HI all, looking for a bit of feedback on next steps to get my updated gen 1 small block running as best possible.

It’s a ‘74 350 block with 30 over dished pistons (with the 4 valve reliefs).

Modifications are:

64cc Dart Pro 1 Platinum 200cc – spring setup for hydraulic flat tappet (max lift 0.52)

Fel Pro 0.041" High Performance head gaskets (part number as suggested by Dart)

Scorpion 1:6 Roller Rockers

Comp XE268H-10 cam, 224 int./230 exh.@ 050, 0.477 /0.480 @ 050 (1:5 ratio), 110 LSA

Performer RPM Air-Gap intake

Edelbrock AVS2 1906 650 CFM Carb sitting on 0.5” phenolic spacer

New HEI distributor, 65k coil, and new 9mm plug wires.

Plugs: NGK FR5 (as suggested by Dart) set at 50 gap based on distributor info

Other Stuff

Melling 55HV oil pump

Carter High Volume mechanical fuel pump

GMB High volume water pump (standard rotation)

New HD cooling fan clutch, and GM later model plastic cooling fan (had to flip fan so it was pulling air)

Running 95 octane, CR estimated to be around 9.5:1



Process thus far,

The mechanical timing has been set at 18 initial, with 36 total mechanical. Running the supplied weights / springs. Full mechanical advance is coming in around 2000 rpm with the standard springs.

Adjustable Vaccum advance at “stock” setting, currently connected to manifold vacuum (as suggested by Edelbrock for longer duration cam)

Initially, the car had a bad stumble / miss, and was running hot 220+

Checked and confirmed that the new water pump is clockwise rotation and turning clockwise, installed a tested 180 degree thermostat

Rejetted primaries to next largest jet and next richest needle, with some improvement, moved pump arm to get biggest pump shot, which has reduced the off idle hesitation. Changing to stiffest step up spring has also helped the transition a bit.

Have backed off the secondary tension half a turn

The car still gets hot over time, runs at normal temp level for around 10 minutes then starts heating up at highway speed (light throttle) and performance degrades a bit.

The plugs look to be around the right range with slight tan discolouration on the back side of center electrode, though they are one grade removed from stock.

But I feel that is likely still running too lean, as I’m not seeing black smoke on mashing the gas, and performance seems a bit weak, though it pulls strongly from 4k to 6k

Seems like the next step are

- Go up to largest main jet

- If some improvement, go up one size on the secondary

- Replace radiator cap

- Reinstall original 7 blade metal fan to compare cooling

I am a bit conflicted on using the ported vacuum for timing, there is so much contradictory stuff out there.

I realise that my trans / converter (700R4 / stock) and tall diff gears (can’t recall if 3.08 or 2.73 now – measured it like 20 years ago!) is not helping, but one thing at a time….

Thinking that I really need to fit an AFR gauge to figure out what is going on, but I look forward to any suggestions from the experienced folks out there.
Cheers.

 

Try closing the plug gap to 35

Try either vac type(ported/manifold) and see what your car likes, there are arguments for either or none.

What type of spacer open or four hole, I'd suggest four hole if it's open.

Do you have an air-dam? AC condensor that's beat up or has junk trapped between it and the radiator?

Does the exhaust route under the oil pan? Didn't see/notice what type of headers you have. Is the muffler or exhaust system restrictive?

Don't know much bout eddy carbs but puff of smoke on the hit is too much pump shot for a holley

 

Your next step is your last comment and that should be to install an O2 sensor and wide band AFR gauge. It will help IMMENSELY.
Add to that a vacuum gauge in the cabin and carb tuning gets a lot easier.

Manifold vacuum can be tricky to dial in. If you're on the threshold of acceptable vacuum for the vacuum advance can you're using, you can get a toggling effect where the timing comes in and out as you hover around the set point. It can be maddening and many give up and resort to ported vacuum.

