If you want 70, stroke em to 383, put on good heads have cams designed to the rest of the build. That should get you there. IMO with stock sbc you will gain very little with exhaust.

You are looking at 15 MPH more ,,,,,,figure 10 HP per mile more is what you need to get there !!!!!!!!!

The exhaust kit "buys more" the more you do to the engines.
Even though the mph/rpm gain on a stock engine will be minimal- you MUST do the exhaust or any further gains will fall short due to poor exhaust.

383 kit- that's one really good way to get there - or just a new top end and a bottom freshening if your tight on cash. A couple of 383 kits and well matched top end combos(heads/cam/intake) will give that rig about another 70-100 hp per engine. (more can be had for sure but allow for a good idle and the occasional tank of 87 you get on a lake)

You must decide if on your budget you can go into the short blocks or not- run a leak down test and see what shes holding. If your bottom end is shot you can buy aftermaket short blocks really cheap and swap the accessories.

Remember every dollar you spend on the heads gains way more power than spending it on the short block and with such mild power anyway I wouldn't bother with steel cranks and fancy rods. - spend the money on the top end on a rig like this.

On alphas I would go much further and Id check the gimbals before I did anything. They may need a rebuild.


Uncle Dave

Laveycraft 2750 -710
Laveycraft 20.8 Sebring

I was told each 20 hp will yield about 1 mph.....by more than 1 person, but I guess every situation is different; seems to be close as a "rule of thumb"

I put Revolution Marine manifolds on my SBC, and picked up almost 400 rpm.

Chris

http://revolutionmarine.com/shopsite...bcexhaust.html

My smallblock CMI's I have had them for 13 years on the boat but the boat has never been out They .Look really nice and sound awesome.

Some of the stories on here scare me.If i was to do it again i would go for the Stainless Marine . Less bling but all the performance and killer warranty without the header worry.

Tube type headers (your cmi's) will significantly outperform any manifold type header on a hot small block build.

On a a mild build- no, they wont.

high lift, high duration cam, big valve heads (2.08 and up) , lots of valve overlap- yes it will outperform - Stainless imco & eddie.

Ever seen a performance engine on a dyno with a manifold? NO.

BTW- they do look great.


Uncle Dave

Laveycraft 2750 -710
Laveycraft 20.8 Sebring

Eddie, stainless, and imco are not true manifolds. They all have individual runners inside.

Thats what their marketing material says and they are better than an automotive style manifold for sure.

They have tiny little runners inside them- then they all dump to a single tube under a foot.

However the runners are of unequal length and inside the manifold piece and not long enough to cause the proper amount of scavenging in a really high performance engine.

When using a cam that has a large amount of valve overlap say more than about 22 degrees the pulses will "fight" each other at the point they join the main tube.

This is is also why I use the term "type" when I talk about them.

All the units you mention are way better than the factory pieces and the older log style units- but will not make the power a true tube will.

As I said a mild cam setup with mild compression wont yield a lot of difference- so for most guys it doesn't matter- step it up a couple of notches with a 600HP+ small block and youll see large differences between the 2.


Uncle Dave

Laveycraft 2750 -710
Laveycraft 20.8 Sebring

434" motown smallblocks. i saw the dyno pulls with my own eyes. 740 hp @ 6000 rpm and climbing. only run 6000 rpm in the boat anyways, no reason to go futher.