A 420 - 450 hp range motor in a C4 is that perfect line scenario of getting your cake and eating it too. The car is already so incredibly light. Get your traction part of the formula down and you have an insanely fast car. It's amazing to see how horsepower to weight ratios truly affect end results than a single number of RWHP does. 300 lbs is the difference between a 12.8 and a 13.2 at the 1/4 mile with a vehicle pushing 300 RWHP. A 300RWHP C4 could keep up with a 2019 Mustang GT until the last two or so seconds of the track.
Maybe at the end of the day, it's cheaper to just go ahead and get the bigger block that still allows a FIRST TPI intake. I.E. maybe a 400 or 383. But can't turn down a 427 if I know a way to bolt up a TPI to it.

 

When I do eventually decide if I want to do a crossfire build (it'll happen...) That is the area I was shooting for. I figure if I build shooting for 500 hp I'll end up around 450. It would be an incredibly fun car either way... not that it isn't already.

 

My car is a manual, so I'm not concerned about making a ton of low end torque. My thoughts on using the stock heads and intake is to keep cost down and start with a good foundation.

I agree that too many people get focused on that max hp number rather than power to weight. I think 400to 450 would be the most I'd want.

 

You really need to consider rebuilding the entire engine to get reliability. The bottom end is probably the most critical part of a performance engine.

Many years ago I started a build using my 427 Big Block. The blocks machining was all done and the inside was painted with Glyptal sealing the pores of the Cast iron block. I started looking for a Crankshaft to use in my build and I went through 11 cranks before I found one that would pass the magnaflux testing. These were FORGED crankshafts and the first 10 all had little tiny cracks in them. I bought the best crank I could afford and used a kit from Comp Cams to build my valve-train. The Rods I bought were a new set and even those were magnafluxed to be sure I was okay. I have Forged Pistons on my Forged Rods on my Forged Crankshaft. This bottom end was balanced at 7000 rpm and it works great 26 years later. I am using 12.25-1 Compression with cast Iron GM heads (3931063, 100.3cc's) that use the Closed Chamber design. The closed chambers were chosen for their resistance to detonating even with higher compression. The combination I chose was my idea to make lots of power. It works very well and pushes my little 1968 C3 down the road quickly. The problem is like mentioned before, what good is the power if you can't get it to the ground? My 1968 will spin the tires half way down the quarter mile track if you let it. It looks impressive and sounds awesome but spinning tires are useless, try some good slicks and then your differential, transmission and half shafts will start breaking, ask me how I know?

Just because you have Forged Pistons doesn't mean your car is ready for making more power. If the 140,000 mile bottom end is "weak" you will soon find out after installing the engine. If it were my car I would seriously think about using a 4 bolt main block and build it using quality forged parts.

Build the engine the right way even if it takes more time. Rushing on an engine can lead to a expensive disaster and ruined parts. Take your time and do it right the first time, build the whole engine at once, adding new heads to a old high mileage block sounds like a recipe for disaster, In my humble opinion of course. I spent a year building my 427 the way I wanted it. I have a spare 350 Lt-1 with the double hump heads (Camel-hump) in my garage. I stuck it in my C3 while the 427 was coming together and kept on driving my C3 for the whole year. The LT-1 engine was able to get 21 mpg with my 3.36 rear-end and my Muncie 4 Speed. I had a buddy who had a real live 1970 LT-1 and my poor little 350 outran him every time and he had the 4.11 rear in his car.

Enjoy your Corvette for all it is worth! Build the engine of your dreams just do the entire engine at one time and you will be happier in the long run!

Best Regards,
Chris

 

That’s weird this thread was started. I have been talking to Ken at FIRST because I plan on getting a first intake and then getting either edelbrock e street heads or afr 180 or 190 heads and a cam to put in sometime. This is in an 85 too. I don’t know what cam yet but I would rather keep flat tappet so not much needs changed and I’m hoping this will get around 400 hp at the crank. I hope to have enough saved up by the end of next year to buy everything and start installing it. I’ve heard the first really performs similar to a superram intake and I think the first looks a lot better.

 

Did a little reading and this post was definitely a bit of a wake up call. Good wholesome story to be read from it. Definitely going to just enjoy the car and make the best of it's quality, I'll build the engine on the side with a whole new block and rotating assembly. Thanks for the awesome words, probably seems like nothing to you but definitely made me think and feel better about this project oddly enough.

