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  1. #1

    Default Next step for V8 performance mods

    I've got a Capri with a 306: AFR 165 heads, aggressive Bullet cam, 9.:1 compression, Performer RPM intake, and Holley 670 Street Avenger carb. The car has 3.22 gears, and weighs 2500 lbs. The engine was balanced, blueprinted, and line bored. Currently, I'm making just over 300 horses at the wheels on a Dynojet dyno. I previously tried out a 600 dp, but after tuning it was still 20 horses shy of the Street Avenger.

    Looking for thoughts on where to go next for a little more power. I have a friend who has a very similar combo, and makes about 320 horses with a 650 dp race-prepped carb. Any ideas? Thanks.

  2. #2

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    Electric fan.

    Full length headers.
    Jack Hidley
    Maximum Motorsports Tech Support

  3. #3
    FEP Power Member Broncojunkie's Avatar
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    Maybe try rejetting that 670 carb, if you haven't already. Invest in a wideband to make it easier. Also, a lower gear might get you in your power band more quickly...not to mention coming outta the hole a lot harder.
    79 Pace Car - 331, t5
    79 Pace Car- 302, 4 spd
    79 Cobra - working on 351w, t5
    82 Capri- working on 302, t5
    82gt - working on 408w, c4

  4. #4

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    Quote Originally Posted by Jack Hidley View Post
    Electric fan.

    Full length headers.
    I already have an electric fan. Looking into full-length headers, but the car is pretty low to the ground. I don't know if i can make them fit

  5. #5

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    Quote Originally Posted by Broncojunkie View Post
    Maybe try rejetting that 670 carb, if you haven't already. Invest in a wideband to make it easier. Also, a lower gear might get you in your power band more quickly...not to mention coming outta the hole a lot harder.
    The car has been tuned on a dyno, with over 50 pulls on this combo. I have a wideband that I hope to install sometime soon. Looking into a lower gear, but debating with myself how it's going to impact highway driving. I go to events that are sometimes 6-8 hours away. I have a T5-Z trans. Currently, the car runs at about 2000 rpm at 70 mph.

    Thanks for the replies

  6. #6
    FEP Power Member Broncojunkie's Avatar
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    Quote Originally Posted by 6for2 View Post
    The car has been tuned on a dyno, with over 50 pulls on this combo. I have a wideband that I hope to install sometime soon. Looking into a lower gear, but debating with myself how it's going to impact highway driving. I go to events that are sometimes 6-8 hours away. I have a T5-Z trans. Currently, the car runs at about 2000 rpm at 70 mph.

    Thanks for the replies
    If it has been tuned on a dyno, then disregard my suggestion. I'm presuming the carb and timing are good. It still seems a little low on power for that combo, though...especially through a t5. At what rpm did it hit peak hp?
    79 Pace Car - 331, t5
    79 Pace Car- 302, 4 spd
    79 Cobra - working on 351w, t5
    82 Capri- working on 302, t5
    82gt - working on 408w, c4

  7. #7

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    Quote Originally Posted by Broncojunkie View Post
    If it has been tuned on a dyno, then disregard my suggestion. I'm presuming the carb and timing are good. It still seems a little low on power for that combo, though...especially through a t5. At what rpm did it hit peak hp?
    I agree that the power seems a bit low. The carb is good. The timing is set at 12 BTDC and has a total of 34-36 degrees. Running an MSD 6AL Digital with one of their HVC coils and an MSD distributor. Basic Autolite plugs, gapped at .045"Name:  2016-05a dyno.jpg
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    The blue line on the dyno sheet is my car

  8. #8
    FEP Power Member Broncojunkie's Avatar
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    You might have a little bit of a bottle neck somewhere. Seems like your intake, heads, and cam should be enough to make decent power. So maybe I should be asking about your exhaust. What do you have? Stock headers and cats?
    79 Pace Car - 331, t5
    79 Pace Car- 302, 4 spd
    79 Cobra - working on 351w, t5
    82 Capri- working on 302, t5
    82gt - working on 408w, c4