Speaking of vacuum and overall advance, do you have an idea of what the timing would be at cruise? Initial plus wherever you are in the mechanical curve plus whatever the vacuum advance is supplying. 40 plus at cruise is a reasonable target if the AFRs are right and that would be slightly lean from stoic. This is typical cruiser stuff and doesn't necessarily apply to everyone. If you're really bold and want maximum mpg, going for a lean cruise AFR of 16:1 isn't uncommon with suitable advance to make up for the slow burning lean mixture. 50 degrees isn't unusual there. I've done it but it's touchy.

FWIW, I'm at 16 initial combined with manifold vacuum advance all in at idle for another 14 degrees. At a 2500 RPM cruise, I'm about 12-15 degrees into the centrifugal advance which is providing a total of 42-45. WOT advance, when the vacuum isn't supplying anything, my target is about 34 at 3000.

As for your overheating issue while cruising, it's a typical problem if the factory air dam under the rad support is missing.

 

Sounds like you are still running lean and need more carb tuning. I second the wideband 02 recommendation.

 

HI there, you might have hit the nail on the head regarding the exhaust. I have some old Mr Gasket headers that were ceramic coated about 15 years ago, Unsure on the primary diameter if 1 5/8 or 1 1/2, but yes the drivers side is connected by a pipe running under the pan, behind the cross member. I fitted a new pan as part of the changes which does not have as much clearance as the old one and is making contact. I had planned to take the car into the nearest exhaust shop to get it adjusted once I had it running right. the two sides collect into a single 3" system with a "cherry bomb" muffler, it is pretty rowdy.

The spacer is a 4 hole one, and have checked that the secondaries and primaries can open fully.

I have removed the remnants of the AC system, so there is only the radiator at the front. All of the front end is intact, and unchanged. The old engine setup had no temperature issues at all.

I did replace the hoses with Gates hoses, and discovered when I went to vacuum fill the coolant that the lower hose does not have a inner spring to prevent collapse - and have read posts where this was said to be a must have?

Noted your comment on the plug gap, might close these up a bit.

 

Thanks for the tips, no not 100% sure on the cruise advance. The mechanical seems to come in quickly. but i was having problems getting good consistent RPM readings on my timing light as my plug wires have a thick outer silicon sleeve that is affecting the ability to get a clean reading. Figured out that if I lightly apply some clamping force on the clamp with a pair of vice grips, then I am able to get a better reading. It is running 10" vacuum at current idle. I understand that the stock vacuum advance on this distributor setting is 14 degree's - but not sure on the vaccum required to generate this. I have bought a jegs spring / weight kit to tweak with.

I could do a series of rpm timing checks with vacuum connected and disconnected to confirm, but mindful of noise and neighbours, which complicates things.

 

Yep, l will order one today. Amazon has the AEM one with all the bits for $180 US a lot cheaper than buying local unfortunately. In the interim I might go up a jet size and see what happens...

 

Well that's what I'd try first, bet that crossover pipe is hotter than the oil pan, I'd also change the oil after it's fixed.

You do have a high-volume water pump so that's possible but think it's more of a high rpm issue like circle track, I always underdrive my pumps so don't know.

35 is the gap spec for my 86 Corvette with factory alum heads, HEI and 9.5 comp. Larger gap sounds nice on paper but if the plug doesn't fire then you loose a lot more than a big gap stands to gain. Unless your goal is mileage and don't plan to rpm.

 

Got a chance to work on the car this afternoon. My first thought was to go to the next richest Main jet / rod combination and see how that ran, I also increased the secondary jet two sizes from stock as well while i was in there and adjusted the floats to spec. It is running more consistently through the rpm range now (couldn't see any black clouds behind me) but still running hot. So I dug the old fan out of the parts bin and compared with new plastic one, and even when reversed the new one was clearly different to the old (seems to have been a flawed concept) so I put the old one back in, and the difference was apparent straight away - that is was moving much, much more air, and driving over the same route the car is running between 180 - 190 now. So that looks to have been the main contributor to the cooling issue - will still need to get the exhaust crossover sorted, but at least I can drive it the 60km to the nearest exhaust shop without a melt down!