Awesome to see another '85, and also one looking into the FIRST intake. 400 rwhp is right where I like personally cause it's not too much and it keeps driveability. And yes, the FIRST looks awesome looking like a stock intake on steroids. Plus, superrams are hard to find, they work great, but I'd rather not have my power band up there if it's just a fun car I'll drive whenever I want. Good luck with your build too and hopefully you have all the fun doing it.

 

So have you done anything with your engine build yet? I ordered my FIRST intake black and red painted last month and it should be here sometime before the end of the month, they just got new castings and had to machine them in.

 

Sub'd

 

I know this topic has been beaten to death, but I don't see the point of building a "torque motor" with a TPI-based intake. The whole idea that torque at the crankshaft has some magical ability to create performance betrays a fundamental misunderstanding of torque and power. Torque at the crank is not what determines a car's acceleration - power is, and only power is. At any given speed, and assuming all else (weight, drag, traction, etc.) is equal, the car that put the most power to its drive tires will always accelerate the fastest. Period. It is 100% true, though, that a car with a peaky powerband (i.e. a narrow rpm range of power that is at or near redline) will make it difficult to put down good power in a range of situations. The broader the torque curve, the broader the powerband. I think that's what trips up a lot of people when they talk about "torque."

So in that light, consider the TPI engine. In stock form, it has no more torque off idle than the later, short-runner LT1 did. It has a torque peak around 2500rpm, and that torque then falls off very rapidly as the intake's resonant tuning becomes a barrier to flow above 4000rpm. So all you really have is a peaky engine whose peak just happens to be at low rpm. The bottom line for that build is that it's slow and you still have to row the gears a lot because it's so rpm-limited. OTOH, the LT1 pulls just as hard off idle, doesn't have a brief peak, and pulls to a much higher rpm. It's powerband is way broader and more flexible, and it can make way more power. It's faster and easier to drive fast. With a little better flow and cam, the LT4 was even more so.

So what's the lesson here? The lesson is that a long-runner TPI-based intake is a bad way to spend $1000. No matter how hogged out the runners and base are, it's still going to impose a hard limit on rpm, meaning power is going to be limited. No matter the heads and cam, on a 350 the OP is going to struggle mightily to make an honest 350rwhp (his stated goal). In fact, I'm going to go ahead and say that if he keeps the cam mild for good street manners (another stated goal), the power goal just isn't achievable. OTOH, it's probably well within reach if he uses a short-runner intake like a Miniram. And because he'd be using a fairly mild cam with wide LSA, it would have good manners and be super-flexible in its useful rpm range. If someone has a TPI intake sitting on a shelf and doesn't want to spend money on an intake, then go for it. But to lay out four figures for an intentionally restrictive intake, all in the name of "torque," seems like a very bad idea.

 

have you ever looked at a dyno graph of a first or seen the torque curve? It is completely different from a regular tpi. It’s ports are giant compared to regular which I saw you knew but it also doesn’t have as long of runners. People have gotten this intake to flow over 6000rpm without hitting a barrier like stock. This is with modifying it of course but it still flows 5000 rpms easy without porting. When people have tested it on a flow bench it will flow better than a SuperRam without porting done to either one. One other thing I can’t remember exactly but someone had a SuperRam I think and changed between the first and a mini ram testing 1/4 mile times with each intake and the first did the best. I know tuning could have been done to help the mini ram probably but still I don’t know why anyone would say the FIRST is a horrible choice.

 

You make alot of great points here! I agree with the concepts you say, but the reason I believe i said "torque motor" earlier this year was because to be honest, I didn't want to make my parents worry about me building an engine that revs so incredibly high because to them that means power and street racing. So I decided I'd try some low rpm power and its great fun with the TPI, but you point out some of the flaws of "torque builds" pretty well! I can say I didn't know as much as I do now. But the FIRST intake does have some shorter runners and just huge ports like 85 CRVET said. But by the way, yes I've paid attention the Miniram too and I'm very intrigued by it, I would like to put it on a 427 and see how well it goes! I'll extend some more of my response at the bottom of this post.

Hey nice to see you check back in and stop by! I hope i don't disappoint you and others but I got way in over my head on this post and I'm sorry for that. I'm just a kid in college who's got a lot to learn, even from all of you who's done this way longer, and my 85 got in a wreck cause someone ran me off the road back in the end of may so for now I'm just enjoying the car after it's done getting fixed and saving my money (Had to shed alot of money to help the other insurance who wanted to be cheap and not fix it... ). Sometime in the future when I'm graduated and got the real money coming in I'll throw a miniram and a FIRST intake onto both of my C4s but until then I'm just dreaming and just checking out everyone else's builds! Good luck you and all the rest of you on your builds and I hope you guys thoroughly enjoy them for 230 flywheel HP ole' me!

