318 TUNNING TIPS?

[Zodiac 318]

I am at present building a 318 lump for my car.The heads will have a mild flow job,carb will be a 600cfm 4bbl,duel plane manifold and the exhust will be tubula headers into 2 1/2" twin exhust system. The gearbox is a 904 I think.
The engine and box came out of a cuda of pre '71 vintage.
Can anyone help with the following questions. Many thanks.

1) Any sugestions for a sutable cam (I think the torque converter is std)
2) What is the std compression ratio?
3) What is a good compression ratio to aim for with unleaded petrol?
4) How mutch to grind off the heads to get the compression up?
5) Will this engine take 100bhp n2o plate kit?
6) Any guesses at approx power output?
7) Any guesses at 1/4 mile times to aim for (car is about 2700lbs)

[MopART]

1) Any sugestions for a sutable cam (I think the torque converter is std)

Something close to the mopar purple 280 duration with .474 lift and make sure you get springs to match. What size vavles do you have ?

2) What is the std compression ratio?

Between 8 and 8.5

3) What is a good compression ratio to aim for with unleaded petrol?

9 or 9.5 : 1 would be sufficient just use good rings and increase the gap over what they suggest by .015 for nitrous.

4) How much to grind off the heads to get the compression up?

.060 is about as far as I'd go.

5) Will this engine take 100bhp n2o plate kit?

OH yes !! I wouldn't be scared of 150 or 175 with 175 being the limit.


6) Any guesses at approx power output?

nope

7) Any guesses at 1/4 mile times to aim for (car is about 2700lbs)

mid 13's

ART

[MopART]

Clarification..

Mid 13's on motor and probably mid to high 12's on nitrous.

ART

[cruzerjd]

Horsepower,about 230 to 250 rear wheel. More with the nitrous. You should also use a set of milled 360 heads with the 1.88" intake and 1.60" exhaust valvestoget the best flow with the 318's bore. Other than that Mopart has it covered. cruzerjd

[DartGT66]

Just finished my 318 project, and have been driving it for a week now.
1. With a stock converter don't go over the MP 268/272 cam; it pulls nicely to 5500 rpm in a 318. In my case this cam is advanced 5 degrees and still it's a little sluggish at the bottom end. Either this or the 260/268 cam if going with MP cam.
2. In my case the stock CR was under 8:1. The piston heights are the same in almost all 318's and so are the head cc's in '68- about '85 heads. My '83 heads were 68cc stock, and the '70 heads I used were 71cc after porting and polishing; this would have given me a 7.5:1 CR with composite gaskets, and about 7.7 with MP 'thin' gaskets.
3. You should get about 9-9.5:1.
4. You can't raise the CR up to that with milling; I milled the heads .080" and ended up with 8.7:1 CR with .040" thick Fel-Pros. Measure everything and decide what you do, the KB pistons with slightly higher compression height may be a good idea. Still may require some milling to get the CR where you want, but not that much. Milling heads the amount I did requires many other things like shortening the pushrods, milling the heads intake faces and special considerations with the intake gaskets. Some heads may also have too thin decks to allow this much milling, I took a risk and in my case it seems to work.
5. 100 hp NOS should be OK. Remember that with NOS it's important that the fuel delivery system is capable of delivering the amount needed and the other things like ring gaps and timing are important too. NOS forgives nothing.
6. I think a stock headed mild 318 produces about 200-230 hp, I haven't timed my car yet, so I don't know how much or little power it makes.
7. With good traction you should be able to go high 13's- 14's with that kind of engine without NOS, if your car really is that light with a driver. My goal is to get in to 15's with a 3500 lbs car and 2.95 gear ratio one legger.
Switching to 360 heads will only make your CR ratio problem worse. This with a big cam and the lower velocity ports will make you loose low end torque. Not good for speed with a stock converter. Installing 360 valves to the 318 head is a way better idea, I think. If you can find late 80's 318 closed chamber 'high swirl' heads, fitting them with 1.88/1.60 valves and some porting will give you the best results performance wise.

[This message has been edited by DartGT66 (edited March 08, 2000).]

[MopART]

Reading DartGT66's post made me realize that I left out one detail. You will need to buy 9:1 pistons.... He's right about using stock pistons, they are way down there in the bore and cutting the heads isn't gonna help much to increase your compression.

sorry for the missing links.

ART

[Zodiac 318]

To Art & Co.
Many thaks for the advise.
the valves std 1.8"In & 1.5" exhust I think.
Also I am hoping to use the old pistons for know as I am planning to put the money towards building a 360 lump next year, so is it still worth takeing some meet off the heads, I realise I may have to take a bit off the inlet face to keep everthig happy?? let use know what you think. bye for now.

[This message has been edited by Zodiac 318 (edited March 12, 2000).]