Installed '68 C8 4V 302 heads on '88 5.0, now engine runs lean!

snakchrmr · 06-29-2002

I put a set of 1968 302 4V heads on my 88 5.0. I've run into an unexpected problem. I knew going in to this, that I couldn't use the factory smog equipment (no rear port hole in the head), fortunately I live where it's not required. So, I took it all of. Problem is that the motor runs lean in the closed loop mode, so lean that the power just falls off at about 4 grand or so. The motor has new O2 sensors, 1.7 roller rockers, equal length headers, off-road H-pipe, Dynomax 2 1/2" exhaust, and OEM everything else. Is there anyway short of putting in a programmable chip to trick the computer to run richer? Or is there something else causing this?

fvpnt0pony92 · 06-30-2002

it sounds like something else than the heads, they wouldnt flow enough to make the car run lean.

have you tried replacing the fuel filter? checked your timing?

snakchrmr · 06-30-2002

My concern is that without the extra air, which is pumped into the exhaust by the smog pump, the O2s might be reporting a rich condition to the computer, which in turn will try to lean the motor out. As far as the head flow, they're factory rated at 230 hp@4800. Rated different than today's method, but still comparable. I'm sure I could use a new filter and I have the timing set at factory 12 degrees. Do you think I go a little further with the timing? Do you think it would help the lean condition?

fvpnt0pony92 · 06-30-2002

i took mine off. my car is running a bit lean but it isnt from that.

and head flow isnt rated by the hp the engine makes. heald flow is rated in cfm. if you look at charts with cfm flow numbers, the E7's will out flow any older model heads found on 302s(except the Boss or Tunnel port, the Boss is a clevland head though) enignes back then were rated a LOT different...they didnt have any assessories hooked up and used open headers when testing for hp.

you can go further with the timing if the fuel being used allows it. i cant tell you how far you can go, you just have to try it out. advance it then take it for a drive and listen for any detonation.

how did you decide that the car is running lean? did you check the plugs?

JUSTNLX · 06-30-2002

The problem is "you took it all off"

The processor is programmed for all that smog equipment. By taking it all off (I feel so nasty

) you have messed with the fine balancing act the processor goes through.

The only way to really "take it all off" is to go with a complete after market operating system.

Your performance gains with the 68 heads are minimal and really not worth the effort you went through. I would suggest putting it all back on

fvpnt0pony92 · 07-01-2002

so removing those tubes will mess up the tuning. but i have ported heads and a ported intake....so i think that is also effecting the lean condition im getting right now.

but you can always just get an adjustable fpr(like im getting soon) and then bump up the pressure and not worry about it any more.

snakchrmr · 07-01-2002

Well, I checked the #1 plug....a little white. (held at 3500 rpm for a couple of seconds and shut the engine off). My point with stating the horsepower was to show the heads flowed enough to make that kind of power. Don't confuse these heads with the anemic heads from the '70's 130 hp 302's. The '68 302 4V heads are as close to 289 hi-po heads (271hp) as it gets. I don't have $1500 for a set of TFS's.The chambers are 53.5cc which equals about 10.5:1, a cry better than the factory, what 8.5:1 I think? I had another 88 GT before this one. It ran great. After going through some deep water, I discovered the previous owner took the smog stuff off. That's why I didn't think it would make too much of a difference on this one. I did change my fuel filter, but I'm working on it at my dad's, and he was sleeping. Do you think maybe with the off-road h-pipe, equal length headers, and 2 1/2" tails, I might be loosing back pressure? Traveling by the O2's too quickly?

snakchrmr · 07-01-2002

I just did some digging on the web and found a site that offered the following flow numbers for the E7TE (the stock 5.0HO head (a truck head)). Int. 154 cfm/ Exh. 107 cfm @.500 . GT-40 heads (E7TZ) Int. 187 cfm/ Exh. 129 cfm @ .500.The TFS's were around 250 cfm. I couldn't find anything on older motors, but I took note during engine assembly that the intake port openings on the '68 heads match identically to '88 gaskets ( the water ports are about 1/4" smaller on the '68's), so the ports are the same size. I understand that a closed-chamber head shrouds the valves, but how can the E7TE's flow better with that big chunk of iron (EGR bump) stuck in the middle of the exhaust port? The '68 castings have a nice clear shot out the port. No bumps. The intake valves are a little smaller (1.84 vs 1.94) in the '68 heads, but barely. Bowl area? I don't know.All I know is by comparison to today's aftermarket heads, factory small block heads leave alot to be desired.

fvpnt0pony92 · 07-03-2002

believ me, im not confusing them with the 70's heads....especially when you said 68 302 heads. i have two pairs of 68 302 heads in my garage right now, one set is going on my dads 1968 Mustang coupe and the other set i rebuilt in a class at my community college. i know what they look like.

dont be fooled by the 289 hipo myth. the 289 hi po heads arent that good either compared to the E7's. ive seen them and the ports arent bigger as far as i can tell, the only good thing is they dont have the bumps in the exhaust ports. i just hope your running good gas with that kind of compression!