I'll take the plugs out tomorrow night to check the condition of them, I've got another new spare set sitting there so will gap them to 35 and compare.

In the testing today I also tried running the timing off ported vaccum, it definitely didn't like that at WOT, manifold was much smoother.

I looked at the AFR gauges and saw that a number of AEM one were DOA or died in a short space of time, so think I will go for the Auto-meter Sport comp AFR and Vac gauges, I see they also have a 2 gauge pillar pod for the third gen. Curious to see what people think of these. After pricing it all up, and considering the depleted funds after the build so far, I will need to hold off till next month.

At least I have a driveable unit for now. Thanks for all of the input! Much appreciated.

 

Nice to see some problem solving and getting results. Perfect temps.

At WOT, the vacuum advance doesn't come into play. Neither ported or manifold has any vacuum when the gas pedal is pinned. At least it shouldn't. But you may have uncovered another issue if you're finding problems with the switch.

I've got the AEM gauge. Bought it new about 15 years ago and the gauge itself has worked flawlessly. Now the same can't be said for the O2 sensor. I've gone through a few of those over the years. It seems it's more question of where the sensor is placed and it's general operation conditions. Location-wise mine is in spec but as for operating conditions...maybe not so much.

 

I have an AEM but it's still brand new in the box LOL even think it's an older model. Anyways Innovate is another brand I've herd some about. Still I'm no wide band expert, just rem when looking into them that some have to be recalibrated once in awhile as the actual sensor degrades or w/e

 

The centrifugal advance springs you are using are too light. You get wandering while you are trying to tune.
At least for now, change to slightly stiffer springs - shoot for full advance at 3000 rpm.

The Edelbrock carb does not like to play well with only 10" of manifold vacuum.
If you have a buddy with a 750 cfm version, try it to see what happens to the idle.
If it is better, then you need to swap in the primary metering blocks from a 750 cfm carb, or need to modify yours to be the same.
Jetting changes to the mains are not going to fix this issue.
And with any carb, for the transition circuits to function properly, the primary throttle plates can't be too far open.
If you are there, then air will have to be introduced in some other way - think IAC.

 

Yes there was a significant surge at around 4000 RPM, maybe related to the higher engine temps at that time. I thought I might have mixed up the vacuum lines, but no.

It is basically a one way trip when I have to order product out of the USA, as it is too expensive to return stuff. SO it makes you nervous when you see problems posted in recent reviews....

 

Took out the # 1 plug tonight to check. Well, it's not black and sooty....


Plug # 1 Running largest main jet in tuning kit plus 2 stages up on secondary jets

 

I was surprised that the stock springs were coming in so quick, but figured they would be a good starting point. The jegs recurve kit has a few sets of springs, but assume I have to fit their weights as well to get the stated effect. There are some plastic bushings but no explanation in the instructions regarding what they are for ... more research required...

Unfortunately I don't have any access to a 750 cfm. I agonized over this when deciding what carb to get, heart said to get a 750 cfm (was looking at the street demon originally) but read a lot of published articles about not over sizing carbs and that the 650 was the right size with room for extra rpm. My old carb is a 600 Holley with vaccum secondaries. But now I am wondering if that was the right choice... Was also looking for something as low profile as possible to fit under the hood, with the rpm manifold and 1/2" spacer (to clear the tall valve covers to clear the roller rockers etc etc) I have no hood clearance at all, a matter of a few mm...

 

That seems unusually low given the cam spec and ignition timing.
Have you done a compression test? Very low cranking compression can explain a lot of things especially a low idle vacuum.

For what it's worth, I'm running COMPs XR288HR cam. That's 288 degrees seat to seat timing on the intake. It also has 71 degrees of overlap but even with a very worn shortblock and cranking compression now around 150 PSI, I still manage 10" of idle vacuum (@ 800 RPM).

