Tire size question...??

[k5 krawler 50]

I have just recently put a lift on my blazer, it already had 33x12.5x15 tires on it, it has some 15x8 rims too. I wanna upgrade to bigger tires but dont really have the money to regear, so i want ur guys opinions on this please. I have a small block chevy 400 that is pretty stout. i have a th350 tranny that was built to handle about 550 hp, well thats what the guy said who built it, and it has a np208 trans case. it has 3 73 gears. I know i will lose some gas mileage with 35s, but how much power will i lose. I really want 35x12.5 ssr tires, but dont wanna lose much power? Should i upgrade to 35s or keep 33s. Also wheel it about 70-30 ratio to road driving too. Thanks again.
Cory.

 

[pauly383]

If I can pull 33's off road and on the street and highway with a 305 and 3.08's, you can pull 35's with 3.73's and a 400 /forums/images/graemlins/k5.gif

 

[Z3PR]

I guess it all depends on how you wheel it. I do mostly old logging and miner road (Over grown trails) I not much into rocks. I'm currently on stock tires and 3.08's. Yes it's a pooch, but I have some 3/4 ton axles with 3.73's and some 36x14.50x15's Ground Hawg's waiting to go on.

 

[k5 krawler 50]

Yea rite now i am not into rocks, cuz i just dont have the money to fix all the stuff that would break, but i am into hill climbs and some trails. See, its a really responsive motor, its a 10:1 compression and its pretty quick. I wanna keep it pretty quick so you guys dont really see a problem throwin some 35s under there and losing a lot of quickness, i mean i know i will lose some, but i would really like to keep it faster then all the little rice rockets around here cuz its fun to beat them in the 1/4 mile.

 

[Z3PR]

All I can say is put them on and see how it does. There really isn't a whole lot between 33's and 35's. So you should be okay.

 

[BulldogK5]

I'm running 35's with 3:73 and a 350. The problem is when you try to get into a passing gear. The 700R4 is fine until 3rd gear then everything goes to feeling sluggish. Take the top off and shed some weight where you can to improve the response and throttle feel. Don't know how a TH350 will respond to this.

 

[bigyellowjimmy]

Go with the 35's....just do it /forums/images/graemlins/waytogo.gif

 

[rjfguitar]

10.1:1 compression? What heads are you running? What octane rating is available there in Nevada? That high of a comp ratio with iron heads and a 400 is not a very good idea, with today's crappy gas you will be plagued with pinging and short live the motor. I fight pinging with only 9.2:1 comp ratio in my 406 and I can ONLY run 91 octane Chevron, 76, Shell and if I pull any kind of trailer I have to dump in a gallon or 2 of race fuel or a bottle of octane booster to keep it from pinging.

 

[k5 krawler 50]

I am running the iron heads, they where machined, the i ported and polished them for better flow, i am running an 91 octane, and its damn expensive.

 

[84_Chevy_K10]

[ QUOTE ]
10.1:1 compression? What heads are you running? What octane rating is available there in Nevada? That high of a comp ratio with iron heads and a 400 is not a very good idea, with today's crappy gas you will be plagued with pinging and short live the motor. I fight pinging with only 9.2:1 comp ratio in my 406 and I can ONLY run 91 octane Chevron, 76, Shell and if I pull any kind of trailer I have to dump in a gallon or 2 of race fuel or a bottle of octane booster to keep it from pinging.

[/ QUOTE ]

You run crappy smog cylinder heads and that's why you have ping issues. Probably have too much quench distance as well.

Stock 305 V8s are 9.2:1 and really aren't all that knock prone although they're more so than the majority of SBCs. Only due to the nature of the horrible cylinder heads on a 400 should you have ping issues.

That is, unless you've got more compression than you think, or your fuel mixture is too lean, timing overly advanced, etc.

 

[rjfguitar]

[ QUOTE ]
I am running the iron heads, they where machined, the i ported and polished them for better flow, i am running an 91 octane, and its damn expensive.

[/ QUOTE ]
Well than I am POSITIVE you are having detonation issues if your compression ratio is in fact 10.1:1 on a 400ci SBC.