CR Question - 3400 w/3500 heads

[bob442]

With a 3500 hybrid, what would the CR be with 11.5:1 pistons (thats a 3400 bottom end) i tried to figure it out on the CR calculator, and it told me i was a Failer! lol actually it told me 1:1 ratio and interferance. I feel so bad having to ask questions all the time to you guys. I'm thinking i should stick to fab. work where i belong, not building motors lol

Bob

[IsaacHayes]

Stock 3400 pistons the CR is about 8.9:1 or something like that.

With Iron head 3.4L RWD pistons, the CR is 11.51:1. That is what my motor has. 3400 shortblock, 3.4 RWD pistons, 3500 heads/intakes, cam, port work, headers.

[bob442]

so if i have 11.5 CR pistons on a stock 3400, putting on the 3500 head would give me 10.67, i want to run a higher CR but still be streetable on pump gas.

[IsaacHayes]

Wait, I'm confused.... What do you mean by 11.5:1 CR pistons? Do you have custom pistons already that are 11.5:1 when installed in a 3400??

To run on pump gas, you need a decent cam with high compression.
My cam is like 210/215 dur, .531 lift and 11.5:1 CR and runs on 93 octane. I hope I can get it to run on 91 cause that's all I have here. Going to a colder plug and pulling spark may be needed.

12.:1 or 12.5:1 has been done on a 3400 before, but you'll need a good healthy cam to help bleed off some of the pressure.

10.67 would probably work even with the stock cam if tuned well and you went to a higher octane. My 9.6:1 in my 3100 doesn't like 87 in hot summer temps with the stock tune, but now since we are E10 here the 89 octane result means that issue is no more.

Mods might want to split this off to a new topic...

[bszopi]

http://wot-tech.com/shop/all/forged-3400-pistons/prod_186.html

Available in .020 .040 and .060" overbore sizes, in either 9.5, 10.5 or 11.5:1 compression for the 3400 engine. Compression ratio is based on stock cylinder heads, so please adjust for different heads or combustion chamber modifications. If you need a different bore size, such as stock or .030, please select "custom" and put the size you need in the additional information field. Other compression ratios can be done as well but are considered custom pistons compared to our off the shelf versions.

[ForcedFirebird]

Isaac, you will have slightly more than that if you re using the RWD pistons. If you are using FWD gaskets, that's close, but your quench is too large IMO.

[IsaacHayes]

John, I'm running 3500 gaskets with the larger bore and .060, so yeah it is 11.51:1, and yes, my quench is a sucky .070 (which is what the DOHC 3.4's have stock amazingly).

In geldartb's thread I discussed this issue. I know the motor works and runs on 93 octane. I just hope it will on 91.

[geldartb]

yeah but still ive talked to Ben before about this and with the 11.5.1 and the 3500 heads you will end up with 11.5.1 if using the 11.5.1 diamond pistons.

now like issac said we talked about this in my high compression thread. using the .036 thickness MLS gaskets which get you in the green good area for quench but brings the CR up to something like 12.5.1. all the info is in the thread i mentioned.

using the stock thickness gaskets you get the 11.5.1 but brings your quench up there. now also discussed in the thread was the flycutting, which when i either use the rwd pistons or get some diamond ones i will get the tool and do the flycutting to make the reliefs for the pistons.

[bob442]

i'm talking about the 11.5:1 pistons avalible from the WOT store, those Diamond forged pistons are for the 3400 FWD are they not? i just want to run a 11:1 CR, or as close to that as possible with a cam. mainly i want to know how close to my goal can i get with out getting custom made pistons. i would like to go with "off the shelf" pistons to cut down on the costs a little bit on my build, i'm hitting up the wreckers insearch of a 3500 top end for under $200. i always go to bucks auto as there prices are set to one price regardless of what its from. i payed 20$ for a m90 the otherday :P
its -36 outside right now so i hope i make it back haha

[3400-95-Modified]

3400 with 3500 heads stock is 9.15:1 Don't make it sound worse than it is...

