Hello after two failed attempts at purchasing a built motor; Ive decided to take my 305 block and see how much power I can make. I bought a supposedly built 400 block that was supposed to be pulling 425 horse N/A . Lets just say that didnt work out. So I plan on building my 1985 305 Trans Am block.
BUILD SHEET:

305 bored .60 over

350 double hump heads ported and polished\

Self aligning 1.5 Roller rockers

Pistons 11:1 domed with 2 valve relief to prevent shrouding

Intake valve 2.02

Exhause: 1.60

Cam: 580 to 610 lift split duration

Custom cut rings

400 crank with 400 rods
Crank and Rods ESP Armor coated for strength and less friction

Crank cut to fit a 305block

Please let me know how much power you think I can make. Doing it this way for cost savings and to use the parts I already have.

 

I would be careful with the big cam,big vales,and dome pistons! You might have to have them fly cut for clearance(pistons). I'm not even sure you can fly cut dome pistons. you might have to go with flat tops. Only reason I say this is cause I have had this issue before. But as long as you get that worked out you should be making big H.P. A 305 bored 60 is a 309 I think

 

Mr. Morinaga:
Welcome to the forum.
Feel free to join the conversation in the Members Daily Blog!
Thanks for joining the MCF! Please post pics when your able and keep us posted as your build continues!

I have a cpl of concerns:
With the numbers and parts you posted... clearances will be critical.
What is your build idea? Is it for the street?,Strip,? or both or is more for a show and go type vehicle... Some of these numbers suggest a pretty hefty build... Are you doing this build yourself or having it professionally assembled?

I did notice you spoke about the Camel Hump heads (Dbl hump as you called them) These are some really Great Heads.
They were intended and used on the High HP Corvette 327's that pushed upwards of 375/385 HP! But Unless I'm not mistaken..the valves are actually 202/190's ... I see you posted the exhaust valves are 160.... Have these been reworked before porting and polishing? I don't see the advantage of the exhaust valve that small... Were the valve guides knurled? (very important for reliability and performance alignment)


Not sure if you know this...
But the 305 has a little less meat between cylinders with a 60 over bore makes it especially thin on a 305.(cant remember the exact numbers/clearance between cylinders)
Since it was originally designed as an economy motor, I take it that its a 2 bolt main block?

They will tolerate some serious built power..But over the long haul..(Depending on your application) it may be an issue down the road.

I would however, with the cam your running actually going with 1.6 roller rockers...since the exhaust valves are at 160... (Give it a bit more timing for extra breathing room.) to clear the cylinder.

I'm guessing you may end up with around possibly 295 to 335 hp. Provided the 400 parts you putting into it balance out with the 305 block...
There were suttle differences between the Chevrolet and Pontiac build tolerances when it came to the motors.. Especially in the T/A Models.. Vs the bone stockers and the Formula Firebirds.. (Just a little FYI)

I am just curious why you haven't just gotten your self a boneyard 283 or 327 to do this build with.... IMO they had a much higher reliability for small block power. Were you going with HEI distributor or Points and condenser?
What kind and how much carburation are you planning on going with?

I would however, Be concerned about possible overheating issues, (Depending on what your building this motor to do) I would recommend a Griffin Aluminum Radiator (4 row) and Dual auxillary fan setup. This should keep it from overheating, With such thin walls between the cylinders with the 60 over bore. Just my opinion... For reliability.. I would highly recommend ARP Bolts for this build!

I have built many a small block over the years for street, strip, and circle track usage....

I would however, like to hear more about it as your build continues...
You definitely have something unique !

Thanks for joining the MCF Family!

I'm sure someone else will chime in with more help and Ideas!
Good Luck on this build!
I'd be curious what numbers you get out of it on a dyno.

 

Thank You for the feedback. I'am attempting to do a radical daily drive build. I already planned on doing a three row radiator with a high flow water pump. My main goal is to produce 600 horsepower and run it off of part time hydrogen which is possible but not common I guess. My friend builds dragsters and he is tricking out the heads for me and is advising me on the build. He stated that I can do domed pistons with eyebrow cut outs for valve relief. What I'm not sure of is how much power I will be making and at what compression ratio I will be at as to whether or not it will be safe to boost if necessary to get the power I want. I plane on making it a autocross car for the weekends.

 

Sounds like a nice ride... Honestly, why not just put in a crate stroker and save yourself alot of trouble...... Just curious, as I have built up a blue block 400 Pontiac power plant and to my knowledge, building a 305 is a huge hassle and much less performance for the buck...... Have you considered a 383 stroker, I believe it is as direct a drop in with minor modifications as can be for your machine....

 

You do realize that street use and autocross are 2 totally different venues.
Doing a drag racing style motor for basically autocross is a style of circle track racing... That the torque and power values are not the same....
IMO..(As an ex circle track racer) a 60 overbore is only valuable in the upper range of the rpms..(like drag racing).. Where as say a 30 over bore will get you more into the power band your going to need for autocross racing.... I just don't see a vehicle used for auto cross racing..is over time going to be streetable....

You could just take a 350 ci motor, punch it out 30 over with a mildly over stock middle of the road cam, the camel hump heads ...1.6 roller rockers and be very competitive!
by installing a 411 gear with a mini spool ...and a 2 speed power glide trans. That will get you right around 355 cu inchs. as long as its a 4 bolt main...and still attain around 385 HP.. you can then boost it.. and get the extra power/HP that your looking for...

But combineing drag race technology for a circle track style venue of racing...
IMO isn't even close to the correct Torque specs and or Horse power needed..

I guess what I am asking What is your eventual goal?
Autocross... or... a street strip/daily driver...
Daily use or autocross..is the only choice...
Unfortunately you cant realistically make both happen with the 1 vehicle...
I see it as either 1 or the other...

Curiosity has the better of me... What state do you live in?
I just cant see you useing it as a daily driver and also competeing in auto cross at the same time.
IMO I believe you have to deceide what you really want to accomplish with this build..
Doing both just isn't going to work/happen.....

I'm curious...
What state do you live in?
I also noticed you haven't filled out your profile...

I would like to know how/where you got your information from that allows you to think that a 2 in 1 use would even be possible?

Just a little FYI a 600 HP motor would be overkill in an autocross!

 

Technically for just autorcross some would agree with you that 600 horses is too much horsepower. However in one of my Chevy magazines they show Autocross racers with 1000 h.p. cars however they seem to be leaned more to pro street than autocross but none the less they are on the track. They are makking the power with boost there with allowing more control; ( Turning the boost up or down) I live in Texas and the reason I am wanting to use one of my 305's is because they are low cost and everyone says that it cant or rather shouldnt be done. I have a 400 block that needs to be vatted, honed and with custom pistons cut however. I plan on swapping the internals to the 305 and making a stroker that is still able to be driven daily. Also suspension wise you can still make a beastly handling daily driver using a pneumatic setup( however price is a serious concern.) I think it is feasible to make it do both however one leaned more toward streetability than autocross. But thanks for the response and I am certainly open to suggestions.