  9. #9

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    Quote Originally Posted by Broncojunkie View Post
    You might have a little bit of a bottle neck somewhere. Seems like your intake, heads, and cam should be enough to make decent power. So maybe I should be asking about your exhaust. What do you have? Stock headers and cats?
    Could be, but I don't think it's exhaust. I have 2.5" custom duals, with high-flow mufflers. I previously had some "bullet" mufflers. When I removed those, and replaced them with the current mufflers I gained 25 horses on the dyno. The headers are BBK shorties

    I feel like the carb is holding the car back, but IDK. It looks pretty good on the top end, and it should certainly be big enough for a 306. I'd like to try a prepped 650 dp, but they are pretty expensive. I have a standard 4777 lying around, but I got it as a pile of parts, and even after rebuilding it, it won't idle. Maybe the baseplate is wrong or something.

    I'm not opposed to different heads. I debated with myself quite a bit when I selected the AFR 165s about ten years ago. Moving to AFR 185s would mean fly-cutting the pistons, though. Not a simple swap.
    Last edited by 6for2; 08-30-2019 at 09:13 AM. Reason: addition

  10. #10
    FEP Power Member Broncojunkie's Avatar
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    You have any buddies with a carb you can borrow? I guess I'm lucky. A good friend lives just a few houses away and had a couple extra carbs. That's how we finally diagnosed a carb issue on my pace car a while back.
    79 Pace Car - 331, t5
    79 Pace Car- 302, 4 spd
    79 Cobra - working on 351w, t5
    82 Capri- working on 302, t5
    82gt - working on 408w, c4

  11. #11

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    Quote Originally Posted by Broncojunkie View Post
    You have any buddies with a carb you can borrow? I guess I'm lucky. A good friend lives just a few houses away and had a couple extra carbs. That's how we finally diagnosed a carb issue on my pace car a while back.
    Yeah, most everyone I know runs EFI. I will give another shot to reubuilding my dp. Have to find a list of part numbers to make sure that the baseplate matches up with the carb. Also, since it was just parts in a box, I don't know what baseplate gasket to use from the rebuild kit. No old gasket to match up.

    What timing to you run for initial and total?

  12. #12

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    What are the cam specs?

    I think that the biggest thing holding the engine back is the lack of CR. Aluminum heads conduct heat out of the combustion chamber much better than iron heads do, so you need about 1 point more static CR with them. With 92 octane gas this means that the CR should be 10:1. With your current CR, you could probably run the engine on 89 octane fuel without any problem. You can not compensate for the lack of CR with more ignition timing. This is a common misconception.

    With the 306 displacement, I would not use 185 heads. The car will lose a lot of low end power. It will gain top end power, but overall it won't have any more area under the curve and it will be much slower in normal driving.

    With an E303 cam, 10:1 CR, EFI on a 320, we made about 340hp with milled 165 heads.
    Jack Hidley
    Maximum Motorsports Tech Support

  13. #13

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    Quote Originally Posted by Jack Hidley View Post
    What are the cam specs?

    I think that the biggest thing holding the engine back is the lack of CR. Aluminum heads conduct heat out of the combustion chamber much better than iron heads do, so you need about 1 point more static CR with them. With 92 octane gas this means that the CR should be 10:1. With your current CR, you could probably run the engine on 89 octane fuel without any problem. You can not compensate for the lack of CR with more ignition timing. This is a common misconception.

    With the 306 displacement, I would not use 185 heads. The car will lose a lot of low end power. It will gain top end power, but overall it won't have any more area under the curve and it will be much slower in normal driving.

    With an E303 cam, 10:1 CR, EFI on a 320, we made about 340hp with milled 165 heads.
    The compression ratio might be a little higher. Need to check. The cam card has gone missing, but it's pretty aggressive. I used to run a B303 cam, and the current cam is higher lift and longer duration than the alphabet cam.
    Last edited by 6for2; 08-30-2019 at 10:55 AM. Reason: too many words

  14. #14

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    Too much valve overlap and not enough compression? Curious to know the results of a compression test. Induction seems to be all pretty good parts. Really need to know the cam specs.

