Performance questions - HELP....

[Snak Iyz]

Thanks in advance for anyone that can offer insight into my following description. Also, I am professed novice and mechanically challenged when it comes to this stuff, so please don't be afraid to provide as much detail as possible or let me know if you need additional information.

Under the hood: Stroked 351W to 392. Carb is Holley 80870 double pumper, downjetted to 70 primary/ 72 secondary. There was no timing pointer installed, so I think this may be the or one of the problems in getting everything dialed in. My shop is working to get a pointer installed and diagnose from there. Initially was set for 18 degrees up to 38 degrees. Without the pointer though, these could have been wrong.

Problem: Upon easy acceleration everything is fine. With more heavy and even aggressive acceleration there is a 'slight pause' at the beginning of every gear. It grabs then pauses and then grabs again and does fine from there. In addition to the initial pause, under steady acceleration, cruising in 3rd or 4th gear, there seem to be slight spurts. These are not big jolts, but just little 'hiccups' you can feel through your gas pedal foot. It is not smooth.

My new shop is telling me they think the carb is too big for the engine, but they do not seem completely sure. My builder down in San Diego says he puts 870's on these kind of engines all the time. Definitely need your input on this area.

I feel like I am not getting near the horsepower and pull I should be getting, although I have not had it dynoed yet. Suffice it to say, it seems difficult to try and break the rear tires loose with acceleration as opposed to a high RPM rev and letting the clutch out.

Hope this offers enough info to gain your opinions. Thanks again for any help. Feel free to contact me via cell, if it is easier than typing out an answer - 949.466.9746.

[Big-Foot]

I had a similar problem with a customer car.

Turned out to be a missing (broken) ground wire from the breaker plate in the distributor to the distributor body.

You don't indicate what type of ignition you have, but I would make sure that the engine is well grounded to the chassis.

[Clois Harlan]

Go down to 68 jets and 70. Check for a vacuum leak.

Clois

[Snak Iyz]

Randy - I have an MSD 6 ignition.

Clois - Given your recommendation to downjet more, if that does not work, is the carb too big OR do I downjet further...? Obviously don't want to run it too lean........

Thanks to both of you for the feedback.

[Bill Wells]

snak iyz...not sure how different your 392 stroker is to a ford racing svo 392 stroker, which i have.

the engine specs for my engine said 750 carb minimum. i have a custom 'pro systems' built holley 780 on my stroker, with 73 primary's and 82 secondary jets. mechanical secondaries, no choke. msd ignition. timing is at 32 degrees at 4000 rpm, per engine hot test spec sheet. i have had it on a chassis dyno for tuning and the jets were right on for air/fuel ratio and best performance settings and timing , at 32 degrees , was the best for maximum power. every time we changed something, the numbers went backwards. the beauty of a chassis dyno, takes the guess work out of it and gives ya something more meaningful than seat of the pants guesstimates.

started out with a 1/4" heat spacer under the carb and switched to a 1" spacer which added 17 rear wheel horsepower and same torque increase.

if you have a chassis dyno nearby with a good carb guy ( unless you have that expertise) i suggest having it tuned to determine which jet sizes and what timing is optimal for your engine. forget whatever hp / trq numbers you get on the print out, just use it for directional tuning, ie, which settings / changes improves the numbers vs reversing them.

Bill

[dscott]

I wouldn't even drive the car unless you can get it timed properly. How could they know where they set the timing without a pointer. All they could do is guess. Timing will cause a hesitation and slight spurts as you describe. After the timing is set then you can get into carb and such. Accelerator pump not adjusted properly will cause a slight hesitation. Without proper timing you could easily melt down the engine.
Don

[Big-Foot]

Hi Paul,

Okay - MSD-6, but what do you have for a distributor?

[Snak Iyz]

Off the top of my head, I think it is the MSD Billet..... Car is at the shop still so I cannot go out to the garage and peek.

thanks!!

[Big-Foot]

Hmmm.... There have been a couple of cases where MSD wired the hall effect trigger backwards on the plug (two wires - swapped) and this causes the ignition to trigger late in relationship to the postion of the rotor. It's not hard to check it out.

[Curt C.]

Like Don Said. You must know the timing is right. Then start looking at the carb. You may have 50 degrees or 15 degrees

[Snak Iyz]

Thanks to everyone for the feedback. I am sure the shop guys eyes were rolling when I started to ask these questions. Between the things the shop will check and others I can do myself, you guys have been helpful.

Keep 'em coming if there are any other possibilities.

Again, many thanks!!!