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It all has to do with quench-the distance from the top of the piston to the flat part of the combustion chamber. The advantage of a tight quench is that it cools the compressed charge in the combustion chamber to prevent pre-ignition by turbulence. .040 or so is considered ideal in most cases.

Quench causes turbulence in the combustion chamber as the piston comes up to TDC. "Good" quench reduces an engines tendency to ping. Also, the space is so small in cannot support combustion, this reduces the tendency to ping.

Being too much above .060" can lead to some serious issues. Roughly over .060"-.080", the advantage of the quench effect stops. Too large of clearance, not enough turbulence, too little, too fast=no cooling effect. The flame front starts at the plug and proceed outward, an expanding ball of fire. That expanding ball of fire supercompresses the remaining unburned mixture. If the remaining unburned mixture reaches it's flashpoint and ignites before the flame front reaches it, you have ping.

How big a deal it is for a particular motor depends on how close to detonation that motor is in the first place. If it's not close, quench doesn't matter that much. If you're on the raged edge, it's real important.

My first 393 had 9:1 compression with 62 cc heads and the pistons were .030 in the hole. It required 93 octane fuel or else it would ping to high heaven. A cam change would certainly have helped and that and race gas might be the only way you will be able to crutch your motor if you decide to continue with the build. No guaranties though.
 

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My first 393 had 9:1 compression with 62 cc heads and the pistons were .030 in the hole. It required 93 octane fuel or else it would ping to high heaven. .
I had a 306 with the same specs and the same results...I could never figure out why it needed premium fuel until I tore it down and saw the pistons so far down in the hole.
 

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Discussion Starter #23
It all has to do with quench-the distance from the top of the piston to the flat part of the combustion chamber. The advantage of a tight quench is that it cools the compressed charge in the combustion chamber to prevent pre-ignition by turbulence. .040 or so is considered ideal in most cases.

Being too much above .060" can lead to some serious issues. Roughly over .060"-.080", the advantage of the quench effect stops. Too large of clearance, not enough turbulence, too little, too fast=no cooling effect. The flame front starts at the plug and proceed outward, an expanding ball of fire. That expanding ball of fire supercompresses the remaining unburned mixture. If the remaining unburned mixture reaches it's flashpoint and ignites before the flame front reaches it, you have ping.
First of all, brilliant explanation! I never knew the actual science of what happens during a ping, so thank you!

Next, if being much over .060" starts to negatively effect quench, why do they sell head gaskets that are well over that? I have a feeling the answer has something to do with dome pistons. How is quench measured on a dome piston?
 

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Discussion Starter #24
Alright guys here's what I got, I'm looking at a few different pistons and I want to know what y'all think. I've punched everything in and tried to have all the information together in a presentable manner. Note the compression ratio highlighted in yellow (lower left corner) and quench height (upper right corner)

#1


#2


#3


#4


#5
 

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What will be the usage of the car? What octane gas would you tolerate buying? Willing to buy a custom cam to tie it all together?

My opinions:

For street/strip I would prefer something around 10.5 compression and if the right cam is chosen, it would use 92-93 octane.

Of all your choices I would probably go with #3 and use a .050" head gasket which is about 10.74 compression with your heads. Although the .062" quench is border line of the preferred range, it isn't crazy. This combo would work quite well with the right cam.

Not so sure of the funky looking Icon piston. IMHO the added step looks like the makings of some combustion hot spots. I am also wondering how thick the piston to ring land is on the intake valve side as it appears to be cut off there.

For mostly street and a heavy car the #5 option would be a good choice. Using a slightly thinner head gasket would up the compression a smidgeon. I suggest not going less than .035" thick. I would verify PTV clearance to verify that the thinner gasket can be installed.
 

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Discussion Starter #26
It's going in my 69 coupe. It's going to be street/hopefully with more strip car. I definitely want to run it on 93 octane pump gas, and maybe an occasional "special blend". As far as the cam goes:



I was leaning toward #3 also.

I thought the Icons looked pretty funky also. Definitely looks like it's prone to hot spots.