  15. #15

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    Quote Originally Posted by 99GTMichael View Post
    Too much valve overlap and not enough compression? Curious to know the results of a compression test. Induction seems to be all pretty good parts. Really need to know the cam specs.
    Could be. I'll try to run a compression test over the weekend. I wish I had the cam specs. I looked everywhere for the card.

    Interestingly, the head build sheet says that the combustion chambers are 61cc. Seems like what I see out there are 58 cc or 72(?) cc

  16. #16
    FEP Super Member erratic50's Avatar
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    Seems like a low overall timing number. An AFR head usually likes a lot more timing advance than that starting around 2500 RPM .... AFAIK.

    I would expect more based advance. Heck even an E6 high swirl head will allow 13.5. Many people report as much as 16 base with an E7 but I always question their timing marks in those instances.

    Still a working distributor should add around 26 degrees of advance and should ramp it in pretty quickly. Combine 13.5-14 degrees of base advance and you end up at around 39 - 42 all in. That's often where guys end up at in order to get the power that motor can make out.

    Obviously you can't run too rich or too lean if you want the power.

    Most guys AFAIK shoot for a healthy fat power mixture. If I remember correctly, the dyno results usually show that at around 12.5 when compression is around 9. Oh. ..... and they also usually bitch about wanting more compression or some damn boost!

    If your compression is higher, you might see the need for less timing advance of course.

    Oh -- and obviously my comments are regarding premium fuel, not 87 octane and not ethanol blended.

    Do you know if your cam is advanced or retarded and what your rocker ratio is? Having a cam that's not set where it needs to be can make all the difference in the world power output wise.


    Your combo would benefit a TON from a FTI custom cam targeting best power and torque average from 1200-6500, or even 7000. If you put good rod bolts in the bottom end there's no reason a 3" stroke motor can't spin to 7000 or even a little beyond.

    Hell -- Kasse spun a factory shortblock 302 to 7600 during his pulls. Damn impressive power numbers considering the rest of the combo too!
    http://www.mustangandfords.com/how-t...cylinder-heads

    Good luck picking up power!
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  17. #17

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    Quote Originally Posted by erratic50 View Post
    Seems like a low overall timing number. An AFR head usually likes a lot more timing advance than that starting around 2500 RPM .... AFAIK.
    ................

    Do you know if your cam is advanced or retarded and what your rocker ratio is? Having a cam that's not set where it needs to be can make all the difference in the world power output wise.

    Your combo would benefit a TON from a FTI custom cam targeting best power and torque average from 1200-6500, or even 7000. If you put good rod bolts in the bottom end there's no reason a 3" stroke motor can't spin to 7000 or even a little beyond.
    Good information there. The cam was installed "straight up". I'll add some timing and see if that livens things up. All of the internal parts are high quality. On the dyno, the power curve was still going up (slightly) where the operator lifted.

    I'll look into another custom cam. I really want to know the specs of what I'm running.

    Thanks!

  18. #18
    FEP Super Member erratic50's Avatar
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    Some of the older 5.0's called for less gap because they ran a colder plug. If you combine a "normal" plug (spec for 87-93) with the tighter gap you'll get some really hot spark which can cause problems. You can mistake preignition for knocking or detonation and end up pulling timing, etc.

    LMR has a post about plug temps and gaps on these cars -- not sure its entirely accurate but off the top of my head it looks pretty darn close if its not.
    https://lmr.com/products/79-93-fox-b...plug-gap-specs

    Sadly you are running into a situation where the "performance" ignition parts ..... "the good stuff" is not yielding even the performance that IMO you should see from good working OE stock stuff.

    Heck -- there are articles out on the web showing a stock 5.0L long block with nothing more than good induction and exhaust paired up with a stock HO cam and 1.7:1 rockers and AFR 165 heads kicking out over 400 HP at the crank. Throw a cam thats making more than 0.475 lift and more than 220 duration and you should be able to easily beat that number.

