Took a huge road trip this last summer (1200 miles round trip) in the El Camino. Was really stoked to see what kind of mileage I could pull down. I was let down when I averaged just a hair below 13 MPG. It's getting me thinking that I should just forget it and put the 4.10s back in for the fun factor and say forget the mileage. However, $3.20-$3.40 gas in my area has me holding back. Back with the 4.10s the first round, I had a little 600 carb. Since then and putting the 2.73 in I switched to a 770 Holley, which I put a bigger squirter, pump cam and light secondary spring in. Now, it runs a lot better, but I'm afraid that going back to the 4.10s will get me like 5 MPG. I only put 2000 miles on it a year on average, but I think cutting my MPGs in half would severely discourage my driving it much. An OD trans. is out of the question, as we have a child on the way. I think I'm going to be lucky just to be able to hold on to the car. I wonder how long it would take an OD trans to pay for itself over straight 4.10s?
Got the itch . .. .
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What are you running in the 468? Thirteen is about the best the '70 got before the rebuild. 402 with stock 063 heads, cast iron Q-Jet intake, Q Jet, LS6 cam, headers, and 3.31's out back. Depending on how big your cam is it may not like the low RPMs of the 2.73's at all. That may be part of the problem. Just a thought.
I bought a junk 700r4 on craigslist for $25, bought a rebuild kit for $150, and the other hardware was around $100. I admit I found a real good deal on the junk trans but for around $300 and the fact my gas mileage jumped from 11mpg to 17 around town, and about 21 on the hwy you cant beat it.
you should do better than that. what's your cam, cruise RPM, stall speed?
Have you done a detailed workup on your timing? know the iniitial, the total mechanical and at what RPM? how much vacuum advance at what vacuum and how does that compare with the cruise vac?
I'll bet you can get at least another 5 mpg by optimizing this stuff. However, if your cruise RPM is below the stall speed and bottom of the happy part of the cam RPM range it's an uphill battle.
Have you done a detailed workup on your timing? know the iniitial, the total mechanical and at what RPM? how much vacuum advance at what vacuum and how does that compare with the cruise vac?
I'll bet you can get at least another 5 mpg by optimizing this stuff. However, if your cruise RPM is below the stall speed and bottom of the happy part of the cam RPM range it's an uphill battle.
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you can get better than that, thats for sure.
with 3.55 gears, 26" tire, a muncie 4spd, holley 3310 750vs, 355 10:1cr w/ 231/239 cam, and 13.2-13.5 AFR at cruise at 3200rpms i got 23.5mpg on a 97mile cruise in my 71.
get that timing and carb dialed in. find someone in the area that will let you borrow their wideband O2 and tune for best cruise AFR
aaron
with 3.55 gears, 26" tire, a muncie 4spd, holley 3310 750vs, 355 10:1cr w/ 231/239 cam, and 13.2-13.5 AFR at cruise at 3200rpms i got 23.5mpg on a 97mile cruise in my 71.
get that timing and carb dialed in. find someone in the area that will let you borrow their wideband O2 and tune for best cruise AFR
aaron
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There is no point in comparing my milage to yours. Put the 600 back on, and tune it to work with the engine. First, ensure you have full timing, and I would also advise vaccum advance for crusing. Then tune the 600 to work. You should pick up 10% minimum.
If not, junk the trans and put a Richmond 5 speed in.
You'll gain another 10%, but you'll never make up the cost of the trans and kit.
Man, I need to do that wideband test Aaron. I'm stuck at 15+ with the hotter cam.
If not, junk the trans and put a Richmond 5 speed in.
You'll gain another 10%, but you'll never make up the cost of the trans and kit.Man, I need to do that wideband test Aaron. I'm stuck at 15+ with the hotter cam.
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my cruise is 2800-3200 at 55-65mph. total timing of 38* and vacuum advance is 52* at 2800. my cruise AFR with the 3310 was 13.2-13.5 at 2800-3200 its been a while so i cant remember exactly.
i did put a 4777 650 dp on the car. didnt cruise real well.. needs to be played with, but with WOT AFR in the mid 12's (2 jet sizes up from stock IIRC) i picked up 3mph at the track..
my velle at 55-65 gets better than my gto at 80 in 6th gear at a lower rpm.
aaron
i did put a 4777 650 dp on the car. didnt cruise real well.. needs to be played with, but with WOT AFR in the mid 12's (2 jet sizes up from stock IIRC) i picked up 3mph at the track..
my velle at 55-65 gets better than my gto at 80 in 6th gear at a lower rpm.
aaron
so, you currently have a 2.73 and you're running 2800-3200 at 55-60? That RPM is more a 3.73 deal than a 2.73. whassupwiddat?
You need to drop the cruise RPM by about 1000, calls for an OD tranny. A 200-4R with a 3.42 or 3.73 is where you need to be. you're not going to get any good mileage at 3000.
You need to drop the cruise RPM by about 1000, calls for an OD tranny. A 200-4R with a 3.42 or 3.73 is where you need to be. you're not going to get any good mileage at 3000.
Well I will tell you wassupwiddat. Aaron is not the original poster of this thread.
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