Compression Help!!

Mike91-5oh · Feb 7, 2017

hey guys,
Wanna start by saying this is my first build. I've owned fox's since I was 17 (30 now) but I've never built my own.

I bought a kenne bell for the fox body 302. But I'm afraid I have to high compression and wanna know what if anything I can change to get the compression down. Here is a list of the internals in my block.

the pistons are Keith Black dome pistons, Eagle Light weight rods, scar light weight cranks. Standard 302 stroke with .60 pistons.

I'm ordering the AFR 185's this week was thinking 72cc. Just curious if i could change the dome pistons and get what o need or is it a lost cause.

Davedacarpainter · Feb 7, 2017

Hey Mike, welcome to stangnet.

Lost cause, heck no!

Though if you do actually have domed pistons that clear your valves, I'd think you'd want to get new ones if you'll be going forced induction. Domed pistons spell high compression.

Start a new thread in the '79-'95 general talk subforum about your intentions. There are lots of guys there that can help you.

A Kenne Bell huh? I think @Noobz347 is probably one of the smartest with that particular blower. Maybe @a91what could help out those his supercharger isn't a Bell item.

Glad you joined us, and don't forget to start a new thread.

a91what · Feb 7, 2017

-Low compression high boost moderate timing.
-low compression low boost high timing.
-high compression low boost moderate timing
-high compression moderate boost low timing...

See where this is leading.... it's all about getting things to even out. Cylinder pressure is what does the damage, it bends rods and cracks pistons.
This can happen even with low compression builds when the boost is cranked up.

Next issue is flame front speed, to make it simple the higher the compression the faster the flame speed. Add boost to that and boom!
To compensate we need to run high octane fuel, or make the flame speed (peak cylinder pressure) happen at the right time. ie... Lower the compression, timing or boost.
I have seen guys run 11:1 with 8psi on 93 octane....... with a total advance of 16* in boost.

First thing I would do in your shoes is find an online calculator to plug your numbers into, find the head volume that will work for you.

Mike91-5oh · Feb 7, 2017

a91what said:
-Low compression high boost moderate timing.
-low compression low boost high timing.
-high compression low boost moderate timing
-high compression moderate boost low timing...

See where this is leading.... it's all about getting things to even out. Cylinder pressure is what does the damage, it bends rods and cracks pistons.
This can happen even with low compression builds when the boost is cranked up.

Next issue is flame front speed, to make it simple the higher the compression the faster the flame speed. Add boost to that and boom!
To compensate we need to run high octane fuel, or make the flame speed (peak cylinder pressure) happen at the right time. ie... Lower the compression, timing or boost.
I have seen guys run 11:1 with 8psi on 93 octane....... with a total advance of 16* in boost.

First thing I would do in your shoes is find an online calculator to plug your numbers into, find the head volume that will work for you.

Thanks a lot! The car will be going to one of two very reputable shops around my part of town, so I was just hoping that what I've heard isn't right. Ppl have told me I can't run the blowzilla without low compression.
I appreciate all the help. Like I said I'm new to the building my own side of it, and learning as I go.

a91what · Feb 7, 2017

That is old thinking. However, if the tune is not correct damage will ensue.

Things get crazy, with this type of setup.

For instance....Intake temps can cause a runaway meltdown.
Going even slightly lean will burn a piston.

Noobz347 · Feb 7, 2017

What size is the Kenne Bell? It sounds like you might already have more motor than blower.

Mike91-5oh · Feb 7, 2017

Noobz347 said:
What size is the Kenne Bell? It sounds like you might already have more motor than blower.

It's the 2.1 if I'm not mistaken. Blowzilla/flowzilla.

Noobz347 · Feb 7, 2017

Mike91-5oh said:
It's the 2.1 if I'm not mistaken. Blowzilla/flowzilla.

Good... If it were a 1.7, I'd try to talk you out of installing it.. Post up pics of it when you have the chance and we can confirm.

Noobz347 · Feb 7, 2017

What's your fuel and spark system like?

Mike91-5oh · Feb 8, 2017

Noobz347 said:
What's your fuel and spark system like?