 

dude I'd put a 100shot on whatever you have that runs right now and rock it like that till it dies

then swap in an LS when it does

the age, tech, design, is ancient in terms of what is available now, and is somewhere around 10x (yes 10 times) as expensive to make about half the power.

 

I just had the most solid laugh at that first sentence. But yes, an LS would be much easier in terms of tuning/aftermarket hardware. Lots of fab work involved though, but the drivetrain would also be very solid. As long as I get to keep my nice digital dash I'm happy. But I'd also say that in that case why not just have a C4 for the classic SBC builds and then a C6 for the godtier LS builds?


And then a ratnest mustang coked out and hooked on a little 350shot maybe??

 

I've seen a couple graphs. The torque peak moved higher on them, but power still fell off after 5000rpm, which severely limits total power potential. Keep in mind that flow bench numbers don't mean anything here, because a flowbench uses constant flow rather than the pulsed flow that a real engine causes (intake valve opening and closing). So the limitation caused by 24" runners won't show up on the bench - only on a real engine where the resonant tuning and barrier effects happen.

You're the second person to say that the First intake has shorter runners than a stock TPI (or maybe that was you on FB?). I cannot say one way or the other. I have not been able to find any reference that documents a different runner length, including First's own website. I would expect their own site to point out a shorter runner length. Maybe I've just missed it? Also, just visually, they don't look any different. But if someone can document that the mean length of the runners is measurably shorter, that would be useful to know (don't confuse mean length with the length of the short-side on the inside of the bend!).

In the meantime, remember that the much-increased runner cross section does raise the resonant rpm a little bit, per Helmholz's formula. What I see in posted dyno graphs tells me that the runners are the same length, but just a lot bigger in cross section. It is definitely the best TPI-style intake on the market, but I still don't see it outperforming any short-runner intakes.

 

I know I saw the length of the runners were shorter somewhere, I think they were like 19” or something close to that. I emailed Ken, he's the owner, and he will get back with me and I’ll let you know if they are shorter than the stock tpi. It wasn’t me on FB, I don’t mess with that much but I’ve seen it a few times people saying the runners aren’t quite as long.

 

I know what you mean about waiting for it in the future. I started a thread last year asking about what I should do to get more power and I’ve only gotten headers and dual exhaust so far. This next year I will install the intake, which should be here this month but I’m waiting until spring to install, and then the year after I would like to get cylinder heads and a cam. I hope your c4 gets fixed good and not just half fixed, at least you have a backup though haha. I’ll get some pictures of the intake when it gets here and let you know when I install it in the spring.

 

Check out the article 10 times the torque, that article should mention the runner length of the first. It also shows dyno graphs of 10 intakes on the same 383. It is interesting.

I am going from memory so I hope it has the first referenced.

 

Here's a link to "Ten Times the Torque." I couldn't remember the name and was looking for it, so thanks for jogging my brain. Unfortunately it didn't include the First intake. I wish it had.

 

i dont believe the 540 figures for a 350 tpi
OP if you are going to use a FT better call Chris straub or mike jones. Most lifters today are garabge and will go flat.
THey will know which ones will hold up.They arent what they all were 20 yrs ago

 

My advice is based on simple observational analysis of cost vs reward.
A 100 shot is perhaps 1/100 the cost(time and energy are factors of that cost, not just $$) of what you are planning to do to that old engine, has no bearing on wear and tear if done properly, and will yield extremely similar if not superior results (100 shot = 125 shot = 75 shot = 150 shot for our wide berth analysis these are all the same and achieve the same goal) and we can stop right there.

to continue, with a what if:
what If it dies, and it might not but if it did, you would want the modern drivetrain of the LS as a next replacement (for any old car that is not considered antique original), for it's overdrive and sequential EFI, main girdle and pan support, superior oiling and pcv system, poly component seal design, computer aided modelling, high mileage potential valvetrain, and so forth.

Plus the fact that truck LS engines cost less than the one you have now and also offer two to three times the power capacity if desired.
The LS conversion can be a test of car mastery if done by one self. Thus the attractive nature of such things as a proving grounds.
Can you install the LS in a seamless fashion? Make the car look as though it came with that engine originally? As quiet as a stock unit comes.
With twice or three times the power of a new car as well?


IMO start to weigh the cost vs rewards of your time and efforts more heavily than the sole $$money value of the parts.
In other words think of the situation as if parts cost is negligible (free).
This eliminates the benefit of the LS as a free power plant, which hurts it as a swap option.

Is it still superior in all aspects? Weight, balance, tech, delivery, support, yes.