    We've all seen examples of factory ignition parts on these cars being entirely capable of even lighting off a considerable shot of NOS or enough boost to split the blocks. It isn't until needs like a two-step are factored in that I tend to start looking towards an aftermarket ignition part for anything -- maybe that's just me.

    I found a copy of a 50 state ignition stickers posted online for an 88 cali car. It said 0.054-0.056. They used the same components as the rest of that period of cars.

    Double check your plug temperature ratings and gap together because when you tighten up the gap it runs the plugs hotter and can cause preignition and loss of power. (especially when looking at power adders but that's a topic for another day)

    My best advise beyond verifying your timing curve and coil strength -- both steps that are reasonable -- is to make sure you have the right gap for the right temperature of plug.

    Personally I've always seen better performance from the 87+ "hotter" plugs with 0.055 gap than the "cold" plugs at 0.045, but I've also seen them not like to start quite as easily when cold outside if you do that on a non-EFI motor. No big deal really IMO.

    See what the ignition supplier says about heat range and gap on the plugs because different ignition changes a lot of stuff.

    I would run as warm of a plug as I can get away with while avoiding preignition. More gap can yield a better flame front as long as its intense enough to light it off readily. This is true even on factory style ignition setup. Compression does have a big influence on this of course.

    I've seen examples where I've let my plugs wear even up to 0.080. The car stilled ran OK, except for an occasional miss at idle. Of course when I swapped out plugs and got them back down to 0.055 the car acted like a completely different car.

    Here's hoping you can find some power in here somewhere!

  19. #19

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    On the subject of ignitions and power measurements.

    I completely agree that 100% stock ignition parts on these engines will work n/a up to 10:1 CR with absolutely zero problems.

    I did some experimentation with plug gap range. You can get a little bit more power if you start with a 0.055" gap and use less initial timing compared to using a 0.035" gap and more timing. With the larger gap, the flame kernal doesn't have to grow as much to ignite all of the a/f mixture in the chamber, so you can use less ignition advance. This ends up making more power because there is less negative torque happening before TDC. The difference was so small, that I don't think it is worth doing.

    When you dyno the engine, have them turn smoothing way down or off. Smoothing a measurement hides information that can be really useful. For example, make 5 pulls with no changes and see if the curves overlay. If there are spikes in the upper range, that change (move around) with every pull, that could be an ignition problem. If the valves float, this will be hidden also.
    Jack Hidley
    Maximum Motorsports Tech Support

  20. #20

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    Quote Originally Posted by erratic50 View Post
    Some of the older 5.0's called for less gap because they ran a colder plug. If you combine a "normal" plug (spec for 87-93) with the tighter gap you'll get some really hot spark which can cause problems. You can mistake preignition for knocking or detonation and end up pulling timing, etc.

    LMR has a post about plug temps and gaps on these cars -- not sure its entirely accurate but off the top of my head it looks pretty darn close if its not.
    https://lmr.com/products/79-93-fox-b...plug-gap-specs

    Sadly you are running into a situation where the "performance" ignition parts ..... "the good stuff" is not yielding even the performance that IMO you should see from good working OE stock stuff.

    Heck -- there are articles out on the web showing a stock 5.0L long block with nothing more than good induction and exhaust paired up with a stock HO cam and 1.7:1 rockers and AFR 165 heads kicking out over 400 HP at the crank. Throw a cam thats making more than 0.475 lift and more than 220 duration and you should be able to easily beat that number.

    We've all seen examples of factory ignition parts on these cars being entirely capable of even lighting off a considerable shot of NOS or enough boost to split the blocks. It isn't until needs like a two-step are factored in that I tend to start looking towards an aftermarket ignition part for anything -- maybe that's just me.

    I found a copy of a 50 state ignition stickers posted online for an 88 cali car. It said 0.054-0.056. They used the same components as the rest of that period of cars.

    Double check your plug temperature ratings and gap together because when you tighten up the gap it runs the plugs hotter and can cause preignition and loss of power. (especially when looking at power adders but that's a topic for another day)

    My best advise beyond verifying your timing curve and coil strength -- both steps that are reasonable -- is to make sure you have the right gap for the right temperature of plug.

