I am putting together a 2.8 rwd block with 3400 top end ,a delta 260 cam, probe forged pistons and headers. The problem I have is I have not found an external crank trigger for a rwd block yet.

 

You will have to make one custom. There are not any available at this point in time...that's why most people suggest using the 3.4 block as it already has a crank sensor hole and timing wheel on the crank.
Plus, what year car do you have? Your ECM might not be able to pick up the signal from the crank sensor needed to run DIS.

(I don't think any 2.8s had the 7730 ECM...or am I wrong?)

 

2.8 had the 7302 ECM, no matter what car it was installed in be it RWD or FWD. You're out of luck without an external trigger as NO 2.8 crank has the reluctor wheel in the center counterweight thing (except MAYBE FWD, but I never had one, so IDK). Only select RWD 3.1 and ALL FWD 3.1 had the reluctor wheel for the sensor which would be mounted to the lower passenger's side of the block in RWD orientation.

BTW, wouldn't a 3400 top end kill the 2.8's compression ratio due to inconsistant bore to chamber size, with the bore being smaller than the chamber? Or is that not a problem?

 

The motor is going in a fiero that has a7730 ecm swap. The compression will work out 11.75 to1. I hope the 260 cam is enough to lower the compression.

 

it'll be fine......my other car has 12.2:1 compression :P

 

What's the cam specs (in/ex opening/closing points)?

 

Holy misinformation, Batman!!

The FWD 2.8s did indeed get a '7730 in some applications, other service numbers are NOT the '7302, but variations of the '7730.

ALL 1987 to 1989 FWD 2.8s have a reluctor wheel cast into the crank just like the 3.1s did.

2.8 and 3.1 share the same bore size.

3400 top ends have been installed on MANY 3.1s over the years and never had a proble with bore to chamber size. Also the 3400 chamber is the same size as the 3.1 FWD chamber, which guess what, is exactly the same as the FWD 2.8 chamber.

A custom trigger wheel can be used or WOT performance or tuning or what ever it's called has external trigger wheels that could be adapted to a RWD application.

This is what I did on my 3.2L (which was a 1986 2.8L block):

Test fitting before putting the notches in the wheel and smoothing out the sensor mount.




Here it is installed in the truck, with the notches. Worked like a charme for about 2 years as a daily driver, then I parked the truck for some upgrades and hasn't been back together since.

 

cline dur open close vlv lift lb sep overlap
int: 108.0 209.6 -3.4 33.0 .429 111.9 -13.0
exh: 115.7 212.1 41.6 -9.6 .436 3.9 advance

I purchased this cam with a set of 3400 haeds.I am not sure if I wil use it .
Joe

 

You won't be able to use that cam on pump gas. It'll only bring your dynamic compression down to 10.3. If I'm not mistaken probe's pistons are flattops aren't they? That would put your compression at 13.8 with .06 head gaskets.

 

Yes the probe pistons are flat tops I was going to have the tops cut down.I also have a set of low output pistons that are std. Would a 270 cam work out better?
This is not going to be a daily driver but I do want something that will run.


Joe

 

You're going to need a cam with an intake closing point of atleast 55* ABDC @ .05" lift. That'll bring dynamic compression down to 8.8:1 (9:1 is considered max on pump gas). Make sure you've got a good quench height as well, I'd shoot for .05". The crane 251241 closes at 51* ABDC, which is the largest cam you're going to get without having a custom grind made. It's a solid cam so you might consider lowering your static compression more or going with race gas. You won't be able to use a speed density ecm ('730) with a cam that large without some compromises. It'll idle like crap and have very little vac. A maf ecm would fair slightly better, but it would still suffer from serious intake reversion making it idle rich as hell. You could use some rhoads lifters to bring idle vac up, but you'll still need less compression.

 

u have another option for dis

36-1 crank wheel with a ms 1 and edis
whole setup would run u about 300-400 bucks

u could do ignition control only with it but if u got it u might as well do fuel and ignition

 

If we lived in the 1960s....

Making the rest of this post pretty much nothing but drivel.....

 

Dynamic compression is a little more complicated than that formula, but still holds somehwhat true in the aspect that you need to lower your cranking pressure for an easy tune. We've had guys as much as 12.6:1 with about a 52* IVCE, well over .550" lift and pump gas.