 

These are the Jegs kit curves, confirmed the bushing purpose from another brands instructions...

So judging by this I will have to either go with the gold spring and maybe knock initial back. But it seemed happy at 18 and even 20 when adjusting the cap back and forth, so I might be better to go to 20 initial and go with the black spring?


Jegs HEI recurve kit

 

No I haven't checked compression. What vacuum would you expect to see? When I first started trying to tune I was getting 14" on the gauge, thinking about it, this was with the line to the ECU capped ( i asked about the purpose of this line in another thread) I hooked it back up to manifold vacuum as I was getting some odd transmission behaviour - and it was suggested that the ecu (not disconnected) may be providing some input to the transmission - although I made some TV cable changes at the same time which may have caused / resolved that issue.

I supposed I should try blocking all vaccum connections apart from the vaccum gauge and see what I get then, and then isolate any one which may be causing a loss. What is the purpose of that little vacuum tank on the firewall? I have disconnected the cruise control system and did an a/c delete on the remnants, so not sure what else it might be used for? any vacuum lines that were disconnected have been plugged.

 

That's more like what I would expect.
I'd be checking all of the possible vacuum fittings to ensure nothing was left uncapped.
Any number of those individual components you've removed from the system may be causing an issue.
And a compression test is invaluable with respect to troubleshooting and tuning.

 

Don't mess with the weights for now. Just do the spring change.

OH, and a power brake booster with a hole in it is a huge vacuum leak. Check that and the 90* inlet one-way valve.

 

Did you reuse the stock balancer and timing cover with timing tab? If you didn't and have a different balancer and/or an aftermarket timing tab what you're reading may not be where you actually are. Best way to check without using a piston stop and degree wheel is to loosen the distributor hold down bolt, still keeping some resistance, but where you can rotate the distributor. Run the engine up to about 3,000 RPM and rotate the distributor back and forth until the engine revs the highest - that'll be within a couple degrees of where it needs to be. Bolt down the distributor, then check the timing. If you get some off the mark (pun intended) high or low timing reading with the timing light, then the timing tab is off.

 

Thanks all for the suggestions. Yesterday I started off with intentions of removing plugs and knocking the gap back a little, and found an as yet unused compression tester in my box of "bought on special" tools for future use.

So, as I was removing the plugs, removed the dipstick and ended up with a dipstick handle without a dipstick attached in my hand! You can imagine my reaction and what was going through my mind at that time!

I tried all sorts of things to extract the dipstick, eg flexi magnet that was able to pass down the tube, but it appeared not to be in the tube. so had to remove exhaust, starter and drop the pan (luckily using one of the one piece neoprene fel-pro gaskets) Couldnt drop it enough to reach in but was able to get a flat led torch in to see through the drain hole, and was able to see part of it, tried a few things to get it out but in the end made a hook out of a bbq skewer and manged to hook it and drag to the hole and latch on to it with some needle nose pliers, twist and then pull it out the drain hole! F'g crazy, nearly screwed by a $20 dipstick. Luckily the stick was intact / coiled up and apart from some minor wear, looks like a lucky escape. Anyway, after redressing the drain plug threads and getting it back together with new oil and filter, and attempting to reshape the exhaust crossover pipe and pan with limited success, got it all back together and back to square 1.

I went to look at doing the compression testing but the way the headers are it is impossible to get straight access to them, really need a two piece system one bit to thread in and then a right angle attachment (not sure if they exist), so I thought f' it and just gapped the plugs to 40 and refitted them (not my best of days).