    Personally I've always seen better performance from the 87+ "hotter" plugs with 0.055 gap than the "cold" plugs at 0.045, but I've also seen them not like to start quite as easily when cold outside if you do that on a non-EFI motor. No big deal really IMO.

    See what the ignition supplier says about heat range and gap on the plugs because different ignition changes a lot of stuff.

    I would run as warm of a plug as I can get away with while avoiding preignition. More gap can yield a better flame front as long as its intense enough to light it off readily. This is true even on factory style ignition setup. Compression does have a big influence on this of course.

    I've seen examples where I've let my plugs wear even up to 0.080. The car stilled ran OK, except for an occasional miss at idle. Of course when I swapped out plugs and got them back down to 0.055 the car acted like a completely different car.

    Here's hoping you can find some power in here somewhere!
    That's really interesting. The dyno guy, who used to road-race a 5.0 Mustang, has always insisted that I not use more than .045" plug gap. I'll read that LMR post. Opening up the spark plug gaps is pretty cheap, lol. I would like to give that a shot.

    The current plugs are Autolite 3924. Looks like that's a direct crossover for what LMR recommends for aluminum heads.
    Last edited by 6for2; 08-31-2019 at 10:24 AM.

  21. #21

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    Quote Originally Posted by Jack Hidley View Post
    On the subject of ignitions and power measurements.

    I completely agree that 100% stock ignition parts on these engines will work n/a up to 10:1 CR with absolutely zero problems.

    I did some experimentation with plug gap range. You can get a little bit more power if you start with a 0.055" gap and use less initial timing compared to using a 0.035" gap and more timing. With the larger gap, the flame kernal doesn't have to grow as much to ignite all of the a/f mixture in the chamber, so you can use less ignition advance. This ends up making more power because there is less negative torque happening before TDC. The difference was so small, that I don't think it is worth doing.

    When you dyno the engine, have them turn smoothing way down or off. Smoothing a measurement hides information that can be really useful. For example, make 5 pulls with no changes and see if the curves overlay. If there are spikes in the upper range, that change (move around) with every pull, that could be an ignition problem. If the valves float, this will be hidden also.
    Excellent. We just had a dyno day last month, but it was 95 degrees, and the car was down ten horses from her best. Next trip out, I'll give this a shot.

  22. #22
    FEP Super Member erratic50's Avatar
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    Be sure to read your plugs while they are out. Fuel starvation or running too rich can definitely influence performance also.

    Sometines people mistakenly drop timing instead of adding fuel

    those parts should produce more than you are seeing.

    what do other combos do? Is everyone seeing vastly lower than expected results?

  23. #23

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    Quote Originally Posted by erratic50 View Post
    Be sure to read your plugs while they are out. Fuel starvation or running too rich can definitely influence performance also.

    Sometines people mistakenly drop timing instead of adding fuel

    those parts should produce more than you are seeing.

    what do other combos do? Is everyone seeing vastly lower than expected results?
    The dyno sheet (above) shows that the fuel is OK in the higher-rpm area. The plugs looked fine when they were out. I took a pic of one. And I agree: this combo is under-performing. I'm honestly at a loss. Yes, another cam might awaken a few missing ponies, but it just seems like with everything as-is, it should be giving me more. Do you think that the Street Avenger could be the problem?

    Name:  IMG_20190831_111546169.jpg
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    Last edited by 6for2; 09-02-2019 at 07:18 PM.

  24. #24

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    As a general note on reading plugs on a carbed engine, you need to key the engine off, immediately after your WOT run or whatever you are testing for. If you don't, the plug color will get changed by the idle or part throttle mixture that happened right before the engine was turned off.
    Jack Hidley
    Maximum Motorsports Tech Support

  25. #25

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    Quote Originally Posted by Jack Hidley View Post
    As a general note on reading plugs on a carbed engine, you need to key the engine off, immediately after your WOT run or whatever you are testing for. If you don't, the plug color will get changed by the idle or part throttle mixture that happened right before the engine was turned off.
    For sure. This pic just shows that the plugs are clean, and not fouled out.

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