One of my last customers decided to against my advice on using a Comp 272 and used the 260 instead. Pinged like crazy after warmup and the compression was enough to have to decrease the plug gap. Went to the 272 and he was able to tune as a novice. Cranking pressure with the 260 was in the 260's and the 272 brought tit down to 225. You have to remember these heads are about 95-98% or more efficient, and the ramming effect alone will fill the cyls nicely and push the exhaust out just fine.

As for the external DIS wheels for the RWD's, please stay tuned. I have a prototype almost complete, and they will be in the $150 range.

 

So what are you suggesting then, six-shooter? He doesn't need leaded gas to run 9:1 dynamic c/r on pump gas. We're talking a small bore engine with superior a/f homogenation and heart-shaped chamber with quench pads, not an open chamber carbureted dinosaur. I agree cam timing doesn't give the whole picture when it comes to running c/r, but still gives a much more realistic view when planning a build.

 

No, he doesn't need leaded fuel to run 9:1.

The 3100s and 3400s run 9.5/9.6:1 SCR from the factory, and run on unleaded.
3500s run 9.8:1 on unleaded.
Many engines run over 10:1 on unleaded.
If you take into account the "effective SCR" of forced induction engines being up around 12 and 13:1, then you can run that SCR on unleaded, in fact I know that can be done. A friend of mine has an N/A 3400 with between 11 and 12:1 SCR (I don't recall the exact numbers) and it runs just fine, tuned by yours truely. His cam wasn't anything spectacular either, but runs just fine on unleaded fuel.

Dynamic CR is not something that is easily compared, since there are so many variables that will influence a rise or drop in CR from static. Most people don't understand the difference between static and dynamic CR, so it only confuses people when you try and use dynamic CR to "give advice".

The aluminium heads are known to work well with higher compression and unleaded fuel, so I don't see why you're on this "it needs to use leaded fuel" kick, just doesn't make sense to me.

 

I don't want to go that radical on this engine.My concerns are that the cam I have did not have enough overlap. I will get a new 270 and go from there. The car has a 4 speed.

 

??? I think you're confusing issues here. I'm not talking static compression, I'm talking dynamic. His dynamic compression will end up being too high with compression that high and a smallish cam. I'd rather not see someone go through the trouble of a 3x00 swap to see it pop on pump gas.

Forced induction is a completely different situation, requiring extra measures such as intercooling or water injection to prevent detonation. That really doesn't apply here.

And where did I say he needed leaded gas? I said he either needed to lower the static compression, use better fuel or get a lumpy cam. Somehow you see nearly 12:1 compression with a 260 cam on pump gas as feasable? Explain.

 

This cam runs 12.6:1 N/A, pump gas...

216/224 112LSA 108/117 ICL .517/.538


I am about to attempt to tune a 11.56:1 3.4/3500 with a small 252 or 260 cam, car is being shipped here in March, more on that later...


To make things easier, use a bigger cam, but it's not necessary.

 

Well call me cautious but I've never been one for high compression. I'd rather keep modest compression put a big cam in and rev that b**ch to 9k. Another thing to consider when building a street motor is carbon buildup. If you're not keeping up on those fuel additives or burning premium to keep it clean you could see some problems. I worked on a car awhile ago that pinged whenever you opened it up. Did a cranking test and holy crap 2 cyls were close to 230 psi. Popped the plugs out and it was nice and caked up. Not burning oil either, just never cleaned out. Cleaned it up with a 3-step (ended up being a 4-step, I wasn't satisfied the first time so I ran another bottle of decarbonizer through it) and stopped pinging.

 

.

 

3.4 RWD with stock pistons and a 3500 top end with a 270 cam would be nice.

 

Firstfirebird any progress on the external crank trigger? I can not find a crane
270 cam so I was considering an Engle cam.

pn 21640h
lift .453 .471
dur@.050 .215 .222
lsl 112
any advise on this grind?

 

Nothing new to report, my shop has been bang-up with work lately, and there are a few prototypes that are on the table (none getting worked on the past several weeks )

I can run a simulation for you on that cam if you like, right now it's almost midnight and still working at the shop, software is at home...

That doesn't sound like enough lift to me for taking advantage of the aluminum heads, what spring combination are you using? Yellow LS6 springs, you can have as much as .525 lift. To use them you will need LS1 spring shims, seals from a 1991 Cavilier 2.2 and stock locks/retainers.

 

The heads are stock rebuild. I haven't purchased the cam or springs yet.I am going to order the cam,springs and rockers soon so I can get the swap done.I appreciate any advise you can give me on this set up.