Also its not a definate static loss, so you cant say you loose .35 CR going from a stock 3400 head to a 3500 head... and then apply that to a starting CR of 11.5

Go to the CR calculator... do custom, leave all the values at default and ONLY play with the piston dish, stock shows 9.64:1... so to get 11.5:1 you have a dome volume of 17.125cc

That's assuming your not changing the deck clearance and all that good stuff... So now take the 3500 head CC's and put that in, 32.4cc... you end up with 10.9:1 and that's assuming your also using a stock 3400 headgasket bore and thickness.

Assumption... but I got a good estimate, and can be accomplished, by using stock 3400 headgaskets, OR the standard size MLS gaskets for a 3500 at the stock .060 thickness. Those are 3.72 dia IIRC for the bore.

[geldartb]

yeah the diamond pistons are for the FWD motor and thats what i was talking about when i said if you picked the 11.5.1 you would end up around 11.1.1.

[3400-95-Modified]

Its 10.9, but whats .2 points... lol

[geldartb]

that .2 points isnt going to amount to much. ooh a whole 2 or 3hp. when i was talking to Ben about this i asked him how much different it would be from 11.1.1 to 11.5.1 needless to say it wasnt much maybe like 5hp or something stupid small.

[bob442]

Well back from my search, I couldn't find a top end to pull off myself, but I did find a complete 3500 for 500$, 86xxxkm. I'm not sure if i'll grab it or not. I also found this halarious car, I thought it would be appropriate to share with you guys:


Thanks 3400-95-modified and everyone else for clearing everything up. I'm just learning my way through engine internals, I couldn't have figure out what you said on my own. I'm also having throubles learning all your acronyms that you guys use. I didn't know where to start with all the differnet variables with the heads, pistons dish and combustion chamber size, but you seem to know it from heart.

I feel like a pain in the ass asking questions that I *may* be able to figure out on my own, but I do try, search, and research as much as I can trying to figure it out before i start a thread and get flamed by people saying "use the effin search button noob" I just dont want to hear that. But Thankfully someone started this thread for me and I got my answer.

With A 11:1 CR I wanted to be in the middle of things with out getting custom pistons made. i figure thats the highest i should want to go for my goals with building my motor, its high, but not too high. I remember asking about this awhile ago, and recall 10.5-11.5 being ideal for a build up on a motor, and running pump gas on a N/A motor.

My intentions for the motor is a daily driver, with lots of jam, I would like to stay above 25 mpg for fuel economy, seeing as though i'm getting 31-34 mpg now with a heavy foot. I do want as much power possible, so I will be getting all the ports polished, and gasket matched myself, I'll have a good cold air intake, and a very free flowing exhaust including headers. Getting roller tip rockers maybe in the budget for that little bit less of engine drag that it may take away, i'll put in a single or double roller timing chain, pening on how heavy my cam selection is. I don't want to replace it with in 70000 km of me driving it. I want this motor to be very reliable, I mean extremly reliable, so I'm not going to push any internals that hard, so if that means only putting in a street strip cam, thats fine. The motor will be tuned once it is broken in on a dyno. If I had a goal of a HP number that I wanted it would be 230-250, but, I don't know what variables will accomplish that. That is where i need help. It's not like my neighbours build up these motors on a regular basis and run them on Pinks All Out lol

EDIT: I forgot to mention, it would be a huge, huge plus if i had a loby idle, it doesn't have to be crazy but noticble.

The car that it is going in is a 2005 monte carlo LS, its got 80,000 km on it with upkept oilchanges using synthetic oil. I probably will have to get the clinders machined but probably not that much. I absolutly hate that piston slap on cold startups. I want it gone and never to return!

If I should move this to a new thread someone say so, I dont' want to clutter up the forum.

Thanks alot guys.

Bob

[SappySE107]

Don't gasket match exhaust or polish intake.