The goal for this build is to build a really solid, reliable bottom end and eventually swap out the heads, cam, valvetrain, etc. I think we all know how it goes..

As always Dennis, thanks for the input!
 

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Although I will admit that I don't know crap about choosing a proper cam for a given combination, I feel that the Lunati cam is quite a bit on the small side for a performance 408.

Hopefully someone will jump in and give you a recommendation that would work well with you chosen combo.

Otherwise, I suggest that you contact a cam specialist (not necessarily a manufacturer's tech line) and have them make a recommendation. It will cost a little more, but is generally worth it in the long run.
 

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Discussion Starter #28
It is a little on the small side for a 408. I've got a few more to choose from in the shop but I'm going to stick with this one for now, strictly because of funds. They would require new roller lifters, springs, push rods, etc. That's all going to be in the near future.

So it looks like piston Option #3 is out of stock and will take 6+ weeks to drop ship...figures. However, I am looking at Option #5 with a thicker .060 head gasket to get me closer to the 10.9:1-11:1 range and still keeping it under .060 of quench.
 

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I am looking at Option #5 with a thicker .060 head gasket to get me closer to the 10.9:1-11:1 range and still keeping it under .060 of quench.
Increasing gasket thickness will decrease compression. Are you talking about a different option than #5?

Option #1 is listed as a Chevy piston. The SRP 4032 is not as robust and forgiving as the 2618 material. I have 5 burnt pistons to prove it.
 

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Discussion Starter #30
Typo! I meant I was leaning toward Option #1, but if you've already burned up 5 of those kind, I'm not so sure now...

Back to the drawing board..
 

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Discussion Starter #31
Back from the drawing board..
After months of waiting for the machine shop to try and order me a set of custom pistons, I've decided to take Willy and other's advice and get a different set of heads.

Originally, I wanted to re-use the AFR 185's I already have but after re-reading through this thread, a 70cc chamber and an .061 gasket will get me just below 11:1. So this leads me to my next question...

I've been looking at these heads:
#1 Trick Flow® High Port® 240 Cylinder Heads for Small Block Ford TFS-5171T018-C02 - Free Shipping on Orders Over $99 at Summit Racing

#2 AFR 220cc SBF Outlaw Race Heads 1456 - Free Shipping on Orders Over $99 at Summit Racing

#3 AFR 205cc SBF Renegade Race Heads 1458 - Free Shipping on Orders Over $99 at Summit Racing


What are yall's thoughts?
 

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Are you reusing headers? Probably need custom headers for the big boys.. The AFR heads should be a little easier and cheaper to find an off the shelf header that will fit your chassis and fit the heads properly.
 

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What is your trans?


GOAL

Ok, this is a bit complicated.

"I've got 4.30 gears and a 27" tire. As for the cam, its a fairly mild"

"I's going to be street/hopefully with more strip car."

"It is a little on the small side for a 408. I've got a few more to choose from in the shop but I'm going to stick with this one for now, strictly because of funds. They would require new roller lifters, springs, push rods, etc. That's all going to be in the near future."

You need to determine your exact ultimate goal . . swapping heads and cams at a later date complicates things . . if you swap to 70 cc heads then imo, the heads you are looking at are a bit too big for your current cam choice . . if you are absolutely positively going to switch to a bigger cam later than get the big heads but smaller heads will run better overall with that cam.


CUSTOM PISTONS

If you want custom pistons just call Racetec and ask for Randy and tell him Mustang Mike sent you . . They might be around $600.00 without rings and might take 3 weeks and they are high quality . . The owner was half owner of JE pistons where Randy worked for many years.

RaceTec & AutoTec Pistons specializes in custom pistons for Sprint Cars, Dirt Modified & Dirt


CAM

That lunati price is a little high for a flat tappet cam . . you can have Chris Straub make you a custom cam that will be best matched to your app for only $275.00 which obviously is only a paultry $95.00 more.

http://www.straubtechnologies.com/contact-us/


GEARING

With that gearing, you can run a big ass cam and pretty big heads . . if you want a nasty idle and a wicked fast car, that is what i would do.


