, depends a lot on what material the drivers foot is made out of. Mine happens to be lead lol

 

sofa, I kiinda feel the same way on the power valve thing. Finally took their advice and did the half thing;have always gone about 3"+- lower than idle vacuum and had better results. Runs good but will go back up anyway takes a few minutes....Thinking, now that I have mine running pretty clean of bumping mine up to a 6.5 just for kicks. Before it was masking another issue I had.
Both my machinists who have been regulars at the track recommended 8.5 for a 10" at idle motor, no less than 6.5 go figure!

I think their idle/transition circuits are too rich but what do I know. From my understanding the latest Gens of Holleys have totally revised and updated cicuits, you get those with the billet metering block Holley DPs and the Holley HP?!

For cruising Id get the mixture screws right, floats to where the motor wants it then lean it til the motor just starts to surge then jet back up 2 sizes or so. For WOT go by the plug reading. Fun learning curve.

 

My method is to drive it around on the street with a vacuum gague hooked up. You'll quickly see the vacuum levels generated during regular driving. Keep the PV number below those levels so it's not kicking in except when you lean into it a little. You don't want the power valve to open every time you pull away from a stop sign.

Idle vacuum is meaningless. The PV doesn't affect idle or off-idle mixture at all.

Low stall converters and big cams are the hardest to balance. They draw very little vacuum when you start off from a stop sign but quickly rise when speed comes up. That's where you have to make some compromises.

Generally speaking, if you were to block off the power valve completely you should still be able to drive the thing around without any stumbles or flat spots (from idle to mid-throttle). Obviously, you don't want to go wide open like this since you won't have power enrichment, but from idle to modest throttle you souldn't need it at all if the carb is tuned right. PV shouldn't be used as a crutch to fill a lean spot every time you dip into the throttle a little.

 

What exactly happens when you have a flat spot? Is it just fuel dumping out of the PV before you have all your "power" in?

Basically whenever I take off from a stop sign I would need to take the average vacuum I'm getting under those driving conditions and take of that and thats what my PV should be

I have 3500 Hughes 9 inch stall btw so it's not a small converter but not big either.. About like my cam lol

 

The power valve isn't a fixed "reservoir" of fuel, that you can empty; rather, it's a vacuum-operated valve that opens a passage in parallel with the jets, such that whenever the vacuum is below its "number", it lets in about 15-20% more fuel, to richen up the mixture for "power" (12.8:1 A/F ratio or thereabouts) as opposed to "cruise" (14.7:1 more or less).

"Flat spot" = LEAN: the jets by themselves don't feed enough fuel for a proper "power" mixture, but the power valve's setting is too "remote" from cruise vacuum. The result is, you get that lllllloooooooonnnnnnngggggggggggg bog when you slowly push the gas but the PV stays closed, and then as you kind of mash it more and more, all the sudden you drop the vacuum to the point that the PV opens, and voilŕ! instant fuel, and the engine suddenly begins to run again.

The CORRECT PV setting gives you better fuel economy because the jets can be leaner in the first place; and crisper off-idle acceleration because the fuel appears the instant you need it; and better fuel economy also because you're not jacking up the pump shot to cover up the bog. That last is CRITICAL with a stick car, since you cycle the pedal completely from idle to power 3 or 4 or 5 times EVERY SINGLE TIME you accelerate from a stop to a cruise, whereas with an auto it's usually only once. I can sometimes DOUBLE the gas mileage on a stick car by tuning it right.

 

That's awesome. My gas mileage is nothing to brag about either so this should be pretty fun. I'll post pictures of my wide band readings from before and after it's tuned to the best of my knowledge. Thanks for the clarification sofa

 

It's probably also worth mentioning that the vast majority of street cars have their ignition timing set up incorrectly, which STRONGLY affects what people perceive to be carb problems. The old saying goes, 90% of carb problems are caused by ignition; and 90% of ignition problems are caused by carbs.

First thing to do is to locate #1 TDC ACCURATELY, to verify the timing mark. It's almost never right. Use a piston stop or similar method to find TDC ACCURATELY; add a mark to the damper at that point; then add marks every 10° around the balancer on the advance side, up to 50°. You can get this distance ACCURATELY by measuring the OD of the damper ACCURATELY (such as with calipers, NOT a measuring tape), multiplying by pi (3.14159265359...), and dividing the result by 36. You might even want to mark them with numbers to eliminate the possibility of confusion later in the process.

Disconnect the vacuum advance. Adjust the "static" timing to where the "total" timing is at 36° when the engine RPM is high enough that it has stopped advancing, 4000 RPM should do it. DO NOT use a "dial-back" timing light for this!! This is where the 10° marks come in handy.

An "ideal" timing curve would be something like "total" timing at 36°, centrifugal advance of about 18°, "static" timing about 18°; centrifugal advance starting just off idle, like 1200 RPM, and "all in" well before 3000 RPM. Odds are, you'll find you don't have that; more likely, your "static" timing will turn out to be 10-12°, and you will be found to have about 24-28° of centrifugal advance. This won't give good performance results. I'd suggest getting the Crane distributor kit; this one has an adjustable vacuum can, and a set of srings and weights. Swap springs and weights around until you get as close to the curve that I described as possible.

