I am in the process of a new build for my car. I already have the LSX block, manley billet rods, TFS 245's, sheetmetal intake. My question is I am supercharged F1R and have 1/2 inch head studs going in, what stroke and bore will be best suited? I already have a lunati 4.125 crank and was wondering what the ups or downs with this crank and a large bore will be? The only thing I havent ordered yet is the pistons for this reason. I was also thinking of trying 10:1 static compression since I am running E-85 and wont have a problem running better fuel for high boost. Any info/suggestions are appreciated. 4.125 stroke and 4.2 bore is 454 correct? If rpm is a limiting factor, by how much? My last 408 with eagle crank and oliver rods diamond pistons with lq9 heads and same sheetmetal manifold would spin 7000 no problem. I dont need that much Id rather make it down low with more cubes and more compression. Thanks in advance, Mason

 

With a 4.125" arm you're not going to have a lot of CH on the piston for a high boost application, and 4.2" bore you are DEFINITELY not going to want to boost that. We're talking a 4.4" bore spacing leaving you with .2" to hold all that cylinder pressure. The head gasket becomes really thin and you won't be able to keep from pushing water.

How are you going to limit boost with a s/c...rpm? Something to think about, you may just have to run low timing on E85 and then run it on kill with good gas. Don't take this the wrong way, but you should call a sponsor and have them set something up for you. Sell your 4.125 crank, send the block to the shop of your liking, and have them handle it. Too many variables that you really haven't thought about to be doing a build like this.

 

you would be much better off with a 4.0'' stroke in the engine,short pistons with the ring lands up high dont like boost-more suited to a n/a application.4'' stroke with a 4.125 bore is 427 cubes,you dont need any more than that.

 

Marty, I understand what you are saying, but dont think I havent already called sponsors including LME. The problems that I saw were they all have a very different opinion and many said they would do a 4.185 bore, 4.2 was just a question. All of these companys have a great price on a X shortblock, between $5,500-$6,500 but when you ask to work up a qoute on something best suited for your application the price is between $8,500-$10,000 for a shortblock no cam no nothing. I also have a 4'' crank and a 4.1'' crank not a big deal.Lingenfelter does my machine work and has said the block is good to 4.25 bore so I take it you discredit them as well. As far as the boost goes I have run 14psi on pump gas with no meth. So e-85 with meth, how much boost are you suggesting I cant run? There is nothing on my car that is untouched and I have done it all, paint , trans, engine and put down more than 800rwhp. This engine is now in my truck with a KB 2.8. I own and operate a transmission shop. I asked for some input not a booster for your self esteem. Shawn, thanks for the advise there are many 427's putting it down very well.

 

^^^wow that was an awesome response, still laughing. he did however make one good point the 4.125 stroke is gonna force the pin higher. if this is an all out race motor that will be torn down often than no big deal. street/strip application FI 427 all the way 19 cubes doesnt sound like much but it will be a badass setup. just out of curiousity whats rods are you gonna use 6.2's. good luck with your choice i am def jealous. and that color on the vette is badass btw.

 

With that block I would run the 4.000 crank and keep the CH like people are saying for a big boost deal. The LSX is a lil over 9.250 tall so you get a little there but with a real blower you need a really strong piston. NA use I would maybe go a lil more stroke but probably not on the blower deal.

 

Racer7088: If I were to run a 4.125 crank and a 4.125 bore in a LS7 block how much piston would I have from the top ring up? 200,250,300 thousands? Could I still run a normal ring stack like say a 1/16th,1/16th, 3/16ths? Traver

 

Yes with that LS7 sleeve you could run a .250 top land and a .150 second and an .080 third even with 1/16, 1/16, 3/16 and still have enough skirt in the cylinder at BDC to run virtually any LS1 skirt shape being used. You could run even thinner rings and have thicker lands of course too. You could probably achieve a .280 top and .160-.170 second with race type rings and have even more skirt in the bottom with a 3mm oil rail.