COMPRESSION

In general, the bigger the cam, the more static compression it requires, therefore if you get the compression optimal for a wimpy cam, it will likely be as high as it could be for a big cam . . it could easily be .5 point or more less than you could run and compression increases power everywhere in the rpm range.

You could always run a little less compression now in anticipation of installing a bigger cam or you could run as much as you can now and remove your heads and mill them if the new cam needs more compression than you previously had.


GEARING

is there a particular reason you went to 4.30 gears . . those are certainly fun with an engine that revs but are a bit low for a street car even with overdrive . . if your not set on those then may think about some 3.91's.


HEADS

Popular heads for BIG power at high rpm are afr 205 and trick flow 11r's . . The only 70 cc 11r' heads they have are 225 which will work well with a big cam and high rpm

The smallest heads i would use for impressive power so to speak are the AFR 195 heads . . Very few people even look at these because they think that bigger is better but these flow around the same as the 205 heads but with higher velocity.


Trick Flow 225 high exhaust port . . These may require custom headers so call and ask.

http://www.trickflow.com/parts/tfs-5171t013-c01


AFR 195 CC P/N 1383

http://www.airflowresearch.com/index.php?cPath=21_128


HEADERS

As frdnut mentioned, you will need big tube headers for bg heads to get the most out of them . . with a big cam and big heads, i would use 1 7/8 tubes . . for your 185 heads and that lunati cam, i would use 1 3/4 tubes.

The best deal on headers is hedman elites.


INTAKE MANIFOLD

If you plan to drag race it and don't care that much about bottom end performance, I would definitely run an open plenum intake like a VICTOR JR. . If you want good power down low with just the occasional drag run, I would get the ubiquitous Eddy Air Gap.


CARBURETOR

You need to decide if you want mechanical or vacuum secondaries . . With a big cam and big heads you will need a 750 at the very least . . With your AFR 185 heads and Lunati cam, you could get away with a Quick Fuel vacuum secondary 680 cfm carb.


COMBOS

For more of a street oriented car that still hauls ass, the combo below is just one of several that works really well and will work well with your gearing and down to 3.73 gears.

AFR 1383 195 CC HEADS

EDELBROCK AIR GAP OR RPM INTAKE

TRICK FLOW 750 VACUUM SECONDARY CARB WITH A LIGHT SECONDARY SPRING

CAMS

http://www.lunatipower.com/Product.aspx?id=1670&gid=289


This works well in 408's but I would call comp cams and ask them what they think about making it with a 112 or 112.5 lobe center.

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=1068&sb=0


COMPRESSION

10.5:1 to 10.6:1

.
 

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Discussion Starter #34
Are you reusing headers? Probably need custom headers for the big boys.. The AFR heads should be a little easier and cheaper to find an off the shelf header that will fit your chassis and fit the heads properly.
I'm not as worried about headers. The one's I have now are junk and I'll need to get something different or get some made anyway. But it is a valid concern. Headers aside, would you pick one over the other?



barnett468, I'll give him a call. Thanks!
 

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Although I have not used Racetec yet, my current head builder (Ford guru Duane Busch) recommended them for my new build. He also mentioned Randy by name. Duane wouldn't have suggested them if they didn't do great work. Their Racetech brand is the 2618 material, their Autotec brand is 4032. If you are consider spraying, then the 2618 material is what I recommend as it has much better resistance to detonation.

I have dealt indirectly with Diamond and was happy with the custom pistons I received last year. Took somewhere around 5 weeks and set me back $850 but they were the good 2618 material.
 

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barnett468, I'll give him a call. Thanks!
No prob . . They typically answer the phone quickly and you won't get transferred 5 times until you reach someone . . They are also extremely user friendly and Randy knows all there is to know about pistons . . I have had him make several for me before including Boss 302 and Chevy 427 ones for my 1965 450 hp L72 engine.
 

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Discussion Starter #37
The trans is an Astro T5 (build will begin soon).

As for intent of the car, I'm shooting for a drag motor that's bearable on the street.

Didn't get a chance to call anyone today but I'll talk to your contacts tomorrow and see what my options are. Hell this far in, I might as well put in a proper cam along with heads. It's just money...
 