Vacuum advance should be around 12-15° ON TOP OF the "total" advance, for about 50° with the vac adv hooked up, the RPMs above the "all in" RPM, and the engine vacuum above about 12" (it will be). What vac adv does, is ONLY provide advance during low-power, high-vacuum, high-speed operation (aka "cruise"); it is NOT active during "power" operation. Using the adjustable feature of the vacuum can, adjust it so that it stays operated at the highest possible vacuum; drive the car; and see if it pings when you "tip in" the throttle. If it does, back it off slowly until the pinging goes away.

This also has a HUGE impact on gas mileage, engine running temp, and overall driveability. It's REALLY AMAZING sometimes how much improvement can be made to how an engine runs by proper tuning.

Once you get the distributor set up this way, WRITE DOWN the "static" ignition timing it ended up at, so that you can put it back if it ever gets disturbed. Leave it alone during normal tune-ups and such, as it DOES NOT CHANGE in an electronic system, unlike the old "points" systems where it was constantly changing due to parts wear. Set it, leave it alone, know where it belongs so you can put it back.

You may find that the carb needs AHELLUVALOT LESS work once the dist is right.

 

sofa, the OP is running locked-out timing with no vacuum advance. I tried to advise against that, but that fell on deaf ears.

Maybe he'll listen to you.

 

Does this rule nullify if i am running a blow-thru supercharger set-up on the street? I hope i do not have a stumble like this!!!

 

this does make sense but ive ran 12s with locked out timing in several cars that were heavier and no trans brake that didnt stumble like this. also other carburetors ive tried, including a tunnel ram with 2 600's;800 DP and 650 DP didnt stumble like this, and the tunnel ram set up ran quicker than what my 750 rpm air gap is running. im not saying that vacuume advance wont help me, im just saying theres a good chance its carburation.

 

also, the street is not where i have my issues.

 

this crane distributor kit will work pretty good on the strip you think?

also is there a version of crane's distributor in MSD? no big deal but i'd like to keep all my ignition components the same..

correct me if im wrong but check on these PN's
Crane Cams #271-1000-1501

MSD Ignition #121-8394

 

After reading back through your posts, I would suggest that you concentrate on the pump cams, squirters and initial throttle blade settings. If it is stumbling right off the line, it probably is not getting enough pump shot. Make sure there is no slack in the arm. Is this a new carb? If not, make sure the spring on the pump lever isn't compressing instead of moving the pump lever. I had this happen on an old, used Holley. A few small shims on the spring solved it. If all of that is good, set up the blue pump cams in the #2 hole and use #35 squirters. This should be a good ball-park setup.

 

My advice would be the EXACT OPPOSITE. Just MO.

Reason being, if the carb's jetting, PV, transition, and all that, were already PERFECT, the pump would be ENTIRELY UNNECESSARY. All it is SUPPOSED TO be, is a "crutch" to "cover up" the inertia-driven lag in fuel delivery behind air flow, since fuel is heavier. A properly calibrated carb ALMOST doesn't need a pump AT ALL.

Furthermore, Holley pumps are MASSIVE HUGE to begin with. For virtually any engine that could be defined however liberally as "streetable", they're WAY bigger than they really need to be.

Therefore, if you THINK the pump needds work, about 99.9999% of the time, it's because the carb isn't right, and there's too much error for the pump to "cover up".

The parts about "initial throttle blade settings" and the pump lever adjustment are right on the money though. I didn't detail how to set the throttle blades, but that's CRITICAL to getting premium operation from a Holley.

The pump lever setting should be, such that with teh pump lever fully depressed by hand and the throttles fully open, there should be about .030" - .050" of gap between the spring & screw thing and the lever. When the throttles are at idle, the lever should be held partway depressed by the screw thing. Under NO circumstances should their be a gap between anything in that system, at idle.

 

I don't look at the pump as a crutch for bad carb tuning...more of a crutch against physics. When you crack the throttle, the air demand is nearly instantaneous. The fuel flows according to a pressure differential. The fuel is heavy and there is friction inside the passages of a carb. This takes time to overcome. The pump shot covers that lag. I don't think you could eliminate it. Anyone who has a vacuum secondary Holley on a drag car knows you have to tread lightly when it comes to opening the secondaries too quickly because there is not enough available pump shot from the primaries to cover that hole. It would be nice to be able to turn the pump shot off during normal cruise and keep it just for the track.

I do agree 100% that a properly tuned carb will put less demand on the pump shot. On my first carb, I thought the hot setup would be 50cc pumps and the biggest squirters I could find. Man, was that car a dog!! you live and learn (hopefully).

 

Right: as I said, the pump is a CRUTCH to cover up the LAG in fuel delivery behind that of air flow, due to its INERTIA.

In a "perfect world", it would be unnecessary; but as we all know, that's wishful thinking. Some amount of it will always be needed, due to the simple physics.