To be honest, I haven't gotten that far. I bought the bbk fuel rails and braided fuel lines but I was gonna wait until it gets to the shop to buy more components. I'm gonna take the car to Tim lynch at lynch mob racing or Jeff Harris at mo's speed shop. Both guys are known in ga for building mustang pretty well. I just wanted to see if the blower was a lost cause before I went to she shop asking for something that can't be done. I believe either of these 2 guys can set me up with what I need. I have a meeting scheduled next week and will post a update for you guys.
Super glad I joined this forum. I figured I'd get a lot of about being a rookie but y'all were all a big help!!!!

Noobz347 · Feb 8, 2017

You could probably have gotten away with the stock fuel rails but it might have been close.

Other supporting mods necessary to do it right?

42-47 lb injectors
80MM+ Mass Air Flow meter (MAF)
80MM Throttle body
255L High pressure in-tank pump
Boost-a-Spark
Boost-a-Pump
Digital Dyno Tune
Billet Steel Flywheel
Stout Clutch
PCV System Upgrade
Brakes!
Red-Line 50 WT Gear Oil

The MAF doesn't need to be "calibrated" but as a friend of mine pointed out not long ago, "It does make it easier to get the car to the dyno".

I'll holler if I think of anything else.

Oh... Cable quadrant and FW adjuster.

Mike91-5oh · Feb 8, 2017

Noobz347 said:
You could probably have gotten away with the stock fuel rails but it might have been close.

Other supporting mods necessary to do it right?

42-47 lb injectors
80MM+ Mass Air Flow meter (MAF)
80MM Throttle body
255L High pressure in-tank pump
Boost-a-Spark
Boost-a-Pump
Digital Dyno Tune
Billet Steel Flywheel
Stout Clutch
PCV System Upgrade
Brakes!
Red-Line 50 WT Gear Oil

The MAF doesn't need to be "calibrated" but as a friend of mine pointed out not long ago, "It does make it easier to get the car to the dyno".

I'll holler if I think of anything else.

Oh... Cable quadrant and FW adjuster.

Awesome man!! I had planned on 42 lb injectors and the boost a pump, but had no clue about the rest. I can't thank you enough. This is more stuff u can buy before taking it to the shop and having them order. I'll order injectors and boost a pump tonight. Any preference on brand of injectors? I was looking at the detchworks, but I'm open to all input.

This has been a breath of fresh air cuz a few ppl I talked to said compression would make the kb useless and that the kb were to hard to tune due to instant full boost!!
Again thanks for all the input, I had all but given up on the kb!!!

Noobz347 · Feb 8, 2017

I've always bought Ford Injectors but I have no real preference.

They're not hard to tune at all. Make sure that your tuner spends some time on part power tuning along with WOT tuning.

One tip about the BAP and BAS: Don't use the pressure switches. Just find the sweet spot and run them at that voltage continuously. If you're not sure what that means, you will be once they arrive with instructions.

You're also going to have to beat and bang on your firewall seam to get that Flowzilla inlet to fit correctly.

a91what · Feb 8, 2017

Tuning for the instant full boost is easy. It's all in the acceleration enrichment.. or the tpsdot% to be specific. That's the amount of tps voltage change over a set period of time.......
Kinda like tuning the pumpshot on a carb.

Mike91-5oh · Feb 8, 2017

Noobz347 said:
I've always bought Ford Injectors but I have no real preference.

They're not hard to tune at all. Make sure that your tuner spends some time on part power tuning along with WOT tuning.

One tip about the BAP and BAS: Don't use the pressure switches. Just find the sweet spot and run them at that voltage continuously. If you're not sure what that means, you will be once they arrive with instructions.

You're also going to have to beat and bang on your firewall seam to get that Flowzilla inlet to fit correctly.

I'm about to order, the kb , boost a pump . Single 40 amp.
Sound right? Trying to upload a pic but having a hard time getting it to post

Noobz347 · Feb 8, 2017

Yeah... Single for a Fox

Noobz347 · Feb 9, 2017

http://www.stangnet.com/mustang-forums/threads/kenne-bell-boost-a-pump-kb-bap-40-amp.895947/

Mike91-5oh · Feb 22, 2017

Hey guys, just a update. Car will be going to mo's speed shop. To begin assembly. This week. I'm about to order the heads so I guess it will be a little while before we get started. I'm ordering AFR 185's 72cc. The cc's were my main concern but I think 72 is the right call. Open to opinions tho

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