I had already fitted the jegs curve kit one night during the week using the black spring, as the gold seemed a light. I was not very impressed with the quality and design of the parts. had to file the plastic bushing a lot to get to the same height as the weight thickness and be able to refit the E clips. And when fitted there is more play on the pin than you would expect / like. After messing around with this I thought bugger this an decided my next spend was to get a fully computerized hei distributor from progressionignition.com, and have placed an order for one. You can connect / program it with your phone via bluetooth, plus get a vaccum reading / rpm reading, set rev limit etc - if you haven't heard of them it is worth looking up, you can also disable the distributor from your phone as an anti theft device. So no more springs and weights, just set a map of what you want and away you go - or at least I hope so!

I have also ended up ordering an innovate AFR gauge / sensor and a mounting cup, so in a couple of weeks should have dialled in timing and then some data on AFR to confidently tweak the carb.

In the interim I will go on the hunt for vacuum leaks when I next get time to work on the car.....

 

Will do..

 

Hi there, thanks for the tip. No I got a new 8 inch summit damper with etched timing marks and a 8 inch pointer. When I had the heads off I verified TDC on cylinder one, checked it before and after TDC to confirm, so pretty sure that is ok. Needed to do that to check my valve clearances etc. All quite a learning curve ;-)

 

Good deal. Many miss that step. I’d still rotate around and see where you end up though. It can help determine if your springs are too light and if you have too much advancement dialed into the vacuum pod.

 

Hi All, ready to take the next steps in getting this thing tuned properly.

My Progression Ignition HEI turned up yesterday and installed it last night. As a starting point I used the same settings that i was trying to achieve with mechanical, ie 18 deg initial and slightly reduced max of 34 total. A manifold Vaccum line is also connected and set to 8 deg maximum vaccum advance.

Here is the resulting Map



I took the car for a run tonight and it is running well but with a little less urgency at lower RPM than it had with the last mechanical dizzy setting (jegs weights and black spring from earlier post). But there was no hesitation at all when mashing the accelerator.

My AFR gauge has also arrived. Any suggestions for the best way to route the wiring for this into the cabin? The O2 bung is on the left hand side (Driver side) header. I was thinking to use the speedo cable hole / grommet.

After looking at the suggested tuning changes for midrange punch I am going to apply this updated map after hooking up the AFR gauge. And after that try bringing the all in to 2750 RPM.




Cheers,

 

Got the Innovate AFR gauge installed today, had a bit of time to take the car for a quick run. AT idle (750 rpm) it is running at around 11.1 and when driving it it stayed between this and high 11's, I did notice some peaks of 12.6 , and when applying light throttle at 100kph when it went into the low 14's and on deceleration where I saw it drop to 10.6 , but majority of the time it was in the low - mid 11's .

I forgot to check the vacuum reading on the phone. So will do some more runs tomorrow hopefully, and capture more info and will plug the vaccum lines individually to check for leaks

Forgot to mention I have ordered a new brake booster check valve and grommet and some new hose (seems to be a worldwide shortage on these things). I did notice some readings on the electronic vacuum sensor as high as 17 "Hg while driving the other night after installing the new distributor.

It looks like I should be targeting 12.8 - 13.2 range? So will need to revert some of the jetting / rod changes, pretty much back to the stock settings. Probably a good starting point!

 

Your AFR targets will be different for the various scenarios.
WOT: AROUND 13:1. Some engines make more power on either side of that.
Cruise: I always go for a lean cruise at highway speeds, low load. That's 15:1. I've gone as far as 16:1 with almost 50 degrees of spark advance for best fuel economy.

Here's where the AFR and vacuum gauges really pay for themselves and that's moderate acceleration.
Knowing what the PV value is and being able to monitor engine vacuum and AFR, the onset of the valve opening can be plainly seen. I opened up my PV channel restriction to the point where I can see obvious enrichment. Once the PV is dialled in, part throttle acceleration, without bringing the secondaries into play (on a VS carb), will be very acute, almost is if the secondaries are opening.
It's a bit of back and forth but I've managed to get the PV enrichment to reach WOT values of 12.5.
Easing into the throttle while climbing a hill for example, eliminates the need for a downshift or even kicking out the converter lockup. It's quite something.