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Didn't get a chance to call anyone today but I'll talk to your contacts tomorrow and see what my options are. Hell this far in, I might as well put in a proper cam along with heads. It's just money.

I'm shooting for a drag motor that's bearable on the street.

The trans is an Astro T5 (build will begin soon).

ok, xlnt I like the way you think . . Below are some options.

TRANSMISSION

I would call the guy at Astro and tell him exactly what you are doing and ask him if your trans will grenade . . He makes a trans that will take high hp but it uses a special case and costs around $3000.00 and for that price, you can get a modified TKO 600 trans . . The problem with the 485 tq trans will be if you put high traction tires on it then dump the clutch at 4000 rpm or speed shift it . . If you do NOT have either the 485 or 575 tq trans, you will likely turn it into shrapnel with the engine combo posted at the bottom of the page.

575 TORQUE CAPABILITY TRANS

https://www.astroperformance.com/product/575-torque-ford-a-5-transmission/


CLUTCH PRESSURE PLATE

Don't know if you have anything already but depending on the disc size, I would get at least a 2600 lb one, otherwise it will likely slip but it will take a little bit of effort to depress which might get unpleasant quickly in stop and go traffic.

I'm not a fan of diaphragm pressure plates but some people are.


HEADS

AFR 205 69cc or Trick Flow 225 11R . . Both will kick major ass . . I would suggest Trick Flow 205's as an option but they are 58 cc's . . For your app, I would lean towards the AFR 205's.


INTAKE

Forget the wimpy Eddy Air Gap and get a Vic Jr p/n 2981 or Super Vic p/n 2924 depending on your final specs . . The Super Vic is better for really high rpm power and big hp engines but you can get into the 10's with the Vic Jr and it will have a little more bottom end . . Bigger is not always better.


IGNITION

MSD 6A box . . It has the same full range multi spark feature the other MSD boxes do but doesn't have all the fancy options so it costs less . . If you want a rev limiter then get the 6AL box.


COIL

MSD epoxy coil p/n 8222


SPARK PLUGS

Autolite AR3924 gapped at .042".


LIFTERS

There are a few different types . . With moderate cams, you can run morel 5323 or 5327 . . the 5327 are limited travel type . . These are around $350.00 . . With big cams with spring pressures around 400 or more, and rpm close to 6300 or more, the safer bet are the morel 5879's but they cost around $500.00 more . . If you call Chris Straub about a cam, he will tell you what lifters he thinks you can get away with using.

If you don't mind adjusting valves periodically, you could run a solid lifter cam and this would save you some money if you need the high dollar rollers


CAMS

I would think about a solid roller cam . . For a more racing oriented cam, there are many, but you will get a little more overall power with a custom made one, however, it's not like you will get another 50 hp if you chose a good off the shelf cam to start with, however, if you're going all the way, a custom cam is your best option . . Chris Straub could also offer suggestions for you heads if you ask him . . He is also a friend of Jon Kaase's.

Here's a couple off the shelf cams that will get pretty big hp and still be "bearable" for street use but there are others from the same companies plus some from Crane, Howards and Bullet as well.

Voodoo Hydraulic Roller Cam - Ford 351W & 302 H.O. 292/300 - Lunati Power

Ask Comp about making the one below with a 112 or 112.5 lobe center.

35-776-8 - XFI? Stroker Hydraulic Roller Camshafts, Computer controlled (E.F.I.) with O.E. hydraulic roller cams 1985-95


SOLID ROLLER

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=920&sb=0

http://www.compcams.com/Company/CC/cam-specs/Details.aspx?csid=921&sb=0

http://www.lunatipower.com/Product.aspx?id=1651&gid=290


ROCKER ARMS - Yours are 3/8" . . You will need to buy 7/16" ones for the other heads.


PUSH RODS

.080" wall chromoly


CRANK DAMPER

I hope you have a good one, if not, I often use ATI dampers, but for a budget one you can use a Durabond.


TIRES

Mickey Thompson DOT approved ET Street Radials which will wear quickly, or just use standard tires on the street which will spin like crazy and use the drag tires for the drags only to keep from wearing them out prematurely.