 

Cool.....this has been kind've the route we're working towards. I want to spray 150 shot on it and would like at least 250 thous. up top or even a little more if possible. With the 1/16, 1/16,3/16 things might be getting a little tight? I like that ring stack because the more I have been investigating I've been finding less oil control problems with it. What do you think? Traver

 

Oh, I forgot to mention that it will be a Darton sleeve, so it will be a little shorter. But actually the LS7 just has the longer sleeves because of the tangs at the bottom and not all the way around like the Darton which is actually shorter but the full sleeve around the bottom. Traver

 

The darton is still more than long enough. It would work great with the 6.125 rod and that longer cylinder

 

Thanks for the info, 4" it is. Can you tell me the equation/formula for determining cubic inches from X bore and X stroke. And what piston / ring combo would you recomend? Do you think 10:1 is a good idea or not. Thanks again, Mason

 

displacement = (bore^2 x stroke x number of cylinders) x .785

 

I don' thnk you will have problems with the 10:1 on e-85. it is possible that you could gain a little more power with a lower compression and more boost, but I cannot say for sure.

As far as the LSX block and 4.25 bore that LPE said it could run.

Yes, GM rates the block to that, HOWEVER the biggest problem with that would be keeping a gasket between the cylinders. I honestly do not know of any respectable shop that would build you a 4.2" bore or larger LS series motor for boost.

You have an incredible car there. Keep it up.

 

Yeah I figured you would be butt hurt from my comments. I'm not trying to flame so lets get that out of the way and go through your post to provide a little more insight. I'm not an engine builder so obviously you'll take my words with a grain of salt...but I do have a good amount of experience of actual builds, not bench racin.

But just like Erik is saying, with a big boost motor your biggest problem is going to be keeping heads down. With 6-bolt heads that will probably alleviate a lot of issues, but with a 4.2"+ bore you're still only talking .2" of material between cylinders and even less material on the head gasket as it's not going to be smaller than the bore. So .190" materal between two chambers trying to hold 18-20 psi on a large motor is a LOT of cylinder pressure.

I would keep the bore at 4.125". How much power are you really going to gain from that slightly larger bore? 10 or 15rwhp? I think it is a moot point when you're talking engine longevity.

The LSX does have a longer sleeve so you can get away with a longer stroke, but it does place the pin higher in the piston taking away from CH. When you decrease CH you take away meat from where you want it most. This makes the sleeve shorter, usually requires less material in the RL's and makes the ring package a little harder to engineer.

Lastly on the boost comment, you were talking about "running low boost on e-85 and upping the boost with good gas". I was merely asking how you are going to limit boost on a supercharger when running 10:1 compression and "low boost". Limiting rpm's or running a mondo bypass valve that will considerably raise IAT's...? Just saying that if you did want to run high boost (20+psi) on good gas that you would run the same psi on e85, and could simply get away with low timing.

Your build sounds badass, it just didn't seem like you were trusting the opinions of the builders you did talk to. I don't really have an opinion of LPE. They build badass cars yes but I have never dealt with them. I have seen some weird stuff come out of their shop for streetcars and that is all I will say.

 

Ok, I never had intentions of running a 4.2 bore I simply didnt have the formula for coming up with cubic inches. I figured with two known bores and strokes I could come up with the formula. After recieving it on here I realized I probably didnt stand a chance. I simply use LPE because I am sure that they have all of the proper maching / balancing equipment needed to complete the job and have used / seen all local machine shops near me. They do take awile as I understand they will get their own engines moved before someone elses. They never told me to run a 4.2 bore, But I did have several suggest a bore as big as 4.185 with that being said, I was wondering who has solid info/testing on the optimum bore and stroke. Not who can tell me what they think it would be. I appologize for the remarks. And thanks for all the good info and the compliments on my car, Mason

 

Check out the Ross pistons website. They have a very good compression ratio calculator that lets you play with bore and stroke combos.

 

A bypass valve does not limit boost.. a bypass valve lets excess pressure out between the blower and the throttle body when the throttle is shut and it does this by sensing vacuum in the intake manifold. You're thinking more of a wastegate type functionality.

 

hey go to a displacement calculator and type those numbers in and they will give you your cubic inchs and you can also play around with the numbers and make a bad *** motor

 

What is amazing is that an idiot like this actually gets well meaning members to give him intelligent advice which he uses to futher prove that he is more than a little full of it.