However IMO the pump is THE ABSOLUTE LAST SYSTEM in a carb to tune on, after ALL others (main, power, idle, transition) have been PROPERLY tuned. IOW, tune ALL THOSE OTHER things, and get them as PERFECT as possible, FIRST; THEN AND ONLY THEN, go to work on the pump.

Virtually everybody that tries to immediately jump to hacking on the pump to band-aid improper calibration, INCREASES its delivery. That's a SURE SIGN that something is wrong. Holley pumps as stated are ALMOST ALWAYS too large, except for occasional specialized situations encountered in racing. The street carbs, you could probably take the word "almost" out from in front of "always", and not get made a fool of too often. If a correctly functioning (not broken) street carb on a correctly functioning (not broken) engine seems to need work on the pump, it's a DEAD GIVEAWAY SURE SIGN that the carb needs SOMETHING ELSE calibrated correctly FIRST, after the resolution of which, the pump will probably be found totally adequate if not excessive.

For that reason, the OP needs to focus on lots of other things FIRST before skipping over all the important stuff and jumping directly to the pump. He needs to get rid of the locked-out timing, go to work on the jets and PV as described, get the transition slot right (search the Performance forum at chevelles.com about that, there's a couple of good write-ups over there), make sure the pump linkage is set corrrrectly as derscribed, and THEN AND ONLY THEN start messing with cams & squirters.

 

Will do on the locked out timing.. can you verify a p/n for me on the distributors? And which one would be better(I have msd ignition) but I like that there's a lot of settings to choose from with these 2 distributors but could also be more challenging. My car always is slow off the start do you think this would also improve 60 ft times?

Crane Cams #271-1000-1501

MSD Ignition #121-8394

 

I would recommend the GM performance parts HEI. Why? Low price, appropriate mechanical advance (15* total), appropriate vacuum canister for your type of engine and a melonized gear which should be compatible with your camshaft. It may not look as fancy as the MSD, but I think it is more functional (I have used both). If you buy the MSD, you'll need a different gear, the advance curve tuning kit and maybe a different vacuum canister. With the GM Performance HEI, all I did was change out one advance spring to a lighter one. I also removed the module and use my MSD 6AL to fire it.

The extra timing off idle may help your 60'. I wouldn't count on it though. It will make idling around the pits and stagging lanes much better. It will keep the plugs clean.

 

I might have one laying around somewhere to try and see what that does but I've never really messed with timing curves and such and both cranes and msd's offer a lot of tuning options which I think will be fun to play with. I have bronze gear for my roller cam and I think with their distributors they come with tuning kit

 

lots of good tips here

Carburetor Tuning the Scientific Way
or
How to Tune Your Holley Carburetor
and Other Fuelish Ramblings
By ASE Certified Master Auto Mechanic, Engineer, and Inventor, Gerard Forgnone
http://www.bob2000.com/carb.htm

 

I'd run away from that bronze gear if you put on any street miles. They are considered a yearly maintenance item by racers who do no street miles!

Love the "bob2000" site. Been there many times. Very good reading.

 

Thanks for the site that's definitely a good read.. I don't drive my car enough for it to be considered "yearly maintenance".. I've never had issues running bronze on the street with any other of my roller cammed cars..what would you suggest then for a low 12 second strip/street car?

 

I am surprised you haven't seen any wear. I ran one once and the teeth were definitely thinned out after just a few thousand miles. Racers that I know replace them yearly because the thinner teeth causes the timing to jump around.

The melonized gear that GM uses on all its distributors running on roller cams will work with most aftermarket camshafts. There are also composite gears out there that can be used with all camshaft gears.

 

While it's been a few years since I was into the fast cars(raising a family is EXPENSIVE!!), this was my experience as well. The only car I ever saw then that had locked timing and running on the street, shouldn't have been on the street to begin with.
But hell, it was sure fun watching this guy tear up the asphalt(1967 Chevelle SS; L-88 with M-22 huge slicks, barely fit under the wells.. 4.56's IIRC. Absolutely wicked fast, considering as heavy as it was.

 

This is the 68 SS chevelle I traded for a vega. I race it in pro class and it's treated me pretty good. Same ignition set up as my iroc except this has 6al box instead of 6a. Very fun street car runs 10 70s 468 BBC turbo 350 manual valve body and trans brake. I never have had any problems with this cutting out anywhere I drive it, so what should be so different about my iroc? Besides displacement, there's really not much difference between the two

 

This is the 68 SS chevelle I traded for a vega. I race it in pro class and it's treated me pretty good. Same ignition set up as my iroc except this has 6al box instead of 6a. Very fun street car runs 10 70s 468 BBC turbo 350 manual valve body and trans brake. I never have had any problems with this cutting out anywhere I drive it, so what should be so different about my iroc? Besides displacement, there's really not much difference between the two

 

This is the 68 SS chevelle I traded for a vega. I race it in pro class and it's treated me pretty good. Same ignition set up as my iroc,t except this has 6al box instead of 6a. Very fun street car runs 10 70s 468 BBC turbo 350 manual valve body and trans brake. I never have had any problems with this cutting out anywhere I drive it, so what should be so different about my iroc? Besides displacement, there's really not much difference between the two