 

I got the chance to go for a short drive today after changing the jetting / metering rods. In the end I went from configuration 15 to 11 on chart below, basically 1 stage rich from stock, rather than going full stock and finding it lean, then having to work back.

The AFR gauge is now showing low 12's at idle. But seemed to be varying a lot more than the previous setup when driving. I did a couple of WOT runs it would shoot up to 15 then down to low 10's. Apart from an initial hesitation it would then pull hard all the way through to 6K

ON the vacuum side, at idle it is sitting between 9-10 "Hg at 750rpm, I saw it get up as high as 22 " Hg while driving. Hard to see everything going on whilst accelerating hard in a short timeframe... I blocked each vacuum line but observed no change in idle vacuum reading. Thinking about it now, I did not try blocking the PCV valve line, could this be an issue? The PCV valve is original to the car, I put some new hose on it, and there is a new grommet in the valve covers.

So from the chart below it looks like going back to stock is probably getting closer to ideal. The temperature issues that I was experiencing initially (due to the new fan) seems to have lead me up the wrong path of enrichment.

I currently have the strongest "plain" step-up springs installed, I also have the secondary flap spring tension on the minimum setting - this could explain the spike in WOT, with the flap opening a bit too quickly.

Next step, I'll return everything back to stock settings and reassess.

 

I won't offer any tuning advice on the AVS carb as my experience is very limited. A lot of what I'm blathering about relates to the Holley platform. My apologies for any confusion.

That said, certain things transcend the branding. Tuning the idle for example. A target AFR using the AFR gauge doesn't work as we might think it should. It's handy for a reference but that's about it. Idle is all about achieving maximum engine vacuum at the desired idle speed. Timing at idle is also critically important. I can't tell from your charts what that timing is although it looks to be 18°. Not bad but I wouldn't hesitate to add 5 more keeping in mind the total.

As for the PCV vale, it can absolutely and does have an effect on the vacuum. It is after all really just a metered vacuum leak. Different valves have different operating characteristics too. Once you get into modifying an engine, it may be necessary to look for a valve that's more suited to the new vacuum profile of your car rather than what the OEM had.
There a discussion about that here.

 

Thanks SkinnyZ I appreciate all of the tips you are giving me. I did have to think what PV was lol, and them remembered that the Holleys have power valves. These have an accelerator pump which you can change the stroke using the three different linkage holes. You can also buy a set of different pump squirter nozzles. Which I did think about getting, but just got the kit with jets needles and springs.

Interesting reading about the PCV valve. I pinched the hose going to mine and the rpm dropped noticeably, and ran a bit rougher. DId you end up going with the adjustable one? Your scenario in that thread sounds very similar to mine, in terms of the numbers you were getting.



Today I set everything on the carb back to stock settings, except the pump shot (Stroke) which is still on the max. (primary, secondary jets, metering rods, step-up springs).

AFR still fluctuating but on average seemed higher. High 12 low 13 at idle, When driving it was varying between 11s up as much 15 on initial acceleration. so it has shifted things up the scale by some degree.

When I got back from the return to stock , the idle RPM had increased by 100 RPM, so readjusted the idle air valves for max rpm and then back a tad, then set the low speed idle back to 750 it was idling at low 13 on the AFR after that

Yes, on the current map the base timing is set at 18, with max 34, using an "aggressive" curve ramp, all in at 2750 rpm.

When messing around with timing previously it did seem to idle nice with around 20° initial mech timing (vacuum capped). I'll try upping that and see how she goes.

 

I've ordered a couple of different model PCV (orifice ones) recommended for low vacuum engines and a stock one to take the plastic elbow off, since those 2 don't come with them. I've also received a new compression tester. What is annoying is how nearly all diesel ones have a right angle quick connect fitting, but gasoline kits don't. The one i've got has a short thread in section with a quick connect but the hose section is a straight fitting, not 90 degree. hopefully it will work around the headers...