HERE'S ONE BUILD COMBO FOR AROUND 525 HP AND AROUND 11's in the 1/4 MILE THAT WILL REV TO AROUND 6500 RPM

1. HEADS - AFR 205 69cc p/n 1458

2. COMPRESSION - Make it around 10.7:1 for 91 octane with the cams below.

3. QUENCH/SQUISH - .034" - .036" if possible but no more than .042"

4. CAM - Comp Cams XR292R or Lunati Voodoo 63034 . . Both are solid rollers . The Comp Cam costs around $50.00 less than the Lunati.

5. LIFTERS - Morel p/n 4713 . . They are needle bearing solid roller with the big .750" diameter wheel . . Only $355.00 at the site below which is the lowest price in the country and is $500.00 less than the good Morel hydraulic lifters.

http://www.coloradospeed.com/roller-lifters-c-3788_3258/morel-mechanical-roller-lifters-ford-875d-tb-mech-roller-wind-260302351400-cu-in-p-33805.html

6. INTAKE - Vic Jr, but have it port matched closer to the heads, but Eddy says don't go bigger than 2.10 x 1.18 . . I usually make the intake a hair smaller than the head to allow for a little misalignment and I go into the runners on that one around 1 1/4" to reduce the taper in the end . . Do NOT modify the heads.

7. CARB - Holley 850 HP mechanical secondary . . This is the best deal on an 850 carb.

http://www.summitracing.com/parts/hly-0-82851/overview/

8. CARB SPACER - Try engine with and without a 1" Jomar or HVH 4 hole spacer . . Sometimes a spacer helps and sometimes it doesn't.

http://www.summitracing.com/parts/qft-300-4150-1/overview/

http://www.competitionproducts.com/Jomar-Power-Cone-Tapered-Phenolic-Carb-Spacer-4150_4160/productinfo/JOM5016-X/#.VjMtiSuVVLM

9. CAM CHAIN- If you have a budget cam chain, I would swap it out with a Rollmaster Red Label chain set . You can get it with a torrington thrust bearing and/or hardened gears but it costs a little more.

10. OIL PUMP - I sure hope you have a good one.

11. OIL PUMP DRIVE - I sure hope you have a good one.

12 - ROCKER ARMS

http://www.summitracing.com/parts/scc-scp3018/overview/make/ford

http://www.summitracing.com/parts/cca-19044-16/overview/make/ford

http://www.summitracing.com/parts/cca-1632-16/overview/make/ford

12. HEADERS - Crites or Accufab 1 7/8 4 into 1.

Accufab - 909-930-1751 . . $800.00 . . Will not fit with stock mechanical clutch linkage but will fit with cable system.

13. MUFFLERS - Straight thru like Magnaflows.

14. EXHAUST PIPE - A least 2 5/8" to 2 3/4" preferably with X pipe . . 3" i unnecessary and will likely cost you some power.

15. ROCKER STUD GIRDLE - Wouldn't hurt but not absolutely necessary for your app.

http://www.summitracing.com/search/part-type/rocker-arm-stud-girdles/make/ford/engine-size/5-8l-351/engine-family/ford-small-block-windsor/product-line/lunati-pro-series-stud-girdles?SortBy=Default&SortOrder=Ascending&autoview=SKU&ar=1

http://www.summitracing.com/parts/hrs-90201/overview/make/ford

16. REAR TIRES

For 15" x 7" inch rims.

http://www.mickeythompsontires.com/strip.php

For 15" x 8" to 9" inch rims . . these will go better with your 5 speed and 4.30 gears.

http://www.mickeythompsontires.com/strip.php

The ones below are for drag race only with 15" x 8" rim.

http://www.mickeythompsontires.com/strip.php
.
 

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Are you reusing headers? Probably need custom headers for the big boys.. The AFR heads should be a little easier and cheaper to find an off the shelf header that will fit your chassis and fit the heads properly.
Hey frdnut, now that it sounds like he wants more of a drag car, you could just tell him what your combo is if you want since your car is also a 408 and it hauls ass and is streetable.
 
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